Helix Induction Mechanisms in Poly(phenylacetylene)s bearing Oligopeptides as Pendants

INTERNATIONAL DOCTORAL SCHOOL OF THE USC Elena Rivadulla Cendal PhD Thesis Helix Induction Mechanisms in Poly(phenylacetylene)s bearing Oligopeptides as Pendants Santiago de Compostela, 2022 Doctoral Programme in Chemical Science and Technology HELIX INDUCTION MECHANISMS IN POLY(PHENYLACETYLENE)S BEARING OLIGOPEPTIDES AS PENDANTS Elena Rivadulla Cendal ESCOLA DE DOUTORAMNETO INTERNACIONAL DA UNIVERSIDADE DE SANTIAGO DE COMPOSTELA PROGRAMA DE DOUTORAMENTO EN CIENCIA E TECNOLOXÍA QUÍMICA SANTIAGO DE COMPOSTELA 2022 DECLARACIÓN DEL AUTOR/A DE LA TESIS D./Dña. Elena Rivadulla Cendal Título da tese: HELIX INDUCTION MECHANISMS IN POLY(PHENYLACETYLENE)S BEARING OLIGOPEPTIDES AS PENDANTS. Presento mi tesis, siguiendo el procedimiento adecuado al Reglamento y declaro que: 1) La tesis abarca los resultados de la elaboración de mi trabajo. 2) De ser el caso, en la tesis se hace referencia a las colaboraciones que tuvo este trabajo. 3) Confirmo que la tesis no incurre en ningún tipo de plagio de otros autores ni de trabajos presentados por mí para la obtención de otros títulos. 4) La tesis es la versión definitiva presentada para su defensa y coincide la versión impresa con la presentada en formato electrónico. Y me comprometo a presentar el Compromiso Documental de Supervisión en el caso que el original no esté depositado en la Escuela. En Santiago de Compostela, 19 de Diciembre de 2022. Firma electrónica AUTORIZACIÓN DEL DIRECTOR / TUTOR DE LA TESIS Helix Induction Mechanisms in Poly(phenylacetylene)s bearing Oligopeptides as Pendants D./Dª. Emilio Quiñoá Cabana D./Dª . Félix Freire Iribarne INFORMA/N: Que la presente tesis, se corresponde con el trabajo realizado por D/Dª. Elena Rivadulla Cendal, bajo mi dirección/tutorización, y a utorizo su presentación , considerando que reúne los r equisitos exigidos en el R eglamento de Estudios de Doctorado de la USC, y que como director de esta no incurre en las causas de abstención establecidas en la Ley 40/2015. De acuerdo con lo indicado en el Reglamento de Estudios de Doctorado, declara también que la presente tesis doctoral es idónea para ser defendida en base a la modalidad de Monográfica con reproducción de publicaciones, en los que la participación del doctorando/a fue decisiva para su elaboración y las publicaciones se ajustan al Plan de Investigación. En Santiago de Compostela, 17 de Enero de 2023 Abbreviations and Acronyms Abbreviations and Acronyms % v/v ºC 1,2-DCE [a] a aobs Å AFM Aib AIBN Ala anh. ap DzPhe BDY BiPy c c-c c-t ca. CD CHCl3 CMPH CNT cod CSP CyD CyHex d D d Volume percentage Celsius degree 1,2-Dichloroethane Standardized optical rotation Optical rotation Angstrom Optical rotation observed Atomic force microscopy a-aminoisobutiric acid Azobisisobutironitryl Alanine Anhydride antiperiplanar Z-a-b-Dehydrophenylalanine Boradiazaindacene Bipyridine Concentration cis-cisoid cis-transoid Latin expression “circa”; around Circular dichroism Chloroform See HPMC Carbon nanotube Cis,cis-1,5-cyclo-octadiene Chiral stationary phase Cyclodextrin Cyclohexanone Chemical shift Heat Doublet Abbreviations and Acronyms dd DCM DIPEA DLS DMF DMSO DNA DSC E e ee ECD EDC EDX e.g. EIHH EPR ESI et al. equiv Et3N f FT-IR g GPC h HATU Hept HOBt HOPG HPLC HPMC Hn HRMS Double doublet Dichloromethane N,N-Diisopropylethylamine Dynamic light scattering N,N-Dimethylformamide Dimethyl sulfoxide Deoxyribonucleic acid Differential scanning calorimetry Energy Dielectric constant Enantiomeric excess Electric circular dichroism 1-Ethyl-3-(3-dimethylaminopropyl)carbodiimide Energy dispersive X-ray analysis Latin expression “exempli gratia”; for example Emulsification-induced-homo-helicity Electron paramagnetic resonance Electrospray ionization Latin expression “et Alii”; and others Equivalents Triethylamine Phi dihedral angle: torsion angle N-Ca Fourier transform infrared spectroscopy Grams Gel performance chromatography Hours Azabenzotriazol-1-yl-1,1,3,3-tetramethyluronium hexafluorophosphate Heptet 1-Hydroxybenzotriazole High oriented pyrolytic graphite High-performance liquid chromatography Helical polymer-metal complex Light High resolution mass spectrometry INTRODUCTION Introduction 1 Introduction The helix is one of the most important structures and it is inherently chiral, left and right-handed scaffolds cannot be superimposed. Thus, it can be found in nature at both microscopic and macroscopic level such as oligomers, peptides, polymers, etc and their assemblies can be optically active due to their helicity. In the 50’s, took place the two most important discoveries of molecular biology: the first one was the discovery of the structure of the right-handed a-helix for proteins proposed by Pauling and Corey (1951), 1 and the second one was the double helical structure of DNA proposed by Watson and Crick (1953). 2 This helical structure is responsible for functions that these macromolecules adopt in living systems like catalysis, genetic information storage, ion transport, recognition, replication, etc. 3 Figure 1 . Naturally occurring helical polymers. Taking these findings into account, the scientific community is making a great effort to emulate these structures; trying to develop new structures with new functionalities. 4 1 Pauling, L.; Corey, R. B.; Branson, H. R. Proc. Natl. Acad. Sci. U. S. A. 1951 , 37, 205-211. 2 Watson, J. D.; Crick, F. H. C. Nature 1953 , 171, 737-738. 3 a) Alberts, B.; Johnson, A.; Lewis, J.; Morgan, D.; Raff, M.; Roberts, K.; Walter, P. Mol. Biol. Cell, 6th ed.; Garland Science: New York, 2014 ; b) Saenger, W. Principles of Nucleic Acid Structure, 1 ed., Springer-Verlag New York, 1984 , p 556; c) Schulz, G. E., Schrimer, R. H. Principles of Protein Structure, 1 ed., Springer-Verlag New York, 1979 . 4 a) Schwartz, E.; Koepf, M.; Kitto, H. J.; Nolte, R. J. M.; Rowan, E. Polym. Chem. 2011 , 2, 33-47; b) Yashima, E.; Maeda, K.; Iida, H.; Furusho, Y.; Nagai, K. Chem. Rev. 2009 , 109, 6102-6211; c) Liu, J.; Lam, J. W. Y.; Tang, B. Z. Chem. Rev. 2009 , 109, 5799-5867; d) Rosen, B. M.; Wilson, C. J.; Wilson, D. A.; Peterca, M.; Imam, M. R.; Percec, V. Chem. Rev. Natural'Helical'Polymers α-Helix'Peptide Polysacharide-Helix DNA$Double$Helix Introduction 2 The presence of a helical structure in a non-natural polymer was first described by Natta in 1955: an isotactic poly(propylene) (poly1 ). 5 This polymer presents a mixture of rightand left-handed helices in the solid state, losing the helical structure once the polymer is dissolved. Thereby, poly1 was the first example of a synthetic helical polymer reported in literature (Figure 2). In the 60’s, the research community achieved to generate polymers that can adopt a helical structure even in solution. In this way, Pino and co-workers carried out the synthesis of a new series of poly-(vinyl) polymers (poly2 ) by polymerization of optically active monomers, where the pendant group induces a predominant helical sense, that was determined using optical rotation. 6 It was not until 70’s that the most important advances were made in the helical polymers field. In particular, the groups of Okamoto, Nolte, and Green among others, made some of the most extraordinary progresses. Nolte and co-workers determined the structure of poly(tert-butyl isocyanide) (poly3 ) into leftand right-handed helices by chiral HPLC in 1974. 7 Later, Okamoto’s group synthesized the first helical vinyl polymer (poly4 ) using an achiral monomeric unit, triphenylmethyl methacrylate (TrMA), and a chiral catalyst ¾lithium (R)-N-(1phenylethyl)anilide and (-)-sparteine-n-BuLi complex¾ able to form a helix with a preferred helical sense in solution induced by the chirality of the catalyst. These results were applied in fields such as HPLC, using the helical polymeric materials as stationary phase (CSP). 8 In the late 80’s, Green and co-workers reported an important discovery in the helical polymer field. They managed to synthesize a new family of helical polymers, the poly(isocyanate)s (poly5 ), which helical structure is a mixture of both helical senses (rightand left-handed), in the same helical structure by applying different external stimuli. Furthermore, they reported that this helical interconversion takes place through 2009 , 109, 6275-6540; e) Yashima, E.; Maeda, K.; Furusho, Y. Acc. Chem. Res. 2008 , 41, 1166-1180; f) Yashima, E.; Maeda, K. Macromolecules 2008 , 41, 3-12; g) Rudick, J. G.; Percec, V. Acc. Chem. Res. 2008 , 41, 1641-1652; h) Maeda, K.; Yashima, E. Top,. Curr. Chem. 2006 , 265, 47-88; i) Nakano, T.; Okamoto, Y. Chem. Rev. 2001 , 101, 40134038; j) Cornelissen, J. J. L. M.; Rowan, A. E.; Nolte, R. J. M.; Sommerdijk, N. A. J. M. Chem. Rev. 2001 , 101, 40394070; k) Green, M. M.; Jha, S. K. Chirality 1997 , 9, 424-427; l) Okamoto, Y.; Nakano, T. Chem. Rev. 1994 , 94, 349-372. 5 Natta, G.; Pino, P.; Corradini, P.; Danusso, F.; Mantica, E.; Mazzanti, G.; Moraglio, G. J. Am. Chem. Soc. 1955 , 77, 17081710. 6 Pino, P.; Lorenzi, G. P. J. Am. Chem. Soc. 1960 , 82, 4745-4747. 7 Nolte, R. J. M.; Van Beijnen, A. J. M.; Drenth, W. J. Am. Chem. Soc. 1974 , 96, 5932-5933. 8 Okamoto, Y.; Suzuki, K.; Ohta, K.; Hatada, K.; Yuki, H. J. Am. Chem. Soc. 1979 , 101, 4763. Introduction 3 the presence of helical reversals. 9 Thus, poly(isocyanate)s were the first example of dynamic helical polymer, a new family of polymers that includes different kinds of polymers such as poly(acetylene)s 4c, 10 or poly(silanes). 11 Figure 2 . Schematic representation of synthetic helical polymers. 1. Helical Polymers Classification Synthetic helical polymers can be classified in two main groups according to their dynamic behaviour and their helical properties. These dynamic properties are directly related with the interconversion energy barrier between the M and P helical states. Thus, when the helix inversion barrier of the polymer is high the M and P helical states cannot be switched one into the other. These kinds of polymers are known as static helical polymers (Figure 3) and are found in polymers that bear bulky substituents. Otherwise, if a polymer presents a low interconversion barrier, the helical structure can be switched from M to P helices. This family of polymers is designated as dynamic helical polymers (Figure 4). 1.1. Static Helical Polymers Static helical polymers are defined as those polymers that keep a rigid structure with a defined helical sense during their synthesis. Thus, these materials present a high interconversion energy barrier between the two orientations of the helix (M and P) and cannot be modulated using external stimuli once they have been synthetized. These polymers are obtained by a process called “helix-sense-selective polymerization”4I that consists in the polymerization of optically active monomers or achiral monomers using 9 Green, M. M.; Andreola, C.; Munoz, B.; Reidy, M. P.; Zero, K. J. Am. Chem. Soc. 1988 , 110, 4063. 10 Liu, J.; Tang, B. Z. Acc. Chem. Res. 2005 , 38, 745-754. 11 Fujiki, M. Macromol. Rapid Commun. 2001 , 22, 539. R NO O Ph Ph Ph N O n n n n n poly-4poly-3poly-2poly-1poly-5 Synthetic)Helical)Polymers Introduction 4 chiral catalysts. Some of the most representatives examples of static helical polymers are poly(guanidine)s (poly6 ), poly(isiocianurate)s (poly7 ), poly(methacrylamide)s (poly8 ), poly(methacrylate)s (poly9 ) or poly(quinoxaline-2,3-dyl)s (poly10 ).4b,j Figure 3 . Conceptual representation and some representative scaffolds of the static helical polymers. 1.2. Dynamic Helical Polymers Dynamic helical polymers are a group of polymers that can adopt both (P and M) helical structures due to their low interconversion energy barrier. Thereupon, these polymers can be easily switch from left to right-handed helices and vice versa by applying different external stimuli such as chiral molecules, metal ions, pH, polarity of the solvent, temperature, etc.4e,f,h, 12 Moreover, the two helical senses can coexist within the same polymer chain in similar or different proportion, separated by helical reversal (Figure 4). There are two different ways to carry out their synthesis: • Polymerization of optically active monomers that acquire preferably one of the two helices (P or M). 13 • Polymerization of optically inactive monomers where the interaction with a chiral solvent or molecule on a solution provide a specific helical sense due to the establishing of the chiral inducer-polymer complex. 14 12 Yashima, E.; Maeda, K.; Kishimura, T. Chem. Eur. J. 2004 , 10, 42-51. 13 Louzao, I.; Seco, J. M.; Quiñoá, E.; Riguera, R. Angew. Chem. Int. Ed. 2010 , 49, 1430-1433. 14 Freire, F.; Seco, J. M.; Quiñoá, E.; Riguera, R. Angew. Chem. Int. Ed. 2011 , 50, 11692-11696. Static&Helical&Polymers OO R N H OR n n NR n N R1 R3 R2 R4 n N R2 n N R1 Poly-9Poly-8Poly-7Poly-10Poly-6 External&Stimulus External&Stimulus M-Helix M-HelixP-Helix P-Helix Introduction 5 Poly(acetylene)s4c, 10 (poly11 ), poly(isocyanate)s4a (poly12 ) and poly(silane)s11 (poly13 ) are usually classified as dynamic ones. Figure 4 . Schematic representation of synthetic helical polymers. 1.3. Foldamers Foldamers were described by Prof. Samuel Gellman as “polymers with a strong tendency to adopt a specific compact conformation”. Thereby, these macromolecules can be regarded as dynamic helical polymers, which can show a predominant helical sense in solution stabilized by non-covalent interactions between non-adjacent monomeric units (Figure 5). Different examples of foldamers are meta-phenylene ethynylenes (poly14 ) or quinolinecarboxamides (poly15 ) among others. 15 Figure 5 . Some examples of foldamers. 15 (a) Hill, D. J.; Mio, M. J.; Prince, R. B.; Hughes, T. S.; Moore, J. S. Chem. Rev. 2001 , 101, 3893-4012. (b) Appella, D. H.; Christianson, L. A.; Karle, I. L.; Powell, D. R.; Gellman, S. H. J. Am. Chem. Soc. 1996 , 118, 13071-13072. Dynamic(Helical(Polymers HR n N O RnSi R R n Poly-11 Poly-12 Poly-13 External(Stimulus External(Stimulus(1 External(Stimulus(2 M-Helix M-Helix P-Helix P-Helix Axially(Racemic(Helix Foldamers Folded*State Unfolded*State Random*Coil R n O H N O N H N n R Poly-14 Poly-15 M-Helix P-Helix Introduction 6 2. Poly(Acetylene)s Poly(acetylene)s (PA)s are a family of dynamic helical polymers that exhibit a polyene backbone constituted by π-conjugated doble bonds. These polymers can be easily synthesized by polymerization of the corresponding acetylenic monomers (alkyne as polymerizable group). There are several examples of monomers such as aliphatic acetylenes4b,c, 10 (m1 ), phenylacetylenes (m2 ), propargylamides (m3 ), propargyl esters (m4 ) or propionic esters (m5 ) with an alkyne moiety that can provide (PA)s derivatives (Figure 6). Figure 6 . Representative structures of PA family. Poly(phenylacetylene)s (PPA)s are the most studied (PA)s due to their processability, their solubility in common organic solvents, their stability in air and their easy synthesis among others. Taking all this information into account, these kinds of polymers constitute a potential candidates for several applications such as CSP for HPLC, as chiral sensors, asymmetric electrodes, optical polarizing films, and so on.4c, 10 A remarkable structural characteristic of (PA)s is that they present four possible configurations of the conjugated double bonds of the polyenic main chain —trans-cisoid (t-c), trans-transoid (t-t), cis-cisoid (c-c) and cis-transoid (c-t) — being only the c-c and c-t configurations the ones that promote the formation of a helical structure (Figure 7). O OR O O O m-2m-5m-4 R m-1 HN O O m-3 R RR Structure0of0Acetilenic0Monomers Introduction 7 Figure 7 . Possible configuration that the polyene backbone of the (PPA)s can adopt. The most popular catalyst to carry out their polimerization was developed by Noyori and co-workers and consists on a family of Rh (I) catalysts, which produce (PA)s with a high ciscontent of double bonds. Also, high molecular polymers, in high yield and with low polydispersity are generated by a stereospecific living polymerization reaction. 16 There are different examples of catalyst commercially available that work in organic solvents ([Rh(nbd)Cl]2, [Rh(cod)Cl]2) or even in water ([Rh(cod)(BF4)]). The polymerization mechanism of (PPA)s using Rh (I) catalysts consists in a 2,1-alkyne insertion (Figure 8). There is steric repulsion between pendant units that lead to a high stereoregular polymer chain and is the responsible of this mechanism. 17 16 (a) Hirao, K.; Ishii, Y.; Terao, T.; Kishimoto, Y.; Miyatake, T.; Ikariya, T.; Noyori, R. Macormolecules 1998 , 31, 3405. (b) Kishimoto, Y.; Eckerle, P.; Miyatake, T.; Ikariya, T.; Noyori, R. J. Am. Chem. Soc. 1994 , 116, 12131. 17 Ke, Z.; Abe, S.; Ueno, T.; Morokuma, K. J. Am. Chem. Soc. 2011 , 133, 7926. H R H RH R R H R H H R H R H R H RH R trans-cisoid trans-transoid cis-cisoid cis-transoid Promote'the'Helix'Formation Backbone'configurations'in'PPAs Introduction 8 Figure 8 . Polymerization mechanism of PA by Rh (I) catalysts. 3. Stability of Poly(PhenylAcetylene)s Since the discovery of poly(phenylacetylene)s with cis-cisoidal or cis-transoidal polyene backbone were extensively studied. One of the most important features of these particular helical polymers is their stability and degradation, which is close related to their structure. 18 Percec and co-workers developed different structural studies of a cis-transoidal PPA showing a decrease in the ciscontent of double bonds and in their molecular weight (Mw) once that they are in chloroform solution.18f This degradation process goes through an intramolecular electrocyclization followed by a polymer chain break that produces a 1,3,5-triphenylbenzene.18d,f Moreover, this decomposition occurs indistinctly in solution 18 (a) Liu, l.; Namikoshi, T.; Zang, Y.; Aoki, T.; Hadano, S.; Abe, Y.; Wasuzu, I.; Tsutsuba, T.; Teraguchi, M.; Kaneko, T. J. Am. Chem. Soc. 2013 , 135, 602. (b) Huang, K.; Mawatari, Y.; Miyasaka, A.; Sadahiro, Y.; Tabata, M.; Kashiwaya, Y. Polymer 2007 , 48, 6366. (c) Miyasaka, A.; Mawatari, Y.; Sone, T.; Tabata, M. Polym. Degrad. Stab. 2007 , 92, 253. (d) Percec, V.; Rudick, J. G. Macromolecules 2005 , 38, 7241. (e) Deng, J.; Tabei, J.; Shiotsuki, M.; Sandra, F.; Masuda, T. Polymer 2004 , 45, 7395. (f) Percec, V.; Rudick, J.; Nomber, P.; Buchowicz, W. J. Polym. Sci., Part A: Polym. Chem. 2002 , 40, 3212. (g) Abdul Kaim, S. M.; Nomura, R.; Masuda, T. J. Polym. Sci., Part A Polym. Chem. 2001 , 39, 3130. (h) Tabata, M.; Tanaka, Y.; Sadahiro, Y.; Sone, T.; Yokota, K.; Miura, I. Macromolecules 1997 , 30, 5200. (i) Matsunami, S.; Watanabe, T.; Kamimura, H.; Kakuchi, T.; Ishii, F.; Tsuda, K. Polymer 1996 , 37, 4853. (j) Simonescu, C. I.; Percec, V.; Polym. Sci., Part A: Polym. Chem. 1980 , 18, 147. Polymerization Mechanism Rh L R Rh L R Rh R Rh RH Rh RH R Rh RH RRh RH RH R Rh RH RH RH cis-transoidal structure Path A Path B Rh R H R Rh R H R RH R H Rh RH R H Rh R HR H R HR Rh cis-cisoidal structure nbd RPh = = Introduction 15 monomer (phenylacetylene derivative) and chiral one (MPA monomer) was designed. Contrary to Green’s system, our chiral MPA moiety presents an axially racemic behaviour —two conformers in equal population—, which means that it is not able to organize the helical structure. Thus, the chiral moiety only could be the Sergeant by the addition of a small amount of an achiral agent (i.e., monovalent or divalent metal ions). This external stimulus coordinates to one of the two MPA conformers inducing a specific helical sense not only to the other MPA conformer, but also to the achiral unit. As a result, we have a fully folded state where the handedness is determined by the valance of the metal ion added to the MPA moiety. Moreover, the reversibility of this phenomenon was also studied. In this way, we are able to recover the initial racemic state if the metal cation is removed from the helical polymer metal complex. Thus, our research group reported for the first time a Sergeants and Soldiers Effect that can be selectively activated/deactivated by the addition or removal of external stimuli. Figure 12 . Schematic illustration of the chiral amplification phenomena through the Sergeant and Soldiers effect (a) Classical approach and (b) Metal-driven coordination approach. Finally, it is important to say that the helicity induced in poly17 by the addition of monovalent metal ions is produced by the presence of cataion-π interactions, which can be disrupted by the addition of a cosolvent. In particular, our group used a single b) a) Chiral Conformation I Chiral Conformation II Chiral Component Achiral Component Nor Chiral Neither Achiral Components Present Helical Sense Preference Addition of Cations Chiral Conformation I Activated Chiral Conformation II Chiral Component Achiral Component Mn+ Chiral Amplification Single Handed Helical Polymer Chiral Amplification Single Handed Helical Polymer Chiral Component Achiral Component Preferred Helical Sense Non-preferred Helical Sense Chiral Communication Chiral Communication Monoor Divalent Introduction 16 monovalent cation (i.e., Na+), 30 that in the presence of low amounts of cosolvent, coordinates to the pendant group in the ap mode —cation-p interaction on—. Nevertheless, a higher amount of cosolvent disrupt the chelation in ap mode and the coordination mode shifts towards the sp conformation. Figure 13 . Total control on the helical sense of a PPA through the Sergeant and Soldiers effect by selective tunning of the cation-p interactions. 4.5. Majority Rules Green et. al. discovered another chiral amplification phenomenon through the synthesis of poly(isocyanate)s copolymers consisting in a mixture of (R)- and (S)- enantiomers that present a small enantiomeric excess (ee). They found that this small ee is able to generate a predominantly one-handed helical conformation —only a 12% of ee is enough to promote a single-handed helical polymer—. 31 This means that the minor component adopts the helical sense of the major component in order to avoid the presence of helical reversals. This phenomenon is known as “Majority Rules” and has also been observed for dynamic helical poly(acetylene)s through non-covalent chiral interactions.14 This study was reported by Yashima and co-workers who synthetized a new racemic PPA (poly19 ) bearing an aza-18-crown-6-ether —a very common and 30 Arias, S.; Bergueiro, J.; Freire, F.; Quiñoá, E.; Riguera, R. Small 2016 , 12, 238. 31 Green, M. M.; Garetz, B. A.; Munoz, B.; Chang, H. P.; Hoke, S.; Cooks, R. G. J. Am. Chem. Soc. 1995 , 117, 4181. Chiral Conformation I Chiral Conformation II Chiral Component Achiral Component Nor Chiral Neither Achiral Components Present Helical Sense Preference Addition of Na+ Chiral Conformation I Activated Chiral Conformation II Chiral Component Achiral Component Na+ Chiral Amplification Right-Handed Chiral Communication Low Amount Cosolvent Addition of Na+ High Amount Cosolvent Chiral Conformation I Chiral Conformation II Activated Chiral Component Achiral Component Na+ Chiral Communication Chiral Amplification Left-Handed Switchable Helicity Tunning Cosolvent Ratio Introduction 17 useful functional group involved in host-guest chemistry— as pendant group. 32 This polymer generates a one-handed helix once interacts with L-Alanine and another natural or non-natural amino, where the final helicity is determined by the absolute configuration of the amino acid. The complex shows an induced circular dichroism (ICD), responsible of a cooperative complexation. Additionally, mixtures of Land D-Ala in different ratios were evaluated, where a very small ee of chiral guest (less than 0.005%) was able to promote a specific screw sense. For this reason, poly19 is considered one of the most sensitive receptors for detecting the amino acids chirality.12 Figure 14 . Schematic illustration of the Majority Rules effect in (a) covalent systems and (b) in a supramolecular system. 4.6. Chiral Conflict Another phenomenon described by Green and co-workers was the “Chiral Conflict” where they studied poly(isocyanate)s systems composed by chiral monomers with a preferential and opposite helical sense at a certain ratio. Due to their different structure these monomers can induce a new chiral communication along the polyenic chain. 33 Thus, depending on the ratio between each chiral unit and playing with temperature they can shift from P helix (low temperature) to M helix (high temperature) or vice versa 32 Nonokawa, R.; Yashima, E. J. Am. Chem. Soc. 2003 , 125, 1278. 33 Tang, K.; Green, M. M.; Cheon, K. S.; Selinger, J. V.; Garetz, B. A. J. Am. Chem. Soc. 2003 , 125, 7313. Axially Racemic Helical Polymer O NO O O O O O NO O O O O OH O +H3NN+ H H HR Ala (e.e.< 0.01%) Single-handed Helical Polymer b) a) Chiral Amplification (S)-Mono-1 (R)-Mono-1 Copolimerization + Monomer Ratio (R)/(S) (49:51) (S) (R) Major component Decides Final Helical Sense Introduction 18 going through a medium stated where the polymer presents an axially racemic behaviour. Moreover, it is possible to modify the starting helicity and the temperature of helical inversion changing the ratio between the comonomers. Figure 15 . Schematic illustration of the Chiral Conflict and its modulation by thermal effects. 4.7. Domino Effect Domino Effect is a chiral amplification phenomenon that takes place in covalent 34 and supramolecular 35 systems such as dynamic helical polymers 36 and peptides 37 . In the particular case of peptides, Inai and co-workers reported the systhesis of several achiral ones, which adopt a mixture of helical senses. However, a preferred handedness can be adopted by the addition of chiral molecules to an unprotected Nor Cterminal peptides. Specially, this group generated achiral peptides composed by fragments of aaminoisobuturic acid (Aib) and Z-α-β-deshidrofenilalanine (AzPhe) (poly20 and poly21 ). This peptide bears an unprotected amino group, which is able to interact with carboxiylic acids through non-covalent acid-base interactions. The absolute configuration of the chiral carboxylic acid leads a specific helicity in the entire peptide. 38 34 (a) Obata, K.; Kira, M. Macromolecules 1998 , 31, 4666. (b) Maeda, K.; Matsuda, M.; Nakano, T.; Okamoto, Y. Polym. J. 1995 , 27, 141. (c) Obata, K. Kabuto, C.; Kira, M. J. Am. Chem. Soc. 1997 , 119, 11345. 35 (a) Inai, Y.; Ousaka, N.; Okabe, T. J. Am. Chem. Soc. 2003 , 125, 8151. (b) Sanji, T.; Takase, K.; Sukaria, H. J. Am. Chem. Soc. 2001 , 123, 12690. (c) Inai, Y.; Tagawa, K.; Takasu, A.; Hirabayashi, T.; Oshikawa, T.; Yamashita, M. J. Am. Chem. Soc. 2000 , 122, 11731. 36 Fukuda, M.; Rodríguez, R.; Fernández, Z.; Nishimura, T.; Hirose, D.; Watanabe, G.; Quiñoá, E.; Freire, F.; Maeda, K. Chem. Commun. 2019 , 55, 7906-7909. 37 (a) Solá, J.; Helliwell, M.; Clayden, J. J. Am. Chem. Soc. 2010 , 132, 4548-4549. (b) Costil, R.; Fernández-Nieto, F.; Atkinson, R.C.; Clayden, J. Org. Biomol. Chem. 2018 , 16, 2757-2761. 38 Ousaka, N.; Inai, Y. J. Org. Chem. 2009 , 74, 1429. Cooling Process Mono-1 Mono-2 Copolimerization + Chiral Monomers with Different Helical Sense Preference Heating Process Thermal effects modify the conformational composition of the monomeric units within the polymer chain and trigger the addoption of a preferred helical sense. Not fully folded dynamic polymers Introduction 19 Figure 16 . (a) Examples of peptides showing Domino Effect. (b) Schematic illustration of the chiral amplification phenomena through the Domino Effect. 4.8. Chiral Communication through spacers: chiral teleinduction and chiral harvesting Poly(phenylacetylene)s are dynamic helical polymers with potential applications in different fields such as asymmetric synthesis, 39 chiral separations, 40 sensing, 41 etc., whose helicity and/or length can be by the application of several external stimuli.4, 41, 42 , 43 , 44 , 45 In these polymers, the chirality of the pendant groups selectively commands the helical sense of the polyenic skeleton (P/M helix)4a-e, 42 depending on its R/S absolute configuration. Additionally, these changes produced in the helical structure can be also determined by the spatial dispositions adopted by the pendant group. Related to this topic, Yashima 46 and Nolte4j, 47 have reported that the secrew sense of polymers bearing more than one chiral center is controlled by the group closer to the backbone. Likewise, Veciana and co-workers 48 have demonstrated that the effective helical induction 39 (a) Megens, R. P.; Roelfes, G. Chem. Eur. J. 2011 , 17, 8514-8523. (b) Tang, Z.; Iida, H.; Hu, H-Y.; Yashima, E. ACS Macro Lett. 2012 , 1, 261-265. (c) Iida, H.; Tang, Z.; Yashima, E. J. Polym. Sci., PartA: Polym. Chem. 2013 , 51, 28692879. 40 Shimomura, K.; Ikai, T.; Kanoh, S.; Yashima, E.; Maeda, K. Nat. Chem. 2014 , 6, 429-434. 41 (a) Anger, E.; Iida, H.; Yamaguchi, T.; Hayashi, K.; Kumano, D.; Crassous, D.; Vanthuyne, N.; Rousselc, C.; Yashima, E. Polym. Chem. 2014 , 5, 4909-4914. (b) Iida, H.; Miki, M.; Iwahana, S.; Yashima, E. Chem. Eur. J. 2014 , 20, 4257-4262. 42 Yashima, E.; Ousaka, N.; Taura, D.; Shimomura, K.; Ikai, T.; Maeda, K. Chem. Rev. 2016 , 116, 13752-12990. 43 Sakurai, S.-I.; Okoshi, K.; Kumaki, J. Yashima, E. J. Am. Chem. Soc. 2006 , 128, 5650-5651. 44 Okoshi, K.; Sakurai, S.; Ohsawa, S.; Kumaki, J.; Yashima, E. Angew. Chem. Int. Ed. 2006 , 45, 8173-8176. 45 Feringa, B. L. Acc. Chem. Res. 2011 , 34, 504-513. 46 Kamikawa, Y.; Kato, T.; Onouchi, H.; Kashiwagi, D.; Maeda, K.; Yashima, E. J. Polym. Sci. A Polym. Chem. 2004 , 42, 4580. 47 Cornelissen, J. J. L. M.; Donners, J. J. J. M.; de Gelder, R.; Graswinckel, W. S.; Metselaar, G. A.; Rowan, A.E.; Sommerdijk, N. A. J. M.; Nolte, R. J. M. Science 2001 , 293, 676. 48 (a) Ramos, E.; Bosch, J.; Serrano, J. L.; Sierra, T.; Veciana, J. J. Am. Chem. Soc. 1996 , 118, 4703. (b) Amabilino, D. B.; Ramos, E.; Serrano, J. L.; Sierra, T.; Veciana, J. J. Am. Chem. Soc. 1998 , 120, 9126. H2N Achiral+Peptide+Showing+Left-+and+Rigth-Handed+Helices+in+Equilibrium CO2H2N O OH Adition+of+a+ Chiral+Acid +H3N Salt+Bridge+ Formation Chiral+Transmision Domino+Effect H2N H N O N H O O O N H H N O OO H2NO 4 4 Poly-20 Poly-21 a) b) Introduction 20 decreases when the chiral center is shifted away along the pendant chain. Therefore, it is necessary to place the chiral group close to the backbone in order to achieve an effective helical induction. Our group have taken one step further in the helicity control of (PPA)s and have reported different remote chiral induction mechanisms. An effective transmission of chiral information from the pendant to the polyenic scaffold was demonstrated by the introduction of both flexible —chiral tele-induction— 49 -, 50 , 51 , 52 , 53 , 54 , 55 and rigid achiral spacers —chiral harvesting—.35a, 36, 38, 56 In the firts mechanism, transmission of the chiral information from a remote position takes place through space, thus overcoming the distance triggered by the spacer. In this way, we have reported an effective chiral induction in two (PPA)s series that bear pendants formed by one or two consecutive glycine redisues —acting as an achiral, flexible and well-organized spacers—and (R)- or (S)-a-methoxy-atrifluoromethylphenylacetic acid (MTPA) —as the remote chiral inductor— (poly22 to poly25 , Figure 17a). These glycines residues form a parallel b-sheet structure with the neighboring pendants, stabilizing the helical structure of the polyene by hydrogen bonding and orienting the chiral groups in specific directions. In addition, the helicity of the polyenic chain (P/M) can be modulated by the application of different external stimuli (i.e., polarity of the media, metal cations) fixing the conformation of the MTPA moiety connected to the achiral b-sheet spacer.54 49 Amabilino, D. B.; Ramos, E.; Serrano, J. L.; Sierra, T.; Veciana, J. Polymer 2005 , 46, 1507-1521. 50 Gomar-Nadal, E.; Veciana, J.; Rovira, C.; Amabilino, D. B. Adv. Mater. 2005 , 17, 2095-2098. 51 Percec, V.; Aqad, E.; Petarca, M.; Rudick, J. G.; Lemon, L.; Ronda, J.C., De, B. B.; Heiney, P. A.; Meijer, E. W. J. Am. Chem. Soc. 2006 , 128, 16365-16372. 52 Percec, V.; Petarca, M.; Rudick, J. G.; Aqad, E.; Imam, M. R.; Heiney, P. A. Chem. Eur. J. 2007 , 13, 9572-9581 53 Abe, Y.; Aoki, T.; Jia, H.; Hadano, S.; Namikoshi, T.; Kakihana, Y.; Liu, L.; Zang, Y.; Teraguchi, M.; Kaneko, T. Chem. Lett. 2012 , 41, 244-246. 54 Rodríguez, R.; Quiñoá, E.; Riguera, R.; Freire, F. Chem. Mater. 2018 , 30, 2493-2497. 55 Rodríguez, R.; Quiñoá, E.; Riguera, R.; Freire, F. Small 2019 , 15, 1805413. 56 Fernández, Z.; Fernández, B.; Quiñoá, E.; Riguera, R.; Freire, F. Chem. Sci. 2020 , 11, 7182-7187. Introduction 21 Figure 17 . Structure of the polymers with (a) one and (b) two flexible spacers. (c) Conceptual representation of the chiral teleinduction produced in a helical polymer when an achiral flexible linker is fixed by internal supramolecular interactions. As aboved mentioned (see section 4.7), these achiral residues can be used as building bloks generating achiral peptides composed by fragments such as a-aminoisobuturic acid (Aib) among others.34-37 Clayden and co-workers have reported an interesting work employing this kind of oligopeptides. This research was focused on the membrane phase which requires probes sensitive to conformational change in membrane-active dynamic foldamers. Thus, enantiomers of chiral peptide foldamers bearing bis(pyrene) fluorescent probes were synthesized, analyzed and designed to distinguish between rightand lefthanded screw sense conformers of 310-helical a-aminoisobutiric acid (Aib), both in solution and bilayer membranes. Conformational interchange between P and M helical sense in Aib foldamers could be monitored in real rime by these optimized probes both in organic solvents and bilayers. The mentioned probes were attached to the C-terminus of Aib tetramers presenting different chiral residues at the N-terminus where the two pyrene units located closer allowed to obtain a higher excimer fluorescence than pyrene units spaced further away. In bilayers, fluorescent probes made it possible to poly-(R)-22(and(poly-(S)-23 N O H N O H OCF3 N O H H n N O H H N O O CF3 H n * * poly-(R)-24(and(poly-(S)-25 a) b) c) folding a flexible spacer bending a flexible spacer 12 “Selective action on a flexible spacer” “axially racemic helix” “single-handed helix” “planar structure” R R R RR R R R R R R Introduction 22 demonstrated for the first time that the chirality of natural phospholipids has a significant influence on the conformation of oligomers in the membrane. 57 Figure 18 . Schematic bis(pyren-1-yl) probe attached to M and P screw-sense conformers of a controlled Aib4 helix. Additionally, our group have described a chiral induction mechanism in poly(phenylacetylene)s whose pendants groups are maded by these short oligopeptides [(Aib)n, (n = 1, 2, 3)] —the achiral units— that place the chiral moiety [(R)-MTPA] far away from the helical structure. The chiral information of the MTPA is transmitted along the achiral Aib to the helical scaffold through chiral tele-induction and/or chiral harvesting mechanism depending on the length of the achiral spacer. In addition, these length modifications as well as the application of external stimuli alow us to modify the helical sense of the generated macromolecular gears (Figure 19). 58 57 Lister, F. G. A.; Eccles, N.; Pike, S. J.; Brown, R. A.; Whitehead, G. F. S.; Raftery, J.; Webb, S. J.; Clayden, J. Angew. Chem. Sci. 2018 , 9, 6860-6870. 58 Suárez-Picado, E.; Rodríguez, R.; Quiñoá, E.; Riguera, R.; Freire, F. Angew. Chem. Int. Ed. 2020 , 59, 8616-8622. (P)#helical#excess D-Phe#controller:#X"="H,"Y"="CH2Ph L-αMeVal#controller:#X"="CHMe2,"Y"="Me (M)#helical#excess L-Phe#controller:#Y"="H,"X"="CH2Ph D-αMeVal#controller:#Y"="CHMe2,"X"="Me Introduction 23 Figure 19 . (a) Structures of polymers. (b) Conceptual illustration of the chiral information transmission mechanism. CD/UV-Vis spectra showing (c) the helix inversion and stretching process of poly26 , (d) the stretching process of poly27 and (e) the three different helical state with different elongation degree of poly28 . The second mechanism —chiral harvesting— describes how the helix induction is harvested by the polymer main chain when chiral information is transmitted through achiral spacers itself. It is possible to generate a preferred helical structure into the achiral spacer by modifying the chiral center conformation or even just changing its absolute configuration, which in turn will be harvested by polyenic backbone. Another chiral harvesting process was reported by our group where the arrangement of the achiral spacer within the helical structure is determined by the chiral center which does not generate a conformational change at the achiral spacer. To achieve this goal polymers bearing oligo(p-phenyleneethynylene)s (m = 1, 2, 3) (OPEs) as rigid spacers — placing the chiral pendant group away from the polyene backbone— were developed. The stacking of the OPE units within the helical scaffold is affected by the arrangement of the chiral moiety, which is further harvested by the polyene backbone giving rise to a preferred P or M internal helix.56, 59 59 Fernández, Z.; Fernández, B.; Quiñoá, E.; Freire, F. J. Am. Chem. Soc. 2021 , 143, 20963-20969. 300 400 500 600 -20 -15 -10 -5 0 5 10 1 2 3 Wavelength [nm] CD [mdeg] Abs CHCl3 THF DMF 300 400 500 -60 -50 -40 -30 -20 -10 0 10 0.2 0.4 0.6 0.8 1.0 Wavelength [nm] CD [mdeg] CHCl3 DMSO Abs 300 400 500 -90 -75 -60 -45 -30 -15 0 15 30 1 2 3 4 Wavelength [nm] CD [mdeg] CHCl3 THF NMP Abs aib$=$1,$Poly-26 aib$=$2,$Poly-27 aib$=$3,$Poly-28 N O H H N O O CF3 H n a) c) b) Screw Sense Induction Chiral Information Harvesting (Aib)n oligopeptide (achiral) PPA main chain chiral group a d) e) Introduction 24 Figure 20 . Conceptual side view and top view of the chiral information transmission from stereocenters at the far end of OPE spacers to the polyene backbone via chiral harvesting. 4.9. Helix Inversion One of the most interesting features of dynamic helical polymers is the helix inversion, a macromolecular process where the control of the helicity between leftand righthanded helical conformations is done by the presence of several external stimuli like changes in solvent polarity 60 or temperature, 61 addition of anionic species 62 or metal ions,26, 27 pH 63 or even light.4b, 64 With this information in mind, our research group developed a polymer formed from the amine of 4-ethynylbenzoic acid with the amino acid (S)-phenylglycine methyl ester (PGME) (poly29 ). This PPA presents two main conformers in equilibrium in equal population in the pendant group: the syn conformer, where the two carbonyls are in synperiplanar orientation and the ap conformer, in which the two carbonyls are antiperiplanar oriented. This conformational equilibrium can be modulated by organic solvents with different polarity. In polar solvents (e.g. DMF), the pendant moiety of PGME adopts the syn conformation, while in low-polar solvents (e.g. CHCl3 or THF) the anti conformer of the pendant group commands the helical sense displaying a negative CD signal. Also, the addition of metal cation (e.g., Ba2+) is able to shift the ap conformer 60 Maeda, K.; Kamiya, N.; Yashima, E. Chem. Eur, J. 2004 , 10, 4000-4010. 61 Zhou, Y.; Zhang, C.; Qiu, Y.; Liu, L.; Yang, T.; Dong, H.; Satoh, T.; Okamoto, Y. Molecules 2016 , 21, 11. 62 (a) Kakuchi, R.; Shimada, R.; Tago, Y.; Sakai, R.; Satoh, T.; Kakuchi, T. J. Polym. Sci., Part A: Polym. Chem. 2010 , 48, 1683-1689. (b) Kakuchi, R.; Tago, Y.; Sakai, R.; Satoh, T.; Kakuchi, T. Macromolecules 2009 , 42, 4430-4435. (c) Otsuka, I.; Sakai, R.; Satoh, T.; Kakuchi, R.; Kaga, H.; Kakuchi, T. J. Polym. Sci., Part A: Polym. Chem. 2005 , 43, 5855-5863. 63 Janssen, P. G. A.; Ruiz-Carretero, A.; González-Rodríguez, D.; Meijer, E. W. Angew. Chem. Int. Ed. 2009 , 48, 81038106. 64 Wang, L.; Dong, H.; Li, Y.; Liu, R.; Wnag, Y.-F.; Bisoyi, H. K.; Sun, L.-D.; Yan, C.-H.; Li, Q. Adv. Mater. 2005 , 27, 20652069. Introduction 31 Related to this information, Percec and co-workers reported how the four different configurations of the conjugated double bonds—trans-cisoidal (t-c), trans-transoidal (t-t), cis-cisoidal (c-c) and cis-transoidal (c-t) — can be differentiared by 1H NMR spectra combining theoretical and experimental results.55f,g,h In polymers with trans-configuration of the doble bonds, the vynilic proton resonates around 6.20-7.20 ppm. Moreover, the aromatic protons present different pattern in a trans-cisoidal or trans-transoidal structure: in the first case all the aromatic protons resonate in the same region while in a trans-transoidal configuration only two aromatic protons appears upfield shifted with respect to the other aromatic protons.72 Otherwise, the vynilic proton of a polymer with cisstructure appears around 5.60-5.80 ppm and the aromatic protons also present different splitting patter. Polyenic chain with cis-transoidal configuration display two aromatic protons upfield shifted, while in a PPA with cis-cisoidal polyene backbone, only one aromatic proton should be upfield shifted in comparison with the other aromatic protons. 1H NMR spectra of a PPA with cis-cisoidal structure have the vinyl proton at 5.80 ppm; 1H orthoat 6.70 ppm, 1H paraand metaat 6.85 ppm. In addition, they also propose an equation to determine the cis-content of PPA based on this data. % cis = [Acis/(Atotal x Htotal)] x100 Equation 1 . Equation used for calculating the % cis of a PPA. Where Acis is the peak area of the vinyl proton obtained from 1H NMR (5.6-5.8 ppm), Atotal is the total area of the observed 1H-NMR spectrum, and Htotal is the number of the pendant protons. Another useful technique to obtain information about the polyenic chain configuration is Raman spectroscopy that shows the resonance bands characteristics of the polyene skeleton in a PPA. A polymer with a trans-transoidal structure presents the following bands: trans-C=C (1475 cm-1) and trans-C-C (1200 cm-1),18b,c, 76 while a PPA with a ciscisoidal or cis-transoidal configuration displays cis-C=C (1530 cm-1), cis-C-C (1335 cm-1) Sci.: Polymer Symposia 1980 , 67, 43. (f) Simionescu, C. I.; Percec, V. J. Polym. Sci., Polym. Chem. Ed. 1980 , 18, 147. (g) Simionescu, C. I.; Percec, V. J. Polym. Sci., Polym. Lett. Ed. 1979 , 17, 421. (h) Simionescu, C. I.; Percec, V.; Dumitrescu, S. J. Polym. Sci., Polym. Chem. Ed. 1977 , 15, 2497. 76 Misayaka, A.; Sone, T.; Mawatari, Y.; Setauesh, S.; Müllen, K.; Tabata, M. Macromol. Chem. Phys. 2006 , 207, 1938. Introduction 32 and cis-C-H (965 cm-1) bands. Additionally, deformation bands, trans-C-H (1015 cm-1) and cis-C-H (740 cm-1) can be detected by FT-IR spectroscopy. 77 With all this previous information in hand, obtained from the combination of NMR, Raman spectroscopy and FT-IR techniques, we are able to distinguish a cisor transconfiguration of the double bonds, but is impossible to differentiate c-c from c-t and t-t from t-c. Thereby, additional technique is required to define the secondary structure of (PPA)s: Differential Scanning Calorimetry (DSC) whose thermograms are different for polymers with c-c and c-t structure. The thermogram of a c-c (PPA)s shows only an exothermic transition peak around 200-240oC due to the isomerization process from c-c to t-t, while (PPA)s with c-t configuration present two exothermic bands around 140oC and 240oC, corresponding with the c-t to c-c and c-c to t-t isomerization processes respectively. This quality makes DSC an useful technique to diferenciate between the c-c and c-t scenario. 78 , 79 Figure 27 . (a) Schematic illustration of the w1 angle and the effect over the type of helical scaffold. Representative DSC thermograms of (b) c-c structures and (c) c-t structures. Other technique that can provide informarion about the secondary structure of (PPA)s is UV-Vis spectroscopy that allows us to control the compressiom or stretching degree of the polymer backbone by comparison with other reported (PPA)s helical structures. Deep into details, a more compressed helix will display a hypsocromic shift in the vinylic region due to a less conjugated helical scaffold. However, a bahochromic effect is observed 77 (a) Ito, T.; Shirakawa, H.; Ikeda, S. J. Polym. Sci., Part A: Polym. Chem. 1974 , 12, 11-20. (b) Shirakawa, H.; Ikeda, S. Polym. J. 1971 , 2, 231. 78 (a) Motoshige, A.; Mawatari, Y.; Yoshida, Y.; Motoshige, R.; Tabata, M. Polym. Chem. 2014 , 5, 971. (b) Yoshida, Y.; Mawatari, Y.; Motoshige, A.; Motoshige, R.; Hiraoki, T.; Wagner, M.; Müllen, K.; Tabata, M. J. Am. Chem. Soc. 2013 , 135, 4110. (c) Motoshige, A.; Mawatari, Y.; Motoshige, R.; Yoshida, Y.; Tabata, M. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 5177. 79 Motoshige, R.; Mawatari, Y.; Motoshige, A.; Yoshida, Y.; Sasaki, T.; Yoshimizu, H.; Suzuki, T.; Tsujita, Y.; Tabata, M. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 752. ω1 Angle ω1< 90º c-c structure ω1> 90º c-t structure a) 125 150 175 200 225 250 T/ ºC c-t c-c t-t T1= 135 ºC T2= 200 ºC 175 200 225 250 275 T/ ºC T1= 135 ºC c-c t-t b) c) Introduction 33 when conjugation of the doble bonds increase, which corresponds to a more stretched structure than the previous one. 80 , 81 5.2. Determination of the Screw Sense of (PPA)s The helical pitch and the helical handedness excess in the macromolecule structure can be determined by differect techniques. The two most common techniques are circular dichroism (CD) and optical rotation that are based on the interaction of the corresponding macromolecules with light. 5.2.1 Circular Dichroism Circular dichroism (CD) is a very useful technique in the helical polymers field where CD studies allow us to detect the presence of a preferred helical sense in the polymer, namely, it is able to distinguish between the absorption of right-handed circularly polarised light (R-CPL) and left-handed circularly polarised light (S-CPL) of molecules that bear one or more chiral chromophores (light-absorbing groups). In addition, this technique can be applied to determine the chirality of small molecules or the chiral content and folding of big macromolecules. The CD spectrum not only gives us information about the secondary structure of peptides (being folded in a-helix, b-sheet or random coil) but also about the conformational changes of molecules with different sizes once external stimuli is added. Thereby, kinetic, structural and thermodynamic parameters can be easily obtained from this technique. 82 , 83 , 84 80 (a) Percec, V.; Peterca, M.; Rudick, J. G.; Aqad, E.; Imam, M. R.; Heiney, P. A. Chem. Eur. J. 2007 , 13, 9572. (b) Percec, V.; Rudick, J. G.; Peterca, M.; Aqad, E.; Imam, M. R.; Heiney, P. A. J. Polym. Sci., Part A: Polym. Chem. 2007 , 45, 4974. (c) Percec, V.; Aqd, E.; Peterca, M.; Rudick, J. G.; Lemon, L.; Ronda, J. C.; De, B. B.; Heiney, P. A.; Meijer, E. W. J. Am. Chem. Soc. 2006 , 128, 16365. (d) Percec, V.; Rudick, J. G.; Peterca, M.; Wagner, M.; Obata, M.; Mitchell, C. M.; Cho, W. D.; Balagurusamy, V. S. K.; Heiney, P. A. J. Am. Chem. Soc. 2005 , 127, 15257. 81 Motoshige, A.; Mawatari, Y.; Yoshida, Y.; Matsuyama, C. S.; Tabata, M. J. Polym. Sci., Part A: Polym. Chem. 2012 , 50, 3008. 82 (a) Hammes, G. G.; Circular Dichroism, Optical Rotatory Dispersion, and Fluorescence Polaization, In Spectroscopy for the Biological Sciences, John Wilewy & Sons, Inc. 2005 , p 63. (b) Bereova, N.; Nakanishi, K., Woody, R. W., Circular Dichroism: Principles and Applications, 2nd ed., Wiley-VCH: New York, 2000 p 912. 83 (a) K. Nakanishi, N. Berona, Circular Dichroism: Principles and Applications; ed por N. Berova, K. Nakanishi, W. R Woody, 2000 , Wiley-VCH, 2nd ed, Cap 13, p 361. (b) Harada, N.; Nakanishi, K. Circular Dichroic Spectroscopy-Exciton  Coupling in Organic Stereochemistry; 2nd ed., University Science Books: Mill Valley, CA, 1983 . 84 (a) Suzuki, Y.; Tabei, J.; Shiotsuki, M.; Inai, Y.; Sanda, F.; Masuda, T. Macromolecules 2008 , 41, 1086. (b) Buffeteau, T.; Ducasse, L.; Poniman, L.; Delsuc, N.; Huc, I. Chem. Commun. 2006 , 2714-2716. (c) Tang, H.-Z.; Novak, B. M.; He, J.; Polavarapu, P. L. Angew. Chem. Int. Ed. 2005 , 44, 7298. (d) Tanatani, A.; Yokoyama, A.; Azumaya, I.; Takakura, Y.; Mitsui, C.; Shiro, M.; Uchiyama, M.; Muranaka, A.; Kobayashi, N.; Yokozawa, T. J. Am. Chem. Soc. 2005 , 127, 8553. (e) Tabei, J.; Shiotsuki, M.; Sanda, F.; Masuda, T. Macromolecules 2005 , 38, 9448. (f) Kaneko, T.; Umeda, Y.; Yamamoto, T.; Tereguchi, M.; Aoki, T. Macromolecules 2005 , 38, 9420. (g) Takei, F.; Hayashi, H.; Onitsuka, K.; Kobayashi, N.; Takahashi, S. Angew. Chem. Int. Ed. 2001 , 40, 4092. Introduction 34 Thus, the CD spectroscopy gives us information about the response to external situmulus and the folding of helical polymers where the amount of polymer needed is very small (less than 0.1 mg) and the envorinment conditions to carry out these studies can be easily modified (temperature, solvents…). In helical polymers, the presence of an excess of helical sense and helical changes can be detected by the CD signal of the polymeric main chain.4b 5.2.2 Theoretical Calculations of Circular Dichroism During the last years, theoretical calculations have attracted the attention of the scientific community for its usefulness in elucidating helical structures. Deep into details, the secondary structure of some helical polymers can be determined by exploring ECD simulation together with MMFF94 energy minimization, where the time-dependent selfconsistent field (SCF) ZernerQs Intermediate Neglect of Differential Overlap (ZINDO/S) method is employed. For instance, the formation of two different helical scaffolds (different dihedral angle at the single bond along the main chain) was demonstrated by Masuda and co-workers when working with a series of polymers derived from propargylamides.82a In the case of (PPA)s, an example has been report focusing on the CD bands corresponding to the pendant and not on those related to the polyenic chain.82f Recently, DFT theoretical studies on oligomers obtained from experimental techniques were used to correlate the CD signal in the vinylic region with the helicity adopted by the poly(phenylacetylene). This occurs when a good match is observed/obtained between the experimental ECD spectra for some (PPA)s – that present a known helical scaffold– and the calculated ECD spectra for small oligomers. To calculate the ECD spectra, the Time-Dependent Density Function Theory (TD-DFT) was employed and the 3-21G basis set with the CAM-B3LYP functional were selected as base. This work was reported by our research group providing that if the first Cotton effect has a negative sing [CD (-)], the polyenic skeleton adopts a M internal helix. On the contrary, a P internal helix is obtained when the first Cotton effect is positive [CD (+)]. 85 85 (a) Fernández, B.; Rodríguez, R.; Rizzo, A.; Quiñoá, E.; Riguera, R.; Freire, F. Angew. Chem. Int. Ed. 2018 , 57, 36663670. (b) Fernández, B.; Rodríguez, R.; Quiñoá, E.; Riguera, R.; Freire, F. ACS Omega 2019 , 4, 5233-5240. Introduction 35 From these results, theoretical calculations could have been applied in differents works such as predicting the structural and dynamic behaviour by rational design of polymers; 86 in more complex helices presenting rigid spacers between pendants and the backbone56, 57 and even in the formation of supramolecular helical scaffolds. 87 , 88 5.2.3 Vibrational Circular Dichroism and Raman Optical Activity Another interesting thecniques to determine the screw sense in (PPA)s are Vibrational Circular Dichroism (VCD) and Raman Optical Activity, the chiral version of traditional IR and Raman techniques. On the one hand, VCD is a spectroscopic method to measure the difference in absorbance intensity between left-and right-hand circularly polarized light in the infrared and near infrared regions. This is distinguished from electronic circular dichroism (ECD or CD), which focuses on the ultraviolet region. VCD allows not only direct observation and control of supramolecular chirality, but also to differentiate between different conformations of pendants groups in (polyphenylacetylene)s. Likewise, this thecnique shows how an achiral solvent can be organize in a helical form by interacting with the helical polymer and displays an interesting sensitivity in the formation of protein fibril structures in solution. 89 , 90 , 91 On the other hand, ROA is more localized, and more reflective of configuration, than VCD. Also, there is a non-equivalence between the scattered and incident circular polarization light beam. 92 Recently, it has been used not only to define the srew sense of the helix but also to elucidate the helical structure of (PPA)s despite being a weak effect and requiring large amounts of sample. 93 , 94 86 Cobos, K.; Rodríguez, R.; Domarco, O.; Fernández, B.; Quiñoá, E.; Riguera, R.; Freire, F. Macromolecules 2020 , 53, 3182. 87 Fernández, B.; Fernández, Z.; Quiñoá, E.; Freire, F. Molecules 2021 , 26, 3530. 88 Fernández, Z.; Fernández, B.; Quiñoá, E.; Freire, F. Angew. Chem. Int. Ed. 2021 , 60, 9919. 89 Ma, S.; Cao, X.; Mak, M.; Sadik, A.; Walkner, C.; Freedman, T. B.; Lednev, I. K.; Dukor, R. K.; Nafie, L. A. J. Am. Chem. Soc. 2007 , 129, 12364. 90 Kurouski, D.; Lombardi, R. A.; Dukor, R. K.; Lednev, I. K.; Nafie, L. A Chem. Commun. 2010 , 46, 7154. 91 Nieto-Ortega, B.; Rodríguez, R.; Medina, S.; Quiñoá, E.; Riguera, R.; Casado, J.; Freire, F.; Ramírez, F. J. J. Phys. Chem. Lett. 2018 , 9, 2266. 92 Nafie, L. A. Theor. Chem. Acc. 2008 , 119, 39. 93 Li, G.; Kessler, J.; Cheramy, J.; Wu, T.; Poopari, M. R.; Bour, P.; Xu, Y. Angew. Chem. Int. Ed. 2019 , 58, 16495; Angew. Chem. 2019 , 131, 16647. 94 Palomo, L.; Rodríguez, R.; Medina, S.; Quiñoá, E.; Casado, J.; Freire, F.; Ramírez, F. J. Angew. Chem. Int. Ed. 2020 , 132, 9165. Introduction 36 5.2.4 Optical rotation The optical rotation provides the degree of deviation of the polarized light produced when interacts with optically active molecules in solution. This data depends on the concentration, solvent and temperature of the sample and also depends on the length of the cuvette employed to perform the measurement. However, this technique is low sensitivity and a large amount of sample required. In helical polymers, the [a] value is at least one order of magnitude higher that the corresponding monomeric unit. The [a] value is calculated form equation. 2, where a obs is the observed optical rotation (degrees), c is the concentration (g/mL) and l is the path length (length of the cell in dm). [ 𝛼 ] =𝛼%𝑜𝑏𝑠 𝑐. 𝑙 %%%%%%%%%%%% Equation 2 . Equation used for the calculation of the optical rotation. Nevertheless, the combination of these structural techniques (CD, DSC, IR, NMR and Raman) cannot provide the 3D structure of the polymers so their helical pitch as well as their w1 value are unknown. In order to resolve these limitations and achieve the secondary structure of a helical PPA other techniques such as XDR (X-ray diffraction) and AFM (Atomic Force Microscopy) must be applied.4b 5.3. X-ray Diffraction It is possible to obtain information about the secondary structure of a PPA by X-ray diffraction, where the most important drawback is the preparation of the sample: a uniaxially oriented film of the polymer with a regular helical structure over a long distance. The presence of rigid rods in the polymer promotes the formation of these kind of oriented films with tendency to form lyotropic or thermotropic liquid crystals (LC). Also, they can be fabricated by physical shearing or under electric or magnetic fields. 95 From these measurements, several data related to the main chain helical structure can be obtained (helix width, helix length, interpendant distances and helical pitch). Nevertheless, not allways all these different parameters can be assignable, and even in this best case it is impossible to obtain the helicity of the polymer. 95 Yashima, E. Polym. J. 2010 , 42, 3-16. Introduction 37 5.4. Atomic Force Microscopy Analysis Atomic Force Miscroscopy (AFM) represents the most powerful structural technique to define the helical structure of helical polymer, providing the main structural information like helical sense described by the pendants, helical pitch and packing angle. Nevertheless, the preparation of a hight-resolution AFM image is the main disadvantage of this technique being necessary to obtain a 2D-crystal or well-ordered monolayers of the polymer. The different protocols to prepare AFM samples are described next. 5.4.1. Drop-casting and spin coating The first approach to solve the helical structure by AFM was reported by Yashima and co-workers. They deposited the following three polymers by drop casting on an AFM substrate, in this case, mica: lowand high-molecular-weight poly(4carboxyphenylacetylene)s (poly16 ), their salts with (R)-(+)-1-(1-naphthyl)ethylamine [(R)- 38 ] and their corresponding carboxyamides (poly39 ). Then, an AFM analysis was performed where the helical structure of isolated chains was obtained. 96 However, the quality of the images was not good enough to obtain reliable values for the helical pitch and packing angle (Figure 28a-b). 97 That’s the reason why they decided to carry out a second approach, introducing a long alkyl chains in the pendant moiety of the PPA, which should promote its self-assembly by interdigitation of the long chain.43, 98 Next, the spin coating of a dilute solution of the polymer onto a solid AFM substrate —mica or highly oriented pyrolytic graphite (HOPG)— was made. The substrate was also kept under solvent atmosphere overnight to promote the self-assembly of the polymer chains. From this new methodology, Yashima and co-workers acquired the helical structure of poly-D40 and poly-L40 , bearing Dand L-alanine decyl esters.69c Aditionally, AFM analysis showed well-ordered 2D-crystals due to the strong and epitaxial adsorption of the alkyl chains of the pendant on the graphite lattice (Figura 28d). The AFM images of poly-L40 displayed a helical structure with a helical pitch of 2.34 nm and a packing angle of 40°, where the pendant groups define an external M helical structure 11/5, with two residues 96 Sakurai, S.-I.; Kuroyanagi, K.; Morino, K.; Kunitake, M.; Yashima, E. Macromolecules 2003 , 36, 9670-9674. 97 (a) Sakurai, S. -I.; Ohira, A.; Suzuki, Y.; Fujito, R.; Nishimura, T.; Kunitake, M.; Yashima, E. J. Polym. Sci. Part A Polym. Chem. 2004 , 42, 4621. (b) Nishimura, T.; Maeda, K.; Ohsawa, S.; Yashima, E. Chem. - A Eur. J. 2005 , 11, 1181. 98 (a) Nishimura, T.; Takatani, K.; Sakurai, S.; Maeda, K.; Yashima, E. Angew. Chem. Int. Ed. 2002 , 41, 3602-3604. (b) Okoshi, K.; Sakurai, S.; Ohsawa J. K.; Yashima, E. Angew. Chem. Int. Ed. 2006 , 45, 1245-1248 (c) Ohsawa, S.; Sakurai, S.-I.; Nagai, K.; Banno, M.; Maeda, K.; Kumaki, J.; Yashima, E. J. Am. Chem. Soc. 2011 , 133, 108-114. Introduction 38 per turn (Figure 28d). The internal polyenic backbone shows a c-t configuration and describes a right-handed (P) helical sense with a pitch of 2.3 nm. From these results, a right-handed helical structure is determined by the polyene backbone, while a lefthanded helical array is described by the pendant groups (AFM, Figure 28d). Figure 28 . (a) Schematic illustration of the drop casting technique. (b) Structure and AFM image of Poly16 /(R)- 38 )-naphtylethylamine complex and poly39 . (c) Schematic illustration of the spin-coating and solvent exposure process. (d) Structure and AFM images of poly40 . c) Dilute Solution Spin Coating Solvent Annealing a) Dilute Solution Drop Casting Solvent Annealing AFM Analysis High Resolution AFM Images Solvent Atmosphere b) H O NH n Poly-(X) O O9 c) H O NH n Poly-(X) O O9 Poly-42 Poly-43 a) Dilute Solution Drop Casting AFM Analysis b) Mica%substrate 8 398 39 Introduction 39 In parallel to Yashima’s work, Percec and co-workers described a similar protocol to produce 2D crystals by spin coating approach, where a dilute solution of the polymer is deposited over the corresponding substrate —either mica or HOPG—. The process is followed by thermal annealing instead of solvent exposure and was applied to a library of dendronized (PPA)s (poly41 and poly42 ) with long alkyl tails, essentials to promote the PPA self-assembly (Figures 29a and 29c). 99 Despite of the successful creation of 2Dcrystals, no high-resolution AFM images could be obtained and therefore, parameters like helical sense, helical pitch and packing angle continue to be unknown (Figure 29). Figure 29 . (a) Structure of poly41 . (b) AFM of poly41 on HOPG after thermal annealing. (c) Structure of poly42 . (c) and (d) AFM images of poly42 in mica and HOPG respectively after thermal annealing. 5.4.2. Langmuir-Blodgett Monolayers As previous mentioned, the preparation of PPA monolayers by drop casting and spin coating consists in the evaporation of a solution of the polymer on a solid support where an air/solid interface is formed. In those conditions, the solvent evaporation and the polymer substrate affinity are critical factors. 99 (a) Percec, V.; Obata, M.; Rudick, J. G.; De, B. B.; Glodde, M.; Bera, T. K.; Magonov, S. N.; Balagurusamy, V. S. K.; Heiney, P. A. J. Polym. Sci., Part A: Polym. Chem. 2002 , 40, 3509. (b) Percec, V.; Rudick, J. G.; Peterca, M.; Staley, S. R.; Wagner, M.; Obata, M.; Mitchell, C. M.; Cho, W.-D.; Balagurusamy, V. S. K.; Lowe, J. N.; Glodde, M.; Weichold, O.; Chung, K. J.; Ghionni, N.; Magonov, S. N.; Heiney, P. A. Chem. Eur. J. 2006 , 12, 5731. (c) Percec, V.; Rudick, J. G.; Wagner, M.; Obata, M.; Mitchell, C. M.; Cho, W.-D.; Magonov, S. N. Macromolecules 2006 , 39, 7342. a) H n Poly-(43) N RO OR RO R= -(CH2)11CH3 b) c) H n Poly-(44) O O OC12H25 OC12H25 OC12H25 OC12H25 d) e) f) g) poly-41 poly-42 Introduction 40 Affortunatelly it is possible to resort to another procedure, the Langmuir-Blodgett (LB) method, that prepares monolayers in an air/water interface. The formation of Langmuir monolayers starts with dropwise deposition of the target molecule in an organic solvent on a water surface. Next, two processes happen at the same time: the water suface is gradual compressed by the barriers of the LB system and the pressure of the polymer increases until a compact monolayer of molecules is formed. Then, the monolayes are transferred from the air/water interface to the AFM substrate, which was immersed on water (Figure 30a). 100 Although HOPG is adequate for the polymer, its hydrophobic properties are incompatible with its use in LB because the substrate has to be extracted from the water layer. Moreover, it’s known that the best AFM images acquired for this family of polymers are obtained when HOPG is used as solid substrate. Tang and co-workers applied the LB method to different different polymers bearing (L)- Aline (poly43 ) and (L)-Valine (poly44 ) methyl ester residues as pendant groups. They achieved the formation of the monolayers, but their qualities were poor and they could not solve the helical structure of the polymer (Figure 30b-c). 101 100 (a) Kawauchi, T.; Kumaki, J.; Kitaura, A.; Okoshi, K.; Kusanagi, H.; Kobayashi, K.; Sugai, T.; Shinohara, H.; Yashima, E. Angew. Chem. Int. Ed. 2008 , 47, 515-519. (b) Roberts, G. G. Langmuir-Blodgett Films; Plenum: New York, 1990 . 101 (a) Li, B. S.; Kang, S. Z.; Cheuk, K. K. L.; Wan, L.; Ling, L.; Bai, C.; Tang, B. Z. Langmuir 2004 , 20, 7598. (b) Li, B. S.; Lam, J. W. Y.; Yu Z.-Q.; Tang, B. Z. Langmuir 2012 , 28, 5770. Introduction 47 Figure 34 . (a) Structure and schematic illustration of the c-c and c-t structures adopted by poly33 . (b) Structural model of the polymeric self-assembly. (c) Stereocomplex formation and SEM images of the soft gel and fiber aggregates. Recently, new SCs based on polycarbonates were reported by Auriemma et al. and Liu et al., consinting in a mixture of enantiometic pure polymers where crystals of the SC were also obtained. 114 Other examples of fibber-like aggregates based on (PPA)s different from SCs can be found in literature. In this way, a polymer bearing menthoxycarbonylamino groups (poly45 ) were reported by Shinohara, Shigekawa and co-workers. 115 They used Scanning Tunnelling Microscopy (STM) to display the formation of double helical structures when a solution of poly45 was drop-cast onto HOPG substrate. Therefore, they found that the interaction between the double helical structure and the scanning probe gave mobility to these macromolecules. As a result of these modifications during the STM measurement, the double helical structure was loosened. (Figure 35). 114 (a) Auriemma, F.; De Rosa, C.; Di Caprio, M. R.; Di Girolamo, R.; Coates, G. W. Macromolecules 2015 , 48, 2534-2550. (b) Auriemma, F.; De Rosa, C.; Di Caprio, M. R.; Di Girolamo, R.; Ellis, W. C.; Coates, G. W. Angew. Chem. Int. Ed. 2015 , 54, 1215-1218. (c) Liu, Y.; Ren, W.-M.; Wang, M.; Liu, C.; Lu, X.-B. Angew. Chem. Int. Ed. 2015 , 54, 2241-2244. 115 Shinohara, K.; Yasuda, S.; Kato, G.; Fujita, M.; Shigekawa, H. J. Am. Chem. Soc. 2001 , 123, 3619-3620. poly-(R)-33 poly-(S)-33 a) b) c) c-t structurec-c structure THF HN O H R2 R1 n poly-(R)-33,)R1)=)CF3,)R2)=)OMe poly-(S)-33,)R1)=)OMe,)R2)=)CF3 SOFT&GEL&FORMATION FIBER&AGGREGATES Introduction 48 Figure 35 . Structure of poly45 . (a) STM image of the supramolecular helical assembly and (b) conceptual representation of the assembly generated. Related to these findings, the effect in the supramolecular aggregation of (PPA)s bearing different methyl ester aminoacids as pendant group [e.g. valine (poly46 )] was reported by Tang and co-workers (Figure 36).72, 47, 116 The researchers found that changing the conditions of deposition the polymers could adopt intramolecular/intermolecular hydrogen bonds leading to different types of supramolecular structures. On one side, the formation of intermolecular hydrogen bonds interactions is favored by the pendant groups when a high concentration of poly46 is dissolved in low polar solvents (Figure 36a). Likewise, when solutions of those (PPA)s are drop-casted and slowly evaporated on mica, high order aggregates, such as fibbers with different length and diameters, colud be observed by AFM (Figure 36d and 36e).72 Otherwise, when poly46 is dissolved in polar solvents different supramolecular aggregates are generated due to their amphipathic character (non-polar backbone and polar pendants). This produces the formation of micelle-like structures, with the apolar polyenic backbone in the core and polar amino acid pendants pointing out to the shell (Figure 32b). The pendants outside of these micelles interact through hydrogen bonds, holding them together and triggering larger micelles that collapse to produce fibber-like structures (Figure 36c).72 116 (a) Cheuk, K. K. L.; Li, B. S.; Lam, J. W. Y.; Xie, Y.; Tang, B. Z. Macromolecules 2008 , 41, 5997-6005. (b) Li, B.S.; Cheuk, K. K. L.; Ling, L.; Chen, J. Xiao, X.; Bai, C.; Tang, B. Z. Macromolecules 2003 , 36, 77-85. (c) Li, B. S.; Chreuk, K. K. L.; Yang, D.; Lam, J. W. Y.; Wan, L. J.; Bai, C.; Tang, B. Z. Macromolecules 2003 , 36, 5447-5450. (d) Li, B. S; Cheuk, K. K. L.; Salhi, F.; Lam, J. W. Y.; Cha, J. A. K.; Xiao, X.; Bai, C, Tang, B. Z. Nano Lett. 2001 , 1, 323-328. b) O N O O O N O O O N O O O N O O H H H H a) O N O O H O N O O H Intermolecular Asociation Intramolecular Asociation e) f) h) g) H HN O O n Poly-49 Poly-49 Poly-49 poly-45 Introduction 49 Figure 36 . Schematic representation of (a) intermolecular hydrogen bonds between the pendant groups of different helices responsible for the formation of high-order aggregate, (b) intramolecular hydrogen bonds between the pendant groups stabilizing the helical structure of the PPA. AFM images of (c) pearl-like and (d-e) fiber-like structures. It’s possible to find a third example of supramolecular aggregates based on (PPA)s that can form fibber-like helical aggregates or superhelices but, in this case, their aggregation process takes place is a semiplanar structure instead of a helical one. Working on this idea, Yashima and co-workers reported a representative example of planar-mediated aggregation induced by the size of the pendants. They studied (PPA)s bearing bulky groups like cyclodextrins (CyD) as pendants moieties that aggregate into long and welldefined fibber-like structure.4d, 69b, 107 Sakuari et al. reported another example where poly19 /Alanine complexes generate superhelical structures once deposited onto mica. 117 In 1998, Nolte et al. described the first example of helical superstructures formed by synthetic helical polymers. 118 One feature of these superhelices is that the helical sense can be totally controlled once they are formed in aqueos media. An amphiphilic block copolymer (poly47 )—composed of a hydrophobic tail of flexible polystyrene, and a hydrophilic rigid-rod helical poly(isocyanopeptide) bearing a negative charged group on 117 Sakurai, S. I.; Kuroyanagi, K.; Nonokawa, R.; Yashima, E. J. Polym. Sci. Part A Polym. Chem. 2004 , 42, 5838. 118 Cornelissen, J. J. L. M.; Fischer, M.; Sommerdijk, N. A. J. M.; Nolte, R. J. M. Science 1998 , 280, 1427-1430. a) b) Intermolecular.hydrogen.bond Intramolecular.hydrogen.bond b) O N O O O N O O O N O O O N O O H H H H a) O N O O H O N O O H Intermolecular Asociation Intramolecular Asociation e) f) h) g) H HN O O n Poly-49 Poly-49 Poly-49 poly-46poly-46 Introduction 50 the side chain— is used to get their sel-assembly. Amazingly, the right-handed helical structure of the amphiphilic copolymer results in the formation of helical superstrtuctures that present an opposite helical sense (left-handed superhelix) (Figure 37). Figure 37 . Schematic illustration of the formation of superhelix by self-assembly of an amphiphilic polymer. Another interesting example of supramolecular helical assemblies was reported by Cheng and co-workers. 119 They crystallized chiral but non-helical main chain LC polyesters (poly48 ), obtaing flat-elongated and left-handed helical lamellar single crystals (Figure 38). Figure 38 . TEM images and schematic drawings of a twist model of a double-twisted helical lamellar crystal. 119 (a) Lotz, B.; Cheng, S. Z. D. Polymer 2005 , 46, 577-610. (b) Li, C. Y.; Cheng, S. Z. D.; Ge, J. J.; Bai, F.; Zhang, J. Z.; Mann, I. K.; Chien, L. C.; Harris, F. W.; Lotz, B. J. Am. Chem. Soc. 2000 , 122, 72-79. (c) Li, C. Y.; Yan, D.; Cheng, S. Z. D.; Bai, F.; He, T.; Chien, L. C.; Harris, F. W.; Lotz, B. Macromolecules 1999 , 32, 524-527. poly-47 poly-48 Introduction 51 Finally, Akagi and co-workers described supramolecular assemplies based on (PPA)s polymerized in liquid crystal phases with chiral dopant agents (axially chiral binaphthyl derivates). 120 These structures grow from single polymers chains to pruduce polymer bundles that in a final step self-assembly to form spiral structures (Figure 39). Figure 39 . (a-b) SEM images of superhelical structures obtained by synthesis of polyacetylene in liquid crystals. 6.2. Nanostructures based on (PPA)s Microand nanostructured materials present different and several features compared with bulk materials. Polymer nanoparticles are included in this kind of nanoarchitectures and can be defined as nanospheres or nanocapsules made by a polymeric cover with a specific size range (10−1000 nm). Nanospheres are spherical and solid, and they are commonly used to adsorb molecules on their surface or encapsulate them inside. However, nanocapsules are colloidal particles consisting in a hollow core surrounded by the polymeric membrane. These vesicular systems are usually employed to encapsulate substances into their cavity. 121 During the last years, these materials have been studied and prepared in multiples sizes (bulk, micro, nano) and morphologies developing important properties and functions for being applied in fields such as controlled release, drug delivery, liquid chromatography, self-assembly materials, and so on. 122 In the same way, chirality can be incorporated into 120 Akagi, K. Chem. Rev. 2009 , 109, 5354. 121 Reese, C. E.; Asher, S. A. J. Colloid Interface Sci. 2002 , 248, 41. 122 (a) Li, W.; Huang, H.; Li, Y.; Deng J. P. Polym. Chem. 2014 , 5, 1107-1118. (b) Song, C.; Liu, X.; Liu, D.; Ren, C.; Yang, W.; Deng, J. P. Macromol. Rapid Commun. 2013 , 34, 1426-1445. Introduction 52 these nanostructures (nanofibers, nanospheres, nanotubes, etc) providing applications in catalysis, chiral sensing, enantiomeric separation,etc. Polymer particles can be prepared through two main protocols: emulsification method and emulsion polymerization. 6.2.1. Emulsification method This methodology consists in the emulsification of a performed polymer chains into micelles. Following this technique, polymer chiral particles (PCPs) were prepared by Zhang et al. Firstly, they synthetized the polymer using a Rh(I) catalyst in an organic solvent (poly49 ) (Figure 40). Then, a concentrated polymer solution in THF was added droplet-by-droplet onto an aqueous solution of the surfactant, sodium dodecyl sulphate (SDS), getting nanoparticles which size depends on the emulsifier concentration: lower polymer particle size with an increasing concentration of surfactant due to the higher number of micelles in the medium. 123 Figure 40 . Schematic illustration of the emulsification driven polymer particle formation. A few years ago, Deng and co-workers applied emulsification-induced homo-helicity effect to prepare PCPs using an axially racemic helical polymer (mixture of rightand lefthanded helical sense) (poly50 ). 124 Thus, in the presence of chiral addictive the polymer is emulsified in micelles and will experiment a single-handed helical sense induction upon the emulsification process, achieving optically active polymer nanoparticules (Figure 41). 123 Zhang, Y.; Luo, X.; Deng, J.; Yang, W. Macromol. Chem. Phys. 2011 , 212, 353-360. 124 Zhao, B.; Deng, J.; Deng, J. P. Macromol. Rapid Commun. 2016 , 37, 568-574. Rh (I) Catalyst Emulsifier Polymer Emulsion Introduction 53 Figure 41 . Schematic illustration displaying proposed mechanism of the EIHH process (ref. 93 and 94). 6.2.2. Emulsion polymerization This methodology consists in a polymerization process carried out in a heterogeneous media, frequently an aqueous and a non-aqueous phases. 125 This protocol requires a monomeric unit with low solubility in water, a water-soluble initiator and emulsifier. Deng and co-workers investigated this method to form optically active polymer nanoparticles derived from substituted acetylenic monomers using either chiral monomers or chiral emulsifiers. 126 In most cases, the generated (P)As show a preferred helical sense, resulting in chiral nanoparticles.97b Thereby, while the monomer insoluble in water stays trapped inside the micelle, the hydrophobic Rh (I) catalyst is dispersed into the micelles, which contains the monomer. In consecuence, the polymerization occurs inside the micelle getting the polymer particles with small diameter.97c Figure 42 . Schematic illustration of the emulsion polymerization process. 125 Chern, C. S. Prog. Polym. Sci. 2006 , 31, 443-486. 126 (a) Deng, J.; Chen, B.; Luo, X.; Yang, W. Macromolecules 2009 , 42, 933-938. (b) Chen, B.; Deng, J.; Tong, L.; Yang, W. Macromolecules 2010 , 43, 9613-9619. (c) Chen, B.; Liu, X.; Xu, C.; Song, C.; Luo, X.; Yang, W.; Deng, J. Macromol. Chem. Phys. 2012 , 213, 603-609. poly-50 Mechanism*of*EIHH*process Rh (I) Catalyst Emulsifier Polymer Emulsion Monomer Emulsion Introduction 54 6.3. Nanostructuration based on helical polymers by cross-linked agents The first example of chiral polymer nanoparticles generated by using metal cations as supramolecular cross-linking agents was developed by our group. The chiral amplification phenomenom of poly17 (see the section 4.3) is promoted by the addition of metal ions that act not only as helical inducer14 but also as a cross-linking agent. 127 The interaction between the polymer and the metal ion —as a cross-linking agent— forms nanospheres whose size and chiral content can be controlled by the nature of the metal ion, the polymer/metal ratio and the solvent properties (Figure 43a). These nanospheres presented the ability to encapsulate iron oxide magnetic nanoparticles, organic molecules (e.g., fluorescent dyes) or quantum dots (Figure 43d). Moreover, it was possible to obtain other types of nanostructures like nanotubes or toroidal nanostructures by variation of the solvent (Figure 43d-e). 128 Finally, the chirality of the nanoparticles in both monovalent 129 and divalent 130 HMPCs can be switched in a reversible way modifying in the coordination mode between the metal and the pendant moiety. 127 Freire, F.; Seco, J. M., Quiñoá, E.; Riguera, R. J. Am. Chem. Soc. 2012 , 134, 19374-19383. 128 Arias, S.; Freire, F.; Quiñoá, E.; Riguera, R. Angew. Chem. Int. Ed. 2014 , 53, 13720. 129 (a) Arias, S.; Bergueiro, J.; Freire, F.; Quiñoá, E.; Riguera, R. Small 2016 , 12, 238. (b) Arias, S.; Núñez-Martínez, M.; Quiñoá, E.; Riguera, R.; Freire, F. Small 2017 , 13, 1602398. 130 Arias, S.; Núñez-Martínez, M.; Quiñoá, E.; Riguera, R.; Freire, F. Polym. Chem. 2017 , 8, 3740. Introduction 55 Figure 43 . (a) Schematic illustration of the metal coordination driven formation of nanospheres based on HPMCs. (b) SEM images of nanospheres based on HPMCs. (c) TEM image showing FeNPs encapsulated within a HPMC nanosphere. (d) Confocal image of HPMCs nanospheres showing fluorescence due to the encapsulation of fluorescein and SEM images of nanotubes based on HPMCs. (e) SEM images of nanotorus based on HPMCs. 7. Applications of (PPA)s Helical polymers based on (PPA)s are interesting and promising materials due to their chiral nature and the possibility to manipulate their helical parameters. For instance, the potential functions of optically active helical polymers —asymmetric catalysis, chiral recognition and chiral sensing among others— will be discussed next. 7.1. Sensors A remarkable feature of (PPA)s is the opportunity to modify the helical sense or the helical scaffold of the polymer by the interaction with external stimulus, being also possible to detect these small variations by CD and UV-Vis techniques. For this reason, during the last decade dynamic helical polymers have been employed as optical and Introduction 56 chiroptical sensors to detect species like anions, 131 metal ions,14, 29, 44a solvent properties50 or even act as thermal sensors.40 As it was mentioned previously, our research group reported a PPA, poly17 , that displays large chiral amplification phenomena when interacts with monovalent and divalent metal ions, acquiring M or P helix respectively and making poly17 a suitable sensor for the valence of metal ions.14 In addition, we have developed several polymers (poly29 and poly33 ) as solvent sensors: poly29 is able to identify the polarity of the solvent (polar/non-polar)65a producing different CD spectra while poly33 can classify solvents according to the polar/non-polar donor/non-donor properties showing four different helical structures.71 Otherwise, optical sensors are related to the presence of the conjugated double bonds of the polyenic chain where a colorimetric change from yellow to red is observed when a compressed helical structure moves to a stretched one. As aforementioned, Yashima and co-workers reported this colorimeric change on solution of a PPA (poly30 ) bearing a bulky group (b-cyclodextrins) at the pendant moiety. Thus, when the polymer interacts with some alcohols the colour for the polymer’s solution goes from yellow to red and can also be observed by changes in the solvent composition or by thermal modifications of the media where it is dissolved.47a, 69 Working on colorimetric detection systems, different polymers can be used as colorimetric sensors for anions —not only in organic solvents but also in aqueous media— were carried out by Kakuchi and co-workers. They prepared poly51 bearing an urea group adequate to interact with anions. These interactions are responsible of colorimetric changes due to an elongation in the polyene backbone minimizing the generated repulsions (Figure 44).131 131 (a) Sakai, R.; Barasa, E. B.; Sakai, N.; Sato, S.-I.; Satoh, T.; Kakuchi, T. Macomolecules 2012 , 45, 8221-8227. (b) Sakai, R.; Sakai, N.; Satoh, T.; Li, W; Zhang, A.; Kakuchi, T. Macromoleules 2011 , 44, 4249-4257. (c) Sakai, R.; Okade, S.; Barasa, E. B. Kakuchi, R. Ziabka, M.; Umeda, S.; Tsuda, K.; Satoh, T.; Kakuchi, T. Macromolecules 2010 , 43, 74067411. (d) Qu, Y.; Hua, J.; Jiang, Y.; Tian, H. J. Polym. Sci., Part A: Polym. Chem. 2009 , 47, 1544-1552. (e) Kakuchi, R.; Nagata, S.; Tago, Y.; Sakai, R.; Otsuke, I.; Satoh, T.; Kakuchi, T. Macromolecules 2009 , 42, 1476-1481. (f) Kakuchi, R.; Kodama, T.; Shimada, R.; Tago, Y.; Sakai, R.; Satoh, T.; Kakuchi, T. Macromolecules 2009 , 42, 3892. (g) Kakuchi, R.; Nagata, S.; Saki, R.; Otsuka, I.; Nakada, H.; Satoh, T.; Kakuchi, T. Chem. Eur. J. 2008 , 14, 10259-10266. Introduction 63 Figure 48 . Schematic illustration showing the structure of and the catalysed reaction for (a) poly57 . (b) poly58 . (c) poly59 and poly60 copolymer series. Suginome and co-workers have reported a new way of single-handed screw-sense induction in poly(quinoxaline-2,3-diyl)s (PQX) bearing only achiral substituents. This was favored due to chiral non-bonding interaction with N-protected amino acid methyl esters used as chiral additives in achiral solvents. In addition, the effects of achiral solvents have shown to be significant owing to the better screw-sense induction obtained with ether solvents (MTBE) than with halogenated solvents (CHCl3). Furthermore, phosphine ligands were employed to generate PQXphos —acting as a helically dynamic ligand—, together with a chiral additive (Lor D-Ac-Pro-OMe) led to a highly enantioselective Suzuki– Miyaura coupling reaction with up to 95% enantiomeric excess. 148 148 Ikeda, S.; Takeda, R.; Fujie, T.; Ariki, N.; Nagata, Y.; Suginome, M. Chem. Sci., 2021 , 12, 8811. a) poly-57 H n X=%O%poly-59a X%=%NH%poly-59b poly-52c poly-60 Copolymer%Series OO NPd Cl b) n O RR=%Ala-ONa%Poly-56a %%%%%%Ala-Gly-ONa%Poly-56b %%%%%%Ala-Ala-ONa%Poly-56c %%%%%%Ala-Gly-Gly-ONa%Poly-56d %%%%%%Ala-Ala-Gly-ONa%Poly-56f %%%%%%Ala-Ala-Ala-ONa%Poly-56g poly-58x H n X N N O R H S n O N N O R O c) Hn N N H N N H Bn O R1 R1 R2 R3 O d) Achiral%Catalityc%unit Chiral%Inductor + CHO Ph CHO Ph + Ph CHO Endo%38%%e.e. Exo%23%%e.e. Endo/Exo%ratio:%3.3/1 R H O+CH3NO2 R OH NO2 * Ph Ph OCOCH3poly-55 Ph Ph CH(COCH3)2 R O poly-51x H2O2 R OO Introduction 64 Figure 49 . (a) Two enantiomeric (Pand M-) conformations of achiral PQX, of which equilibrium is shifted by N-protected amino acid esters used as additives in an achiral solvent. (b) Asymmetric Suzuki–Miyaura coupling in the presence of achiral phosphine ligands including PQXphos with chiral additives. Until recently, optically active monomers were indispensable for the production of helical polymers since racemic monomers are optically inactive and hence show no chiral functions. However, Yashima and co-workers have just published an unprecedented enantioselectivity of a PPA triggered by the polymerization of a dynamically racemic monomer units (Figure 50a). These dynamically racemic helical polymers could be transformed into both rightand left-handed helical polymers by non-covalent interaction with a chiral alcohol. These helical polymers showed the ability to memorize its macromolecular helicity and the axial chirality induced in the pendants after complete removal of the chiral alcohol. Finally, catalytic asymmetric reaction was carried out with high enantioselectivity (up to 86% e.e.). 149 149 Ikai, T.; Ando, M.; Ito, M.; Ishidate, R.; Suzuki, N.; Maeda, K.; Yashima, E. J. Am. Chem. Soc. 2021 , 143, 12725-12735.  PQX(n) N N Me Me O O n PPh2 Me N N Ph Ph QXphos Me B(OH)2 Br PO(OMe)2 Me PO(OMe)2 + 123 achiral0ligand!(4!mol%!P) [PdCl(π-allyl)]2!(4!mol%!Pd) chiral0aditive solvent,!K3PO4,!H2O 30!ºC,!72!h a) b) Introduction 65 Figure 50 . (a) Structures of poly(biphenylylacetylene) (PBPA) derivatives. (b) Schematic illustration of emergence of a highly enantioselective catalytic activity in a racemic helical polymer composed of dynamically racemic 2-arylpyridyl-N-oxide monomer units. More specifically, these helical poly-(biarylylacetylene) (PBA) are composed of axially chiral, but fully racemic 2-arylpyridyl-N-oxide monomer units with N-oxide moieties located in the vicinity of the helical polymer structure (Figure 50a). 61a 61b61a 62 62 62 62 OBJECTIVES Objectives 69 Objectives The helix is one of the topological structures and it is inherently chiral; therefore, biological molecules, supramolecules, oligomers, polymers, and their assemblies can be optically active —despite lacking stereogenic centers in their components— when they adopt a preferred-handed helical conformation. A large number of artificial helical polymers and oligomers with controlled helicity have been synthesized, not only to mimic biological helices, but also to develop chiral materials with functionally. More specifically, poly(phenylacetylene)s (PPA)s are a family of dynamic helical polymers where the screw sense, elongation of the polyenic main chain or even both, can be modified by the action of different external stimuli such as pH, polarity of the solvent, temperature, chiral additives or metal, among others. This property makes these materials very helpful in different fields such as sensing, asymmetric catalysis or chiral templates. These interesting properties make (PPA)s excellent candidates for mimicking biomolecules and their interactions. However, dynamic helical polymers bearing multichiral pendants in which the power of the chiral center located at a remote position remains unexplored. In this context, this Doctoral Thesis is focused in developing new methodologies and systems to solve this handicap and evaluate the stimuli-responsive abilities of these materials. The objectives can be classified in four main topics: CHAPTER I: Full Control of the “Chiral-Overpass” Effect in Helical Polymers: P/M Screw Sense Induction by Remote Chiral Centers After Bypassing the First Chiral Residue In literature, it is described that the handedness of helical polymers is governed by the helicity of the pendants. In particular, those structures constituted by pendants with more than one chiral residue present preferentially one helical sense determined by the first chiral moiety, which is attached to the polyenic skaleton. However, the screw sense of poly(phenylacetylene)s with pendants composed by two chiral centers can be tamed by the “chiral-overpass" inductive mechanism where the application of different external stimuli (e.g. metal cations) is necessary to fix a bent Objectives 70 conformation in the pendant group, placing the second chiral center in a closer position to the polyene framework, now being responsible for the helicity adopted by the polymer. The objective of this chapter is to take a step forward in the control of the “chiraloverpass" effect. A new system based on (PPA)s with two different chiral centers is described: the first chiral moiety is an alanine group, known to be part of polyalanines that are involved in turns (e.g. in alfa helices); and the second one is the a-methoxy-amethylacetic acid (MPA) group which display switchable conformation from synperiplanar to antiperiplanar. The combination of elements provided us a multi-switchable “chiraloverpass” induction system. With this idea in mind, we want to corroborate if it is possible to achieve not only a selective activation/deactivation of the “chiral-overpass” effect but also to know if we are able to acquire a full control over the handedness of the polymers. Publication associated with this objective: Rodríguez, R.; Rivadulla-Cendal, E.; FernándezMíguez, M.; Fernández, B.; Quiñoá, E.; Maeda, K.; Freire, F. Angew. Chem. Int. Ed. 2022 , 61, e202209953. CHAPTER II: Diastereomeric Multi-Chiral Pendant Groups: Their Key Role in Stimuli-Responsive Polymeric Properties A variety biological processes are dependent on the dynamism of helical structures. This is one of the reasons why new artificial helical systems, such as dynamic helical polymers, have been developed to mimic interesting biological properties. Because of the difference in stability between the two possible enantiomeric or diastereomeric helices, helical systems bearing more than one chiral unit (i.e., multi-chiral pendant groups) are scarcely studied. As previously stated, the absolute configuration of the chiral residue closest to the polymeric main chain determines the screw sense of most helical polymers. This fact leaves the second one with low-to-null impact on the handedness of the macromolecule. The aim of this new project is to explore the limits of the impact of diastereomeric multichiral pendants in the screw sense induction and stimuli-responsive nature of the (PPA)s. Therefore, we have synthetized a new family of diastereomeric (PPA)s bearing a pendant group composed by two chiral groups: the first residue is L-valine group —that it is known Objectives 71 to promote b-sheet conformations— while the second chiral group is a bulky (R or S)-amethoxy-a-phenylacetic acid. We have studied their dynamic behavior where variations in their stimuli-responsive properties will be found due to their diastereomeric relationship. Eventually, the conformational change at the glycine residue dictated the arrangement of the pendant group, which will adopt two possible conformations depending on the orientation of the amide groups: synperiplanar and antiperiplanar conformations when carbonyl groups are oriented in the same and opposite directions, respectively. This selective disposition of the pendant group will be modulated by changes in the polarity of the solvent. Publication associated with this objective: Rodríguez, R.; Rivadulla-Cendal, E.; Quiñoá, E.; Freire, F. Chirality 2022 , Submitted. CHAPTER III: Greasing Macromolecular Gears: Inclusion of Flexible Spacers In nature, helical structures are commonly adopted by biomacromolecules and their functions are directly related to them. The fact that some significant biological processes are known to depend on the dynamism of these helical motifs has motivated the development of novel materials —such as foldamers or helical polymers— that adopt helical structures capable of emulating biological properties. The screw sense of helical systems built from chiral monomers cannot be switched due to the different stability of the two possible diastereomeric helices (leftand righthanded). Nevertheless, polymers or foldamers based on non-chiral units can overcome this issue —by applying external stimuli— as a result of their low energy barrier interconversion between the P and M helices. In literature, there are several examples of oligomers formed by achiral residues —used as building blocks— whose helicity can be selectively controlled when a chiral amino acid is supramolecularly interacting or covalently linked at one of the two edges of the sequence (Nor C-terminus). As previous mentioned in the introduction, a series of (PPA)s showed the ability to control the helicity/elongation degree in some of them via chiral harvesting mechanism. The pendants were based on a chiral moiety (MTPA) at the Nterminus of an achiral Aib oligopeptide chain and a 4-ethynylalaniline group at the C- Objectives 72 terminus of these peptides. Unfortunately, the handedness of the bulkier peptides could not be selectively modulated due to their low flexibility. For this reason, the main objective of this chapter is to try to release the steric stress generated in these previous systems by introducing a flexible linker between the backbone and the Aib foldamer. Accordingly, the chiral information from a remote position will be transferred to the helical scaffold through chiral harvesting mechanism. Then, the stimuli-responsive nature of the synthesized (PPA)s, their structure and how the conformational changes on the MTPA moiety can affect to their helical behavior will be studied. CHAPTER IV: Multi-helical Scaffolds (up to Five Helices) from Chiral (PPA)s bearing a Gly-AA as Pendant In recent years, our group has successfully demonstrated the chiral teleinduction mechanism from a remote chiral center to the inner helix. Basically, these helical motifs were formed by achiral peptidic linkers (i.e., glycine residues), N-attached to the distant chiral moiety (e.g. MPA, MTPA) and C-linked to the polyene main chain through a peptide bond. These systems adopt a rigid and well-organized b-sheet structure due to the arrangement of the flexible glycine spacers along the pendants. Their helical scaffold can be selectively folded into rightor left-handed helices due to changes in solvent polarity. This property is also accompanied, in some cases, by changes in the elongation of the backbone. Taking these findings into account, the goal is to prepare new helical polymers capable of forming a well-organized b-sheet like orientation in order to obtain an efficient transmission of chiral information through teleinduction mechanism. For this purpose, these (PPA)s will bear an achiral linker (glycine unit) capped at the end of the edge by different chiral centers (L-valine and L-phenylalanine amino acids). We will see that the effect of these remote chiral groups on the final folding of the polymers results in the generation of up to five different helical structures due to the formation of a multiconformational pendant group (anti-anti conformation corresponding to a highly compressed helix, syn-syn and syn-anti conformations related to a more stretched scaffold, and g-turn-syn/g-turn-anti conformations associated with a stretched helix). 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Among helical polymers, poly(phenylacetylene)s (PPA)s 10 represent an appealing family of compounds where both structural features, elongation and handedness, can be modulated either separately or together by the application of proper external stimuli. 11 The adoption of a screw sense excess in a PPA can be achieved following different strategies such as supramolecular interactions with either chiral or achiral moieties, as well as by the inclusion of a single chiral center with a preferred conformation at the pendant group of the polymer. 12 Remarkably, further modifications on the conformational composition of the pendant group can lead to helix induction, 13 helix inversion 14 or even to modifications on the stretching degree of the polymer backbone.3a, 15 Unfortunately, when the pendant is composed by two or more chiral centers, the one closest to the polymer backbone is most likely to control the handedness of the polymer, while the other center has low-to-null impact on the structural features of the helical structure. 16 Interestingly, our group has recently reported the “chiral overpass” inductive mechanism. 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Thus, while the first dihedral angle will be responsible for the activation/deactivation of the chiral overpass induction, the second dihedral angle, located on chiral residue two, will be the cause of the P/M helical sense induced in the PPA when the chiral overpass effect is activated. To do that, we envisaged a monomer unit that combines an amino acid involved in structural motifs such as turns4a, 18 and b-sheets4b, 18 together with a conformationally switchable arylacetic acid.11, 12a, 14c, 19 Therefore, while playing with the conformation of the amino acid it is possible to activate (gturn)/deactivate (extended) the chiral overpass effect, conformational changes at the arylacetic group will position the aryl ring in opposite directions and thus inducing a P or an M helical sense at the PPA without changing the absolute configuration of the second residue (Scheme 1). Scheme 1 . Conceptual representation of multi-state chiral overpass-induction controlling both stretching and handedness. 18 a) T. Ikai, S. Okuda, M. Aizawa, E. Yashima. ChemRxiv. 10.26434/chemrxiv-2022-kzrzz; b) H. Choi, S. Ogi, N. Ando, S. Yamaguchi. J. Am. Chem. Soc., 2021 , 143, 2953-2961; c) R. Rodríguez, E. Quiñoá, R. Riguera, F. Freire. Small, 2019 , 15, 1805413. 19 a) Z. Fernández, B. Fernández, E. Quiñoá, R. Riguera, F. Freire. Chem. Sci., 2020 , 11, 7182–7187; b) M. Fukuda, R. Rodríguez, Z. Fernández, T. Nishimura, D. Hirose, G. Watanabe, E. Quiñoá, F. Freire, K. Maeda. Chem. Commun., 2019 , 55, 7906-7909. Multi-State Chiral Overpass Induction: Control of Both Elongation and Handedness Ala Extended Residue 2 Far from the Backbone Residue 1 Close to the Backbone Extended Conformation commands P handedness (Compressed) Stretched P-Helix Stretched M-Helix Compressed P-Helix Residue 2 Close to the Backbone Conformation 2 commands M handedness (Stretched) N HO NH ON HO NH O N H H N O O Stimulus 1: Conformational Switch Stimulus 2: Turn Manipulation Residue 2 Close to the Backbone Conformation 1 commands P handedness (Stretched) R2 R2 Small R1 on chiral center Bent conformation stabilized by H-Bond R2 R1 R1 R1 Small R1 on chiral center Bent conformation stabilized by H-Bond Stimulus 1 Stimulus 1Stimulus 2 Stimulus 3 Chapter I 82 Results and discussion A set of monomers made up of all possible diastereoisomers of the 4-ethynylanilides of (S)- or (R)-Alanine (Ala) derivatized at the N-terminus with the two enantiomeric forms (R)- or (S)-a-methoxy-a-phenylacetic acid (MPA) —m-(S)-Ala-(R)-MPA; m-(S)-Ala-(S)-MPA; m- (R)-Ala-(R)-MPA; m-(R)-Ala-(S)-MPA—(Figure 1) were prepared following a multistep synthetic protocol (see SI). Figure 1 . Structures of monomers employed in this work. (a) mono-(S)-Ala-(R)-MPA and its X-ray structure. (b) mono-(S)-Ala-(S)-MPA and its X-ray structure. (c) mono-(R)-Ala-(R)-MPA and (d) mono-(R)-Ala-(S)-MPA. Crystal structures of m-(S)-Ala-(R)-MPA and m-(S)-Ala-(S)-MPA were obtained, and their X-Ray studies showed extended structures of the two chiral residues (see Figures S13 and S14). 20 These monomers were polymerized using [Rh(nbd)Cl]2 as catalyst, 21 which produced the corresponding polymers (Figure 2) in high yield, low polydispersity (see Table S2) and cis-stereoregularity of double bonds as inferred by 1H-NMR 22 , 23 (see Figure S15 and S16) and Raman (see Figure S17).23 Differential Scanning Calorimetry (DSC) experiments 20 Deposition numbers 2180644 and 2180647 contain the supplementary crystallographic data for this paper. These data are provided free of charge by the joint Cambridge Crystallo graphic Data Centre and Fachinformationszentrum Karlsruhe Access Structures service. 21 a) N. S. L Tan, A. B. Lowe. Angew. Chem. Int. Ed., 2020 , 59, 5008-5021; b) Z. Ke, S. Abe, T. Ueno, K. Morokuma. J. Am. Chem. Soc., 2011 , 133, 7926. 22 a) C. I. Simionescu, V. Percec, S. Dumitrescu. J. Polym. Sci. Polym. Chem. Ed., 1977 , 15, 2497-2509. 23 a) C. I. Simionescu, V. Percec. Progress in polyacetylene chemistry. Progress in Polymer Science, 1892 , 8, 133-214; b) H. Shirakawa, T. Ito, S. Ikeda. Polym. J., 1973 , 4, 460-462. N H H N O O O N H H N O O O (S) (R) (S) (S) mono-(S)-Ala-(R)-MPA mono-(S)-Ala-(S)-MPA a) c) d) N H H N O O O N H H N O O O (R) (R) (R) (S) b) mono-(R)-Ala-(R)-MPA mono-(R)-Ala-(S)-MPA Full Control of the Chiral Overpass Effect in Helical Polymers: P/M Screw Sense Induction by Remote Chiral Centers After Bypassing the First Chiral Residue 83 showed the presence of two consecutive exothermic peaks for both polymers suggesting the adoption of cis-transoidal (c-t) stretched structures (w1 > 90º, see Fig. S18). 24 Figure 2 . Structures of the polymers employed in this work. Chiral overpass studies were then performed by ECD, UV-Vis and VCD. To carry them out, polymers poly-(S)-Ala-(R)-MPA and poly-(S)-Ala-(S)-MPA were dissolved in CHCl3 and DMSO. These solvents were chosen to promote the formation and disruption of a bent structure at the pendant. Thus, while CHCl3 favors a bent structure, most probably stabilized by intra-pendant hydrogen bonds to form a g-turn mimetic motif at the pendant, DMSO disrupts these supramolecular bonds due to its interaction with the anilide groups. As a result, a b-sheet mimetic motif is generated at the pendant (extended structure).18 ECD/UV-Vis spectra of poly-(S)-Ala-(S)-MPA in CHCl3 and DMSO depict a variation in the stretching degree in total agreement with the presence of a bent and extended structure at the pendant group, respectively (Figure 3b). To corroborate the presence of this equilibrium between bent and extended structures promoted by the activation/deactivation of an intramolecular hydrogen bond, external stimuli such as F- (added as TBAF salt) or TFA, which act as hydrogen bond disruptors,4b, 11a were added to the CHCl3 solution of poly-(S)-Ala-(S)-MPA giving rise to an ECD/UV-Vis pattern resembling that obtained in DMSO (Figure 3c). Moreover, addition of metal cations (i.e., Li+ and Ba2+ perchlorate salts, 10 mg/mL MeOH solutions) to a solution of poly-(S)-Ala-(S)-MPA in CHCl3 also promoted the adoption of compressed helices analogous to the previous ones. The reason lies in the coordination of the metal ions with the C=O groups that promote the 24 L. Liu, T. Namikoshi, Y. Zang, T. Aoki, S. Hadano, Y. Abe, I. Wasuzu, T. Tsutsuba, M. Teraguchi, T. Kaneko. J. Am. Chem. Soc., 2013 , 135, 602-605. N H H N O O O N H H N O O O (S) (R) (S) (S) poly-(S)-Ala-(R)-MPA poly-(S)-Ala-(S)-MPA HH n n N H H N O O O N H H N O O O (R) (R) (R) (S) poly-(R)-Ala-(R)-MPA poly-(R)-Ala-(S)-MPA HH n n Chapter I 84 formation of an extended structure in the pendant (Figure 3d).13a, 14b, 14c Analogous studies were carried out for the other polymer counterparts displayed in Figure 2, which show the same stretching effects and opposite helical sense of the (PPA)s due to enantio/diastereomeric relationships (See Figures S22 and S23). Figure 3 . (a) Conceptual representation of the conformational manipulation from bent to stretched pendant group of poly-(S)-Ala-(S)-MPA. ECD/UV-Vis and spectroscopy monitoring of the above process triggered by (b) polar effects, (c) hydrogen bond disruptors (TFA/TBAF) and (d) metal coordination. To further corroborate that PPA compression/stretching is due to selective manipulation between a bent and an extended structure in the pendant (Figure 4a), VCD spectroscopy studies were carried out. This technique is a powerful tool in the structural elucidation of supramolecular and covalent helical polymers.19b, 25 Comparison of the VCD patterns of poly-(S)-Ala-(R)-MPA and poly-(S)-Ala-(S)-MPA in CDCl3 and DMSO-d6 reveals a totally different dichroic spectra when shifting from a bent (CHCl3) to an extended conformation at the pendant (DMSO) in both cases (Figures 4b-c) Therefore, VCD is a useful technique to elucidate structural variations at the pendant group. 26 25 M. A. Martínez, A. Doncel-Giménez, J. Cerdá, J. Calbo, R. Rodríguez, J. Aragó, J. Crassous, E. Ortí, L. Sánchez. J. Am. Chem. Soc., 2021 , 143, 13281-13291; b) E. E. Greciano, R. Rodríguez, K. Maeda, L. Sánchez. Chem. Commun., 2020 , 56, 2244-2247; c) K. Maeda, T. Miyagawa, A. Furuko, H. Onouchi, E. Yashima. Macromolecules, 2015 , 48, 4281-4293; d) Y. Hase, K. Nagai, K. Maeda, N. Ochi, K. Sawaba, K. Sakajiri, K. Okoshi, E. Yashima. J. Am. Chem. Soc., 2009 , 131, 1071910732. 26 a) B. Fernández, R. Rodríguez, E. Quiñoá, R. Riguera, F. Freire. ACS Omega, 2019 , 4, 5233-5240; b) B. Fernández, R. Rodríguez, A. Rizzo, E. Quiñoá, R. Riguera, F. Freire. Angew. Chem. Int. Ed., 2018 , 57, 3666-3670. 300 400 500 -80 -60 -40 -20 0 20 1 2 3 Wavelength [nm] CD [mdeg] CHCl3 0.5 Eq Ba2+ Abs 0.2 Eq Li+ Stretched Helix Compressed Helix β-Sheet Extended Pendant Bent Pendant 300 400 500 -100 -80 -60 -40 -20 0 20 1 2 3 4 5 Wavelength [nm] CD [mdeg] CHCl3 DMSO Abs b) 300 400 500 -70 -60 -50 -40 -30 -20 -10 0 10 20 1 2 3 Wavelength [nm] CD [mdeg] CHCl3 (0.3%TBAF) CHCl3 CHCl3 (0.3% TFA) Abs c) d) poly-(S)-Ala-(S)-MPA a) Hydrogen Bond Disruptors N H H N O O O N HO NH O O H Bond Full Control of the Chiral Overpass Effect in Helical Polymers: P/M Screw Sense Induction by Remote Chiral Centers After Bypassing the First Chiral Residue 85 Figure 4 . (a) Conceptual representation of bent and extended conformations in the pendant groups. VCD/IR spectroscopy monitoring the dichroic inversion related to the conformational switch triggered by polar effects of (b) poly-(S)-Ala-(R)-MPA and (c) of poly-(S)-Ala-(S)-MPA. Computational DFT studies were carried out on monomers m-(S)-Ala-(R)-MPA and m-(S)- Ala-(S)-MPA using the wB97XD functional together with the 6-31G(d,p) basis set. As input, the structures of the monomers were introduced with a g-turn conformation at the alanine residue. The obtained optimized geometries indicated that the chirality of the Ala promotes in the g-turn a specific angle of -65o, independent of the absolute configuration of the second chiral center (i.e., the MPA moiety), maintaining in both cases an ap conformation in the MPA moiety (see Figures 5c-d and Figure S24). Comparison of the calculated g-turn VCD pattern with the experimental ones obtained for poly-(S)-Ala-(R)-MPA and poly-(S)-Ala-(S)-MPA in CHCl3 shows a good match between theoretical and experimental data, and almost identical for both polymers. This fact indicates that the VCD pattern (bisignate) observed for either poly-(S)-Ala-(R)-MPA and poly-(S)-Ala-(S)-MPA in CHCl3 is governed by the presence of a bent structure at the pendant in this solvent (g-turn a specific angle of -65o), whose -/+ sign is unaffected by the absolute configuration of the MPA moiety (Figures 5a-b). Next, to further confirm that bent and extended conformations at the pendants have different VCD patterns, theoretical studies were carried out on mimetics of multiparallel b-sheet motifs of monomers m-(S)-Ala-(R)-MPA and m-(S)-Ala-(S)-MPA (see Figure S24). 162516751725 -8 -6 -4 -2 0 2 4 0.5 1.0 1.5 Wavenumber [cm-1] ΔAbs x105 CDCl3 DMSO Abs 162516751725 -8 -6 -4 -2 0 2 4 0.5 1.0 1.5 Wavenumber [cm-1] ΔAbs x105 CDCl3 DMSO Abs b) c) a) N O NH HOON H OH N O O poly-(S)-Ala-(R)-MPA poly-(S)-Ala-(S)-MPA Bent Coformation Extended Conformation Chapter I 86 These studies show a good match between theoretical —using B3LYP functional with the 6-31G(d,p) basis set— and experimental studies performed in DMSO, which confirms this extended structure at the pendant (Figures 5b-c). Interestingly, in the VCD pattern of an extended structure for poly-(S)-Ala-(R)-MPA and poly-(S)-Ala-(S)-MPA is possible to observe the opposite orientation of the carbonyl band of the MPA (ca. 1670 cm-1) due to their enantiomeric relationship [Figures 4b-c (DMSO) and Figure 5]. Figure 5 . (a) and (b) Computed structures for bent conformations (g-turn) of m-(S)-Ala-(R)-MPA and m-(S)-Ala-(S)-MPA and comparison of experimental vs calculated VCD/IR spectra with the corresponding polymers poly-(S)-Ala-(R)-MPA and poly-(S)-Ala-(S)-MPA in CDCl3. (c) and (d) Computed vs experimental VCD/IR spectra of the extended conformation of poly-(S)-Ala-(R)-MPA and poly-(S)-Ala-(S)-MPA in DMSO-d6. ECD studies were performed for these polymers in CHCl3 and DMSO to determine how the conformational changes at the pendant affect to the helical sense excess of the polyene main chain. As expected, when the pendant group adopts an extended structure —poly-(S)-Ala-(R)-MPA and poly-(S)-Ala-(S)-MPA dissolved in DMSO—, the helical sense is induced by the chiral residue closest in sequence to the polyene backbone, in this case the alanine group (Figure 6a). As a result, a M helical sense is induced in poly-(S)-Ala-(R)-MPA Full Control of the Chiral Overpass Effect in Helical Polymers: P/M Screw Sense Induction by Remote Chiral Centers After Bypassing the First Chiral Residue 87 and poly-(S)-Ala-(S)-MPA even though the absolute configuration of the second chiral residue, i.e. MPA, is different in both. On the contrary, when these studies are carried out in CHCl3, a helical sense inversion happens when the absolute configuration of MPA changes (Figure 6d). This outcome confirms the activation of the chiral overpass effect in CHCl3 due to the presence of a bent structure in the pendant. Similar effects were obtained for the enantiomeric series poly-(R)-Ala-(R)-MPA and poly-(R)-Ala-(S)-MPA, with opposite helicities induced in the (PPA)s due to the enantiomeric relationships (see Figures S22 and S23). Figure 6 . Conceptual representation and ECD of the activation and deactivation of the chiral overpass by controlling the presence of (a-b) an extended (DMSO) conformation or (c-d) a bent conformation (g-turn, CHCl3) in the pendants of poly-(S)-Ala-(R)-MPA and poly-(S)-Ala-(S)-MPA. Next, the total control of the chiral overpass effect was explored by playing with the conformational composition of the MPA moiety while the alanine fragment remains in a bent structure. To do that it is necessary to have two solvents that do not disrupt the intrapendant hydrogen bond of alanine, but at the same time possess different polarities to play with the antiperiplanar/synperiplanar conformational equilibrium of the MPA moiety. Thus, while an antiperiplanar conformation is favored in low-polar solvents, an increase in the solvent polarity favors the adoption of a synperiplanar conformation in this fragment. 300 400 500 -75 -50 -25 0 25 50 2 4 6 Wavelength [nm] CD [mdeg] Abs Poly-2 DMSO Poly-1 DMSO N HO H NH O O N HO H NH O O 300 400 500 -125 -100 -75 -50 -25 0 25 50 75 2 4 6 Wavelength [nm] CD [mdeg] Poly-2 CHCl3 Poly-1 CHCl3 Abs b) Opposite Handedness (S)-Ala-(R)-MPA (S)-Ala-(S)-MPA NH OHN O O NH OHN O O a) poly-[(S)-Ala-(R)-MPA]poly-[(S)-Ala-(S)-MPA] Same Handedness (S)-Ala-(R)-MPA (S)-Ala-(S)-MPA d) poly-[(S)-Ala-(R)-MPA] poly-[(S)-Ala-(S)-MPA] c) (S)-MPA (R)-MPA Commands P Helix (R)-MPA (S)-Ala(S)-Ala (S)-MPA Commands M Helix (S)-Ala Commands M Helix (S)-Ala Commands M Helix (S)-Ala (S)-Ala (R)-MPA (S)-MPA DMSO CHCl3 DMSO studies CHCl3 studies Chapter I 88 To achieve this goal, CHCl3 was chosen as low-polar solvent while cyclohexanone and acetone were selected as polar solvents. ECD and UV-Vis studies of poly-(S)-Ala-(R)-MPA and poly-(S)-Ala-(S)-MPA in these solvents indicate the presence of a scaffold with similar elongation but opposite helical sense (Figure 7). Thus, a positive ECD band centered at 448 nm was obtained for poly-(S)-Ala-(R)-MPA in CHCl3 indicating the adoption of a P helix by the polyene backbone, while a negative band is obtained for poly-(S)-Ala-(R)-MPA in acetone or cyclohexanone, indicative of a M helicity (Figure 7a).26 Figure 7 . Conceptual representation of the chiral overpass induction by conformational modulation of the second chiral center monitored by ECD/UV-Vis spectra of (a-b) poly-(S)-Ala- (R)-MPA and (c-d) poly-(S)-Ala-(S)-MPA (CyHex and acetone, respectively). This helical inversion is a consequence of a conformational change in the MPA fragment, from antiperiplanar (CHCl3) to synperiplanar (acetone or cyclohexanone), which places its aromatic ring in different orientations, producing the inversion. In the case of poly-(S)-Ala- (S)-MPA, the results were the opposite, showing a negative ECD band centered at 448 nm when dissolved in CHCl3 (M helix), while a positive band (P helix) is obtained when dissolved in acetone or cyclohexanone (Figure 7d). These studies were also carried out for 300 400 500 -45 -30 -15 0 15 30 1 2 3 4 Wavelength [nm] CD [mdeg] Poly-2 CHCl3 Poly-2 Acetone Abs 400 500 -20 -10 0 10 20 0.5 1.0 Wavelength [nm] CD [mdeg] Poly-1 CHCl3 Poly-1 CyHex Abs poly-(S)-Ala-(R)-MPA N HO NH O O c) poly-(S)-Ala-(S)-MPA a) Helix Inversion N HO NH O O N HO NH O O N HO NH O O Helix Inversion CHCl3 CyHex CHCl3 Acetone poly-(S)-Ala-(S)-MPA poly-(S)-Ala-(R)-MPA b) d) γ-Turn on (R)-MPA in ap Commands P Helix (R)-MPA (S)-Ala (S)-MPA in ap Commands M Helix (S)-MPA (S)-Ala (S)-MPA in sp Commands P Helix (S)-MPA (S)-Ala γ-Turn on (R)-MPA in sp Commands M Helix (R)-MPA (S)-Ala Phelix Phelix Mhelix Mhelix 95 Chapter II. Diastereomeric Multi-Chiral Pendant Groups: Their Key Role in StimuliResponsive Polymeric Responses. Adapted from: Rafael Rodríguez, Elena Rivadulla-Cendal, Emilio Quiñoá and Félix Freire. Chirality, 2022 , Submitted. Abstract Chiral information transmission in helical polymers bearing multi-chiral pendant groups is usually determined by the absolute configuration of the first chiral center. The second chiral residue usually has low-to-null influence in the macromolecular handedness of the polymer, due to its remote position respect to the polyene main chain. Here we demonstrate how the stimuli-responsive properties of diastereomeric polymers, obtained by changing the absolute configuration of the second chiral center, are different due to the unlike properties of diastereoisomers. Diastereomeric Multi-Chiral Pendant Groups: Their Key Role in Stimuli-Responsive Polymeric Responses 97 Introduction Helical macromolecules have attracted the attention of the scientific community due to the properties and functionalities associated with this structural motif. 1 , 2 In consequence, a large variety of non-natural foldamers and helical polymers have been studied during the last decades. In the special case of helical polymers, families such as poly(isocyanide)s, 3 poly(isocyanate)s, 4 poly(diphenylacetylene)s, 5 , 6 or poly(acetylene)s, 7 , 8 among others, provide a large variety of helical scaffolds with different static/dynamic which properties find applications in different fields such as asymmetric catalysis, 9 , 10 , 11 , 12 , 13 chiral recognition, 14 , 15 CPL sources,5, 6, 15, 16 chiroptical switches 17 , 18 or chiral stationary phases for HPLC among others. 19 , 20 , 21 To be functional, these helical polymers must adopt macromolecular helical structures with screw sense excess. This can be achieved using supramolecular interactions with different external stimuli, 22 , 23 by controlling the conformational composition of the pendant groups 24 , 25 , 26 , 27 or by means of different chiral 1 Yashima, E.; Ousaka, N.; Taura, D.; Shimomura, K.; Ikai, T.; Maeda, K. Chem. Rev. 2016 , 116, 13752-13990. 2 Yashima, E.; Maeda, K.; Iida, H.; Furusho, Y.; Nagai, N. Chem. 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S.; Metselaar, G. A.; Rowan, A. E.; Sommerdijk, N. A. J. M.; Nolte, R. J. M. Science 2001 , 293, 676–680. 42 Kamikawa, Y.; Kato, T.; Onouchi, H.; Kashiwagi, D.; Maeda, K.; Yashima, E. J. Polym. Sci., Part A: Polym. Chem. 2004 , 42, 4580–4586. 43 Cornelissen, J. J. L. M.; Graswinckel, W. S.; Adams, P. J. H. M.; Nachtegaal, G. H.; Kentgens, A. P. M.; Sommerdijk, N. A. J. M.; Nolte, R. J. M. J. Polym. Sci., Part A: Polym. Chem. 2001 , 39, 4255–4264. 44 Rodríguez, R.; Rivadulla-Cendal, E.; Fernández-Míguez, M.; Fernández, B.; Maeda, K.; Quiñoá, E., Freire, F. Angew. Chem. Int. Ed. 2022 , 61, e202209953. 45 Suárez-Picado, E.; Quiñoá, E.; Riguera, R., Freire, F. Angew. Chem. Int. Ed. 2020 , 59, 4537–4545. Diastereomeric Multi-Chiral Pendant Groups: Their Key Role in Stimuli-Responsive Polymeric Responses 99 Herein, we want to explore how the point chirality of the second residue affects the stimuli-responsive properties of a poly(phenylacetylene) (PPA) where the first chiral residue commands the helix through the adoption of a b-sheet conformation in the pendant group.38, 40, 41, 43 It is well known that physical and chemical properties of diastereomers are different, and therefore, the stimuli-responsive properties of diastereomeric (PPA)s towards solvent polarity can also be different. To study that, we designed a phenylacetylene monomer that bears the anilide of (S)-valine connected to the (R) or (S)-a-methoxy-a-phenylacetic acid (MPA) —m-(S,R)- 1 , m-(S,S)- 2 — (Figure 1a). In the corresponding polymers —poly-(S,R)- 1 , poly-(S,S)- 2 —, valine must govern the helix resorting to its two major conformations —syn and anti—, controlled by solvent polarity. The role of the second chiral center is just to alter the polarity of the polymers due to their diastereomeric relationship. As a result, the syn/anti conformational control of the valine residue in the two diastereomeric polymers can be produced at different solvent polarities, allowing us to detect a certain solvent. Results and discussion To test our hypothesis monomers, m-(S,R)- 1 , m-(S,S)- 2 , were prepared according to the protocol shown in the Supporting Information (SI). Next, the corresponding polymers, poly-(S,R)- 1 , poly-(S,S)- 2 , were prepared by using a Rh(I) catalyst —(i.e., [Rh(nbd)Cl]2— which produces the desired (PPA)s with a high ciscontent of the conjugated double bonds as inferred by 1H NMR and Raman (see Figures S7-S9). 46 , 47 46 Tan, N. S. L.; Lowe, A. B. Angew. Chem. Int. Ed. 2020 , 59, 5008-5021. 47 Ke, Z., Abe, S.; Ueno, T.; Morokuma, K. J. Am. Chem. Soc. 2011 , 133, 7926-7941. Chapter II 100 Figure 1 . (a) Chemical structures of m-(S,R)- 1 , m-(S,S)- 2 , poly-(S,R)- 1 , poly-(S,S)- 2 . (b) syn/anti conformation of the valine residue in poly-(S,R)- 1 , poly-(S,S)- 2 . ECD studies of poly-(S,R)- 1 , poly-(S,S)- 2 were carried out in solvents with different polarity such as DCM, CHCl3, THF, DMF and DMSO (Figure 2). In low polar solvents, e.g., DCM and CHCl3, both polymers show ECD traces composed by two strong negative Cotton effects with maxima at 228 and 288 nm that corresponds to a compressed M helix. 48 , 49 This structure is adopted when the two amides of the valine residue are anti oriented, conformation that is favored for (PPA)s derivatized with amino acids in low-polar solvents (Figure 2a). 50 , 51 , 52 , 53 To corroborate the presence of a helical structure, optical rotation (OR) measurements were done for poly-(S,R)- 1 , poly-(S,S)- 2 in DCM and the corresponding monomers. The values obtained for the polymers are much higher than those obtained for the monomers, indicating the presence of a helix (see Table S3). Interestingly, the ECD traces obtained for poly-(S,R)- 1 , poly-(S,S)- 2 in a medium polar solvent like THF are completely different. Thus, while poly-(S,R)- 1 shows a spectrum similar to that obtained in low-polar solvents (see above), poly-(S,S)- 2 shows a more stretched helix with three consecutive and alternating -/+/- Cotton effects with maxima at 280, 345 and 290 nm (Figure 2c), indicating the adoption of a preferred stretched M-helix.48, 49 This 48 Fernández, B.; Rodríguez, R.; Quiñoá, E.; Riguera, R.; Freire, F. ACS Omega, 2019 , 4, 5233-5240. 49 Fernández, B.; Rodríguez, R.; Rizzo, A.; Quiñoá, E.; Riguera, R.; Freire, F. Angew. Chem. Int. Ed. 2018 , 57, 3666-3670. 50 Leiras, S.; Suárez-Picado, E.; Quiñoá, E.; Riguera, R.; Freire, F. Giant. 2021 , 7, 100068. 51 Alzubi, M.; Arias, S.; Louzao, I.; Quiñoá, E.; Riguera, R.; Freire, F. Chem. Commun. 2017 , 53, 8573-8576. 52 Leiras, S.; Suárez-Picado, E.; Quiñoá, E.; Riguera, R.; Freire, F. Angew. Chem Int. Ed. 2010 , 49, 1430-1433. 53 Arias, S.; Núnez-Martínez, M.; Quiñoá, E.; Riguera, R.; Freire, F. Polym. Chem. 2017 , 8, 3740-3745. N H H N O O OMe Chiral Center 1 Chiral Center 2 m-(S,R)-1 N H H N O O OMe Chiral Center 1 Chiral Center 2 m-(S,S)-2 N H H N O O OMe N H NH O O OMe (S)(R or S) (S) (R or S) “anti” “syn” b) N H H N O O OMe poly-(S,R)-1 N H H N O O OMe poly-(S,S)-2 HH n n Compressed Helix Stretched Helix Diastereomeric Multi-Chiral Pendant Groups: Their Key Role in Stimuli-Responsive Polymeric Responses 101 helical stretching is associated to an anti to syn conformational change at the valine residue, conformation favored in (PPA)s derivatized with amino acids in polar solvents. Therefore, both polymers show different stimuli-responsive properties towards THF due to their diastereomeric relationship. When analogous ECD studies are carried out in more polar solvents such as DMSO or DMF, both polymers show similar ECD traces with three consecutive and alternating -/+/- Cotton effects with maxima at 280, 345, and 390 nm, virtually identical to that observed for poly-(S,S)- 2 in THF. As a result, poly-(S,R)- 1 and poly-(S,S)- 2 adopt stretched M-helical scaffold in polar solvents due to the syn conformation of the valine residue. Comparison of the UV-Vis spectra for poly-(S,R)- 1 and poly-(S,S)- 2 in DCM and DMSO shows a large bathochromic shift of the polyene band from 310 nm in DCM to 425 nm in DMSO in agreement with the ECD observations (Figure 2d and Figure S12). Figure 2 . (a) Schematic illustration of the helical transformation of poly-(S,R)- 1 and poly-(S,S)- 2 triggered by polarity effects. ECD spectra in (b) DCM, (c) THF and (d) DMSO (c = 0.3 mg/mL). Next, we decided to demonstrate the presence of the anti to syn conformational change by adding different stimuli such as TBAF, TFA or Ba(ClO4)2 to a DCM solution of poly-(S,R)- 1 and poly-(S,S)- 2 . From previous studies it is known that these stimuli produce conformational changes at the pendant, anti to syn, by interacting with the amide groups.44, 50-53 Here, we show that the compressed M-helix is transformed into the 250 300 350 400 450 500 -40 -20 0 20 Wavelength [nm] CD [mdeg] Poly-(S,R)-1 Poly-(S,S)-1 250 300 350 400 450 500 -45 -30 -15 0 15 Wavelength [nm] CD [mdeg] Poly-(S,R)-1 Poly-(S,S)-1 250 300 350 400 450 500 -40 -20 0 Wavelength [nm] CD [mdeg] Poly-(S,R)-1 Poly-(S,S)-1 250 300 350 400 450 500 0.5 1.0 1.5 Wavelength [nm] Abs Poly-(S,S)-1 DMSO Poly-(S,S)-1 CH2Cl2 a) N H H N O OOMe N H NH OO OMe (S)(R or S) (S) (R or S) “anti” “syn” b) Compressed M Helix Stretched M Helix c) e) Vinylic Region 295 nm Vinylic Region 385 nm Bathochromic Shift: 100 nm d) THF CH2Cl2 DMSO Low Polar Media Polar Media Chapter II 102 stretched one when these stimuli are present, corroborating the anti to syn conformational change at the pendant (Figures 3a-c). Figure 3 . (a) Schematic illustration of the elongation of poly-(S,S)- 2 monitored by ECD after interacting with (b) TFA, (c) TBAF and (d) metal coordination (i.e., Ba2+) (0.3 mg/mL, DCM). Conclusions In conclusion, we have demonstrated that although the helical senses induced in helical polymers possessing multi-chiral pendants groups is governed by the chiral center places closer to the backbone, the chiral centers placed in remote positions can have important consequences in the stimuli-responsive properties although their influence in the helical sense induction is limited. In this work, two different (PPA)s bearing as pendant (S)-Valine- (R)-MPA and (S)-Valine-(S)-MPA were prepared. The helical sense in all the solvents tested is commanded by the (S)-valine obtaining a M helix in all cases. However, this helix is compressed in low-polar solvents and stretched in polar solvents, difference attributed to an anti to syn conformational change produced at the pendant group. This anti to syn conformational change is activated by the solvent polarity, and because the two diastereomeric polymers, poly-(S,R)- 1 and poly-(S,S)- 2 have different physical properties, the value of the dielectric constant of the solvent needed to produce this conformational change is different for both polymers. As a result, these two polymers show different stimuli-responsive properties in THF. While poly-(S,R)- 1 adopts a compressed helix due to an anti-conformation at the pendant, in poly-(S,S)- 2 an anti to syn conformational change is triggered producing a stretched helix. Consequently, these two polymers allow to sense THF due to the different helical scaffolds induced by a different conformational 250 300 350 400 450 500 -40 -20 0 20 Wavelength [nm] CD[mdeg] TFA DCM b) CH2Cl2 250 300 350 400 450 500 -40 -20 0 20 Wavelength [nm] CD[mdeg] TBAF DCM c) Compressed M Helix Stretched M Helix a) CH2Cl2 250 300 350 400 450 500 -40 -20 0 20 Wavelength [nm] CD[mdeg] Ba2+ DCM d) CH2Cl2 Diastereomeric Multi-Chiral Pendant Groups: Their Key Role in Stimuli-Responsive Polymeric Responses 103 composition at the pendants. We believe these findings will encourage the scientific community to study more complex multi-chiral pendant groups and their potential impact in the folding/stimuli-responsive nature of the polymers. Efforts in that direction are currently ongoing in our laboratory. Greasing Macromolecular Gears: Inclusion of Flexible Spacers 111 Another unique example of asymmetry induction —reported by Inai and coworkers in folded synthetic oligomers (Foldamers)— 11 is the “Domino effect”. 12 These foldamers are based on non-natural amino acids or combinations of natural and non-natural amino acids that fold into helical structures mimicking natural peptides (e.g., a-aminoisobutyric acid (Aib) and a,b-didehydrophenylalanine). This effect is based on the adoption of a preferredhanded helix in foldamers composed by achiral building blocks via supramolecular interactions of chiral compounds at either the Nor Cterminus.14 This pioneering discovery promoted the application of these systems as efficient chiral communicators. Toniolo, 13 Yashima 14 and Clayden 15 reported several models of chiral information transmission through these moieties by including chiral centers within the foldamer sequence. Interestingly, further manipulation of foldamer handedness can also be obtained by controlling the hydrogen bonding network of the helical scaffold by pH modifications or photochemical triggers. Unfortunately, often as a result, changes in the helical sense of the oligopeptide require changes in the absolute configuration of the peptide or in the net number of atoms in the foldamer.6b 11 a) Koehlner, V.; Roy, A.; Huc, I.; Ferrand, Y. Acc. Chem. Res. 2022 , 22, 1074-1085; b) Girvin, Z. C.; Gellman, S. H. J. Am. Chem. Soc. 2020 , 142, 17211-17223; c) Hecht, S.; Huc, I. Foldamers: Structure, Properties, and Applications; WileyVCH:Weinheim, 2007 ; d) Hill, D. J.; Mio, M. J.; Prince, R. B.; Hughes, T. S.; Moore, J. S. Chem. Rev. 2001 , 101, 3893-4012; e) Gellman, S. H. Acc. Chem. Res. 1998 , 31, 173-180. 12 a) Ousaka, N.; Inai, Y.; Kuroda, R. J. Am. Chem. Soc. 2008 , 130, 12266-12267; b) Ousaka, N.; Inai, Y. J. Am. Chem. Soc. 2006 , 128, 14736-14737; c) Inai, Y.; Ousaka, N.; Okabe, T. J. Am. Chem. Soc. 2003 , 125, 8151-8162; d) Inai, Y.; Ishida, Y.; Tagawa, K.; Takasu, A.; Hirabayashi, T. J. Am. Chem. Soc. 2002 , 124, 2466-2473; e) Inai, Y.; Tagawa, K.; Takasu, A.; Hirabayashi, T.; Oshikawa, T.; Yamashita, M. J. Am. Chem. Soc. 2000 , 122, 11731-11732. 13 a) Mazaleyrat, J. P.; Wright, K.; Gaucher, A.; Toulemonde, N.; Wakselman, M.; Oancea, S.; Peggion, C.; Formaggio, F.; Setnička, V.; Keiderling, T. A.; Toniolo, C. J. Am. Chem. Soc. 2004 , 126, 12874-12879; b) Toniolo, C.; Crisma, M.; Formaggio, F.; Peggion, C. Biopolymers 2001 , 60, 396-419; c) Toniolo, C.; Benedetti, E. Trends Biochem. Sci. 1991 , 16, 350-353. 14 a) Urushima, A.; Ousaka, N.; Yashima, E. Chem. Asian J. 2018 , 13, 3150-3154; b) Ousaka, N.; Mamiya, F.; Iwate, Y.; Nishumura, K.; Yashima, E. Angew. Chem. Int. Ed. 2017 , 56, 791-795; c) Mamiya, F.; Ousaka, N.; Yashima, E. Angew. Chem. Int. Ed. 2015 , 54, 14442-14446; d) Ousaka, N.; Takeyama, Y.; Yashima, E. Nat. Chem. 2011 , 3, 856-861. 15 a) Francis, G. A.; Eccles, N.; Pike, S. J.; Brown, R. A.; Whitehead, G. F. S.; Raferty, J.; Webb, S. J.; Clayden, J. Chem. Sci. 2018 , 9, 6860-6870; b) Lister, F. G. A.; Le Bailly, B. A. F.; Webb, S. J.; Clayden, J. Nat. Chem. 2017 , 9, 420-425; c) Mazzier, D.; Crisma, M.; De Poli, M.; Marafon, G.; Peggion, C.; Clayden, J.; Moretto, A. J. Am. Chem. Soc. 2016 , 138, 8007-8018; d) De Poli, M.; Zawodny, W.; Quinonero, O.; Lorch, M.; Webb, S. J.; Clayden, J. Science 2016 , 352, 575-580; e) Jones, J. E.; Diemer, V.; Adam, C.; Raferty, J.; Ruscoe, R. E.; Sengel, J.; Wallace, M. I.; Bader, A.; Cockroft, S. L.; Clayden, J.; Webb, S. J. J. Am. Chem. Soc. 2016 , 138, 688-695; f) Le Bailly, B. A. F.; Clayden, J. Chem. Commun. 2016 , 52, 4852-4863; g) Le Bailly, B. A. F.; Byrne, L.; Clayden, J. Angew. Chem. Int. Ed. 2016 , 55, 2132-2136; h) Brioche, J.; Pike, S. J.; Tshepelevitsh, S.; Leito, I.; Morris, G. A.; Webb, S. J.; Clayden, J. J. Am. Chem. Soc. 2015 , 137, 6680-6691; i) Pike, S. J.; Boddaert, T.; Raferty, J.; Webb, S. J.; Clayden, J. New J. Chem. 2015 , 39, 3288-3294; j) Byrne, L.; Solá, J.; Boddaert, T.; Marcelli, T.; Adams, R. W.; Morris, G. A.; Clayden, J. Angew. Chem. Int. Ed. 2014 , 53, 151-155; k) Brown, R. A.; Diemer, V.; Webb, S. J.; Clayden, J. Nat. Chem. 2013 , 5, 853-860; l) Boddaert, T.; Solá, J.; Helliwell, M.; Clayden, J. Chem. Commun. 2012 , 48, 3397-3399; m) Solá, J.; Morris, G. A.; Clayden, J. J. Am. Chem. Soc. 2011 , 133, 3712-3715; n) Solá, J.; Helliwell, M.; Clayden, J. Biopolymers 2011 , 95, 755-762; o) Solá, J.; Fletcher, S. P.; Castellanos, A.; Clayden, J. Angew. Chem. Int. Ed. 2010 , 49, 6836-6839; p) Solá, J.; Helliwell, M.; Clayden, J. J. Am. Chem. Soc. 2010 , 132, 4548-4549; q) Clayden, J.; Castellanos, A.; Solá, J.; Morris, G. A. Angew. Chem. Int. Ed. 2009 , 48, 5962-5965. Chapter III 112 Recently, we have shown that the introduction of a single enantiomer of a-methoxy-atrifluoromethylphenylacetic acid (MTPA) 16 at the N-terminus of an achiral Aib oligopeptide, allowed the selective preparation of the P/M helical senses of the oligopeptide by tuning the conformational composition of the terminal MTPA. Upon polymerization of the monomers through the alkyne site at the N-terminus, efficient asymmetry induction was observed in the resulting poly(phenylacetylene) (PPA) backbone. 17 Additional modifications of the conformational composition of the MPTA moiety were effectively transmitted to the PPA skeleton, only resulting in helix inversion in the case of the shorter linker bearing a single Aib unit. The longer counterparts —carrying two or three Aib units— result in stretching of the polyene backbone rather than inversion of the helix. Despite the effective transmission of chiral information, lack of flexibility results in stretching of the polymer backbone and inefficient chiral stimuli-response readout. The main reason behind this phenomenon is the lack of flexibility in the connection between the bulky peptide and the PPA skeleton, which is not able to accommodate new conformations of the peptide chain.17 We envision here that the introduction of a flexible linker between the PPA backbone and the Aib foldamer should release steric stress, therefore resulting in (PPA)s with higher dynamism, enhanced chiral content and, accordingly, improved stimuli-responsive nature. As a flexible linker, we selected a simple glycine (gly) unit, as it has been used previously as effective linker in (PPA)s6b, 18 and also fits well with the 310 helical structure adopted by Aib foldamers. In fact, it acts as a chiral communication conductor, as demonstrated by Clayden and coworkers. 19 In addition, introduction of a 4-ethynylaniline group at the C-terminus of these peptides and subsequent rhodium-catalyzed polymerization produces the corresponding poly(phenylacetylene) (PPA). 20 16 a) Dale, J. A.; Mosher, H. S. J. Am. Chem. Soc. 1973 , 95, 512-519; b) Dale, J. A.; Dull, D. L.; Mosher, H. S. J. Org. Chem. 1969 , 34, 2543-2549. 17 Rodríguez, R.; Suárez-Picado, E.; Quiñoá, E.; Riguera, R.; Freire, F. Angew. Chem. Int. Ed. 2020 , 59, 8616-8622. 18 Rodríguez, R.; Quiñoá, E.; Riguera, R.; Freire, F. Small 2019 , 15, 1805413. 19 Boddaert, T.; Solá, J.; Helliwell, M.; Clayden, J. Chem. Commun. 2012 , 48, 3397–3399. 20 a) Tan, N. S. L.; Lowe, A. B. Angew. Chem. Int. Ed. 2020 , 59, 5008–5021; b) Ke, Z.; Abe, S.; Ueno, T.; Moruma, K. J. Am. Chem. Soc. 2011 , 133, 7926-7941; c) Mayershofer, M. G.; Nuyken, O. J. Polym. Sci., Part A: Polym. Chem. 2005 , 43, 57235747; d) Simionescu, C. I.; Percec, V. Polym. Sci., Polym. Chem. Ed. 1980 , 18, 147-155; e) Simionescu, C. I.; Percec, V.; Dumitrescu, S. J. Polym. Sci., Polym. Chem. Ed. 1977 , 15, 2497-2509. Greasing Macromolecular Gears: Inclusion of Flexible Spacers 113 In this way, polarity-induced conformational changes in the MTPA unit produce screw sense changes in the oligopeptide that are transmitted to the poly(phenylacetylene) backbone as changes on the elongation and/or sense of the helix. Scheme 1 . Schematic illustration of the impact of the flexible linker in the transmission of chiral information through the Aib foldamer towards the PPA backbone in a polymeric macromolecular gear. Results and discussion The designed monomers (Figure 1a) were prepared via a multistep synthetic route depicted in the SI, and were fully characterized through a battery of NMR, HRMS and Xray diffraction experiments. Figure 1 . (a) Foldamers PA-(Aib)n-(S)-MTPA (a = 1, 2, 3, 4). (b) Poly(phenylacetylene)s (S)-MTPA- (Aib)n-PPA (a = 1, 2, 3, 4). Chiral Inductor Flexible Spacer Polymer Backbone 310Helical Fragment Screw Sense Induction Previous Work: Full (AIB)n Foldamer as Achiral Linker -Inefficient Chiral Transmision -Reduced Dynamism This Work: Gly-(AIB)n Foldamer as Achiral Linker Chiral Inductor 310Helical Fragment Screw Sense Induction -Efficient Chiral Transmision -Enhanced Dynamism Polymer Backbone a) PA-Gly-(Aib)a-(S)-MTPA a = 1, mono-1 a = 2, mono-2 a = 3, mono-3 a = 4, mono-4 Polimerizable Group N H OH N O N H O O CF3 a Turn Promoter Flexible Spacer N H OH N O N H O O CF3 a H n [Rh(nbd)Cl]2 PPA-Gly-(Aib)a-(S)-MTPA a = 1, poly-1 a = 2, poly-2 a = 3, poly-3 a = 4, poly-4 b) Chapter III 114 The adoption of helical structures by different monomers in the solid state was determined by X-ray diffraction of single crystals of the monomers, grown by slow evaporation of DCM/hexane solutions. The 310-helical structures were stabilized by the presence of consecutive i, i+3 hydrogen bonds. Interestingly, P and M helical structures were present in all the crystals, the screw sense being dependent on the conformation of the chiral MTPA moiety. X-ray diffraction of mono1 showed the coexistence of P and M helices in solid state. These structures were stabilized by O=C-C-OMe dihedral angles of -173º and +152º for P and M helices, respectively (Figure 2a and Table S1). In the case of mono2 , X-ray diffraction showed a P-310 helix stabilized by a single intramolecular hydrogen bond between i and i+3 residues. The right-handed orientation of the 310 helix was promoted by an antiperiplanar orientation between the carbonyl and methoxy groups of the (S)-MTPA residue (O=C-C-OMe dihedral angle: -172º). Similar to mono1 , a second structure —M310 helix— was found in solid state, stabilized by an apOMe conformation whose O=C-COMe angle was +162º (Figure 2b and Table S2). Remarkably, X-ray experiments showed, for mono3 , the coexistence in the same crystal unit of four independent molecules, related two by two by hydrogen bonds. Each pair displayed the two helical senses —P and M—of the 310 helix, stabilized by two consecutive i, i+3 hydrogen bonds. The chiral (S)-MTPA residue in the P and M helices showed O=C-COMe dihedral angles of -174º and +161º, respectively (Figure 2c and Table S3). Finally, Xray diffraction of mono4 also showed the Pand M-310 helices. Both structures were stabilized by an apOMe conformation of the (S)-MTPA residue. As in the previous cases, opposite O=C-C-OMe angles were found: -176º for P-310 helix and +151º for M-310 helix (Figure 2d and Table S4). Greasing Macromolecular Gears: Inclusion of Flexible Spacers 115 Figure 2 . X-ray structures showing the representative NOEs found in solution and experimental vs computed CD spectra of (a) mono1 , (b) mono2 , (c) mono3 and (d) mono4 . ap!OMe NH(1) NH(2) NH(3) OMe(1) NH(4) 250 300 350 400 0 Wavelength (nm) Normalized CD Calculated Experimental 250 300 350 0 Wavelength (nm) Normalized CD Calculated Experimental 250 300 350 0 Wavelength (nm) Normalized CD Calculated Experimental 250 300 350 0 Wavelength (nm) Normalized CD Calculated Experimental mono-(S)-1 mono-(S)-2 mono-(S)-3 mono-(S)-4 MTPA apOMe O=C-C-OMe: -173º apOMe NH(1) NH(2) NH(3) OMe(1) O=C-C-OMe: -172º P-3104helix P-3104helix M-3104helix O=C-C-OMe: +152º MTPA apOMe O=C-C-OMe: -162º M-3104helix MTPA apOMe apOMe NH(1) NH(2) NH(3) OMe(1) NH(4) NH(5) O=C-C-OMe: -174º P-3104helix O=C-C-OMe: -162º MTPA apOMe M-3104helix MTPA apOMe O=C-C-OMe: -176º O=C-C-OMe: +151º MTPA apOMe MTPA apOMe apOMe NH(1) NH(2) NH(3) OMe(1) NH(4) NH(5) NH(6) P-3104helix M-3104helix MTPA apOMe mono-(S)-1 mono-(S)-2 mono-(S)-3 mono-(S)-4 a) d) c) b) P-3104helix P-3104helix P-3104helix P-3104helix Chapter III 116 To determine the folding and dynamic behavior in solution, NMR, ECD and Raman experiments in different solvents were carried out for the corresponding monomers. Remarkably, NMR experiments, together with theoretical calculations, revealed that the structures found in solution were virtually identical to those present in the solid state (See Figures 2a-d and SI). A detailed description of key NMR signals confirming the abovementioned structures is shown next. 2D-NMR (NOESY) in THF-d8 of mono1 displayed strong sequential NH-NH cross peaks indicating the presence of a very stable b-turn structure. (Figure S37a, S38a-b). In addition, amide NH(1)/OMe(1) cross peak demonstrated a preferred apOMe conformation at the chiral (S)-MTPA residue (Figure S37c, S38c). Moreover, ECD experiments in the same solvent showed a positive Cotton effect at 270 nm, confirming the apOMe conformation (Figure 2a). Additionally, strong cross peaks between the flexible glycine unit with its neighboring amides —CH2-NH(3) and CH2-NH(2)— were observed (Figure S37b). All these data verified that oligomer mono1 presents, in polar solvents, a P b-turn twisted structure, in agreement with that obtained from the X-ray studies (Figure 2a). ECD studies of mono1 in other solvents (e.g., CDCl3) revealed its static behavior (positive CD spectrum) due to the absence of a conformational switch at the chiral (S)-MTPA moiety. 1D and 2D-NOESY NMR experiments were carried out to further confirm the apOMe conformation adopted by mono1 in CDCl3. As in the case of polar solvents, strong sequential NH-NH and amide NH(1)/OMe(1) cross peaks were observed (see SI Figures S41a-b, S42). Analogous set of NMR, CD and computational studies were carried out for the corresponding counterparts (mono2 to mono4 ) to determine the folding of these structures in solution. Remarkably, these monomers showed similar behavior in solution, folding into a preferred P-handed 310-helix independently of the solvent used. 1D and 2D-NOESY NMR experiments of mono2 , mono3 and mono4 in THF-d8 showed strong sequential NH-NH cross peaks that together with other NOEs corroborated the presence of a P-310 helix in solution (Figures S45a and S46a-d, Figures S53a and S54a-c, Figures S61a and S62, respectively). The absence of long distance NOEs for OMe(1) together with NOEs between OMe(1) with amide NH(1) indicated a major antiperiplanar orientation between methoxy and carbonyl groups in the MTPA moiety that commands a P-310 helix in these three oligomers (Figure 2b-d, and Figures S45b and S46e, Figures S53b and S54d, Figures S61b and S62e, respectively). In all cases, strong cross peaks were again Greasing Macromolecular Gears: Inclusion of Flexible Spacers 117 observed between the flexible glycine unit with its neighboring amides —CH2-NH(4) and CH2-NH(3) for mono2 (Figures S45c and S46f); CH2-NH(5) and CH2-NH(4) for mono3 (Figures S53d and S54e) and CH2-NH(6) and CH2-NH(5) for mono4 (Figure S61d)—. TD-DFT studies using CAM-B3LYP method, together with the 6-31+G** basis, were performed for the different monomers (mono1 to mono4 ). The optimized structures were in good agreement with those found in the solid state, also in perfect agreement with the cross peaks found through the NMR studies. The computed vs experimental ECD spectra of the monomers are shown in Figure 2, and they exhibit a good match between both spectra and thus confirm the existence of such structures both solution and in the solid state (see Figures 2a-d). Raman spectroscopy has recently been applied as an effective tool to study the folding of Aib oligomers into 310-helices. These studies were performed in our monomer set (mono1 to mono4 ) showing in all cases amide I bands at 1670 cm-1, value considered as 310 helix marker (see Figure S23a). 21 The corresponding polymers (poly1 to poly4 , Figure 1b) were prepared by Rh(I) catalyzed polymerization of the terminal alkyne contained in the C-terminus of the foldamers.20 The polymers were obtained in high yield, with high content of cis double bonds as inferred by 1H NMR spectra (see Figures S19-22) and Raman (see Figures S23be) experiments. For all the polymers, an efficient chiral transmission from the MTPA moiety towards the PPA backbone was found. This fact indicated the presence of a well-folded structures of the pendant groups in solution. Additionally, subtle changes in the polarity of the media produced conformational changes in the MTPA moiety, resulting in helical inversion and/or variations of the elongation of the PPA skeleton. A detailed explanation of the features of each polymer can be found next. As depicted in Figure 3, poly1 showed an effective asymmetry induction from the MTPA moiety, through the achiral gly-Aib fragment, towards the polyene backbone as inferred by the presence of an active ECD trace with predominant macromolecular screw sense. As an example, the presence of a positive Cotton effect centered at 375 nm in MeOH— ascribed to the polymer main chain— indicated the presence of a P helix. Interestingly, the polymer presented dynamic behavior as demonstrated by ECD studies in different 21 Lizio, M. G.; Andrushchenko, V.; Pike, S. J.; Peters, A. D.; Whitehead, G. F. S.; Vitórica-Yrezábal, I. J.; Mutter, S. T.; Clayden, J.; Bour, P.; Blanch, E. W.; Webb, S. J. Chem. Eur. J. 2018 , 24, 9399-9408. Chapter III 118 solvents. Thus, solvents with low polarity (e.g., CHCl3 or DCM) induced a M helix, while more polar ones (e.g., DMF, DMSO, NMP) promoted a P helix thus affording inversed CD spectra as shown in Figure 3b. VT-CD experiments carried out in low polar solvents (e.g., CHCl3 and DCM) showed a concomitant helical inversion (see Figures 26a and S26b) of the PPA framework as the temperature increased. Additionally, the UV-Vis studies showed a bathochromic shift in the chromophoric main chain region (from l = 395 to 455 nm) as the polarity of the corresponding solvent increased (see Figure S25b), indicative of an elongation of the polyene backbone. Figure 3 . (a) Conceptual illustration of the stretching process of (S)-MTPA-Aib-gly-PPA. (b) CD and (c) VTCD spectra of poly1 showing the helix inversion process. CD studies of poly2 in different solvents showed the existence of a preferred-handed macromolecular helical structure, whose elongation and handedness were affected by the nature of the solvent. Consequently, for the majority of solvent tested, CD experiments showed a positive Cotton effect with maxima at l = 470 nm —P helix, CD(+), that is shifted 95 nm compared with the abovementioned counterpart poly1 — indicative of stretched P skeleton (Figure 4b). Importantly, CHCl3 and DCM were able to trigger a helix inversion process as demonstrated by ECD experiments — M helix, CD(-)— (Figure 4). Strikingly, VTCD experiments showed two different scenarios depending on the solvent used. A temperature-dependent helix inversion was observed in CHCl3: at 60ºC the Cotton effect ascribed to the polymer main chain was positive, while at low temperature (i.e., T = -5ºC) 300 400 500 -20 -10 0 10 20 Wavelength [nm] CD [mdeg] DCM Dioxane DMF MeOH THF CHCl3 DMSO NMP 300 400 500 -20 -15 -10 -5 0 5 10 Wavelength [nm] CD [mdeg] T= -5ºC T= 20ºC T= 40ºC T= 60ºC T= 80ºC b) c) Stretched P HelixCompressed M Helix a) polar solvents low polar solvents Greasing Macromolecular Gears: Inclusion of Flexible Spacers 119 was negative, therefore indicating an inversion from P to M helix (Figure S28a). Interestingly, a stretching of the PPA skeleton was triggered in DCM as revealed by the large bathochromic shift in the vinylic region (from l = 445 to l = 430 nm) of the CD spectra (Figure S28b). Although the (S)-MTPA chiral unit is separated from the backbone by one glycine and two achiral Aib residues, it is still able to induce a preferred helical sense in the polyene chain. Other modifications in the conformational composition of the MTPA moiety result in helix inversion, an effect not obtained for the previously reported counterpart.17 Figure 4 . (a) Conceptual illustration of the stretching process of (S)-MTPA-(Aib)2-gly-PPA. (b) CD and (c) VTCD spectra of poly2 showing the helix inversion process. CD studies of poly3 in different solvents showed the presence of a preferred helical structure that generated, in all cases, a strong negative Cotton effect in the vinylic region —M helix, CD(-)— (Figure 5b). While the polymer displayed in all cases a M helical structure, variations in the polarity of the media modified the elongation degree of the polymer as concluded by both ECD and UV-Vis experiments (Figure 5b-c). Thus, in lowpolar solvents (i.e., CHCl3), the conjugated PPA backbone had a maximum in absorption at l = 455 nm, while in more polar solvents such as NMP, it underwent a bathochromic shift of 30 nm (l = 485 nm), indicative of the presence of a more stretched helix (Figure 5c). Interestingly, the introduction of glycine as flexible spacer allowed efficient transmission of chiral information and increased tolerance to solvents, as described below. Our previous polar solvents low polar solvents 300 400 500 600 -10 -5 0 5 10 15 20 Wavelength [nm] CD [mdeg] DCM Dioxane DMF THF CHCl3 300 400 500 -10 -5 0 5 Wavelength [nm] CD [mdeg] T= -5ºC T= 20ºC T= 40ºC T= 60ºC T= 80ºC b) c) Stretched P HelixCompressed M Helix a) Chapter III 120 system bearing a pure Aib foldamer linker, with virtually the same length, was not able to transmit chiral information in polar solvents (e.g., DMF and NMP) due to the lack of flexibility of the more rigid fragment, therefore emphasizing the effectiveness of the introduction of glycine in our foldamer design.17 Figure 5 . (a) Conceptual illustration of the stretching process of (S)-MTPA-(Aib)3-gly-PPA. (b) CD and (c) UV-Vis spectra of poly3 displaying the stretching process. Finally, CD studies of poly4 showed a CD response in all the solvents tested, indicating an effective transmission of chiral information through the non-chiral foldamer sequence, implying the presence of a well-ordered 310-helix structure in the pendant groups. However, subtle differences were found in the spectral pattern depending on the solvent used, indicating that the system was more dynamic that expected. The subtle but important differences in the ECD/UV-Vis spectral patterns for the solvents tested are displayed in Figure 6b-c. In DCM and acetone, poly4 showed a first small Cotton effect centered at l = 570 nm and 565 nm followed by consecutive strong positive and negative bands at l = 515 and 345, and 480 and 345 nm, respectively. This spectral pattern was modified in more polar solvents (i.e., DMF), where the first Cotton effect at higher wavelengths disappeared and only a broad positive Cotton effect with two maximum appeared (l = 435 and 525 mn, Figure 6b and S30). The presence of two maxima in the region ascribed to the polymer main chain indicated the presence of an equilibrium between two helical scaffolds with same handedness but different stretching degree. This 300 400 500 600 -120 -100 -80 -60 -40 -20 0 20 40 Wavelength [nm] CD [mdeg] CCl4 CHCl3 DCM Dioxane DMF DMSO NMP THF 300 400 500 600 0.5 1.0 1.5 2.0 Wavelength [nm] Abs CCl4 CHCl3 DCM Dioxane DMF DMSO NMP THF b) c) Stretched M Helix Compressed M Helix a) polar solvents low polar solvents 127 Chapter IV. Multi-Helical Scaffolds (up to Five Helices) from Chiral (PPA)s bearing a Gly-AA as Pendant. Abstract Helical sense of chiral poly(phenylacetylene)s is usually controlled by taming the conformational composition at the chiral pendant group. Sometimes, the P/M helical sense control can be accompanied by variation on the elongation of the polymer, although is not possible to control both parameters (elongation and helical sense) independently. Herein, we will show how up to five different helical structures can be obtained from a PPA that bears the anilide of the Gly-AA-Boc (AA = Phe, Val) as pendant. In this polymer it is possible to control the conformational composition of the two amino acid residues independently, which results in a full control of the polymer elongation (gly, achiral residue) —three scaffolds: helix 1 - 3 —and the helical sense (AA, chiral amino acid) —P/M screw sense excess—. Multi-Helical Scaffolds (up to Five Helices) from Chiral (PPA)s bearing a Gly-AA as Pendant 129 Introduction Biological macromolecules, such as DNA, peptides, polysaccharides and proteins, adopt one-handed helical structures predetermined by the chirality of their constituent units. In addition, part of these biomacromolecules such as proteins combine different structural motifs (i.e., helices, loops, turns, b-sheets) to be folded into high-order macromolecular structures (tertiary and quaternary structures) which are responsible of the protein function. 1-4 Due to this fact, the scientific community has developed a large number of artificial helical structures (i.e. helical polymers or oligomers) with a preferred helicity to study the application/function of these new scaffolds. Among them, dynamic helical polymers, like poly(phenylacetylene)s [(PPA)s], represent an attractive research topic due to their stimuli-responsive properties and their different applications such as sensors,5 chiroptical switches,6-8 chiral stationary phases9 or chiral catalyst,10-15 among others. In most of these polymers, the handedness of the helical polymers is induced by the chiral pendant group directly attached to the poly(phenylacetylene) backbone. Further changes in the conformational composition of the pendant group by the application of external stimuli could result in changes in the helical parameters of the PPA —elongation and/or sense—, as a result, these polymers can act as stimuli-responsive materials. During the last decades, some research groups have been working in the introduction of achiral flexible spacers between the chiral center and the pendant group, obtaining that as the chiral center is being placed further from the polyene backbone, the helix induction 1 Yashima, E.; Ousaka, N.; Taura, D.; Shimomura, K.; Ikai, T.; Maeda, K. Chem. Rev. 2016 , 116, 13752-13990. 2 Yashima, E.; Maeda, K.; Furusho, Y. Acc. Chem. Res. 2008 , 41, 1166-1180. 3 Yashima, E.; Maeda, K.; Iida, H.; Furusho, Y.; Nagai, K. Chem. Rev. 2009 , 109, 6102-6211. 4 Yu, Z.; Hecht, S. Remote control over folding by light. Chem. Commun. 2016 , 52, 6639-6653. 5 a) Anger, E.; Iida, H.; Yamaguchi, T.; Hayashi, K.; Kumano, D.; Crassous, J.; Vanthuyne, N.; Rousselc, C.; Yashima, E. Polym. Chem. 2014 , 5, 4909; b) Iida, H.; Miki, M.; Iwahana, S.; Yashima, E. Chem. - Eur. J. 2014 , 20, 4257; c) Leiras, S.; Freire, F.; Seco, J. M.; Quiñoá, E.; Riguera, R. Chem. Sci. 2013 , 4, 2735. 6 Sakurai, S.; Okoshi, K.; Kumaki, J.; Yashima, E. J. Am. Chem. Soc. 2006 , 128, 5650. 7 Okoshi, K.; Sakurai, S.; Ohsawa, J. K.; Yashima, E. Angew. Chem. Int. Ed. 2006 , 45, 8173. 8 Pijper, D.; Jongejan, M. G. M.; Meetsma, A.; Feringa, B. L. J. Am. Chem. Soc. 2008 , 130, 4541. 9 Shimomura, K.; Ikai, T.; Kanoh, S.; Yashima, E.; Maeda, K. Nat. Chem. 2014 , 6, 429-434. 10 Burgess, M.; Moore, J. S.; López, J. R. Acc. Chem. Res. 2016 , 49, 2649. 11 Iida, H.; Tang, Z.; Yashima, E. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 2869. 12 Tang, Z.; Iida, H.; Hu, H. Y.; Yashima, E. ACS Macro Lett. 2012 , 1, 261. 13 Megens, R. P.; Roelfes, G. Chem. – Eur. J. 2011 , 17, 8514. 14 Liu, X.; Lin, L.; Feng, X. Acc. Chem. Res. 2011 , 44, 574. 15 Iida, H.; Yashima, E. Polymeric Chiral Catalyst Design and Chiral Polymer Synthesis, (Ed: S. Itsuno), John Wiley & Sons, Hoboken, NJ, USA 2011, ch. 7, p 201. Chapter IV 130 is vanished, resulting in a racemic helical conformation.16, 17, 18, 19, 20, 21 Therefore, these studies suggest that the best folding for a PPA is obtained when the distance between the backbone and the chiral motif is as small as possible. For this reason, the closer is the pendant to the polyene framework, the better is the helical control.22, 23 Nonetheless, during these studies it was also found that a full helical sense control can be achieved in (PPA)s that bears an achiral spacer between the chiral center and the polyene backbone if this achiral spacer adopts a well-ordered structural motif —helix, b-sheet, turn, tilting degree—.20, 21, 24-29, 30-32 Moreover, these materials can work as stimuli responsive materials if the addition of external stimuli can alter the secondary structure adopted by the achiral spacer either by acting directly on this motif, or by modifying the conformational composition at the chiral fragment which is further effectively transmitted to the achiral spacer.30 From these materials, we wanted to highlight a previously reported anilide-PPA, which contains an achiral glycine connected to the polyene backbone through the N-terminus, and derivatized with a chiral (R or S)-a-methoxyphenyl acetic acid (MPA) or a chiral (R or S)-a-methoxy-a-trifluoromethylphenyl acetic acid (MTPA) derivative at the C-terminus. In these (PPA)s, a screw sense excess is obtained due to the presence of a well folded extended structure at the pendant (b-sheet mimetic), which is stabilized by hydrogen bond (H-bonds) interactions between neighboring pendants —nth and (n+2)th or nth and (n+3)th, 16 a) Nakako, N.; Mayahara, Y.; Nomura, R.; Tabata, M.; Masuda, T. Macromolecules, 2000 , 33, 3978; b) Tabei, J.; Shotsuki, M.; Sanda, F.; Masuda, T. Macromolecules 2005 , 38, 5860; c) Ishiwari, F.; Nakazono, K.; Koyama, Y.; Takata, T. Chem. Commun. 2011 , 47, 11739. 17 Shi, G.; Dai, X.; Shen, J.; Wan, X. Chirality 2022 , 34, 574-586. 18 Cornelissen, J. J. M.; Rowan, A. E.; Nolte, R. J. M.; Sommerdijk, N. A. J. M. Chem. Rev. 2001 , 101, 4039-4070. 19 Cornelissen, J. J. M.; Donners, J. J. J. M.; de Gelder, R.; Graswinckel, W. S.; Metselaar, G. A.; Rowan, A. E.; Sommerdijk, N. A. J. M.; Nolte, R. J. M. Science, 2001 , 293, 676-680. 20 Kamikawa, Y.; Kato, T.; Onouchi, H.; Kashiwagi, D.; Maeda, K.; Yasima, E. J. Polym. Sci. A Polym. Chem. 2004 , 42, 4580. 21 Cornelissen, J. J. L. M.; Graswinckel, W. S.; Adams, P. J. H. M.; Nachtegaal, G. H.; Kentgens, A. P. M.; Sommerdijk, N. A. J. M.; Nolte, R. J. M. J. Polym. Sci., Part A: Polym. Chem. 2001 , 39, 4255-4264. 22 Ramos, E.; Bosch, J.; Serrano, J. L.; Sierra, T.; Veciana, J. J. Am. Chem. Soc. 1996 , 118, 4703-4704. 23 Amabilino, D. A.; Ramos, E.; Serrano, J. L.; Sierra, T.; Veciana, J. J. Am. Chem. Soc. 1998 , 120, 9126-9134. 24 Gomar-Nadal, E.; Veciana, J.; Rovira, C.; Amabilino, D. B. Adv. Mater. 2005 , 17, 2095-2098. 25 Percec, V.; Petarca, M.; Rudick, J. G.; Aqad, E.; Imam, M. R.; Heiney, P. A. Chem. -Eur. J. 2007 , 13, 9572-9581. 26 Percec, V.; Aqad, E.; Petarca, M.; Rudick, J. G.; Lemon, L.; Ronda, J. C.; De, B. B.; Heiney, P. A.; Meijer, E. W. J. Am. Chem. Soc. 2006 , 128, 16365-16372. 27 Suárez-Picado, E.; Quiñoá, E.; Riguera, R.; Freire, F. Angew. Chem. Int. Ed. 2020 , 59, 4537-4543. 28 Maeda, K.; Tsukui, H.; Matsushita, Y.; Yashima, E. Macromolecules 2007 , 40, 7721-7726. 29 Rodríguez. R; Quiñoá, E.; Riguera, R.; Freire, F. Small 2019 , 15, 1805413 30 Rodríguez, R.; Quiñoá, E.; Riguera, R.; Freire, F. Chem. Mater. 2018 , 30, 2493. 31 a) Fernández, Z.; Fernández, B.; Quiñoá, E.; Riguera, R.; Freire, F. Chem. Sci. 2020 , 11, 7182-7287; b) Fernández, Z.; Fernández, B.; Quiñoá, E.; Freire, F. J. Am. Chem. Soc. 2021 , 143, 20963-20969. 32 Rodríguez, R.; Rivadulla-Cendal, E.; Fernández-Míguez, Manuel.; Fernández, B.; Quiñoá, E.; Maeda, K.; Freire, F. Angew. Chem. Int. Ed. 2022 , 61, e202209953. Multi-Helical Scaffolds (up to Five Helices) from Chiral (PPA)s bearing a Gly-AA as Pendant 131 transforming the flexible spacer into a rigid one.20, 23 Remarkably, in such systems, the helix induction is produced through a tele-induction mechanism, being the screw sense preference lost when two glycine residues are introduced in the achiral spacer. In this work, we wanted to do a step forward in the preparation of stimuli-responsive materials using remote helical sense control of (PPA)s. Thus, we aim to prepare a pendant group consisting of an achiral spacer and a chiral residue, which can adopt different structural motifs under different external stimuli. Considering our expertise in (PPA)s derivatized with amino acids, and the information obtained from literature, we envisioned an PPA bearing either a Gly-Phe or a Gly-Val as pendant groups, connected to the polyene backbone through the N- (anilide-PPA) or C-terminus (benzamide) (Scheme 1). Thus, if we can control the conformational composition at the pendant group, we will be able to generate different extended and bent structures at the pendant group that result in the adoption of different helical scaffolds. In our design, the glycine residue has been chosen as flexible and achiral spacer, which can be involved either into extended or bent structures, while the phenylalanine and the valine has been selected due to the presence their bulky side chain, needed to have a good tele-induction. Scheme 1 . Schematic illustration of the components that form the pendant groups of the polymers bearing glycine spacers: (a) anilide-(PPA)s and (b) benzamide-(PPA)s. Results and discussion Thus, monomers mono-L1 and mono-L2 , containing the anilide of a Gly-Phe-Boc and a Gly-Val-Boc dipeptide respectively (Figure 1a), and monomers mono-L3 and mono-L4 NH2 Polymerizable group Chiral1Group Achiral1flexible linker HO ONH2 ++ R = -CH(CH3)2, -CH2Ph H2NOH ++ O OH O H2NO R = -CH(CH3)2, -CH2Ph O R Anilide connection Benzamide connection HO O N HO O R a) b) R = L-PheAlaBoc, poly-1 R = L-ValBoc, poly-2 R = L-PheAlaOMe, poly-3 R = L-ValOMe, poly-4 N O N H OH NR O H N H O R H H n n Polymerizable group Chiral1Group Achiral1flexible linker Chapter IV 132 containing the benzamide of a Gly-Phe-OMe and a Gly-Val-OMe dipeptide, containing a benzamide connection (Figure 1b) were prepared by using solution peptide chemistry (see SI for details). In these monomers, the chiral residue —L-pheanylalanine or L-valine amino acids— used as chiral inductor is located at the opposite end of the polymerizable group in the dipeptide, the 4-ethynylanilide for N-connection and 4-ethynylbenzamide for the Cconnection (Figure 1). Figure 1 . Structures of monomers bearing pendant groups with a spacer formed by one glycine unit (a) Nand (b) C-attached to the backbone. Next, monomers ( 1 - 4 ) were submitted to polymerization by using [Rh(nbd)Cl]2 as catalyst in THF (see SI for details). The corresponding polymers, [poly-L-( 1 - 4 )] were obtained in high yield and high cis content of double bonds (see SI for details) (Figure2). Figure 2 . Chemical structure of polymers, poly-L-( 1 - 4 ). Next, ECD studies in different solvents were carried out for poly-L-( 1 - 4 ) to determine the dynamic behavior of these polymers. N H OH N O N HO O N H OH N O N HO O Ph mono-L-2 mono-L-1 H NN H O O O O H NN H O O O O Ph mono-L-4 mono-L-3 a) b) a) b) N H OH N O N HO O N H OH N O N HO O Ph H NN H O O O O H NN H O O O O Ph poly-L-2 poly-L-1 poly-L-4 poly-L-3 H H H H nn n n Multi-Helical Scaffolds (up to Five Helices) from Chiral (PPA)s bearing a Gly-AA as Pendant 133 Anilide PPAs: In the case of anilide-(PPA)s, such as poly-L1 and poly-L2 , three helical scaffolds, with different elongation degrees were obtained, fact that indicates as expected the presence of different structural motifs at the pendant groups. Thus, a highly compressed helix was adopted by poly-L1 and poly-L2 in low-polar and non-donor solvents such as chloroform (CHCl3) or dichloromethane (CH2Cl2) (Figure 3). The presence of a helical structure was corroborated by optical rotation measurements, where the values obtained for poly-L1 and poly-L2 are one order of magnitude higher than those obtained for the corresponding monomers, mono-L1 and mono-L2 (see SI Table S3). These compressed helices were obtained due to the presence of an extended conformation at the pendant group, where the two amino acid residues adopted an anticonformation between amide groups. This antigly-antiphe/val conformation at the pendant group is the less congested one, placing the chiral group and the larger substituents in the most remote possible position (Figure 3). As a result, a highly compressed helix was formed (helix 1 ), where polyene bands located at 288 nm reveals a poor conjugation between double bonds, result of the compressed helix, and where the negative sign of the ECD spectra indicated a M orientation of the polyene backbone (Figure 3). Very similar results were obtained for poly-L1 and poly-L2 indicating a structural behavior that can be extrapolated to other anilide-gly-aa dipeptides. Chapter IV 134 Figure 3 . ECD spectra of (a) poly-L1 and (b) poly-L2 in CHCl3 indicating the presence of a highly compressed helix (helix 1 ). However, when polymers poly-L1 and poly-L2 were dissolved in more polar solvents such as THF, a bathochromic shift of the polyene band from 280 nm to 380 nm was observed, revealing the presence of a more elongated helix (helix 2 ) (Figure 4). In this case, the helical sense induced in the polyene band of the PPA was kept into a counterclockwise orientation (M helix 2 ), as inferred from the negative sign of the Cotton band at 380 nm (Figure 4). This helical sense can be explained by a anti to syn conformational change at the glycine residue, remaining the chiral residue, Phe or Val, in an anti-conformation. Analogous results were obtained for poly-L1 and poly-L2 indicating a structural behavior that can be extrapolated to other anilide-gly-aa dipeptides. 300 400 500 600 -30 -20 -10 0 10 Wavelength [nm] CD [mdeg] 300 400 500 600 -30 -15 0 Wavelength [nm] CD [mdeg] a) N H OH N O N HO O anti anti N H OH N O N HO O anti extended conformer Highly Compressed Helix Ph anti Highly Compressed Helix CHCl3 poly-L-1 b) extended conformer poly-L-1 poly-L-2 poly-L-2 280 nm (M helix 1) 280 nm (M helix 1) CHCl3 Multi-Helical Scaffolds (up to Five Helices) from Chiral (PPA)s bearing a Gly-AA as Pendant 135 Figure 4 . ECD spectra of (a) poly-L1 and (b) poly-L2 in THF showing the presence of a more stretched helix (helix 2 ). Interestingly, the M helical sense adopted by poly-L1 and poly-L2 can be inverted by using MeOH as solvent to dissolve the polymers. In this case, a positive Cotton band was obtained for the polyene band at 380 nm, indicative of the presence of a P helix 2 (Figure 5). This change in the screw sense of poly-L1 and poly-L2 , without modifying the polymer scaffold was due to an anti to syn conformational change at the chiral residue, preserving the syn conformation of the glycine residue. Thus, while in THF the pendant group of polyL1 and poly-L2 adopted a preferred syngly-antiphe/val conformation, in MeOH, the pendant adopted a preferred syngly-synphe/val conformation. 300 400 500 600 -15 -10 -5 0 5 Wavelength [nm] CD [mdeg] THF a) H N ONH O HN BuOt O Ph syn anti Helix 2 H N ONH O HN BuOt O syn anti Helix 2 300 400 500 600 -15 -10 -5 0 5 Wavelength [nm] CD [mdeg] THF poly-L-1 poly-L-1poly-L-2 poly-L-2 380 nm M helix 2 380 nm M helix 2 b) Chapter IV 136 Figure 5 . ECD spectra of (a) poly-L1 and (b) poly-L2 in THF and MeOH which reflected a conformational change at the chiral residue in the pendant (helix 2 ). To corroborate the presence of a syngly-antiphe/val and a syngly-synphe/val conformation at the pendant group, Ba(ClO4)2 was added as external stimulus to a chloroform solution of poly-L1 and poly-L2 , where the pendant adopted a preferred antigly-antiphe/val conformation. From previous studies, it is known that this metal produced a tripodal chelate with (PPA)s bearing dipeptides at the pendant.27 It was found that a low equivalents of Ba(ClO4)2 —poly-L-( 1-2 )/Ba2+ 1/0.75 mol/mol ratio— a tripodal chelate was formed between the dipeptide pendant group and the metal ion. As consequence, an anti to syn conformational change is produced at the two amino acids, which results in an elongation of the polymer scaffold from helix 1 (280 nm) to helix 2 (380nm), accompanied with a helix inversion, from M to P (Figure 6). 300 350 400 450 -4 -2 0 2 4 Wavelength [nm] CD[mdeg] 300 350 400 450 -4 -2 0 2 4 6 Wavelength [nm] CD[mdeg] a) H N ONH O HN BuOt O Ph syn anti M Helix 2 H N ONH O HN BuOt O syn anti M Helix 2 poly-L-1 poly-L-1poly-L-2 poly-L-2 380 nm M helix 2 380 nm M helix 2 b) THF MeOH THF MeOH 380 nm P helix 2 380 nm P helix 2 N H O NH O NH O OtBu N H O NH O NH O OtBu Ph syn syn P Helix 2 P Helix 2 syn syn MeOHTHF MeOHTHF Experimental Section Chapter III 239 Figure S11 . (a) 1H-NMR, (b) 13C-NMR and (c) 19F-NMR spectra of mono3 in CDCl3. 1.01.52.02.53.03.54.04.55.05.56.06.57.07.58.08.59.0 H1 (ppm) 3.00 3.00 3.00 3.00 3.00 3.00 0.68 3.17 1.05 1.03 1.01 1.00 1.97 5.28 1.01 1.06 2.00 1.02 0102030405060708090100110120130140150160170180 24.1 24.6 24.7 25.4 25.9 26.0 44.3 55.2 57.2 57.4 57.5 76.5 84.2 117.2 120.0 127.9 129.3 130.3 131.5 132.8 139.6 167.5 169.1 174.1 175.1 175.6 -120-110-100-90-80-70-60-50-40-30-20-100102030405060708090100110120 -67.9 N H OH N O N H OH N O N H O CF3 O Experimental Section Chapter III 240 2-bromo-N-(1-((1-((1-((2-((4-ethynylphenyl)amino)-2-oxoethyl)amino)-2-methyl-1oxopropan-2-yl)amino)-2-methyl-1-oxopropan-2-yl)amino)-2-methyl-1-oxopropan-2-yl)- 2-methylpropanamide (9) General Protocol 3: 2-azido-N-(1-((1-((2-((4-ethynylphenyl)amino)-2-oxoethyl)amino)-2methyl-1-oxopropan-2-yl)amino)-2-methyl-1-oxopropan-2-yl)-2-methylpropanamide ( 8 , 0.20 g, 1.00 equiv) and triphenylphosphine (0.12 g, 1.05 equiv) were dissolved in 30 mL of MeOH/water solution (95/5) and this mixture was refluxed for 2 h. Next, the organic layer was evaporated, diluted with water (20 mL) and extracted with ethyl acetate (5 x 30 mL). The organic layer was dried with anhydrous Na2SO4 and used for acylation with (S)-MTPACl without further purification. The ethyl acetate was evaporated to yield 2-amino-N-(1- ((1-((2-((4-ethynylphenyl)amino)-2-oxoethyl)amino)-2-methyl-1-oxopropan-2-yl)amino)- 2-methyl-1-oxopropan-2-yl)-2-methylpropanamide in 94 % yield (0.18 g). Following General Protocol 1, 2-amino-N-(1-((1-((2-((4-ethynylphenyl)amino)-2oxoethyl)amino)-2-methyl-1-oxopropan-2-yl)amino)-2-methyl-1-oxopropan-2-yl)-2methylpropanamide (0.18 g, 1 equiv) in DCM (10 mL) was added triethylamine (0.14 mL, 2.50 equiv) and ⍺-bromoisobutyryl bromide (0.05 mL, 1.05 equiv). The solution was stirred at rt for 1 h. Then, the organic layer was washed with HCl 1M (3 x 20 mL), dried with anhydrous Na2SO4 and was evaporated to obtain 9 in 88 % yield of pure product (0.21 g). 2)#AIB-Br Et3N#DCM 1)#PPh3,#MeOH#H2O N H OH N O N H OH N O N3 (8) N H OH N O N H OH N O N H O Br (9) Experimental Section Chapter III 241 2-bromo-N-(1-((1-((1-((2-((4-ethynylphenyl)amino)-2-oxoethyl)amino)-2-methyl-1oxopropan-2-yl)amino)-2-methyl-1-oxopropan-2-yl)amino)-2-methyl-1-oxopropan-2-yl)- 2-methylpropanamide (9) 1H NMR (300 MHz, CDCl3) d (ppm): 9.03 (s, 1H), 7.88 (m, 3H), 7.40 (m, 3H), 6.95 (s, 1H), 6.43 (s, 1H), 4.06 (d, J=6.3 Hz, 2H), 3.00 (s, 1H), 1.94 (s, 6H), 1.56 (s, 6H), 1.47 (s, 6H), 1.43 (s, 6H). 13C NMR (75 MHz, CDCl3) d (ppm): 176.4, 175.8, 175.2, 172.9, 169.6, 139.1, 132.9, 120.4, 117.7, 84.0, 59.9, 57.5, 57.3, 56.4, 44.5, 31.1, 25.5, 25.3, 24.8. HRMS (ESI) m/z calc for C26H36BrN5O5 [M+H]: 578.1900, found: 578.1973. Figure S12 . (a) 1H-NMR and (b) 13C-NMR spectra of 9 in CDCl3. 1.01.52.02.53.03.54.04.55.05.56.06.57.07.58.08.59.09.5 6.00 6.15 6.05 6.00 0.81 2.00 0.77 0.80 3.05 3.00 0.80 0102030405060708090100110120130140150160170180 f1 (ppm) 24.8 25.3 25.5 31.1 44.5 56.4 57.3 57.5 59.9 84.0 117.7 120.4 132.9 139.1 169.6 172.9 175.2 175.8 176.4 N H OH N O N H OH N O N H O Br Experimental Section Chapter III 242 2-azido-N-(1-((1-((1-((2-((4-ethynylphenyl)amino)-2-oxoethyl)amino)-2-methyl-1oxopropan-2-yl)amino)-2-methyl-1-oxopropan-2-yl)amino)-2-methyl-1-oxopropan-2-yl)- 2-methylpropanamide (10) General Protocol 2: 2-bromo-N-(1-((1-((1-((2-((4-ethynylphenyl)amino)-2oxoethyl)amino)-2-methyl-1-oxopropan-2-yl)amino)-2-methyl-1-oxopropan-2-yl)amino)- 2-methyl-1-oxopropan-2-yl)-2-methylpropanamide ( 9 , 0.21 g, 1.00 equiv) was dissolved in 5 mL of DMSO and to this solution sodium azide (0.03 g, 1.20 equiv) was added. The mixture was stirred at 80ºC for 2 h. Then, it was diluted with 25 mL of ethyl acetate, extracted with water (5 x 15 mL) and dried with anhydrous Na2SO4. The organic layer was evaporated to obtain 10 in 97 % yield (0.19 g). N H OH N O N H OH N O N H O Br (9) DMSO NaN3 N H OH N O N H OH N O N H O N3 (10) Experimental Section Chapter III 243 2-azido-N-(1-((1-((1-((2-((4-ethynylphenyl)amino)-2-oxoethyl)amino)-2-methyl-1oxopropan-2-yl)amino)-2-methyl-1-oxopropan-2-yl)amino)-2-methyl-1-oxopropan-2-yl)- 2-methylpropanamide (10) 1H NMR (300 MHz, CD3OD) d (ppm): 9.33 (s, 1H), 8.26 (t, J=6.2 Hz, 1H), 7.93 (s, 1H), 7.897.78 (m, 4H), 7.40 (d, J=8.7 Hz, 2H), 3.99 (d, J=6.2 Hz, 2H), 3.40 (s, 1H), 1.53 (d, J=6.9 Hz, 12H), 1.43 (d, J=7.7 Hz, 12H). 13C NMR (75 MHz, CD3OD) d (ppm): 176.9, 176.3, 175.7, 173.4, 169.2, 138.7, 132.0, 119.8, 117.9, 82.9, 76.7, 63.4, 56.9, 56.7, 43.5, 24.2, 24.0, 23.4, 23.2. HRMS (ESI) m/z calc for C26H36N8O5 [M+H]: 541.2809, found: 541.2881. Figure S13 . (a) 1H-NMR and (b) 13C-NMR spectra of 10 in CD3OD. 1.01.52.02.53.03.54.04.55.05.56.06.57.07.58.08.59.09.510.0 f1 (ppm) 12.06 12.00 0.70 2.00 1.83 3.77 0.92 0.95 0.89 0102030405060708090100110120130140150160170180 f1 (ppm) 23.2 23.4 24.0 24.2 43.5 56.7 56.9 63.4 76.7 82.9 117.9 119.8 132.0 138.7 169.2 173.4 175.7 176.3 176.9 N H OH N O N H OH N O N H O N3 Experimental Section Chapter III 244 (S)-N-(1-((1-((1-((1-((2-((4-ethynylphenyl)amino)-2-oxoethyl)amino)-2-methyl-1oxopropan-2-yl)amino)-2-methyl-1-oxopropan-2-yl)amino)-2-methyl-1-oxopropan-2yl)amino)-2-methyl-1-oxopropan-2-yl)-3,3,3-trifluoro-2-methoxy-2-phenylpropanamide (mono-4) General Protocol 3: 2-azido-N-(1-((1-((1-((2-((4-ethynylphenyl)amino)-2-oxoethyl)amino)- 2-methyl-1-oxopropan-2-yl)amino)-2-methyl-1-oxopropan-2-yl)amino)-2-methyl-1oxopropan-2-yl)-2-methylpropanamide ( 10 , 0.15 g, 1.00 equiv) and triphenylphosphine (0.08 g, 1.05 equiv) were dissolved in 30 mL of MeOH/water solution (95/5) and this mixture was refluxed for 2 h. Next, the organic layer was evaporated, diluted with water (20 mL) and extracted with ethyl acetate (5 x 30 mL). The organic layer was dried with anhydrous Na2SO4 and used for acylation with (S)-MTPACl without further purification. The ethyl acetate was evaporated to yield 2-amino-N-(1- ((1-((1-((2-((4-ethynylphenyl)amino)-2-oxoethyl)amino)-2-methyl-1-oxopropan-2yl)amino)-2-methyl-1-oxopropan-2-yl)amino)-2-methyl-1-oxopropan-2-yl)-2methylpropanamide in 91 % yield (0.13 g). (S)-MTPA-Cl was prepared according to our previously reported method,[S1] (S)-⍺-methoxy- ⍺-trifluoromethylphenylacetic acid was dissolved in hexane, and oxalyl chloride and DMF were subsequently added. This mixture was stirred at rt for 30 minutes, then the solution was filtrated and the organic layer was evaporated. The crude was diluted in DCM (10 mL) and combined with PA-gly-(Aib)4-NH2, and then Et3N (0.04 mL, 1.20 equiv) was added. The mixture was stirred at rt for 1 h and the organic layer was evaporated and the crude was purified by chromatographic column using silica gel as stationary phase with a mixture of hexane/ethyl acetate (20/80) as eluent, obtaining mono4 in 86 % yield (0.16 g). 1H NMR (500 MHz, DMF-d7) d (ppm): 9.19 (s, 1H), 8.77 (s, 1H), 8.19 (s, 1H), 7.99 (t, J=6.3 Hz, 1H), 7.87 (d, J=8.7 Hz, 2H), 7.73 (s, 1H), 7.52-7.47 (m, 3H), 7.43-7.35 (m, 3H), 7.33 (d, J=8.6 Hz, 2H), 3.79 (qd, J=17.2 Hz, 6.2 Hz, 2H), 3.35 (s, 1H), 3.32 (s, 3H), 1.42 (s, 6H), 1.38 (d, J=4.6 Hz, 6H), 1.28 (d, J=4.8 Hz, 6H), 1.23 (s, 3H), 1.19 (s, 3H). 13C NMR (500 MHz, DMF-d7) d (ppm): 177.1, 176.2, 175.6, 175.4, 169.1, 167.5, 140.3, 133.4, 132.8, 130.1, 129.2, 128.1, 119.7, 117.4, 84.0, 79.1, 57.6, 57.2, 57.0, 57.0, 55.3, 44.2, 25.5, 25.1, 25.0, 24.7, 24.4, 24.0 19F NMR (750 MHz, DMF-d7) d (ppm): -68.8. HRMS (ESI) m/z calc for C36H45F3N6O7 [M+H]: 731.3302, found: 731.3375. aD20 = -10 (c = 10 mg/mL, DMF). S1 Leiras, S.; Freire, F.; Seco, J. M.; Quiñoá, E.; Riguera, R. Chem. Sci. 2013 , 4, 2735. N H OH N O N H OH N O N H OH N O CF3 O 2)#(S)-MTPA-Cl Et3N#DCM 1)#PPh3,#MeOH#H2O N H OH N O N H OH N O N H O N3 (10) mono-4 Experimental Section Chapter III 245 Figure S14 . (a) 1H-NMR, (b) 13C-NMR and (c) 19F-NMR spectra of mono4 in DMF-d7. 1.01.52.02.53.03.54.04.55.05.56.06.57.07.58.08.59.09.5 f1 (ppm) 3.00 3.00 6.00 6.00 6.00 3.00 0.72 1.93 2.00 3.00 3.00 0.97 2.04 0.99 0.96 0.96 0.94 0102030405060708090100110120130140150160170180190 f1 (ppm) 24.0 24.4 24.7 25.0 25.1 25.5 44.2 55.3 57.0 57.0 57.2 57.6 79.1 84.0 117.4 119.7 128.1 129.2 130.1 132.8 133.4 140.3 167.5 169.1 175.4 175.6 176.2 177.1 -160-150-140-130-120-110-100-90-80-70-60-50-40-30-20-10010203040 f1 (ppm) -68.8 N H OH N O N H OH N O N H OH N O CF3 O Experimental Section Chapter III 246 3. X-ray structure of monomers Single crystals of monomers were grown by slow evaporation of the corresponding monomer solutions in a mixture of DCM/hexanes. The crystallographic data is depicted below in detail. • Crystal data structure refinement for mono1 Table S1 . Torsion Angle Values (deg) for mono1 structures. mono1 y (i+1) f (i+1) y (i+2) f (i+2) O=C-C-OMe ap OMe P-310 helix 39º 50º 3º 83º -173º ap OMe M-310 helix -45º -50º 2º -87º +152º φ (i+2) = -87º ψ (i+2) = 2º ψ (i+1) = -45º φ (i+1) = -50º X-ray'structures (S)-MTPA-Aib-gly-PA'(1) (S)-MTPA-Aib-gly-PA'(2) MTPA apOMe ψ (i+1) = 39º φ (i+1) = 50º φ (i+2) = 83º ψ (i+2) = 3º P'310'helix M'310'helix Experimental Section Chapter III 247 Figure S15 . ORTEP representation of the mono1 conformation obtained from X-ray studies. • Crystal data structure refinement for mono2 Experimental Section Chapter III 248 Table S2 . Torsion Angle Values (deg) for mono2 structures. mono2 y (i+1) f (i+1) y (i+2) f (i+2) y (i+3) f (i+3) O=C-C-OMe ap OMe P-310 helix 42º 51º 26º 57º 24º 67º -172º ap OMe M-310 helix -40º -53º -30º -54º -24º -61º +162º Figure S16 . ORTEP representation of the mono2 (1) and mono2 (2) conformations obtained from X-ray studies. P!310!helix M!310!helix (S)-MTPA-(Aib)2-gly-PA!(1) MTPA apOMe MTPA apOMe (S)-MTPA-(Aib)2-gly-PA!(2) X-ray!structures φ (i+2) = 57º ψ (i+2) = 26º ψ (i+1) = 42º φ (i+1) = 51º φ (i+3) = 67ºψ (i+3) = 24º φ (i+2) = -54º ψ (i+2) = -30ºψ (i+1) = -40º φ (i+1) = -53º φ (i+3) = -61º ψ (i+3) =-24º C1 O2 C3 C4 F5 F6 F7 C8 C13 C9 C10 C11 C12 C14 O15 N21 C22 C23 C24 C25 O26 N31 C32 C33 C34 C35 O36 N41 C42 C43 O44 N51 C52 C53 C54 C55 C56 C57 C58 C59 C101 O102 F107 F106 F105 N121 N131 O126 O115 O136 N141 O144 N151 Experimental Section Chapter III 255 Figure S21 . 1H-NMR of poly3 (300 Mz, DMF-d7). Figure S22 . 1H-NMR of poly4 (300 Mz, DMSO-d6). 0.00.51.01.52.02.53.03.54.04.55.05.56.06.57.07.58.08.59.09.510.010.5 0.51.01.52.02.53.03.54.04.55.05.56.06.57.07.58.08.59.09.510.0 Experimental Section Chapter III 256 6. Raman characterization of monomers and polymers Figure S23 . Raman spectra of (a) monomers mono1 — mono4 , (b) poly1 , (c) poly2 , (d) poly3 and (e) poly4 showing the characteristic bands of a cis-polyene backbone. 7. ECD Theoretical Calculations ECD theoretical calculations of the (S)-MTPA-(Aib)n-gly-PA, (n = 1, 2, 3, 4) were performed using as input structural data obtained from X-ray (see Tables S1-S4). All computations were carried out using Gaussian-16 (G16RevC.01).[S2] Geometry optimization, as well as ECD theoretical calculations (80 excitation energies), were performed by using the DFT CAM-B3LYP/6-31+G**[S3-S5] methodology. Frequency calculations on the optimized geometries revealed no imaginary frequencies, indicating that the calculated structures correspond, at least, to local minima on the potential energy surface. The energies shown are the thermally corrected energies at 298K. S2 Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman, J. R.; Scalmani, G.; Barone, V.; Petersson, G. A.; Nakatsuji, H.; Li, X.; Caricato, M.; Marenich, A. V.; Bloino, J.; Janesko, B. G.; Gomperts, R.; Mennucci, B.; Hratchian, H. P.; Ortiz, J. V.; Izmaylov, A. F.; Sonnenberg, J. L.; Williams-Young, D.; Ding, F. ; Lipparini, F. ; Egidi, F.; Goings, J.; Peng, B.; Petrone, A.; Henderson, T.; Ranasinghe, D.; Zakrzewski, V. G.; Gao, J.; Rega, N.; Zheng, G.; Liang, W.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai, H.; Vreven, T.; Throssell, K.; Montgomery Jr., J. A.; Peralta, J. E.; Ogliaro, F.; Bearpark, M. J.; Heyd, J. J.; Brothers, E. N.; Kudin, K. N.; Staroverov, V. N.; Keith, T. A.; Kobayashi, R.; Normand, J.; Raghavachari, K.; Rendell, A. P.; Burant, J. C.; Iyengar, S. S.; Tomasi, J.; Cossi, M.; Millam, J. M.; Klene, M.; Adamo, C.; Cammi, R.; Ochterski, J. W.; Martin, R. L.; Morokuma, K.; Farkas, O.; Foresman, J. B.; Fox, D. J. Gaussian 16 Revision C.01. Gaussian Inc: Wallingford CT 2019. S3 Runge, E.; Gross, E. Phys. Rev. Lett. 1984 , 52, 997–1000. S 4 Yanai, Y.; Tew, D. P; Handy, C. C. A. Chem. Phys. Lett. 2004 , 393, 51-57. S5 Peach, M. J. G.; Helgaker, T.; Salek, P.; Keal, T. W.; Lutnaes, O. B.; Tozer, D. J.; Handy, N. C. Phys. Chem. Chem. Phys. 2006 , 8, 558-562. 1640 1660 1680 1700 Wavenumber (cm-1) mono-3 mono-2 mono-1 mono4 1662$cm-1 1000 1200 1400 1600 Wavenumber [cm-1] 1000 1200 1400 1600 Wavenumber [cm-1] b) (S)-MTPA-(Aib)1-gly-PPA cis C-H 1006 cm-1 cis C-C 1340 cm-1 cis C=C 1568 cm-1 c) (S)-MTPA-(Aib)2-gly-PPA cis C-H 973 cm-1 cis C-C 1333 cm-1 cis C=C 1576 cm-1 1000 1200 1400 1600 Wavenumber [cm-1] 1000 1200 1400 1600 Wavenumber [cm-1] b) (S)-MTPA-(Aib)1-gly-PPA cis C-H 1006 cm-1 cis C-C 1340 cm-1 cis C=C 1568 cm-1 c) (S)-MTPA-(Aib)2-gly-PPA cis C-H 973 cm-1 cis C-C 1333 cm-1 cis C=C 1576 cm-1 1000 1200 1400 1600 Wavenumber (cm-1) 1000 1200 1400 1600 Wavenumber [cm-1] d) (S)-MTPA-(Aib)3-gly-PPA cis C-H 972 cm-1 cis C-C 1329 cm-1 cis C=C 1570 cm-1 e) (S)-MTPA-(Aib)4-gly-PPA cis C-H 966 cm-1 cis C-C 1326 cm-1 cis C=C 1568 cm-1 1000 1200 1400 1600 Wavenumber (cm-1) 1000 1200 1400 1600 Wavenumber [cm-1] d) (S)-MTPA-(Aib)3-gly-PPA cis C-H 972 cm-1 cis C-C 1329 cm-1 cis C=C 1570 cm-1 e) (S)-MTPA-(Aib)4-gly-PPA cis C-H 966 cm-1 cis C-C 1326 cm-1 cis C=C 1568 cm-1 Experimental Section Chapter III 257 Table S7 . Calculated energy difference for the two sp/ap conformers of each P/M-turn in terms of the enthalpy (ΔH) and Gibbs free energy (ΔG), where sp conformations were considered the zero as ap configuration are the most stable in all cases. monomer P/M-turn DH (kcal.mol-1) DG (kcal.mol-1) mono1 P turn 4.4 3.7 M turn 3.2 3.1 stretched 4.0 3.8 mono2 P turn 4.5 4.3 M turn 4.9 4.3 stretched 3.6 3.1 mono3 P turn 4.5 4.8 M turn 2.9 4.0 stretched 1.4 0.7 mono4 P turn 4.6 5.6 M turn 3.5 3.7 stretched 2.1 1.6 Considering the shape of the experimental spectra, the theoretical ECDs were built from the calculated rotational strengths assuming a Gaussian band shape with a half width at half height of 0.62 eV. For a more efficient correlation between the theoretical and the experimental results and considering the known differences of DFT in getting accurate ECD spectra, we adjusted each theoretical spectra with correlation factors obtained for comparison (between theory and experiment) of the wavelength and intensity at maximum/minimum corresponding to the first Cotton effect. In this way, we evaluated a correction factor for lambda as the difference between the theoretical and experimental wavelengths, and we shifted the rest of the theoretical spectrum accordingly. Regarding the intensity, from the above comparison we rescaled the theoretical values to get experimental intensity at the first Cotton effect. Experimental Section Chapter III 258 8. CD experiments of monomers CD studies of the monomers were carried out in different solvents (1 mm cuvette). Figure S24 . CD spectra in different solvents of (a) mono1 (0.6 mg/ml), (b) mono2 (0.6 mg/ml), (c) mono3 (0.9 mg/ml) and (d) mono4 (0.9 mg/ml). Additional CD/UV experiments of poly-1 Figure S25 . (a) CD spectra of poly1 in different solvents and (b) UV-Vis spectra showing a bathochromic shift from compressed helix in low polar solvents to stretched helix in polar solvents (0.3 mg/mL, 1 mm cuvette). 250 300 350 400 0 10 20 Wavelength [nm] CD[mdeg] CHCl3 THF DCM 250 300 350 400 -10 0 10 20 30 Wavelength [nm] CD[mdeg] CHCl3 THF DCM 250 300 350 400 -10 0 10 Wavelength [nm] CD[mdeg] CHCl3 THF DCM 250 300 350 400 -10 -5 0 5 10 Wavelength [nm] CD[mdeg] THF CHCl3 DCM a) b) c) d) 300 400 500 -15 -10 -5 0 5 10 15 Wavelength [nm] CD [mdeg] CHCl3 DCM dioxane DMSO DMF MeOH NMP THF 350 400 450 500 550 0.2 0.4 Wavelength [nm] Abs CHCl3 DCM Dioxane DMF MeOH NMP a) b) Experimental Section Chapter III 259 Figure S26 . VT-CD of poly1 in (a) CHCl3 and (b) DCM (0.3 mg/mL, 1 mm cuvette). Additional CD/UV experiments of poly-2 Figure S27 . (a) CD and (b) UV-Vis spectra of poly2 in different solvents (0.15 mg/mL, 1 cm cuvette). Figure S28 . VT-CD of poly2 in (a) CHCl3 and (b) DCM (0.3 mg/mL, 1 cm cuvette). 300 400 500 -10 -5 0 5 10 Wavelength [nm] CD [mdeg] -5º 20º 40º 60º 300 400 500 -20 -15 -10 -5 0 5 10 Wavelength [nm] CD [mdeg] -5º 20º 40º 60º 80º a) b) 350 400 450 500 550 600 0.2 0.4 0.6 0.8 Wavelength [nm] Abs CHCl3 DCM Dioxane DMF THF 300 400 500 600 -10 -5 0 5 10 15 20 Wavelength [nm] CD [mdeg] DCM Dioxane DMF THF CHCl3 a) b) 300 400 500 -10 -5 0 5 Wavelength [nm] CD [mdeg] -5º 20º 40º 60º 80º 300 400 500 -10 -5 0 5 Wavelength [nm] CD [mdeg] -5º 20º 40º 60º 80º a) b) Experimental Section Chapter III 260 Additional CD/UV experiments of poly-3 Figure S29 . (a) CD spectra of poly3 in different solvents and (b) UV-Vis spectra showing a bathochromic shift from compressed helix in low polar solvents to stretched helix in polar solvents (0.1 mg/mL, 1 cm cuvette). Additional CD/UV experiments of poly-4 Figure S30 . (a) CD spectra of poly4 in different solvents and (b) UV-Vis spectra showing a stretching process of the PPA skeleton (0.2 mg/mL, 1 mm cuvette). 300 400 500 600 -120 -100 -80 -60 -40 -20 0 20 40 Wavelength [nm] CD [mdeg] CCl4 CHCl3 DCM Dioxane DMF DMSO NMP THF 300 400 500 600 0.5 1.0 1.5 2.0 Wavelength [nm] Abs CCl4 CHCl3 DCM dioxane DMF DMSO NMP THF a) b) 300 400 500 600 -30 -20 -10 0 10 20 30 Wavelength [nm] CD[mdeg] Acetone CHCl3 DCM Dioxane DMF THF NMP 400 500 600 0.1 0.2 Wavelength [nm] Abs Acetone CHCl3 DCM DMF THF NMP a) b) Experimental Section Chapter III 261 9. DSC Studies DSC experiments have been used to determine the configuration of the polymer skeleton in poly(phenylacetylenes) due to the different thermogram pattern for a cis-cisoidal or a cis-transoidal polyene backbone. For detailed explanation of thermal transitions in PPA's. Both DSC traces were recorded using a heating rate of 10ºC/min and showed the characteristic thermogram of a c-t polymer backbone with the corresponding transitions from c-t to c-c and a final isomerization from c-c to t-t.[S6] Figure S31 . DSC trace of (a) poly1 and (b) poly2 . 10. Thermal studies TGA studies were carried out to determine the thermal stability of the polymers. As a general protocol a polymer sample was kept in a platinum pan and heated from 40ºC to 800ºC with a heating range of 10ºC/min. Figure S32 . TGA thermograms of (a) poly1 . (b) poly2 . (c) poly3 and (d) poly4 . S6 For detailed DSC studies on (PPA)s see: Liu, L.; Namikoshi, T.; Zang, Y.; Aoki, T.; Hadano, S.; Abe, Y.; Wasuzu, I.; Tsutsuba, T.; Teraguchi, M., Kaneko, T. J. Am. Chem. Soc. 2013 , 135, 602. 100 125 150 175 200 225 250 275 300 T/ ºC 100 125 150 175 200 225 250 T/ ºC 100 125 150 175 200 225 250 275 T/ ºC 100 125 150 175 200 225 250 275 300 325 T/ ºC a) b) c) d) T1=)150º)C c-t c-ct-t T2=)199º)C T1=)200º)C c-ct-t 0200 400 600 800 0 50 100 T/ ºC % mass 0200 400 600 800 0 50 100 T/ ºC % mass 0200 400 600 800 0 50 100 T/ ºC % mass 0200 400 600 0 50 100 T/ ºC % mass a) b) c) d) Experimental Section Chapter III 262 11. IR studies of monomers Figure S33 . IR spectra of (a) mono1 . (b) mono2 . (c) mono3 and (d) mono4 . 12. IR studies of polymers Figure S34 . IR spectra of (a) poly1 . (b) poly2 . (c) poly3 and (d) poly4 . 1000200030004000 Wavenumber [cm-1] 1000200030004000 Wavenumber [cm-1] 1000200030004000 Wavenumber [cm-1] 1000200030004000 Wavenumber [cm-1] a) b) c) d) 1000200030004000 Wavenumber [cm-1] 1000200030004000 Wavenumber [cm-1] 1000200030004000 Wavenumber [cm-1] 1000200030004000 Wavenumber [cm-1] a) b) c) d) Experimental Section Chapter III 263 13. NMR studies of mono-1 Experiments 1D and 2D-NMR in THF-d8 were carried out to confirm the presence of the P torsion of mono1 . Thus, 2D-NOESY spectrums were obtained in order to observe the corresponding cross peaks that are indicated below at Figure S35. Figure S35 . Representative NOEs of mono1 in THF-d8. Figure S36 . 1H NMR of mono1 in THF-d8 at 268 K. 1H NMR (500 MHz, THF-d8) d (ppm): 9.05 (s, 1H), 8.12 (s, 1H), 7.70 (d, J=8.7 Hz, 2H), 7.64 (t, J=5.9 Hz, 1H), 7.59 (d, J=6.9 Hz, 2H), 7.37 – 7.31 (m, 3H), 7.23 (d, J=8.7 Hz, 2H), 4.00 – 3.90 (m, 2H), 3.51 (s, 3H), 3.36 (s, 1H), 1.54 (d, J=4.8 Hz, 6H). (s)-MTPA-Aib-gly-PA 123 4 apOMe NH(1) NH(2) NH(3) OMe(1) 1.52.02.53.03.54.04.55.05.56.06.57.07.58.08.59.0 f1 (ppm) 6.00 0.65 3.00 2.03 1.75 3.00 2.00 1.08 2.02 0.92 0.90 1.54 1.55 3.36 3.51 3.58 THF-d8 3.90 3.91 3.94 3.95 3.95 3.96 3.98 3.99 7.22 7.24 7.32 7.33 7.33 7.35 7.36 7.58 7.60 7.64 7.65 7.66 7.69 7.70 8.12 9.05 Experimental Section Chapter III 264 a) b) 7.47.57.67.77.87.98.08.18.28.38.48.58.68.78.88.99.0 ppm 7.1 7.2 7.3 7.4 7.5 7.6 7.7 7.8 7.9 8.0 8.1 8.2 8.3 8.4 8.5 8.6 8.7 8.8 8.9 9.0 9.1 9.2 H1(ppm) 3.73.83.97.07.17.27.37.47.57.67.77.88.99.0 ppm 3.7 3.8 3.9 4.0 4.1 6.9 7.0 7.1 7.2 7.3 7.4 7.5 7.6 7.7 7.8 7.9 8.8 8.9 9.0 9.1 9.2 9.3 H1(ppm) NH(3) – NH(2) NH(3) – Ar(4) Ar(4) – NH(3) NH(2) ) – NH(3) and Ar(1) – NH(3) NH(3) – CH2 NH(2) – CH2 CH2 – NH(3) CH2 – NH(2) NH(3) – Ar(1) Ar(1) – NH(1) NH(1) – Ar(1) Experimental Section Chapter III 271 a) b) 1.01.52.02.53.03.54.04.55.05.56.06.57.07.58.08.59.0 1.58 1.62 3.93 3.94 3.95 3.96 4.15 4.16 4.17 4.18 6.58 7.43 7.44 8.68 0.51.01.52.02.53.03.54.04.55.05.56.06.57.07.58.08.59.09.5 1.58 1.61 3.92 3.93 3.95 3.96 4.14 4.15 4.17 4.18 6.58 7.44 7.44 7.46 8.68 Experimental Section Chapter III 272 c) Figure S42 . 1D-NMR experiments (NOESY) of mono1 in CDCl3 at 268 K showing the cross peaks that (a) NH(3) is close in space to protons of Ar(4), NH(1), NH(2), CH2 (gly) and Aib2, (b) NH(2) is close in space to protons of NH(3), NH(1), CH2 (gly) and Aib2, (c) OMe(1) is close in space to protons of Ar(1), NH(1) and Aib2. 14. NMR studies of mono-2 1D and 2D-NOESY NMR experiments of mono2 in THF-d8 show strong sequential NH-NH cross peaks which confirms the presence of P-310 helix of the oligomer in solution. The apOMe conformation at the pendant group was confirmed by the presence of NOE cross peaks between the anilide (NH1) and the methoxy group. Figure S43 . Representative NOEs of mono2 in THF-d8. 0.00.51.01.52.02.53.03.54.04.55.05.56.06.57.07.58.0 1.58 1.61 3.36 7.45 7.46 7.47 (s)-MTPA-Aib-Aib-gly-PA 123 4 ap-OMe NH(1) NH(2) NH(3) OMe(1) 5 NH(4) Experimental Section Chapter III 273 Figure S44 . 1H NMR of mono2 (THF-d8, 268 K). 1H NMR (750 MHz, THF-d8) d (ppm): 9.11 (s, 1H), 8.27 (s, 1H), 7.91 (d, J=8.6 Hz, 2H), 7.74 (t, J=6.3 Hz, 1H), 7.51 (d, J=7.9 Hz, 2H), 7.39 – 7.34 (m, 3H), 7.31 (d, J=8.6 Hz, 2H), 7.21 (s, 1H), 3.78 – 3.71 (m, 2H), 3.38 (s, 1H), 3.35 (s, 3H), 1.53 (d, J=3.7 Hz, 6H), 1.46 (d, J=7.5 Hz, 6H). 1.01.52.02.53.03.54.04.55.05.56.06.57.07.58.08.59.0 f1 (ppm) 6.26 6.09 3.00 0.69 2.15 0.95 1.80 3.00 2.00 1.00 2.00 0.97 1.00 1.46 1.47 1.53 1.53 2.62 3.35 3.38 3.58 THF-d8 3.71 3.72 3.73 3.74 3.74 3.75 3.77 3.77 7.21 7.30 7.32 7.36 7.37 7.37 7.37 7.50 7.52 7.73 7.74 7.75 7.90 7.92 8.27 9.11 Experimental Section Chapter III 274 a) b) 7.07.17.27.37.47.57.67.77.87.98.08.18.28.38.48.58.68.78.88.99.09.19.29.39.4 H1(ppm) 6.8 7.0 7.2 7.4 7.6 7.8 8.0 8.2 8.4 8.6 8.8 9.0 9.2 9.4 H1(ppm) 3.43.73.83.97.17.27.37.47.57.67.77.87.98.08.18.28.38.48.58.68.78.88.99.09.19.29.3 H1(ppm) 3.4 3.8 7.0 7.2 7.4 7.6 7.8 8.0 8.2 8.4 8.6 8.8 9.0 9.2 9.4 H1(ppm) NH(3) – NH(2) NH(2) – NH(1) NH(1) – NH(2) NH(3) – NH(4) NH(3) – NH(4) NH(2) – NH(3) Ar(5) – NH(4) NH(4) – Ar(5) NH(4) – CH2 CH2 – NH(4) NH(1) – OMe(1) NH(3) – CH2 CH2 – NH(3) OMe(1) – NH(1) OMe(1) – Ar(1) Ar(1) – OMe(1) Experimental Section Chapter III 275 c) d) Figure S45 . 2D-NOESY of mono2 in THF-d8 at 268 K showing (a) all NH-NH cross peaks: NH(4)- NH(3), NH(3)-NH(2) and NH(1)-NH(2), (b) NH(4)-CH2 (gly), NH(3)-CH2 (gly), NH(1)-OMe(1) and Ar(1)-OMe(1), (c) NH(4)-CH2 (gly), NH(3)-CH2 (gly), Aib2-OMe(1), (d) Aib3-NH(3), Aib3-NH(2), Aib2NH(2), Aib2-NH(1), Ar(1)-Aib2, Ar(5)-Aib2. 1.41.51.63.43.73.87.67.77.87.98.08.18.28.38.49.19.2 H1(ppm) 1.2 1.4 1.6 3.4 3.8 4.0 7.8 8.0 8.2 8.4 9.0 9.2 H1(ppm) 1.41.51.67.27.37.47.57.67.77.87.98.08.18.28.38.48.5 H1(ppm) 1.4 1.6 1.8 6.6 6.8 7.0 7.2 7.4 7.6 7.8 8.0 8.2 8.4 H1(ppm) OMe(1) – Aib2 Aib2 – OMe(1) NH(1) – Aib2 Aib2 – NH(1) NH(3) – Aib3 NH(2) – Aib3 NH(2) – Aib2 Aib3 and Aib2 – NH(2) Aib3 – NH(3) Ar(1) – Aib2 Ar(5) – Aib2 Aib2 – Ar(5) Aib2 – Ar(1) NH(3) – CH2 NH(4) – CH2 CH2 – NH(4) CH2 – NH(3) Experimental Section Chapter III 276 1D-NMR experiments (NOESY) of mono-2 in THF-d8 1D-NMR experiments (NOESY) of mono2 in THF-d8 were carried out where selective signals were irradiated (positive signal) to observe the coupled protons of the molecule that are closed in space (negative signal). a) b) Experimental Section Chapter III 277 c) d) Experimental Section Chapter III 278 e) f) Figure S46 . 1D-NMR experiments (NOESY) of mono2 in THF-d8 at 268 K showing the cross peaks that (a) NH(4) is close in space to protons of Ar(5), NH(3) and CH2 (gly), (b) NH(3) is close in space to protons of NH(4), NH(2), CH2 (gly) and Aib3, (c) NH(2) is close in space to protons of NH(3), NH(1), Aib2 and Aib3, (d) NH(1) is close in space to protons of NH(2), Ar(1), OMe(1) and Aib2, (e) OMe is close in space to protons of NH(1), Ar(1), Aib2 and Aib3, (f) CH2 (gly) is close in space to protons of NH(4), NH(3) and Aib3. Experimental Section Chapter III 279 1D and 2D-NOESY NMR experiments of mono-2 in CDCl3 show the same strong sequential NH-NH and OMe(1)-NH(1) cross peaks than mono2 in THF-d8 confirming the apOMe conformation. Figure S47 . Representative NOEs of mono2 in CDCl3. Figure S48 . 1H NMR of mono2 in CDCl3 at 268 K. 1H NMR (750 MHz, CDCl3) d (ppm): 8.87 (s, 1H), 7.82 (d, J=8.7 Hz, 2H), 7.60 (s, 1H), 7.56 (t, J=6.3 Hz, 1H), 7.43 – 7.35 (m, 7H), 6.29 (s, 1H), 4.05 (dd, J=17.2 Hz, 7.0 Hz, 1H), 3.66 (dd, J=17.2 Hz, 5.7 Hz, 1H), 3.29 (s, 3H), 3.00 (s, 1H), 1.58 (s, 3H), 1.54 (s, 3H), 1.51 (s, 3H), 1.45 (s, 3H). (s)-MTPA-Aib-Aib-gly-PA 123 4 apOMe NH(1) NH(2) NH(3) OMe(1) 5 NH(4) 1.01.52.02.53.03.54.04.55.05.56.06.57.07.58.08.59.09.5 f1 (ppm) 3.00 3.00 3.00 3.00 0.68 3.00 1.00 1.00 0.96 6.75 1.03 0.98 1.92 0.98 1.45 1.51 1.54 1.58 3.00 3.29 3.64 3.65 3.66 3.67 4.04 4.05 4.06 4.07 6.29 7.26 CDCl3 7.36 7.37 7.39 7.39 7.40 7.55 7.56 7.57 7.60 7.81 7.83 8.87 Experimental Section Chapter III 280 a) b) Figure S49 . 2D-NOESY of mono2 in CDCl3 at 268 K showing (a) all NH-NH cross peaks: NH(4)-NH(3), NH(3)-NH(2), and NH(1)-NH(2), (b) OMe(1)-NH(1), OMe(1)-Ar(1). 6.26.36.46.56.66.76.86.97.07.17.27.37.47.57.67.77.87.98.08.18.28.38.48.58.68.78.88.99.09.1 f2 (ppm) 6.5 7.0 7.5 8.0 8.5 9.0 f1 (ppm) 3.203.253.303.353.407.157.207.257.307.357.407.457.507.557.607.657.707.757.807.857.907.95 f2 (ppm) 3.2 3.3 3.4 7.0 7.1 7.2 7.3 7.4 7.5 7.6 7.7 7.8 7.9 8.0 8.1 8.2 8.3 f1 (ppm) NH(2) – NH(3) NH(3) – NH(2) NH(2) – NH(1) NH(1) – NH(2) NH(4) – NH(3) NH(3) – NH(4) Ar(4) – NH(4) NH(4) – Ar(4) OMe(1) – NH(1) OMe(1) – Ar(1) NH(1) – OMe(1) Ar(1) – OMe(1) Experimental Section Chapter III 287 1D-NMR experiments (NOESY) of mono-3 in THF-d8 1D-NMR experiments (NOESY) of mono3 in THF-d8 were carried out where selective signals were irradiated (positive signal) in order to observe the coupled protons of the molecule that are closed in space (negative signal). a) b) Experimental Section Chapter III 288 c) d) Experimental Section Chapter III 289 e) Figure S54 . 1D-NMR experiments (NOESY) of mono3 in THF-d8 at 268 K showing the cross peaks that (a) NH(5) is close in space to protons of Ar(6), NH(4), Aib3 and Aib4, (b) NH(4) is close in space to protons NH(5), Ar(6), NH(3), CH2 (gly), and Aib4, (c) NH(1) is close in space to protons NH(2), Ar(1), OMe(1) and Aib2, (d) OMe is close in space to protons NH(1) and Ar(1), (e) CH2 (gly) is close in space to protons NH(5) and NH(4). 1D and 2D-NOESY NMR experiments of mono-3 in CDCl3 show in a similar manner to the other (S)-MTPA-(Aib)n-gly-PA (n = 1, 2) oligomers studied strong sequential NH-NH and OMe(1)-NH(1) cross peaks, confirming the presence of apOMe and M-310 helical structure of the polymer in solution. Figure S55 . Representative NOEs of mono3 in CDCl3. apOMe NH(1) NH(2) NH(3) OMe(1) NH(4) (s)-MTPA-Aib-Aib-Aib-gly-PA 123 4 56 NH(5) Experimental Section Chapter III 290 Figure S56 . 1H NMR of mono3 in CDCl3 at 268 K. 1H NMR (750 MHz, CDCl3) d (ppm): 9.00 (s, 1H), 7.88 (d, J=8.7 Hz, 2H), 7.72 (t, J=6.4 Hz, 1H), 7.57 (s, 1H), 7.44 (m, 5H), 7.39 (d, J=8.6 Hz, 2H), 7.19 (s, 1H), 6.25 (s, 1H), 4.18 (dd, J=17.2 Hz, 6.8 Hz, 1H), 3.85 (dd, J=17.3 Hz, 5.4 Hz, 1H), 3.35 (s, 3H), 3.00 (s, 1H), 1.51 (s, 3H), 1.49 (s, 3H), 1.46 (s, 3H), 1.39 (s, 3H), 1.35 (s, 3H), 1.27 (s, 3H). 0.00.51.01.52.02.53.03.54.04.55.05.56.06.57.07.58.08.59.09.5 H1 (ppm) 3.00 3.00 3.00 3.00 3.00 3.00 0.68 3.17 1.05 1.03 1.01 1.00 1.97 5.28 1.00 1.06 2.00 1.02 1.27 1.35 1.39 1.46 1.49 1.51 3.00 3.35 3.83 3.84 3.86 3.86 4.16 4.17 4.18 4.19 6.25 7.19 7.26 7.26 CDCl3 7.39 7.40 7.43 7.44 7.45 7.45 7.57 7.71 7.72 7.73 7.87 7.88 9.00 Experimental Section Chapter III 291 a) b) 6.16.36.56.76.97.17.37.57.77.98.18.38.58.78.99.1 H1 (ppm) 6.0 6.2 6.4 6.6 6.8 7.0 7.2 7.4 7.6 7.8 8.0 8.2 8.4 8.6 8.8 9.0 9.2 9.4 H1 (ppm) 1.21.31.41.51.66.26.36.46.56.66.76.86.97.07.17.27.37.47.57.67.77.87.98.0 H1 (ppm) 1.5 6.0 6.5 7.0 7.5 8.0 H1 (ppm) NH(5) – NH(4) NH(4) – NH(5) NH(3) – NH(2) NH(1) – NH(2) NH(4) – NH(3) NH(3) – NH(4) NH(2) – NH(3) NH(2) – NH(1) NH(1) – Aib2 NH(2) – Aib2 NH(3) – Aib4 NH(2) – Aib3 NH(3) – Aib3 Aib2 and Aib3 – NH(2) Aib3 and Aib4 – NH(3) Aib2 – NH(1) Experimental Section Chapter III 292 c) Figure S57 . 2D-NOESY of mono3 in CDCl3 at 268 K showing (a) all NH-NH cross peaks: NH(5)-NH(4), NH(4)-NH(3), NH(3)-NH(2), NH(2)-NH(1), (b) NH(1)-Aib2, NH(2)-Aib2, NH(2)–Aib3, NH(3)-Aib3 and NH(3)-Aib4, (c) OMe(1)-NH(1) and OMe(1)-Ar(1). 1D-NMR experiments (NOESY) of mono-3 in CDCl3 1D-NMR experiments (NOESY) of mono3 in CDCl3 were carried out where selective signals were irradiated (positive signal) in order to observe the coupled protons of the molecule that are closed in space (negative signal). NH(1) and Ar(1) – OMe(1) OMe(1) – Ar(1) OMe(1) – NH(1) Experimental Section Chapter III 293 a) b) Experimental Section Chapter III 294 c) d) Experimental Section Chapter III 295 e) Figure S58 . 1D-NMR experiments (NOESY) of mono3 in CDCl3 at 268 K showing the cross peaks that (a) NH(5) is close in space to protons of Ar(6), NH(4), Aib2 and Aib4, (b) NH(4) is close in space to protons NH(5), NH(3), CH2 (gly), Aib2, Aib3 and Aib4, (c) NH(3) is close in space to protons NH(4), NH(2), Aib3 and Aib4, (d) NH(2) is close in space to protons NH(3), Aib2 and Aib3, (e) NH(1) is close in space to protons of OMe(1) and Aib2. 16. NMR studies of mono-4 1D and 2D-NOESY NMR experiments of mono4 in THF-d8 show strong sequential NH-NH cross peaks which confirms the presence of P-310 helix of the oligomer in solution. The apOMe conformation at the pendant group was confirmed by the presence of NOE cross peaks between the anilide (NH1) and the methoxy group. Figure S59 . Representative NOEs of mono4 in THF-d8. (s)-MTPA-Aib-Aib-Aib-Aib-gly-PA 123 4 apOMe NH(1) NH(2) NH(3) OMe(1) 5 NH(4) NH(5) 67 NH(6) Experimental Section Chapter III 296 Figure S60 . 1H NMR of mono4 (THF-d8, 268 K). 1H NMR (750 MHz, THF-d8) δ = 9.16 (s, 1H), 8.44 (s, 1H), 8.05 (t, J=6.4 Hz, 1H), 8.00 (d, J=8.7 Hz, 2H), 7.72 (s, 1H), 7.57 (d, J=9.5 Hz, 2H), 7.50 (s, 1H), 7.48 – 7.44 (m, 3H), 7.32 (d, J=8.7 Hz, 2H), 7.19 (s, 1H), 3.93 – 3.79 (m, 2H), 3.42 (s, 3H), 3.37 (s, 1H), 1.50 (s, 3H), 1.49 (d, J=2.4 Hz, 6H), 1.48 (s, 3H), 1.38 (d, J=3.0 Hz, 6H), 1.32 (d, J=2.6 Hz, 6H). 0.51.01.52.02.53.03.54.04.55.05.56.06.57.07.58.08.59.09.5 f1(ppm) 6.00 6.00 3.00 6.00 3.00 0.70 3.00 1.97 1.00 1.78 3.00 1.00 2.00 1.00 1.89 1.00 0.99 0.93 1.32 1.32 1.38 1.38 1.48 1.49 1.49 1.50 3.37 3.42 3.58 THF-d8 3.85 3.86 3.87 7.19 7.32 7.33 7.45 7.45 7.46 7.47 7.47 7.50 7.57 7.58 7.72 7.99 8.01 8.04 8.05 8.06 8.44 9.16 Experimental Section Chapter III 303 Figure S64 . 1H NMR of mono4 in CDCl3 at 268 K. 1H NMR (500 MHz, CDCl3) δ = 9.16 (s, 1H), 8.05 (t, J=6.3 Hz, 1H), 7.88 (d, J=8.8 Hz, 3H), 7.53 (s, 1H), 7.49 – 7.40 (m, 5H), 7.37 (d, J=8.4 Hz, 2H), 7.34 (s, 1H), 6.50 (s, 1H), 4.05 (dd, J=17.0 Hz, 6.2 Hz, 1H), 3.91 (dd, J=17.7 Hz, 5.8 Hz, 1H), 3.32 (s, 1H), 2.99 (s, 1H), 1.52 (s, 6H), 1.49 (s, 3H), 1.47 (s, 3H), 1.34 (d, J=4.5 Hz, 6H), 1.31 (s, 3H), 1.28 (s, 3H). a) 1.52.02.53.03.54.04.55.05.56.06.57.07.58.08.59.09.5 f1 (ppm) 3.08 3.18 6.01 3.00 3.00 6.00 0.89 3.00 0.90 0.95 0.91 0.90 2.04 5.21 1.00 2.95 0.99 0.92 1.28 1.31 1.33 1.34 1.47 1.49 1.52 2.99 3.32 3.89 3.90 3.92 3.94 4.03 4.04 4.07 4.08 6.50 7.26 CDCl3 7.34 7.36 7.38 7.42 7.42 7.43 7.45 7.46 7.46 7.47 7.53 7.87 7.88 7.89 8.03 8.05 8.06 9.16 0.51.01.52.02.53.03.54.04.55.05.56.06.57.07.58.08.59.09.510.010.5 f1 (ppm) 7.91 7.92 9.14 Experimental Section Chapter III 304 b) c) 0.51.01.52.02.53.03.54.04.55.05.56.06.57.07.58.08.59.09.510.0 f1 (ppm) 1.30 1.37 1.55 7.48 8.03 9.14 0.51.01.52.02.53.03.54.04.55.05.56.06.57.07.58.08.5 f1 (ppm) 1.37 1.55 6.33 Experimental Section Chapter III 305 d) e) Figure S65 . 1D-NMR experiments (ROESY) of mono4 in CDCl3 at 268 K showing the cross peaks that (a) NH(6) is close in space to protons of Ar(6), (b) NH(5) is close in space to protons NH(6), NH(4), Aib5, Aib4 and Aib3, (c) NH(2) is close in space to protons Aib3 and Aib2, (d) NH(1) is close in space to protons Ar(1) and Aib2, (e) OMe(1) is close in space to protons Ar(1) and Aib2. -0.50.00.51.01.52.02.53.03.54.04.55.05.56.06.57.07.58.08.59.09.5 f1 (ppm) 1.54 7.47 7.53 7.73 -1.0-0.50.00.51.01.52.02.53.03.54.04.55.05.56.06.57.07.58.08.5 f1 (ppm) 1.58 3.37 7.47 EXPERIMENTAL SECTION CHAPTER IV Experimental Section Chapter IV 309 1. Materials and methods CD measurements were done in a Jasco-720. UV spectra were registered in a Jasco-630. The optical rotation was measured in a Jasco P-2000. NMR experiments were measured in a Varian 300 operating at 300 MHz for proton NMR and 75 MHz for carbon. CDCl3 signal (d = 77.2 ppm) was used as standard for 13C experiments. FT-IR measurements were carried out on a Bruker IFS-66v while Raman spectra were carried out in a Renishaw confocal Raman spectrometer (Invia Reflex model), equipped with two lasers (diode laser 785 nm and Ar laser 514 nm). DSC traces were obtained in a DSC Q200 Tzero Technology (TA Instruments, New Castle, UK), equipped with a refrigerated cooling system RCS90 (TA Instruments, New Castle, UK), using a Tzero low-mass aluminium pan. TGA traces were obtained in a TGA Q5000 (TA Instruments, New Castle, UK) using a platinum pan. GPC studies were carried out in a Waters Alliance equipped with Phenomenex GPC columns. 2. Synthesis of monomers The monomers employed in this work have been prepared according the following synthetic scheme. N H OH N O N HO O N H OH N O N HO O Ph H NN H O O O O H NN H O O O O Ph m-L-2 m-L-1 m-L-4m-L-3 Anilide-(PA)s Benzamide-(PA)s Experimental Section Chapter IV 310 Benzyl (tert-butoxycarbonyl)-L-phenylalanylglycinate (1) N-(3-Dimethylaminopropyl)-N'-ethylcarbodiimide hydrochloride (EDC·HCl, 0.69 g, 1.05 equiv), Hydroxybenzotriazole (HOBt, 0.49 g, 1.05 equiv), (tert-butoxycarbonyl)-Lphenylalanine (1.00 g, 1.10 equiv) and diisopropyltriethylamine (DIPEA, 0.72 mL, 1.20 equiv) were dissolved in 40 mL of DCM, and the mixture was stirred for 20 min to activate the acid. Then, benzyl glycinate (1.16 g, 1.00 equiv) and diisopropyltriethylamine (DIPEA, 0.60 mL, 1.00 equiv) were added and the reaction mixture was stirred overnight. Then the solvent was evaporated at reduced pressure and the crude was diluted in DCM, the organic layer was washed with HCl 1M, saturated solution of NaHCO3 and brine. The combined organic layers were dried over anhyd Na2SO4, filtered and the solvent was evaporated at reduced pressure. The crude product was chromatographed on silica gel (40-63 mesh) with hexane/ethyl acetate (4/6) as eluent obtaining 1 in 53 % yield respectively of pure product (0.75 g). O O NH2HO O NHBoc O OH N O NHBoc EDC-HCl,(HOBt DIPEA,(DCM + Experimental Section Chapter IV 311 Benzyl (tert-butoxycarbonyl)-L-phenylalanylglycinate (1) 1H NMR (300 MHz, CDCl3) d (ppm): 7.40 – 7.16 (m, 10H), 6.91 (t, J=5.4 Hz, 1H), 5.33 (s, 1H), 5.14 (s, 2H), 4.49 (s, 1H), 4.01 (t, J=5.2 Hz, 2H), 3.14 (m, 1H), 2.98 (m, 1H), 1.37 (s, 9H). 13C NMR (75 MHz, CDCl3) d (ppm): 172.0, 169.5, 155.6, 136.8, 135.2, 129.3, 128.6, 128.5, 128.3, 126.8, 80.1, 67.1, 55.5, 41.3, 38.5, 28.2. HRMS (ESI) m/z calc for C23H28N2O5 [M+H]: 413.2013, found: 413.2071. Figure S1 . a) 1H-NMR and b) 13C-NMR spectra of 1 in CDCl3. 0.00.51.01.52.02.53.03.54.04.55.05.56.06.57.07.58.08.5 f1 (ppm) 9.02 1.05 1.01 2.00 0.81 1.99 0.85 0.95 10.00 0102030405060708090100110120130140150160170180 f1 (ppm) 28.2 38.5 41.3 55.5 67.1 80.1 126.8 128.3 128.5 128.6 129.3 135.2 136.8 155.6 169.5 172.0 O OH N O NHBoc Experimental Section Chapter IV 312 (tert-butoxycarbonyl)-L-phenylalanylglycine (2) Pd/C (0.16 g) was suspended in 40 mL of EtOAc and submitted to three cycles of vacuum/purge with hydrogen. Then the Pd/C suspension was stirred under hydrogen atmosphere for 20 min and next a solution of benzyl (tert-butoxycarbonyl)-Lphenylalanylglycinate ( 1 , 0.75 g, 1.82 mmol) in 15 mL of EtOAc was injected to the reaction vessel via syringe. After one hour TLC analysis showed no presence of the starting material and the suspension was filtered through celite and washed throughly with EtOAc, obtaining 2 in quantitative yield. O H NNHBoc HO O H2,$Pd/C AcOEt O OH N O NHBoc Experimental Section Chapter IV 319 (tert-butoxycarbonyl)-L-valylglycine (4) 1H NMR (300 MHz, CDCl3) d (ppm): 10.40 (s, 1H), 7.46 (s, 1H), 5.71 (d, J=9.1 Hz, 1H), 4.09 – 3.78 (m, 2H), 3.34 (s, 1H), 2.16 – 1.85 (s, 1H), 1.33 (s, 9H), 0.86 (t, J=8.2 Hz, 6H). 13C NMR (75 MHz, CDCl3) d (ppm): 173.0, 172.1, 156.3, 80.0, 59.7, 41.1, 31.1, 28.2, 19.0, 18.0. HRMS (ESI) m/z calc for C12H22N2O5 [M+H]: 275.1529, found: 275.1601. Figure S5 . a) 1H-NMR and b) 13C-NMR spectra of 4 in CDCl3. 0.51.01.52.02.53.03.54.04.55.05.56.06.57.07.58.08.59.09.510.010.511.0 f1 (ppm) 6.00 9.03 0.93 0.38 2.68 0.70 0.69 0.94 0102030405060708090100110120130140150160170180 f1 (ppm) 18.0 19.0 28.2 31.1 41.1 59.7 80.0 156.3 172.1 173.0 O H NNHBoc HO O Experimental Section Chapter IV 320 tert-butyl (S)-(1-((2-((4-ethynylphenyl)amino)-2-oxoethyl)amino)-3-methyl-1-oxobutan-2yl)carbamate [m-(L)-2] N-(3-Dimethylaminopropyl)-N'-ethylcarbodiimide hydrochloride (EDC·HCl, 0.33 g, 1.05 equiv), Hydroxybenzotriazole (HOBt, 0.23 g, 1.05 equiv), (tert-butoxycarbonyl)-Lvalylglycine ( 4 , 0.50 g, 1.10 equiv) and diisopropyltriethylamine (DIPEA, 0.34 mL, 1.20 equiv) were dissolved in 20 mL of DCM, and the mixture was stirred for 20 min to activate the acid. Then, 4-ethynylaniline (0.19 g, 1.00 equiv) was added and the reaction mixture was stirred overnight. Then, the reaction mixture was washed with HCl 1M (x3), saturated solution of NaHCO3 and brine. The combined organic layers were dried over anhyd Na2SO4, filtered and the solvent was evaporated at reduced pressure. The crude product was chromatographed on silica gel (40-63 mesh) with hexane/ethyl acetate (1/1) as eluent obtaining m-(L)- 2 in 59 % yield respectively of pure product (0.36 g). NH2 + N H OH N O NHBoc O H NNHBoc HO OEDC-HCl,(HOBt DIPEA,(DCM Experimental Section Chapter IV 321 tert-butyl (S)-(1-((2-((4-ethynylphenyl)amino)-2-oxoethyl)amino)-3-methyl-1-oxobutan-2yl)carbamate [m-(L)- 2 ] 1H NMR (300 MHz, CDCl3) d (ppm): 9.15 (s, 1H), 7.53 (m, 3H), 7.36 (d, J=8.2 Hz, 2H), 5.42 (d, J=7.3 Hz, 1H), 4.22 – 3.89 (m, 3H), 3.02 (s, 1H), 2.15 – 2.02 (hept, 1H), 1.38 (s, 9H), 0.92 (t, J=7.5 Hz, 6H). 13C NMR (75 MHz, CDCl3) d (ppm): 173.4, 167.9, 156.6, 138.5, 133.1, 120.1, 118.1, 83.7, 80.7, 77.1, 61.1, 44.3, 30.9, 28.6, 19.6, 18.4. HRMS (ESI) m/z calc for C20H27N3O4 [M+Na]: 396.2043, found: 396.1894. aD20 = +43 (c = 10 mg/mL, CHCl3). Figure S6 . a) 1H-NMR and b) 13C-NMR spectra of m-(L)- 2 in CDCl3. 0.00.51.01.52.02.53.03.54.04.55.05.56.06.57.07.58.08.59.09.510.0 f1 (ppm) 6.02 9.03 0.90 0.91 3.05 0.71 2.00 2.83 0.71 0102030405060708090100110120130140150160170180 f1 (ppm) 18.4 19.6 28.6 30.9 44.3 61.1 77.1 80.7 83.7 118.1 120.1 133.1 138.5 156.6 167.9 173.4 N H OH N O NHBoc Experimental Section Chapter IV 322 Methyl (4-ethynylbenzoyl)glycinate (5) 2-(7-Aza-1H-benzotriazole-1-yl)-1,1,3,3-tetramethyluronium (HATU, 2.49 g, 1.05 equiv), 1Hydroxy-7-azabenzotriazole (HOAT, 0.89 g, 1.05 equiv), 4-ethynylbenzoic acid (2.00 g, 1.10 equiv) and diisopropyltriethylamine (DIPEA, 1.30 mL, 1.20 equiv) were dissolved in 60 mL of DCM, and the mixture was stirred for 20 min to activate the acid. Then, methyl glycinate (0.78 g, 1.00 equiv) was added and the reaction mixture was stirred overnight. Then the solvent was evaporated at reduced pressure and the crude was diluted in DCM, the organic layer was washed with HCl 1M, saturated solution of NaHCO3 and brine. The organic layer was dried over anhyd. Na2SO4, filtered and the solvent was evaporated at reduced pressure. The crude product was chromatographed on silica gel (40-63 mesh) with hexane/ethyl acetate (7/3) as eluent obtaining 5 in 42 % yield (1.23 g). OH O (1) HATU,)HOAT DIPEA,)CH2Cl2 NH2 MeO O +N H O OMe O Experimental Section Chapter IV 323 Methyl (4-ethynylbenzoyl)glycinate (5) 1H NMR (300 MHz, CDCl3) d (ppm): 7.72 (d, J=8.6 Hz, 2H), 7.46 (d, J=8.7 Hz, 2H), 7.16 (s, 1H), 4.15 (d, J=5.3 Hz, 2H), 3.72 (s, 3H), 3.20 (s, 1H). 13C NMR (75 MHz, CDCl3) d (ppm): 170.5, 166.9, 133.5, 132.2, 127.1, 125.6, 82.7, 79.9, 52.4, 41.7. HRMS (ESI) m/z calc for C12H11NO3 [M+H]: 218.0817, found: 218.0812. Figure S7 . a) 1H-NMR and b) 13C-NMR spectra of 5 in CDCl3. 0.00.51.01.52.02.53.03.54.04.55.05.56.06.57.07.58.08.59.09.5 0.90 3.00 2.00 0.92 1.98 2.00 0102030405060708090100110120130140150160170180 41.7 52.4 79.9 82.7 125.6 127.1 132.2 133.5 166.9 170.5 O N H OMe O Experimental Section Chapter IV 324 (4-ethynylbezoyl)glycine (6) Methyl (4-ethynylbenzoyl)glycinate ( 5 , 0.56 g, 1.00 equiv) was dissolved in a mixture of MeOH/H2O (95/5) (40 mL) and lithium hydroxide was added (LiOH, 0.31 g, 5.00 equiv). After 30 minutes the solvent was removed under reduced pressure. The residue was redisolved in a small amount of water and acidified to pH = 1. After extracting with ethyl acetate (4 times), the solution was dried over Na2SO4. Next, the organic solvent was removed obtaining the corresponding product in 98 % yield ( 6 , 0.52 g). (1) LiOH MeOH/H2O N H O OMe O (2) N H O OH O Experimental Section Chapter IV 325 (4-ethynylbezoyl)glycine (6) 1H NMR (300 MHz, CD3OD) d (ppm): 7.82 (d, J=8.6 Hz, 2H), 7.53 (d, J=8.6 Hz, 2H), 4.10 (s, 2H), 3.67 (s, 1H). 13C NMR (75 MHz, CD3OD) d (ppm): 171.7, 168.2, 133.6, 131.7, 127.1, 125.8, 82.1, 79.8, 40.9. HRMS (ESI) m/z calc for C11H9NO3 [M+H]: 204.0661, found: 204.0656. Figure S8 . a) 1H-NMR and b) 13C-NMR spectra of 6 in CD3OD. 2.62.83.03.23.43.63.84.04.24.44.64.85.05.25.45.65.86.06.26.46.66.87.07.27.47.67.88.08.28.48.6 0.91 2.04 2.00 2.00 2030405060708090100110120130140150160170180 40.9 79.8 82.1 125.8 127.1 131.7 133.6 168.2 171.7 O N H OH O Experimental Section Chapter IV 326 Methyl (4-ethynylbenzoyl)glycyl-L-phenylalaninate [m-(L)-3] N-(3-Dimethylaminopropyl)-N'-ethylcarbodiimide hydrochloride (EDC·HCl, 0.08 g, 1.05 equiv), 1-Hydroxy-7-azabenzotriazole (HOAT, 0.06 g, 1.05 equiv), (4-ethynylbezoyl)glycine ( 6 , 0.09 g, 1.10 equiv) and diisopropyltriethylamine (DIPEA, 0.08 mL, 1.30 equiv) were dissolved in 10 mL of DCM, and the mixture was stirred for 20 min to activate the acid. Then, methyl L-phenylalaninate (0.09 g, 1.00 equiv) was added and the reaction mixture was stirred overnight. Then, the reaction mixture was washed with HCl 1M (x3), saturated solution of NaHCO3 and brine. The organic layer was dried over anhyd Na2SO4, filtered and the solvent was evaporated at reduced pressure. The crude product was chromatographed on silica gel (40-63 mesh) with hexane/ethyl acetate (1/1) as eluent obtaining the corresponding product in 89 % yield [m-(L)- 3 , 0.11 g]. O N H OH O EDC-HCl,(HOAT DIPEA,(DCM OMe O + O N H H N O OMe O H2N Experimental Section Chapter IV 327 Methyl (4-ethynylbenzoyl)glycyl-L-phenylalaninate [m-(L)- 3 ] 1H NMR (300 MHz, CDCl3) d (ppm): 7.74 (d, 2H), 7.52 (m, 3H), 7.15 (m, 6H), 4.84 (q, 1H), 4.04 (t, 2H), 3.66 (s, 3H), 3.20 (s, 1H), 3.07 (qd, 2H). 13C NMR (75 MHz, CDCl3) d (ppm): 171.9, 169.4, 167.0, 135.9, 133.3, 132.2, 129.2, 128.6, 127.3, 127.1, 125.6, 82.8, 79.9, 53.6, 52.4, 43.6, 37.8. HRMS (ESI) m/z calc for C21H20N2O4 [M+H]: 365.1501, found: 365.1495. aD20 = +50 (c = 10 mg/mL, CHCl3). Figure S9 . a) 1H-NMR, and b) 13C-NMR spectra of m-(L)- 3 in CDCl3. 1.52.02.53.03.54.04.55.05.56.06.57.07.58.08.5 2.00 0.87 3.00 1.84 0.88 6.04 3.00 2.00 0102030405060708090100110120130140150160170180190 37.8 43.6 52.4 53.6 79.9 82.8 125.6 127.1 127.3 128.6 129.2 132.2 133.3 135.9 167.0 169.4 171.9 O N H H N O OMe O Experimental Section Chapter IV 328 Methyl (4-ethynylbenzoyl)glycyl-L-valinate [m-(L)-4] N-(3-Dimethylaminopropyl)-N'-ethylcarbodiimide hydrochloride (EDC·HCl, 0.12 g, 1.05 equiv), 1-Hydroxy-7-azabenzotriazole (HOAT, 0.08 g, 1.05 equiv), (4-ethynylbezoyl)glycine ( 6 , 0.13 g, 1.10 equiv) and diisopropyltriethylamine (DIPEA, 0.12 mL, 1.30 equiv) were dissolved in 10 mL of DCM, and the mixture was stirred for 20 min to activate the acid. Then, methyl L-valinate (0.10 g, 1.00 equiv) was added and the reaction mixture was stirred overnight. Then, the reaction mixture was washed with HCl 1M (x3), saturated solution of NaHCO3 and brine. The organic layer was dried over anhyd Na2SO4, filtered and the solvent was evaporated at reduced pressure. The crude product was chromatographed on silica gel (40-63 mesh) with hexane/ethyl acetate (1/1) as eluent obtaining the corresponding product in 82 % yield [m-(L)- 4 , 0.15 g]. O N H OH O EDC-HCl,(HOAT DIPEA,(DCM + O N H H N O OMe O OMe O H2N Experimental Section Chapter IV 335 TGA studies were carried out in order to determine the thermal stability of the polymers. As a general protocol a polymer sample was kept in a platinum pan and heated from 40ºC to 800ºC with a heating rate of 10ºC/min. Figure S17 . DSC thermograms of (a) poly-L1 . (b) poly-L2 . (c) poly-L3 and (d) poly-L4. 8. IR studies of monomers Figure S18 . IR spectra of (a) m-L1 . (b) m-L2 . (c) m-L3 and (d) m-L4 . 100 200 300 400 500 600 50 100 T/ ºC % mass 100 200 300 400 500 600 50 100 T/ ºC % mass 100 200 300 400 500 600 700 800 0 50 100 T/ ºC % mass 100 200 300 400 500 600 700 800 0 50 100 T/ ºC % mass a) c) b) d) 1000200030004000 Wavenumber [cm-1] 1000200030004000 Wavenumber [cm-1] 1000200030004000 Wavenumber [cm-1] 1000200030004000 Wavenumber [cm-1] a) c) b) d) Experimental Section Chapter IV 336 9. IR studies of polymers Figure S19 . IR spectra of a (a) poly-L-1 , (b) poly-L-2 , (c) poly-L-3 and (d) poly-L-4 . 10. CD/UV-Vis experiments in different solvents Poly-L1 —poly-L4 were measured by CD and UV-Vis in different organic solvents in order to evaluate their helical behavior (CD/UV-Vis studies of poly-L4 could not be measured due to the high insolubility presented by this polymer). Figure S20 . (a) CD and (b) UV-Vis spectra for poly-L1 [PPA] = 0.5 mg/ml. 1000200030004000 Wavenumber [cm-1] 1000200030004000 Wavenumber [cm-1] 1000200030004000 Wavenumber [cm-1] 1000200030004000 Wavenumber [cm-1] a) c) b) d) 300 400 500 0.5 1.0 1.5 2.0 Wavelength [nm] Abs CHCl3 acetone DCM DMSO THF MeOH 300 400 500 600 -45 -30 -15 0 15 30 Wavelength [nm] CD [mdeg] CHCl3 acetone DCM DMSO MeOH THF a) b) Experimental Section Chapter IV 337 Figure S21 . (a) CD and (b) UV-Vis spectra for poly-L2 [PPA] = 0.5 mg/ml. Figure S22 . (a) CD and (b) UV-Vis spectra for poly-L3 [PPA] = 0.5 mg/ml. Figure S23 . (a) CD and (b) UV-Vis spectra for poly-L4 [PPA] = 0.5 mg/ml. 300 400 500 0.5 1.0 1.5 Wavelength [nm] Abs dioxane THF acetone DCM CHCl3 MeOH DMF 300 400 500 600 -30 -20 -10 0 10 20 Wavelength [nm] CD[mdeg] CHCl3 DCM dioxane DMF THF MeOH Acetone a) b) 300 400 500 0.2 0.4 0.6 Wavelength [nm] Abs CHCl3 acetone DCM dioxane DMF THF 300 400 500 600 -30 -20 -10 0 10 20 Wavelength [nm] CD [mdeg] CHCl3 acetone DCM dioxane DMF THF a) b) 300 400 500 600 0.2 0.4 Wavelength [nm] Abs DCM dioxane DMF DMSO THF CHCl3 300 400 500 600 -6 -4 -2 0 2 4 Wavelength [nm] CD [mdeg] CHCl3 DCM dioxane DMF DMSO THF a) b) Experimental Section Chapter IV 338 Additional CD studies in different cetones for poly-L1 and poly-L2 Figure S24 . CD spectra of (a) poly-L1 and (b) poly-L2 [PPA] = 0.5 mg/ml. 11. Optical Rotation measurements Table S3 . Comparison of the Optical Rotation data of stretched and compressed helical structures of poly-L1 and poly-L2 . poly-L1 poly-L2 Highly Compressed (DCM) aD20 = -106 (10 mg/mL) Highly Compressed (DCM) aD20 = -39 (10 mg/mL) Compressed (THF) aD20 = -32 (10 mg/mL) Compressed (THF) aD20 = -98 (10 mg/mL) Stretched (Acetone) aD20 = -16 (c= 10 mg/mL) Stretched (Acetone) aD20 = +53 (c= 10 mg/mL) mono-L1 mono-L2 Highly Compressed (DCM) aD20 = +15 (10 mg/mL) Highly Compressed (DCM) aD20 = +39 (10 mg/mL) Compressed (THF) aD20 = +11 (10 mg/mL) Compressed (THF) aD20 = +22 (10 mg/mL) Stretched (Acetone) aD20 = +16 (c= 10 mg/mL) Stretched (Acetone) aD20 = +42 (c= 10 mg/mL) 400 500 600 -30 -20 -10 0 10 20 30 Wavelength [nm] CD[mdeg] Benzylacetone Butanone Acetone MIBK 400 500 600 -20 -10 0 10 20 Wavelength [nm] CD[mdeg] Benzylacetone Butanone MIBK Acetone a) b) Poly-L-2Poly-L-1 Helical polymers, covalent and supramolecular, have attracted the scientific community's attention due to the structure/ function relationship found in helical biomacromolecules such as DNA, peptides or proteins, among others. Inspired by these works, this Doctoral Thesis is focused on the development of new synthetic chiral materials based on poly(phenylacetylene)s (PPA)s bearing two types of pendant groups: one formed by multi-chiral pendants and the other cosisting of a single chiral motif separated from the polyene main chain by flexible linkers. Their chiral information transmission mechanisms, dynamic helical behavior and stimuli-responsive properties were studied, leading to promising new materials for the future rational design of novel smart materials with specific properties.