The modynamic p ope ies o sodium deoxychola e a he gel-sol
ansi ion
Aida Jo e
a,
⇑
, Jacobo T oncoso
b
, Ma ia Chia a di G ego io
c
, F ancisco F aga López
d
a
Depa amen o de Química Física, Facul ad de Ciencias, Uni e sidade de San iago de Compos ela, A enida Al onso X El Sabio S/N, Lugo, 27002, Spain
b
Depa amen o de Física Aplicada, Uni e sidade de Vigo, Campus Ou ense, 32004 Ou ense, Spain
c
Depa men o Chemis y, Sapienza Uni e si y o Rome, P.le A. Mo o 5, 00185 Rome, I aly
d
Depa amen o de Física Aplicada, Facul ad de Ciencias, Uni e sidade de San iago de Compos ela, A enida Al onso X El Sabio S/N, Lugo, 27002, Spain
a icle in o
A icle his o y:
Recei ed 13 Ap il 2022
Re ised 2 June 2022
Accep ed 12 June 2022
A ailable online 15 June 2022
Keywo ds:
Sodium deoxychola e
Bile sal
Sol-gel ansi ion
Calo ime y
Densi ome y
Elec on mic oscopy
abs ac
Sodium deoxychola e o ms sup amolecula agg ega es in aqueous solu ion ha a e s ongly dependen
on empe a u e and pH. Upon ine uning o hese physicochemical pa ame e s, wo sup amolecula
agg ega es can be achie ed: a nano ubula phase ha ing iscoelas ic, gel-like, beha io and a sponge liq-
uid phase. In his wo k, he he modynamics o he ansi ion be ween he wo phases is cha ac e ized.
Tempe a u es, olumes, and en halpies o such ansi ion ha e been expe imen ally de e mined using
ib a ing ube densi ome y and di e en ial scanning calo ime y. In addi ion, elec on mic oscopy is
used o ollow he mo phological ansi ion be ween he wo sup amolecula s uc u es. The dependen-
cies o he he modynamic p ope ies wi h he pH and su ac an concen a ion o he solu ion a e cha -
ac e ized, and he mic og aphs ob ained om elec on mic oscopy is used o explain he
he modynamics o he sys em.
Ó2022 The Au ho s. Published by Else ie B.V. This is an open access a icle unde he CC BY-NC-ND
license (h p://c ea i ecommons.o g/licenses/by-nc-nd/4.0/).
1. In oduc ion
Na u al bile sal s a e amphiphilic molecules conside ed as non-
classic su ac an s[1–3]. Unlike classic su ac an s wi h a pola
head a ached o an apola lexible chain, bile sal s ha e a igid
s e oid skele on wi h h ee me hyl g oups, one o mo e hyd oxyl
g oups, and a lexible chain ha ends in a ca boxyla e g oup
a ached o his skele on (see Fig. 1). The bi acial o ien a ion o
he pola and apola subs i uen s o e he skele on is esponsible
o hei ensioac i e beha iou in aqueous solu ion, including he
o ma ion o se e al s uc u es, like micelles, nano ubes, o ibe s,
depending on he bile sal and expe imen al condi ions.[2,4–10].
Common su ac an s ollow he agg ega ion model desc ibed by
Is aelach ili, [11,12] whe e di e en s uc u es can be ound: an
iso opic phase in liquid solu ion a e y low concen a ions,
micelles, ods, cubic o sponge phase, depending on he deg ee o
o de ing in hei in e nal s uc u e, lamella phase, in which lamel-
la shee s, esicles and nano ubes can be ound, and he same
s uc u es as he o me phases, bu in e ed a highe concen a-
ions. The p esence o a speci ic phase depends on he ype o su -
ac an , i s concen a ion, and he condi ions o he ex e nal
en i onmen .
In his con ex , i was ecen ly ound ha one o he na u al bile
sal s, sodium deoxychola e (Fig. 1),shows an agg ega ion model in
wa e ha ollows he beha io o classic su ac an s [13]. A nan-
o ube bundle phase wi h a sel -s anding gel consis ency and a liq-
uid sponge phase wi h a hixo opic phase change be ween hem
[14,15] we e de ec ed among he mesophases assembled by his
bile sal . The hyd ogel (nano ube bundles) a e ans o med in o a
liquid phase (sponge) as he pH o he empe a u e a e inc eased
(Fig. 1).
The beha iou o his gel has been ex ensi ely s udied by X- ay,
luo escence, NMR and heological echniques [14–20]. I mus be
poin ed ou ha he obse ed s uc u al changes o his bile sal
appea in physicochemical condi ions o high in e es om a phys-
iological pe spec i e: aqueous solu ions wi h a pH a ound 7 and
sligh ly abo e oom empe a u e, i. e, wi hin he anges whe e
hese molecules a e in ol ed in he li ing o ganisms[21–23].In
o de o ge a wide pic u e on he physical phenomena ha a e
in ol ed in his ansi ion, and hus, o ob ain a mo e p ecise mod-
elling o he in e nal a chi ec u es ha appea in his sys em, in
h ps://doi.o g/10.1016/j.molliq.2022.119621
0167-7322/Ó2022 The Au ho s. Published by Else ie B.V.
This is an open access a icle unde he CC BY-NC-ND license (h p://c ea i ecommons.o g/licenses/by-nc-nd/4.0/).
Abb e ia ions: NaDC, Sodium deoxychola e; HDC, deoxycholic acid; SAXS, Small
Angle X- ay Sca e ing; WAXS, Wide Angle X- ay Sca e ing; TEM, T ansmission
Elec on Mic oscopy; SEM, Scanning Elec on Mic oscopy; T
, empe a u e o
ansi ion; , iscosi y.
⇑
Co esponding au ho .
E-mail add ess: [email p o ec ed] (A. Jo e ).
Jou nal o Molecula Liquids 361 (2022) 119621
Con en s lis s a ailable a ScienceDi ec
Jou nal o Molecula Liquids
jou nal homepage: www.else ie .com/loca e/molliq
his wo k, a he modynamic s udy o his gel-liquid phase change
is ca ied ou . In addi ion, new images o he mic oscopic s uc u e
o bo h phases a e ob ained om elec on mic oscopy expe i-
men s. I mus be no ed ha iny a ia ions in he ex e nal condi-
ions o he medium igge s his mesophase change, and,
he e o e, his could be use ul o u u e p ac ical applica ions such
as he dosage o poo ly soluble d ugs and hei a ge ing o con-
olled elease h ough he ex e nal s imuli modula ion (pH o T)
ei he physiologically o a i icially con olled.
2. Expe imen al
Solu ions we e p epa ed by weigh ing he powde s wi h a Me -
le AE240 balance, ha ing an es ima ed unce ain y o 0.1 mg.
Besides sodium deoxychola e (NaDC), NaH
2
PO
4
o Na
3
PO
4
we e
also added o he solu ions, since hey s abilize he s uc u e o
he agg ega es [13]. The pH was measu ed in a Jenway 3520 pH
me e and adjus ed by adding HCl o NaOH. The solu ions we e
igo ously s i ed o achie e homogenei y. Once he sample is p e-
pa ed, gel consis ence appea s wi hin 5–15 min. The gelling ime is
s ongly dependen on he solu ion pH: he highe he pH alue he
longe he agg ega ion ime.
2.1. Vib a ing ube densime e (VTD)
Densi y was measu ed using an An on Paa VTD DMA5000.
Unce ain y in hese measu emen s is es ima ed in 110
-4
gcm
3
,
al hough much be e ep oducibili y, a ound 210
-6
can be
achie ed [24]. Calib a ion was done using Milli-Q wa e and d y
ai . I is a well-known ac [24] ha samples wi h high iscosi y
p o oke a damping in VTDs oscilla ion ha induces a w ong alue
o he densi y- he measu ed densi y is la ge han he eal one-,
which mus be co ec ed. This ins umen pe o ms au oma ically
his co ec ion, which is e y ele an in he con ex o he p esen
wo k. The gel solu ions p esen a la ge iscosi y, whe eas he liquid
ones a e only sligh ly iscous. The e o e, he iscosi y co ec ion
can be used as an expe imen al, e y sensi i e, p obe o de ec
he ansi ion be ween hese wo s a es. Since his ins umen is
designed o pe o m measu emen s o liquids, and he agg ega ed
s a e has iscoelas ic beha io , densi y measu emen s in his phase
could show la ge unce ain ies. This issue has been s udied o di -
e en ma e ials[25,26], concluding ha his kind o densime e s
a e usually e y eliable o iscoelas ic samples. Howe e , in o de
o check he esul s ob ained wi h his appa a us, densi y measu e-
men s ha e been also pe o med in a dila ome e . I consis s in an
E lenmeye lask closed wi h a sc ew cap connec ed o a capilla y
ube wi h in e nal diame e o 1.9 mm, subme ged in a he mo-
s a ing ba h. The dila ome e was calib a ed wi h milliQ wa e ,
being i s densi y aken om [27]. The solu ion densi y was de e -
mined by weighing and by measu ing he posi ion o he meniscus
in he capilla y. A compa ison o some samples using ib a ing
densi ome y and dila ome y has been ca ied ou , inding excel-
len ag eemen , be e han 0.00003 gcm
3
. The e o e, only da a
om ib a ing ube densi ome y is included h oughou he
pape . Rela i e s anda d unce ain y in ansi ion olume and
unce ain y in ansi ion empe a u e, T
, a e es ima ed in 7% and
3 K, espec i ely.
2.2. Di e en ial scanning calo ime e (DSC)
T ansi ion en halpy o he solu ions was de e mined using a
DSC-Q20 om TA Ins umen s, Eschbo n, Ge many. A ound
15 mg o sample was in oduced in he closed aluminum expe i-
men al pan, whe eas he same amoun o wa e was used as e e -
ence. Expe imen s we e pe o med a 2 Kmin
1
, in he
empe a u e in e al (283.15 – 358.15) K gi ing 30 min o equili-
b a ion a he lowes empe a u e. Calib a ion o he ins umen
was ca ied ou using Milli-Q wa e , being i s usion en halpy da a
ob ained om li e a u e [28]. Rela i e s anda d unce ain y in
ansi ion en halpy is es ima ed in 8%.
2.3. T ansmission elec on mic oscopy (TEM)
TEM images we e eco ded on a JEOL JEM-1011 ansmission
elec on mic oscope (80–100 kV) wi h a MegaView G2 came a.
Samples we e p epa ed by d opping solu ions on o coppe g ids
coa ed wi h Ca bon- ype A ilm. Excess wa e was emo ed by il-
e pape and he samples we e d ied a oom empe a u e. Elec-
on mic oscopy images o sponge- ype phase and lamella
shee s we e collec ed a a sho exposu e ime o a oid damages
Fig. 1. Sodium deoxychola e mesophase ansi ion be ween a sel -s anding gel (nano ube bundles) and a liquid solu ion (sponge phase) [13].
A. Jo e , J. T oncoso, Ma ia Chia a di G ego io e al. Jou nal o Molecula Liquids 361 (2022) 119621
2
o he agg ega es and hei in e nal s uc u e. The mic og aphs col-
lec ed on hese samples exhibi a da k con as since low ol age
elec on in ensi y was used and due o an abundan p esence o
lamella s uc u es ha co e s he whole g id.
2.4. C yogenic- ansmission elec on mic oscopy (c yo-TEM)
The i i ica ion p ocess o he samples was pe o med wi h a
FEI Vi obo . A 3 ml d op o an aqueous solu ion o he samples
was placed on a TEM Lacey ca bon coppe g id, he excess o wa e
was blo ed wi h il e pape and he g id was eeze-plunged in o
liquid e hane. Samples we e hen ans e ed unde liquid ni ogen
a mosphe e o a Ga an TEM c yo-holde equipped wi h a liquid
ni ogen ese oi . In his way, samples we e handled and
obse ed a T = 100 K. C yo-TEM images we e ob ained in a Tecnai
T20 (The mo ishe ) wi h a wo king ol age o 200 KV and a CCD
Vele a (la e al came a).
2.5. Scanning elec on mic oscopy (SEM)
SEM and STEM images we e eco ded on a FESEM Ul a plus-
ZEISS (20–30 kV). Images we e collec ed using InLens, seconda y
elec ons (SE), and STEM ( ansmission mode) de ec o s. Samples
we e p epa ed by placing a d op o samples on coppe g ids coa ed
wi h Ca bon- ype A ilm, emo ing he excess solu ion wi h il e
pape and ai o d ying hem.
2.6. C yogenic-scanning elec on mic oscopy (c yo-SEM)
Fo he sample p epa a ion, a d op o he solu ions was depos-
i ed in a SEM holde and subme ged in o liquid ni ogen. The o-
zen samples we e kep in liquid ni ogen and ans e ed by using
a acuum c yo ans e de ice (GATAN ALTO2100). Samples we e
eeze- ac u ed a 120 °C and we e obse ed a he same em-
pe a u e in an JEOL JSM-6360LV by using a seconda y elec on
de ec o (5 kV).
2.7. C ys alog aphic da a
CCDC 1,123,586 (RbDC-H
2
O (1/10)) [29], CCDC 1,247,414
(RbDC-H
2
O (1/1)) [30], and CCDC 211,570 (HDC-H
2
O (1/2)) [31]
con ain he supplemen a y c ys allog aphic da a used o assemble
he ela ed igu es. These da a can be ob ained ee o cha ge om
The Camb idge C ys allog aphic Da a Cen e ia www.ccdc.cam.ac.
uk/s uc u es.
3. Resul s and discussion
Densi y co ec ion due o he sample iscosi y
D
q
was ob ained
om co ec ed,
q
co
, and aw densi y da a,
q
meas
om:
Dq
¼
q
meas
q
co
ð1Þ
This co ec ion is di ec ly p opo ional o he iscosi y,
g
, o
samples wi h mode a e iscosi y. Howe e , o
g
g ea e han
a ound 700 mPas i emains almos cons an , i. e. he damping
e ec o e he ib a ing pe iod induces e y small u he densi y
inc emen s o
g
J700 mPas[32–34]. Thus, he only egion o
which
D
q
is sensible o a ia ions in he sample iscosi y is
app oxima ely he in e al (10–700) mPas. I ma ches wi h he
iscosi y ange whe e he s udied ansi ion akes place, because
he sample iscosi y s ongly alls a he gel-sol ansi ion. The
ansi ion empe a u e T
was ob ained as he empe a u e o
which
D
q
s a s o all om he pla eau, as Fig. 2 shows o a ep-
esen a i e sample.
The e a e some wo ks [35,36] ha ha e analyzed he densi y o
NaDC solu ions. Howe e , he expe imen al condi ions s ongly
di e om hose o he p esen wo k, making a comp ehensi e
compa ison be ween bo h da a sou ces no easible. As a gene al
commen , i can be said ha he esul s a e consis en wi h li e a-
u e; he inc emen in densi y induced by he NaDC is a ound
0.0002 gcm
3
pe millig am o NaDC dissol ed in 1 g o wa e . Vis-
cosi y and densi y o ei he gel [14–20] o liquid phases [36,37],
ha e been p e iously s udied, bu measu emen s in expe imen al
condi ions close o he sol–gel ansi ion ha e no been epo ed.
Mola olume o he sample
(
¼V=N,Nbeing he o al num-
be o moles o all species and V he o al olume), was ob ained
om densi y da a and i was sub ac ed om ha o he solu ion
wi hou NaDC o obse e he inc emen in mola olume
D
due
o he c ea ion o des uc ion o he agg ega es. Fig. 2 shows he
esul s o one o he s udied samples. The e, i is clea ly shown
ha he gel-like sys em p esen s a smalle olume han he liquid
one; i. e. gelling p ocess in ol es a con ac ion o he sys em. Mo e-
o e , he ansi ion does no seem o ake place a one poin , bu in
a ange o empe a u es o 5–10 K. To ge a quan i a i e es ima ion
o his ansi ion olume,
D
,
D
below and abo e he ansi ion
was i ed o a s aigh line and he ansi ion olume was ob ained
as he di e ence be ween bo h i s a he ansi ion empe a u e
(T
). I mus be poin ed ou ha his ansi ion olume is he di e -
ence be ween he wo phases pe one mole o solu ion, no pe mole
o he solu e. I is wo h o no e ha
D
in he liquid phase ollows
be e he linea i han in he gel, and, he e o e, a na owe em-
pe a u e ange has been selec ed o he la e .
The ansi ion en halpy was ob ained by in eg a ion o he hea
capaci y e sus empe a u e cu es. Fig. 3 shows he di e ence
be ween he measu ed hea capaci y and ha o he baseline o
a selec ed sample. The e, i can be obse ed ha he ansi ion
om gel o liquid s a e is endo he mic; all s udied solu ions show
his beha io . As abo e said, he ansi ion seems o happen wi hin
a wide empe a u e ange. Since he molecules need ime o ea -
ange om ubes o sponge phases, and he calo ime ic measu e-
men s a e dynamic, i. e. empe a u e is no s able, bu a
empe a u e amp is applied, he ansi ion en halpy is ex ended
o e a la ge empe a u e ange. This is signi ican ly wide ha
hose ob ained om densi y measu emen s, whe e he e ec s o
he ansi ion kine ics a e mos ly excluded. This makes he adi-
ional me hods o de e mine phase change empe a u es om
calo ime y o be inaccu a e. The e o e, hese measu emen s a e
used only o e alua e he ansi ion en halpy, and no o he T
,
which was ob ained om he iscosi y es ima ions.
As commen ed in he in oduc ion, pH has a s ong e ec on he
appea ance o he highly o de ed s uc u es obse ed o hese
solu ions. As a esul , hei he modynamic p ope ies a e also
s ongly in luenced by he pH. Fig. 4 and Table 1 show T
e sus
pH o he s udied samples. A clea nega i e co ela ion wi h he
pH is obse ed. T
d ops om 316 K a pH = 6.76 o 298 K a
pH = 7.24 o NaDC and NaH
2
PO
4
concen a ions o 40 mM and
20 mM, espec i ely. Fo la ge pH alues, he gel phase does no
appea , and o pH alues lowe han 6.7, he solu ion is no longe
s able, and a p ecipi a e is obse ed. I sodium deoxychola e o
NaH
2
PO
4
concen a ions a e inc eased o 80 mM and 60 mM,
espec i ely, he T
aises, as shown in Fig. 4, being he lines o T
e sus pH almos pa allel o hose o [NaDC] = 40 mM and [NaH
2
-
PO
4
] = 20 mM. The e ec o inc easing he NaH
2
PO
4
concen a ion
is compa able o ising he NaDC concen a ion. Besides being T
highe , hese solu ions a e in gel phase o e a la ge pH ange,
ob aining s able s uc u es up o pH a ound 7.5.
Fig. 5 and Table 1 show he ansi ion olume e sus pH. This
quan i y ha dly a ies wi h any o he con olled physical pa ame-
e s: almos all solu ions ha e shown qui e simila ansi ion ol-
umes, 0.004 cm
3
mol
1
, i espec i e o he NaDC and NaH
2
PO
4
A. Jo e , J. T oncoso, Ma ia Chia a di G ego io e al. Jou nal o Molecula Liquids 361 (2022) 119621
3
concen a ions and pH alue. Only o he mos basic solu ions
(pH > 7.4), a clea d op in
D
is obse ed. Fig. 6 and Table 2 show
he ansi ion en halpy e sus pH o he s udied solu ions. As done
o ansi ion olume, his quan i y is gi en by mole o solu ion,
no o mole o he solu e. The esul s a e qui e simila o hose
ound o T
, a clea nega i e co ela ion wi h he pH is obse ed
and inc easing he NaDC o NaH
2
PO
4
concen a ion makes he
en halpy o aise. I is wo h o no e ha he ob ained alues, a e
o he same o de o he micelliza ion en halpies o he NaDC
[38,39].
Al hough he modynamic da a p o ide e y impo an in o ma-
ion abou he physics o he ansi ion, ha ing in o ma ion abou
he mic oscopic s uc u es ha o m he obse ed phases would
en ichen he unde s anding o he obse ed beha io o hese sys-
ems. Mo eo e , i would allow o ela e he mic oscopic pic u e
wi h he he modynamics o he sys em. Fo una ely, ecen ly
[13], i has been shown ha his is possible, and elec on mic o-
scopy images in simila condi ions o hose s udied he e ha e been
epo ed. Fig. 7 shows new images o he sup amolecula s uc-
u es exis ing in bo h phases. An in e media e s a e in he phase
ansi ion om he sponge o he nano ube bundles phase is
shown in Fig. 8. The s uc u e o he gel can be obse ed in hese
pic u es: bundles o nano ubes o m his phase (panels a-b o
Fig. 7). On he o he hand, he panels d- o Fig. 7 clea ly show ha
he liquid phase e ains some s uc u e; i is no a simple liquid,
bu a sponge phase. The sys em would be made up o deoxychola e
bilaye s uc u e packed in a back o back way, wi h he apola su -
ace (
a
side) owa ds he inside o he memb ane and he pola
a ea su ace (bside) and he side chain wi h i s coun e ion ac ion,
owa ds he aqueous en i onmen . Such a molecula model was
p e iously discussed by c ossing Small and Wide X ay Sca e ing
(SAXS-WAXS), single c ys al X- ay s uc u es and di e en elec-
onic mic oscopies [11,13,30]. This liquid phase does no p esen
high o ganiza ion a he molecula le el like he linking o he nan-
Fig. 2. Le .- Densi y co ec ion (blue squa es) and ansi ion empe a u e ob ained om hese da a (ma ked wi h he g een line). Righ .- Di e ence be ween he sample
mola olume and ha o he solu ion wi hou NaDC, blue squa es: expe imen al da a; ed line: i s in he liquid and gel phases. Sample wi h [NaDC] = 80 mM,
[NaH
2
PO
4
] = 20 mM and pH = 7.34.
Fig. 3. Di e ence be ween he sample hea capaci y and ha o he base line o he
sample wi h [NaDC] = 80 mM, [NaH
2
PO
4
] = 20 mM and pH = 7.32. This sol–gel
ansi ion shows endo he mic beha io .
Fig. 4. T ansi ion empe a u e T
as a unc ion o pH o he s udied samples: blue
squa es [NaDC] = 40 mM, [NaH
2
PO
4
) = 20 mM; ed diamonds [NaDC] = 80 mM,
[NaH
2
PO
4
] = 20 mM; black ci cles [NaDC] = 40 mM, [NaH
2
PO
4
] = 60 mM.
A. Jo e , J. T oncoso, Ma ia Chia a di G ego io e al. Jou nal o Molecula Liquids 361 (2022) 119621
4
o ubes [13,29,40]. Nano ubes and sponge a angemen s in bo h
phases coexis wi h lamella shee s as can be seen in he c yo-
SEM pho og aphs (panels c and o Fig. 7). I mus be no ed ha
he liquid phase in Figs. 7 and 8 is shown a ambien empe a u e.
This has been accomplished by inc easing he pH (see Figu e cap-
ions). In a p e ious pape , [13] i has been demons a ed ha he
e ec o he pH inc easing on he gel is simila o he e ec induced
by he empe a u e inc ease ( ansi ions obse ed a pH alues
om 7.0 o 7.6 o empe a u es om 20 °C o40°C). The e o e,
he same s uc u es would be obse ed o he liquid phase a
highe empe a u es.
The de ailed molecula s uc u e o he nano ube is ha dly
de ec ed om he elec on mic oscopy images. Howe e , ecen
SAXS da a o he gel-like sys em [13] sugges elonga ed s uc u es
ha p esen six sha p peaks in he WAXS ange 0.83–0.50 nm, hus
indica ing a ele an deg ee o molecula o de inside he agg e-
ga es. Fi e o hese signals a e simila o he spacings o a hexago-
nal a angemen o 8/1 ime helixes obse ed by Giglio e al [40–
42] in solid s a e ibe s d awn om NaDC gels. The highly o ga-
nized a angemen a he molecula le el along wi h he elec on
and op ical mic oscopy echniques s ongly sugges ha nano ube
bundle s uc u es desc ibe he gel mesophase. Fig. 9 displays a
molecula model o he nano ubes [13], buil up om he wo
c ys al s uc u es o monoclinic [30] and hexagonal [29] ubidium
deoxychola e (RbDC). This sal was used ins ead o NaDC because
a emp s o de e mine he NaDC c ys al s uc u e we e unsuccess-
ul. Howe e , i has been con i med ha in he NaDC c ys al has
helices and hexagonal s uc u e, e y likely iden ical o he RbDC
as Giglio e al con i med [28,31,33]. The e iden chemical simila -
i ies be ween bo h sal s, a ails ha he esul s o he RbDC can be
ex apola ed o NaDC. Assuming s uc u e simila i y in bo h
helixes (gel and solid s a e), a wa e channel should exis inside
Table 1
T ansi ion empe a u e T
and olume
D
o he s udied solu ions a di e en deoxychola e and disodium phospha e mola i ies [NaDC] and [Na
2
HPO
4
].
pH T
/K
D
/cm
3
mol
1
pH T
/K
D
/cm
3
mol
1
[NaDC] = 40 mM, [NaH
2
PO
4
] = 20 mM [NaDC] = 40 mM, [NaH
2
PO
4
] = 20 mM
6.76 316 0.0041 7.12 299 0.0042
6.79 314 0.0047 7.13 306 0.0039
6.81 314 0.0042 7.17 300 0.0048
6.86 310 0.0036 7.22 299 0.0039
6.93 309 0.0041 7.22 300 0.0048
6.98 312 0.0041 7.24 299 0.0041
6.99 310 0.0042 [NaDC] = 80 mM, [NaH
2
PO
4
] = 20 mM
7 306 0.0036 6.98 313 0.0049
7.02 309 0.0038 7.05 310 0.0049
7.03 308 0.0038 7.16 308 0.0041
7.03 308 0.0039 7.34 305 0.0038
7.05 308 0.0039 7.42 296 0.0025
7.06 307 0.0039 [NaDC] = 40 mM, [NaH
2
PO
4
] = 60 mM
7.08 306 0.0037 6.84 317 0.0045
7.09 306 0.0036 6.94 314 0.0043
7.11 305 0.0040 7.08 311 0.0041
6.93 309 0.0041 7.17 309 0.0039
6.76 316 0.0041 7.29 307 0.0044
7.05 308 0.0039 7.46 290 0.0009
6.79 314 0.0047
Fig. 5. T ansi ion olume
D
as a unc ion o pH o he s udied samples: blue
squa es [NaDC] = 40 mM, [NaH
2
PO
4
] = 20 mM; ed diamonds [NaDC] = 80 mM,
[NaH
2
PO
4
] = 20 mM; black ci cles [NaDC] = 40 mM, [NaH
2
PO
4
] = 60 mM. Fig. 6. T ansi ion en halpy
D
h
as a unc ion o pH o he s udied samples: blue
squa es [NaDC] = 40 mM, [NaH
2
PO
4
] = 20 mM; ed diamonds [NaDC] = 80 mM,
[NaH
2
PO
4
] = 20 mM; black ci cles [NaDC] = 40 mM, [NaH
2
PO
4
] = 60 mM.
A. Jo e , J. T oncoso, Ma ia Chia a di G ego io e al. Jou nal o Molecula Liquids 361 (2022) 119621
5
he helix connec ing he nano ubes in he gel phase. This helix
would be hyd ophilic in his inne pa and apola in he ex e nal
su ace, as Fig. 9 shows. The channel should ha e inside a mini-
mum o 3.6 wa e molecules o each deoxychola e anion (c ys al
da a [30]) and migh coexis wi h a Na
+
ca ion o neu ali y. The
wa e molecules inside he NaDC channel should be less o ganized
han in he c ys al, bu mo e s uc u ed han wa e molecules in
he bulk solu ion. Ion-ion, ion–dipole in e ac ions, and a ne wo k
o hyd ogen bonds placed inside he helix a e he o ces ha s abi-
lize his s uc u e [29]. As shown in Fig. 9, his helix ac s as a join
be ween he nano ubes and i is, in las e m, he main esponsible
o he appea ance o he gel phase. This s uc u e can be consid-
e ed as he p ecu so o he hexagonal c ys alline a angemen o
NaDC in solid s a e [29,40,41].
A pH dec ease in he global sys em inc eases he ac ion o he
p o ona ed bile sal (deoxycholic acid, HDC) [43]. F om he pe -
spec i e o each single molecule, when he deoxycola e anion cap-
u es a hyd ogen ion, he nega i e global cha ge o he molecule is
cancelled, he pola i y dis ibu ion o he molecule a eas changes,
diminishing he Hyd ophilic-Lipophilic Balance (HLB) [44]. The
pola and apola molecula a eas a e now modi ied and he mole-
cules will be eo ganized inside he agg ega es bilaye , emodelling
Table 2
T ansi ion en halpy
D
h
o he s udied solu ions a di e en deoxychola e and disodium phospha e mola i ies [NaDC] and [Na
2
HPO
4
].
pH
D
h
/Jmol
1
pH
D
h
/Jmol
1
pH
D
h
/Jmol
1
[NaDC] = 40 mM [NaH
2
PO
4
] = 20 mM [NaDC] = 80 mM [NaH
2
PO
4
] = 20 mM [NaDC] = 40 mM, [NaH
2
PO
4
] = 60 mM
6.79 6.5 7.07 13.2 6.68 10.9
6.82 5.9 7.11 9.0 6.95 7.2
7.00 5.1 7.25 7.4 7.10 6.4
7.17 3.6 7.32 4.8 7.31 5.4
7.25 1.5 7.40 5.0 7.60 1.8
7.28 0.9
Fig. 7. a) C yo-TEM, b,e) TEM, e) SEM c, ) C yo-SEM images o ep esen a i e agg ega es ound in sample o a) [NaDC] = 80 mM pH = 7.36, gel b) [NaDC] = 40 mM,
[NaH
2
PO
4
] = 20 mM, solu ion pH 7.00, gel. c) [NaDC] 85 mM NaH
2
PO
4
20 mM, pH 7.45, gel. d) [NaDC] 80 mM, NaH
2
PO
4
20 mM pH 11.65, liquid. e) [NaDC] = 20 mM, pH 11.84
NaH
2
PO
4
20 mM, liquid. ) [NaDC] = 40 mM NaH
2
PO
4
50 mM, pH 9.15 liquid. T = 20 °C. a-c images co espond o he gel-like phase made o nano ube bundles and c- o he
liquid (sponge) phase. Lamella shee s coexis wi h bo h phases and can be seen in c- mic og aphs.
Fig. 8. STEM images o ep esen a i e agg ega es ound in NaDC 80 mM pH 11.65 NaH
2
PO
4
20 mM, T = 20 °C. Lamella shee s (yellow a ow), sponge phase (pink a ow) and
ini ial nano ube bundles (g een a ow).
A. Jo e , J. T oncoso, Ma ia Chia a di G ego io e al. Jou nal o Molecula Liquids 361 (2022) 119621
6
i s in e nal and ex e nal pa s[11–13] as well as he in e molecula
o ces ha hold he agg ega es. Small changes in he HLB can p o-
duce g ea a ia ions in he ex e nal shape o he lamella s uc-
u es [12], and he neu aliza ion o a ac ion o NaDC molecules
in he memb ane should a y he ex e nal shape. HDC has a low
solubili y in wa e a acidic pH [45], and, he e o e, he e is a limi
in he amoun o HDC molecules ha can be ea anged in he
bilaye s uc u e be o e HDC p ecipi a es. The c ea ion o he heli-
coidal s uc u e inside he memb anes, shown in Fig. 9, allows
NaDC molecules o be kep in solu ion in i s ionic o m. Cohe en ly,
i has been ound ou ha he helix o med by NaDC is mo e s able
a low pH, and he e o e, he NaDC con e sion in o HDC does no
happen inside he channel [40]. As a consequence, he ac ion o
NaDC assembling he wa e channel is p o ec ed om he hyd o-
gen exchange and can be main ained in he s uc u e o he ans-
pa en gel sys em. The in ini e nano ubes o ganiza ion in he gel-
like sys em gi es ise o a icon inuous phase [12] whe e h ee di -
e en pe cola ion channels coexis : he mic oen i onmen inside
he ubes, he bulk solu ion, and he bilaye ha o m he nan-
o ubes; his allows he solubiliza ion o he HDC molecules o ak-
ing place in a much g ea e ex en han in he bulk.
The he modynamic measu emen s shown in Figs. 4-6 e eal
ha wo clea di e en phases a e obse ed, he gel a low empe -
a u e and pH and he liquid a high pH and empe a u e. By mak-
ing use o
D
u
¼
D
h
p
D
i can be concluded ha he
con ibu ion o he change in in e nal ene gy
D
u
comes mainly
om en halpy, since he e m p
D
is a ound 0.0004 Jmol
1
, en
housand imes smalle han he ypical alues ound o
D
h
. Thus,
in e nal ene gy is mo e posi i e o he liquid, a ac ha e eals
ha , as expec ed, molecula in e ac ions a e s onge in he gel
phase. Mo eo e , conside ing ha a cons an p essu e he Gibbs
ee ene gy a ia ion,
D
g
, is 0 a he phase ansi ion, since
D
g
¼
D
h
T
D
s
, he ansi ion en opy
D
s
mus be posi i e. As
a esul , he diso de inc eases in he gel-sol ans o ma ion. This
is also cohe en wi h he molecula model in Fig. 9 o he gel
s uc u e: a mo e o de ed sel -assembly helical s uc u e o deoxy-
cola e ions and an o de ed wa e channel inside, di e ing om he
mo e andom bilaye ha gene a es he sponge phase.
The sol–gel ansi ion occu s in di e en sys ems whe e he
gela ion is ca ied ou h ough p ocesses ha di e subs an ially
a he molecula le el. Examples o hese sys ems in liquid solu-
ions a e he connec ion o polyme s gene a ing a h ee-
dimensional ne wo k h ough co alen bonds [46,47] o weak
in e ac ions, as hyd ogen bonds, [48] whe e ions o small mole-
cules can be in ol ed [49]. This ansi ion may also be ela ed o
a change o he sup amolecula s uc u es including sel -
assembled a chi ec u es as ods, shee s o nano ubes [50,51]. All
hese p ocesses can modi y he iscoelas ic p ope ies o he whole
sys em and hey a e he main mechanisms which con ibu e o he
enhancemen o he iscosi y in gels. T adi ionally, gels ha e been
di ided in o wo classes: s ong o quenched, and weak o
annealed [52], being he gela ion i e e sible o he o me and
e e sible o he la e . The s udied deoxychola e sys ems belong
o he annealed gels, since gela ion a e made up h ough hyd ogen
bonds and o he weak in e ac ions, being e e sible as p e ious
wo ks ha e shown [14–19].
The i s heo e ical models o gela ion, based in pe cola ion
concep s [53–56], had conside ed he sol–gel ansi ion as pu ely
geome ic; he e o e, no singula i ies in he ee ene gy would be
expec ed. Thus, ypical phase ansi ion magni udes, like ansi ion
en halpy o olume, would no make sense. La e wo ks, which
used mo e elabo a ed concep s based on pe cola ion heo y, led
o he conclusion ha quenched gels do show singula i ies in i s
ee ene gy [57–61] bu annealed gels do no [59,62]. None heless,
i has been a gued [63,64] ha his is no co ec , because he con-
ibu ion o la ge and complica ed cyclic clus e s o he ee ene gy,
p e iously neglec ed, should ha e been conside ed. As a esul , he
gel-sol ansi ion e en in weak gels would be a genuine he mal
phase ansi ion, in ac , a i s -o de phase ansi ion [63]. In any
case, he na u e o he sol–gel phase change is nowadays an open
subjec and a comple e unde s anding o his ansi ion is s ill lack-
ing [65].
Fig. 9. Molecula model o he NaDC nano ube bundles and he ubes junc ion[13]. Bilaye in he eal s uc u es would p esen ce ain molecula diso de . The helix
connec ing he nano ubes would ha e a simila s uc u e o ha o he Fig. 3D models we e cons uc ed om he c ys al s uc u es o monoclinic [30] and hexagonal [29]
RbDC.
A. Jo e , J. T oncoso, Ma ia Chia a di G ego io e al. Jou nal o Molecula Liquids 361 (2022) 119621
7
The expe imen al esul s e eal ha he obse ed ansi ion has
changes bo h in he olume and en halpy, ha is, i is i s -o de .
On he o he hand, he elec on mic oscopy images e eal ha
nano ubes a e obse ed in he gel, bu hey disappea in he liquid
phase. The e o e, his nano ube anishing mus ha e a con ibu-
ion o he ansi ion olume and en halpy. I he sol–gel phase
ansi ion would be pu ely geome ic, he change in he he mody-
namic p ope ies, i. e. he ansi ion en halpies and olumes, could
no be due o his gel-sol phase change and, he e o e,
D
and
D
h
would come om he ansi ion be ween wo sup amolecula
s uc u es ( om nano ubes o sponge phase). Unde his hypo he-
sis, he gel would appea due o he sel -assembly o he nano ubes
in a h ee-dimensional s uc u e; when nano ubes anish, he
sponge phase would eme ge. Thus, he obse ed changes in he
en halpy and olume would come only om he des uc ion o
he nano ubes, and i would no be di ec ly ela ed o a gel-sol
ansi ion. The e o e
D
and
D
h
would be conside ed as he mo-
dynamic p ope ies ha would co espond o he ans o ma ion
o he nano ube-bundled s uc u e ha o ms he gel in o he
sponge phase. Howe e , i he ansi ion om sol o gel is no
pu ely geome ic, bu i would imply some discon inui ies in he
ee ene gy -i. e. i is a i s -o de phase ansi ion- his does no
apply. In his case, he e would be wo con ibu ions o he ansi-
ion olume and en halpy one due o he sol–gel ansi ion, and he
o he one o he nano ube des uc ion. Dis inguishing which
amoun belong o he ansi ion and which one o he nano ube
des uc ion is no an a o dable ask wi h he a ailable p ecision
o he p esen expe imen al me hods.
The esul s o T
and en halpy (Figs. 4 and 6) clea ly show he
enhancemen o he sup amolecula s uc u es as he solu ion
becomes mo e acidic, since bo h T
and
D
h
inc eases as pH
dec eases. This pe ec ly i s he abo e ci ed explana ion abou
he nano ube assembly: low pH alues make he concen a ion
o he p o ona ed bile sal o inc ease, modi ying he hyd ophilic-
lipophilic balance, and making mo e s able he helix ha links
he nano ubes. The e o e, he nano ube phase becomes mo e
s able a low pH, and, as a consequence o his, he di e ence in
he ene gy be ween his phase and he sponge one becomes
highe , e e ing in la ge ansi ion en halpies as pH becomes
lowe . This also explain he dec ease in T
wi h he pH: since he
nano ube s uc u e is mo e s able a low pH, highe empe a u e
is needed o des oy i . The same endency is a ained i , ins ead
o dec easing pH, NaDC o NaH
2
PO
4
concen a ion is aised,
al hough his e ec is signi ican ly mo e ma ked o he o me :
doubling [NaDC] has almos he same e ec han ipling [NaH
2
-
PO
4
]. This is wha is expec ed, since he NaDC o m he nano ubes,
and NaH
2
PO
4
plays only an adju an ole in de eloping hese
sup amolecula s uc u es [17]. These esul s ma ch p e ious ind-
ings ega ding he heological beha iou o his sys em [19], since
he gel s eng h ollows he same ends. The e o e, any o hese
ac o s –acidi y o he solu ion and NaDC o NaH
2
PO
4
concen a ions- p omo es he o ma ion o he nano ubes bundles,
which makes he gel o become a mo e s uc u ed sys em, as he
aise in T
and
D
h
shows. As o he olume changes be ween
he gel and liquid phase, his e ec is much milde (c .Fig. 5).
The olume con ac ion due o he o ma ion o he nano ube bun-
dles is almos independen o he pH o NaDC o NaH
2
PO
4
concen-
a ion; only o pH > 7.2
D
clea ly dec eases.The e o e, one can
conclude ha he e ec o he gel s uc u e enhancemen o e he
olume con ac ion is only ele an when he sys em is e y diso -
de ed, ha is, a la ge pH. Fu he pH dec emen s s eng hen he
gel s uc u e, bu hey do no ha e a ele an e ec o e he ol-
ume con ac ion o he sys em.
Finally, i is in e es ing o poin ou ha , o a gi en pH,
D
h
is
a ound wice la ge o he solu ions wi h [NaDC] = 80 mM han
o [NaDC] = 40 mM. This implies ha , i he en halpy is calcula ed
pe NaDC mole, ins ead o pe solu ion mole, qui e simila alues
a e ob ained o bo h concen a ions. The e o e, he bonding
ene gy be ween he NaDC molecules ha o m he nano ubes a e
no signi ican ly a ec ed by he NaDC concen a ion. Howe e , his
does no hold o
D
: since i does no change wi h NaDC compo-
si ion, i we conside he ansi ion olume pe NaDC molecule, we
ge alues wice la ge o he solu ions wi h [NaDC] = 40 mM. A
easible explana ion could be a shi in he equilib ium owa ds
he lamella shee s coexis ing wi h he bundles in he gel as he
NaDC concen a ion ises. The NaDC molecules o he bilaye
shee s would ha e a simila olume pe molecule as he sponge
phase as hey do no ha e he helical s uc u e.
4. Conclusions
The he modynamic and s uc u al analysis o sodium deoxy-
chola e in aqueous solu ion p esen ed in his wo k gi es new
insigh s abou he sup amolecula s uc u es ha hese solu ions
p esen . The gel s a e is o med by nano ubes bundles ha o m
a h ee-dimensional s uc u e o e he whole sys em, whe eas
he liquid s a e is a sponge phase. The densi y measu emen s show
ha he olume di e ence be ween he gel and he liquid phases is
almos independen on he pH; only o he mos basic solu ions a
clea dec emen in he ansi ion olume can be obse ed. How-
e e , bo h ansi ion empe a u e and en halpy do a y wi h pH,
signi ying ha , al hough he s uc u e o he sample would be
qui e he same, i is weake as pH aises: empe a u e b eaks easie
he s uc u e as pH becomes la ge –lowe T
and as pH inc eases-,
and he ene ge ic di e ence be ween gel and liquid phases is also
smalle as pH inc eases –lowe
D
h
as pH aises. The e o e, he
gene al pic u e ha can be ex ac ed om hese he modynamic
analyses is ha , al hough pH ha dly a ec s he olume ic beha -
io o he gel s a e, i s ongly a ec s i s s eng h and s abili y.
I is impo an o emphasize ha unlike ce ain classes o ma e-
ials as polyme s [66], he ansi ion en halpy alues be ween di -
e en phases o su ac an s [67–71], and e en mo e no classical
su ac an s, a e uncommonly epo ed. As conce ns bile sal s, o
he bes o ou knowledge, ansi ion en halpy da a ha e been
epo ed only o ew de i a i es [72,73] bu no o pu e bile sal s.
The e o e, u u e expe imen al wo k de o ed o he s udy o he
he modynamics o hese compounds would gi e new insigh s ha
could help o ge a be e unde s anding o he physicochemical
beha io o hese sys ems.
CRediT au ho ship con ibu ion s a emen
Aida Jo e : Concep ualiza ion, Me hodology, In es iga ion,
Da a cu a ion, W i ing – e iew & edi ing. Jacobo Toncoso: Con-
cep ualiza ion, Me hodology, In es iga ion, Da a cu a ion, W i ing
– e iew & edi ing. Ma ia Chia a di G ego io: Fo mal analysis,
W i ing – e iew & edi ing. F ancisco F aga López: Me hodology.
Decla a ion o Compe ing In e es
The au ho s decla e ha hey ha e no known compe ing inan-
cial in e es s o pe sonal ela ionships ha could ha e appea ed
o in luence he wo k epo ed in his pape .
Acknowledgemen s
Funding o he p esen wo k was p o ided by he Minis e io de
Economía, Indus ia y Compe i i idad, Spain (G an numbe
MAT2017-86109-P), Minis e io de Ciencia y Tecnología, Spain
A. Jo e , J. T oncoso, Ma ia Chia a di G ego io e al. Jou nal o Molecula Liquids 361 (2022) 119621
8
(G an numbe PID2020-115722 GB-C22) and Eu opean Syn-
ch o on Radia ion Facili y (ALBA) o he p ojec 2021024910
(2021). We acknowledge o Se icio Gene al de Apoyo a la
In es igación-SAI, Uni e sidad de Za agoza. M. C. di G ego io
acknowledges suppo om he p og amme ‘‘Ri a Le i Mon alcini
o young esea che s” o he I alian Minis y o Uni e si y and
Resea ch. Funding o open access cha ge: Uni e sidade de San i-
ago de Compos ela/CRUE/CISUG.
Re e ences
[1] D. Madenci, S.U. Egelhaa , Sel -assembly in aqueous bile sal solu ions, Cu .
Opin. Colloid In e ace Sci. 15 (1-2) (2010) 109–115, h ps://doi.o g/10.1016/
j.cocis.2009.11.010.
[2] M.C. di G ego io, L. T a aglini, A. Del Giudice, J. Cau ela, N.V. Pa el, L. Galan ini,
Bile Sal s: Na u al Su ac an s and P ecu so s o a B oad Family o Complex
Amphiphiles, Langmui . 35 (21) (2019) 6803–6821, h ps://doi.o g/10.1021/
acs.langmui .8b02657.
[3] L. Galan ini, M.C. di G ego io, M. Gubi osi, L. T a aglini, J.V. Ta o, A. Jo e , F.
Meijide, V.H. So o Tellini, N.V. Pa el, Bile sal s and de i a i es: Rigid
uncon en ional amphiphiles as dispe san s, ca ie s and supe s uc u e
building blocks, Cu . Opin. Colloid In e ace Sci. 20 (3) (2015) 170–182,
h ps://doi.o g/10.1016/j.cocis.2015.08.004.
[4] D.M. Small, Size and s uc u e o bile sal micelles. In luence o s uc u e,
concen a ion, coun e ion concen a ion, pH, and Tempe a u e, Ad . Chem.
Se . 84 (1968) 31–52, h ps://doi.o g/10.1021/ba-1968-0084.ch004.
[5] H. Kawamu a, Y. Mu a a, T. Yamaguchi, H. Igimi, M. Tanaka, G. Sugiha a, J.P.
K a oh il, Spin-label s udies o bile sal micelles, J. Phys. Chem. 93 (8) (1989)
3321–3326, h ps://doi.o g/10.1021/j100345a087.
[6] J. Jo e Ramos, Aida., Meijide del Río, F., Rod íguez Núñez, E.; Vázquez Ta o,
Agg ega ion beha io o bile sal s. Recen Res. De . Phys. Chem., 1999.
[7] A.R. Campanelli, S. Candelo o De Sanc is, E. Giglio, N. Vio el Pa el, C. Quaglia a,
F om c ys al o micelle: A new app oach o he micella s uc u e, J. Incl.
Phenom. Mol. Recogni . Chem. 7 (4) (1989) 391–400, h ps://doi.o g/10.1007/
BF01079774.
[8] S. Mukhopadhyay, U. Mai a, Chemis y and biology o bile acids, Cu . Sci. 87
(2004) 1666–1683, h ps://doi.o g/h ps://www.js o .o g/s able/24109764.
[9] A.F. Ho mann, L.R. Hagey, Key disco e ies in bile acid chemis y and biology
and hei clinical applica ions: His o y o he las eigh decades, J. Lipid Res. 55
(8) (2014) 1553–1595, h ps://doi.o g/10.1194/jl .R049437.
[10] P. Te ech, Y. Talmon, Aqueous suspensions o s e oid nano ubules: S uc u al
and heological cha ac e iza ions, Langmui . 18 (19) (2002) 7240–7244,
h ps://doi.o g/10.1021/la025574 .
[11] J. Is aelach ili, The science and applica ions o emulsions - an o e iew,
Colloids Su aces A Physicochem. Eng. Asp. 91 (1994) 1–8, h ps://doi.o g/
10.1016/0927-7757(94)02743-9.
[12] J. Is aelach ili, In e molecula and Su ace Fo ces, Thi d Edi ion., Academic
P ess, San a Ba ba a, 2011, 10.1016/C2009-0-21560-1.
[13] A. Jo e , F. F aga, F. Meijide, J. Vázquez Ta o, J. Cau ela, A. Del Giudice, M.C. di
G ego io, Re ealing he complex sel -assembly beha iou o sodium
deoxychola e in aqueous solu ion, J. Colloid In e ace Sci. 604 (2021) 415–
428, h ps://doi.o g/10.1016/j.jcis.2021.06.140.
[14] D.M. Blow, A. Rich, S udies on he Fo ma ion o Helical Deoxychola e
Complexes, J. Am. Chem. Soc. 82 (1960) 3566–3571, h ps://doi.o g/
10.1021/ja01499a023.
[15] A. Jo e , F. Meijide, E. Rod íguez Núñez, J. Vázquez Ta o, Agg ega ion kine ics
o sodium deoxychola e in aqueous solu ion, Langmui . 14 (1998) 4359–4363,
h ps://doi.o g/10.1021/la9712754.
[16] A. Rich, D.M. Blow, Fo ma ion o a helical s e oid complex, Na u e. 182 (4633)
(1958) 423–426, h ps://doi.o g/10.1038/182423a0.
[17] H. Sobo ka, N. Czeczowiczka, The gela ion o bile sal solu ions, J. Colloid Sci.
13 (2) (1958) 188–191, h ps://doi.o g/10.1016/0095-8522(58)90024-2.
[18] A. Jo e , F. Meijide, E. Rod íguez Núñez, J. Vázquez Ta o, M. Mosque a, F.
Rod íguez P ie o, Unusual py ene excime o ma ion du ing sodium
deoxychola e gela ion, Langmui . 12 (7) (1996) 1789–1793, h ps://doi.o g/
10.1021/la9506335.
[19] A. Jo e , F. Meijide, E. Rod íguez Núñez, J. Vázquez Ta o, Dynamic heology o
sodium deoxychola e gels, Langmui . 18 (2002) 987–991, h ps://doi.o g/
10.1021/la011178h.
[20] P. Li, C. Mal eau, X.X. Zhu, J.D. Wues , Using Nuclea Magne ic Resonance
Spec oscopy o P obe Hyd ogels Fo med by Sodium Deoxychola e, Langmui .
38 (17) (2022) 5111–5118, h ps://doi.o g/10.1021/acs.
langmui .1c0217510.1021/acs.langmui .1c02175.s001.
[21] L. O esen, F. Bend sen, U. Tage-Jensen, N.T. Pede sen, B.R. G am, S.J. Rune,
In aluminal pH in he s omach, duodenum, and p oximal jejunum in no mal
subjec s and pa ien s wi h exoc ine panc ea ic insu iciency,
Gas oen e ology. 90 (4) (1986) 958–962, h ps://doi.o g/10.1016/0016-5085
(86)90873-5.
[22] A.F. Ho mann, The con inuing impo ance o bile acids in li e and in es inal
disease, A ch. In e n. Med. 159 (1999) 2647–2658, h ps://doi.o g/10.1001/
a chin e.159.22.2647.
[23] M.C. di G ego io, J. Cau ela, L. Galan ini, Physiology and physical chemis y o
bile acids, In . J. Mol. Sci. 22 (2021) 1–23, h ps://doi.o g/10.3390/
ijms22041780.
[24] D. Fi zge ald, C. Du, S. Asaph, Technical Assessmen o he An on Paa
DMA5000 densi y me e , Uni ed Kindom, 2000.
[25] A. Fu ado, R. Pagel, F. Lo enz, I. Godinho, H. Wol , Viscosi y es ima ion o
New onian liquids om da a ob ained by oscilla ion- ype densi y me e s 25
(2017) 321–328.
[26] A. Fu ado, J. Ga ina, A. Napoleão, J. Pe ei a, M.T. Cidade, J. Sousa, Densi y
measu emen s o iscoelas ic samples wi h oscilla ion- ype densi y me e s, J.
Phys. Con . Se . 1379 (1) (2019) 012020, h ps://doi.o g/10.1088/1742-6596/
1379/1/012020.
[27] E.W. Lemmon, M.O. McLinden, D.G. F iend, The mophysical p ope ies o luid
sys ems., in: P.J. Lins om, W.G. Malla d (Eds.), NIST Chem. WebBook, NIST
S and. Re . Da abase Numbe 69, Na ional Ins i u e o S anda ds and
Technology, Gai he sbu g MD, 20899, USA, 1998. h ps://doi.o g/10.18434/
T4D303.
[28] A. Weissbe ge , J. Riddick, W. Bunge , T.K. Sakano, Techniques o chemis y. -
2: O ganic sol en s. Physical p ope ies and me hods o pu i ica ion, 4.ed,.,
Wiley, New Yo k, N.Y, 1986.
[29] A.R. Campanelli, S. Candelo o De Sanc is, E. Giglio, S. Pe iconi, The s uc u e o
helices o ubidium deoxychola e–wa e (3/10), 3(Rb+.C24H39O4).10H2O,
Ac a C ys allog Sec . C C ys . S uc . Commun. 40 (1984) 631–635, h ps://doi.
o g/10.1107/s010827018400514x.
[30] V.M. Coi o, E. Giglio, S. Mo ose i, A. Palleschi, A monoclinic phase o he
deoxycholic acid ubidium sal , Ac a C ys allog , Sec . B S uc . C ys allog .
C ys . Chem. 36 (1980) 1478–1480, h ps://doi.o g/10.1107/
s0567740880006322.
[31] G.R. Pe i , J.C. Knigh , D.L. He ald, R. Da enpo , R.K. Pe i , B.E. Tucke , J.M.
Schmid , Isola ion o lab ado ins 1 and 2 om Pseudomonas sy ingae p .
co ona aciens, J. Na . P od. 65 (12) (2002) 1793–1797, h ps://doi.o g/10.1021/
np020173x.
[32] K.R. Ha is, M. Kanakubo, L.A. Wool , Tempe a u e and P essu e Dependence o
he Viscosi y o he Ionic Liquids 1-Me hyl-3-oc ylimidazolium
Hexa luo ophospha e and 1-Me hyl-3-oc ylimidazolium Te a luo obo a e, J.
Chem. & Eng. Da a. 51 (3) (2006) 1161–1167, h ps://doi.o g/
10.1021/je060082s.
[33] K.R. Ha is, L.A. Wool , M. Kanakubo, Tempe a u e and P essu e Dependence o
he Viscosi y o he Ionic Liquid 1-Bu yl-3-me hylimidazolium
Hexa luo ophospha e, J. Chem. & Eng. Da a. 50 (5) (2005) 1777–1782,
h ps://doi.o g/10.1021/je050147b.
[34] S. Da idson, H. Joos en, H. Fi zge ald, Densi y measu emen o iscous oils
(using ib a ing ube densi y me e s), NPL Repo ENG 39, Uni ed Kingdom,
2012.
[35] K. Fon ell, Micella beha iou in solu ions o bile-acid sal s 111. Viscosi y und
densi y measu emen s in he aqueous solu ions, Kolloid-Z. u. Z. Polym. 246 (1)
(1971) 614–625.
[36] R. Zana, Commen s on he Pape ‘‘The Role o Hyd ogen Bonding in he
Fo ma ion o Bile Sal Micelles” by D. G. Oaken ull and L. R. Fishe , J. Phys.
Chem. 82 (1978) 2240–2243.
[37] C. La Mesa, A. Khan, K. Fon ell, B. Lindman, Phase diag ams and NMR s udies o
some e na y sodium deoxychola e-su ac an -wa e sys ems, J. Colloid
In e ace Sci. 103 (2) (1985) 373–391, h ps://doi.o g/10.1016/0021-9797
(85)90116-X.
[38] A. Maes e, P. Gua dado, M.L. Moyá, The modynamic s udy o bile sal s
micelliza ion, J. Chem. Eng. Da a. 59 (2) (2014) 433–438, h ps://doi.o g/
10.1021/je400903n.
[39] P. Ga idel, A. Hildeb and, R. Neube , A. Blume, The modynamic
cha ac e iza ion o bile sal agg ega ion as a unc ion o empe a u e and
ionic s eng h using iso he mal i a ion calo ime y, Langmui . 16 (12) (2000)
5267–5275, h ps://doi.o g/10.1021/la9912390.
[40] A.A. D’A chi io, L. Galan ini, E. Giglio, A. Jo e , X- ay and quasi-elas ic ligh -
sca e ing s udies o sodium deoxychola e, Langmui . 14 (17) (1998) 4776–
4781, h ps://doi.o g/10.1021/la971312 .
[41] G. Con e, R. Di Blasi, E. Giglio, A. Pa e a, N.V. Pa el, Nuclea magne ic
esonance and X- ay s udies on micella agg ega es o sodium deoxychola e, J.
Phys. Chem. 88 (23) (1984) 5720–5724, h ps://doi.o g/10.1021/j150667a052.
[42] A.R. Campanelli, D. Fe o, E. Giglio, P. Impe a o i, V. Piacen e, The mal and X-
ay s udy o sodium deoxychola e c ys al and ib e, The mochim. Ac a. 67 (2-
3) (1983) 223–232, h ps://doi.o g/10.1016/0040-6031(83)80102-6.
[43] D.J. Cab al, J.A. Hamil on, D.M. Small, The ioniza ion beha io o bile acids in
di e en aqueous en i onmen s, J. Lipid Res. 27 (3) (1987) 334–343.
[44] P. Beche , Hyd ophile-Lipophile Balance: His o y and Recen De elopmen s, J.
Dispe s. Sci. Technol. 5 (1983) 81–96.
[45] Y. Mo oi, M. Ki agawa, H. I oh, Aqueous solubili y and acidi y cons an s o
cholic, deoxycholic, chenodeoxycholic, and u sodeoxycholic acids, J. Lipid Res.
33 (1) (1992) 49–53.
[46] G. Deng, C. Tang, F. Li, H. Jiang, Y. Chen, Co alen c oss-linked polyme gels
wi h e e sible sol-gel ansi ion and sel -healing p ope ies, Mac omolecules.
43 (3) (2010) 1191–1194, h ps://doi.o g/10.1021/ma9022197.
[47] A. Jou dain, R. Asbai, O. Anaya, M.M. Chehimi, E. D ockenmulle , D. Mon a nal,
Rheological P ope ies o Co alen Adap able Ne wo ks wi h 1,2,3-T iazolium
C oss-Links: The Missing Link be ween Vi ime s and Dissocia i e Ne wo ks,
Mac omolecules. 53 (6) (2020) 1884–1900, h ps://doi.o g/10.1021/
acs.mac omol.9b0220410.1021/acs.mac omol.9b02204.s001.
A. Jo e , J. T oncoso, Ma ia Chia a di G ego io e al. Jou nal o Molecula Liquids 361 (2022) 119621
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