551
Ac a Chim. Slo . 2007, 54, 551–557
And uch e al.: In es iga ion o he Acid-base P ope ies ...
Scien i ic pape
In es iga ion o he Acid-base P ope ies
o 2-[[2-(4-Me hoxy-phenylamino)- inyl]]-1,3,3- ime hyl-
3H-indolium Reagen
Vasil And uch,aIoseph S. Balogh,bYa osla R. Bazel,aFe enc Billes,c
Mihály Kádá ,dRoland Ka osi,eGyula Pa lagh,cJózse Pos a,eAnd ás Simon,d
Ras isla Se bin,a,* Ma cel To oka
aDepa men o Analy ical Chemis y, P. J. Ša á ik Uni e si y, Moyzeso a 11, SK-04154 Ko{ice, Slo ak Republic,
* Co esponding au ho : E-mail: as [email protected]
bDepa men o Chemis y, Uni e si y o Nyí egyháza, Sós ói ú 31/b, Nyí egyháza, Hunga y, baloghj@ny .hu
cDepa men o Physical Chemis y, Budapes Uni e si y o Technology and Economics, Muªªegye em kp . 3,
H-1521 Budapes , Hunga y, [email protected]
dDepa men o Gene al and Analy ical Chemis y, Budapes Uni e si y o Technology and Economics, Sz . Gellé é 4,
H-1111 Budapes , Hunga y, and [email protected]
eDepa men o Analy ical Chemis y, Uni e si y o Deb ecen, Egye em é 1, Deb ecen,
Hunga y, pos aj@ ig is.unideb.hu
Recei ed: 22-05-2006
Abs ac
The acid-base p ope ies o 2-[2-(4-me hoxy-phenylamino)- inyl]-1,3,3- ime hyl-3H-indolium dye we e in es iga ed.
The eagen exis s in a eac i e single cha ged o m o e a wide ange o acidi y, om pH 8 o –2.5 H0. The op imum
analy ical wa eleng h o he single cha ged o m is 412 nm, whe e he mola abso p i i y is 4.06 × 104dm3mol–1 cm–1.
Mechanisms o p o ona ion and hyd olysis we e discussed. The esul s sugges he applicabili y o he dye as an e ec-
i e analy ical eac an . Quan um chemical calcula ions o he s uc u al and spec al p ope ies o he dye we e also ca -
ied ou .
Keywo ds: 2-[2-(4-Me hoxy-phenylamino)- inyl]-1,3,3- ime hyl-3H-indolium; spec opho ome y; acid-base p ope -
ies
1. In oduc ion
Complex- o ming eagen s a e widely used in a
a ie y o analy ical echniques. Fo he con inued de el-
opmen o no el analy ical p ocedu es, he in es iga ion
o new eagen s is always necessa y. The s udy o he
acid-base and spec al p ope ies o complex- o ming
eagen s allows o simpli ica ion in choosing he app o-
p ia e eac ion condi ions and be e applica ion o hese
eagen s in analy ical chemis y since acid-base p ope ies
ha e a signi ican in luence on he abili ies o dye
eagen s o o m and ex ac complexes.
The applica ion o complex o ma ion in analy ical
chemis y is based on he di e en abili ies o analy es o
eac wi h a ious complex- o ming eagen s. The com-
plex o ma ion depends on expe imen al condi ions ( he
concen a ion o eagen s, he acidi y o medium, e c.) and
on he na u e o he complex- o ming eagen . The e o e,
he choice o app op ia e expe imen al condi ions and a
sui able complex- o ming eagen enables he use o he
complexa ion p ocess o he sepa a ion, p econcen a ion
and de e mina ion o elemen s. Some use ul in o ma ion
abou elemen complexes can be ound in he wo k o
G eenwood and Ea nshaw.1The ends in o ganic com-
plex- o ming eagen s we e discussed in he wo k o
P asad Rao e al.2
Many a icles ha e been de o ed o he applica ion
o complex- o ming eagen s o he sepa a ion, p econ-
cen a ion and de e mina ion o ce ain elemen s, such as:
coppe (II),3a senic(III),4palladium(II),5lead,6gold,7
552 Ac a Chim. Slo . 2007, 54, 551–557
And uch e al.: In es iga ion o he Acid-base P ope ies ...
anadium(V),8 ellu ium(IV),9,10 bismu h(III),11 heni-
um,12 manganese,13,14 nickel,15 sil e 16 and o he s.17–23 The
applica ion o a ious complexes in spec opho ome ic
analysis has been discussed in a se ies o books and
e iews.24,25
The eac i i y and ex ac ion abili ies o basic dye
eagen s depend on he acidi y o he medium used,26,27
he concen a ion o he dye,28,29 he con en s o he aque-
ous phase,30 and ion s eng h and empe a u e. Oxida ion-
educ ion p ocesses, h ough which colou less o ms o
dye o en o igina e, also in luence he s a e o basic dye
eagen s. The spec al cha ac e is ics o basic dye eagen s
also change depending on he na u e o he sol en .31
The eac ion o complexes wi h basic dye eagen s,
as a ule, occu s in he aqueous phase. The e o e, o he
e alua ion o he ex ac ion capabili ies o basic dye
eagen s, o asce aining he ex ac ion mechanism and
o inding ou he op imal condi ions o de e mina ion, i
is necessa y o ob ain in o ma ion abou he ac ual s a e o
he eagen s in solu ion. Fo his eason, he acid-base
p ope ies o some basic dyes we e s udied.32–35
The aim o his wo k was he s udy o he acid-base
and spec al p ope ies o 2-[2-(4-me hoxy-phenylamino)-
inyl]-1,3,3- ime hyl-3H-indolium (I) (Figu e 1) and he
de e mina ion o i s main analy ical cha ac e is ics, such
as mola abso p i i y and op imum wa eleng h. The in-
es iga ed eagen was p e iously used o he de e mina-
ion o ch omium(VI).36,37
Figu e 1. The s uc u e o I.
2. Expe imen al
2. 1. Reagen s
All chemicals used we e o analy ical eagen g ade
and double dis illed wa e was employed h oughou he
in es iga ion. Iwas pu i ied by ec ys alliza ion om
me hanol, and a 1 × 10–3 mol dm–3 aqueous solu ion o I
was p epa ed by dissol ing a p ecise amoun o I in wa e .
The acidi y o he medium was hen adjus ed by he addi-
ion o sulphu ic acid, sodium hyd oxide o (CH3COOH–
NH4OH) bu e solu ions.
2. 2. Appa a us
Abso p ion spec a in he 220–600 nm egion we e
eco ded using a Unicam model 400 double beam UV-
VIS scanning spec opho ome e wi h ma ched qua z
cells o 10 mm pa h leng h.
FAB MS spec a (posi i e mode) we e eco ded on a
MAT 312 machine equipped wi h an ION TECH FAB
sys em and a MASPEC II32 (Mass Spec ome y Se ices
L d.) da a sys em. The samples we e dissol ed in NOBA
(3-ni obenzyl alcohol) o glyce ol and a gon was used as
he bomba ding gas.
NMR spec a we e eco ded wi h a B uke A ance
DRX-500 spec ome e . Chemical shi s a e gi en on he
δ-scale and we e e e enced o a sol en signal (CDCl3,
300 K, δC= 77.23 and δH= 7.27). Unambiguous 1H and
13C NMR assignmen s we e achie ed h ough 1H, 13C,
APT, HMQC, COSY, ROESY (mixing ime: 350 ms) and
HMBC expe imen s. The HMBC measu emen was op i-
mized o a 7.5 Hz long- ange coupling cons an .
The pH alues o he solu ions we e measu ed using
a digi al labo a o y pH-me e (OP-211/1 Radelkis,
Hunga y) wi h a glass elec ode.
3. Resul s and Discussion
3. 1. In es iga ion o S uc u e
Mass spec a we e measu ed in 3-ni obenzyl alco-
hol (NOBA) and in glyce ol. In NOBA an in ensi e mo-
lecula peak was obse ed a m/z = 307 and a smalle sig-
nal a m/z = 292 (M–CH3). Thus, he molecula weigh o
Ishould be 307. Since NOBA i sel has a mino signal a
m/z = 307, he measu emen was epea ed in glyce ol. The
same wo signals we e obse ed, hus con i ming he mo-
lecula weigh o he ca ion as 307.
The 1H and 13C NMR spec a (Figu es 2 and 3) o I
we e eco ded. The 1H and 13C chemical shi s, mul ipli-
ci ies, and cha ac e is ic H,H–COSY, H,H–ROESY, and
H,C–HMBC co ela ions o Ia e summa ized in Table 1.
The s a ing poin s o s uc u al elucida ion we e he
me hyl signals in posi ions 9 and 10. Iden i ica ion o
hese geminal me hyl g oups was unambiguous owing o
hei mu ual HMBC co ela ion. The HMBC spec a
(Figu e 5) o H3–9 and H3–10 iden i ied he C–2, C–3 and
C–4a ca bon a oms. C–3 ga e a co ela ion wi h a double
signal a 7.32 ppm (H–4). Using he COSY spec um, we
we e able o iden i y he a oma ic CH-uni s om H–4 o
H–7. The HMBC spec a o H–4, H–6 and H3–8 iden i ied
C–7a. H3–8 ga e a c oss peak wi h C–2 allowing us o
close he i e membe ed- ing.
The COSY spec um (Figu e 4) o H–12 iden i ied
an o e lapping signal a 7.27 ppm (H–11). H–12 showed
an HMBC co ela ion o C–14. Double s a 7.40 ppm and
6.86 ppm in he HMBC spec a co ela ed wi h C–14.
Thei in eg al alue (2) p o ed he exis ence o a 1,4-di-
subs i u ed benzene ing. The assignmen o hese wo
double s o posi ion 15/15a and 16/16a was achie ed by
he ROESY (Figu e 6) c oss peak be ween H–12 and he
signals a 7.40 ppm (H–15/15a). The HMBC co ela ion
553
Ac a Chim. Slo . 2007, 54, 551–557
And uch e al.: In es iga ion o he Acid-base P ope ies ...
o he me hyl signal a 3.77 ppm o C–17 and he ROESY
c oss peak be ween H–16/16a and he me hyl signal a
3.77 ppm jus i ied he pa a-subs i u ion o a me hoxy
g oup.
Figu e 4. The COSY spec um o I.
Figu e 2. The 1H spec um o I.
Noa1
H NMR (ppm) 13C NMR (ppm) m, J (Hz) H,H–COSY H,H–ROESY H,C–HMBC
2 – 176.2 – – –
3 – 48.8 – – –
4a – 140.2 – – –
4 7.32 122.0 d; 7.4 7.20 7.20, 1.66 143.1, 128.9, 48.8
5 7.20 124.9 ; 7.5 7.36, 7.32 7.36 143.1 (w), 140.2, 110.5
6 7.36 128.9 ; 7.7 7.20, 7.055 7.20, 7.055 143.1, 122.0, 110.5 (w)
7 7.055 110.5 d; 7.8 7.36 7.36 143.1 (w), 140.2, 124.9
7a – 143.1 – – –
8 3.70 31.9 s – – 176.2, 143.1
9 1.66 29.4 s – 8.32, 7.32 176.2, 140.2, 48.8
10 1.66 29.4 s – 8.32, 7.32 176.2, 140.2, 48.8
11 7.27b93.5 8.32 – –
12 8.32 151.2 d; 8.9 7.27 7.40, 1.66 133.2 (w)
14 – 133.2 – – –
15/15a 7.40 120.2 d; 7.8 6.86 8.32, 6.86 158.4, 120.2
16/16a 6.86 115.1 d; 8.0 7.40 7.40, 3.77 158.4, 133.2, 115.1
17 – 158.4 – – –
18 3.77 55.8 s – 6.86 158.4
aSe ial numbe s o he skele al a oms.
bO e lapping wi h sol en .
Table 1. 1H and 13C NMR chemical shi s, mul iplici ies, and cha ac e is ic H,H–COSY, H,H–ROESY, and H,C–HMBC co ela ions o I.
Figu e 3. The 13C APT spec um o I.
A pH > 9, he compound begins o hyd olyse,
which causes a lowe ing o he abso bance alue a λ=
412 nm. This p ocess is accompanied by a s epwise shi
in abso p ion maximum o he egion o sho e wa e-
leng hs. The hyd olysis o he compound is e e sible. By
inc easing he acidi y o he medium, he abso bance a
412 nm was lowe ed and a new peak was obse ed a 336
nm. The lowe ing o he abso bance begins o appea a
e y high concen a ions o H2SO4. The e o e, Hamme ’s
unc ion o acidi y H0was used in place o pH.38 This
eac ion is no e e sible, sugges ing ha he decomposi-
ion o he compound occu ed, ins ead o he p o ona ion.
A heo e ical s udy o he spec al and chemical
p ope ies o Iwas conduc ed wi h quan um chemical
calcula ions using he DFT me hod wi h he B3LYP unc-
ional and he 6-31G(d) basis se .39 The i s s ep was
554 Ac a Chim. Slo . 2007, 54, 551–557
And uch e al.: In es iga ion o he Acid-base P ope ies ...
3. 2. In es iga ion o Acid-base P ope ies
The in es iga ion o he acid-base p ope ies o I
was ealized in he ange om pH 14 o he concen a ion
o H2SO4 up o 14.3 mol dm–3. The eagen o ms ionic
associa es in he single posi i e cha ged o m. The e o e,
he mos p ac ical in e es appea s in he ange o medium
acidi y a which his o m p edomina es. As ollows om
he abso p ion spec a (Figu e 7), he single cha ged o m
o Ip edomina es in a wide ange o acidi y om pH 8 o
–2.5 H0(Figu e 8). The op imum analy ical wa eleng h o
he single cha ged o m is a 412 nm, whe e mola abso p-
i i y is 4.06×104dm3mol–1 cm–1.
Figu e 6. The ROESY spec um o I.
Figu e 5. The HMBC spec a o I.
Figu e 7. Abso p ion spec a o Ia di e en acidi ies, 4 × 10–5 mol
dm–3 o I, l = 10 mm.
Figu e 8. In luence o he medium acidi y on he abso bance o I,
4 × 10–5 mol dm–3 o I, l = 10 mm, λ= 412 nm.
555
Ac a Chim. Slo . 2007, 54, 551–557
And uch e al.: In es iga ion o he Acid-base P ope ies ...
geome y op imisa ion and calcula ion o he elec onic
p ope ies o he h ee possible au ome s, I, Ia, Ib
(Scheme 1). We assume he apid exchange o a p o on
be ween he e oa oms N1, N13 and O. Calcula ions we e
pe o med o hese au ome s in he gas phase and in a
pola medium (PCM model wi h a p ede ined pa ame e
o wa e as sol en ). Resul s showed a s ong p e e ence
o au ome I, which is mo e s able in all cases despi e
he s abilisa ion e ec o he pola medium on Ia and Ib
(Table 2).
The p e e ence o au ome Ican be shown by
compa ing he elec onic abso p ion spec a, which we e
calcula ed o each s uc u e in he gas phase and in he
pola medium using he TDDFT me hod and he
B3LYP/6-31G(d) basis se . The heo e ically calcula ed
maximum abso bance a 410 nm o he pola medium
(Table 2) is consis en wi h he expe imen al alue, while
alues o Ia and Ib a e conside ably lowe (383 nm and
372 nm).
The heo e ical in es iga ion o he acid-base
p ope ies was ealized by s udying a map o elec o-
s a ic po en ial (MEP) and by na u al bond o bi al
(NBO) analysis. Analysis o he MEP and he cha ge
dis ibu ion o Ishowed he heo e ical possibili y o i s
p o ona ion and he o ma ion o ca ions IIa, IIb and
IIc (Scheme 2). Ene gy and elec onic abso p ion spec-
a o he op imised s uc u e o hese ca ions as isola -
ed s uc u e and in pola medium we e hen calcula ed
(Table 2). Resul s showed he g ea sensi i i y o hei
s abili y on he sol en e ec . The mos s able ca ion as
isola ed s uc u e and in pola sol en is IIa (wi h p o o-
na ion on he oxygen a om o he me hoxy g oup).
Acco ding o ou model, he pola medium has a s ong
s abiliza ion e ec on ca ion IIb and he di e ence
be ween he ene gy o IIa and IIb is only 4.14 kJ/mol.
The e o e, he p esence o IIb in solu ion could also be
expec ed. A e he p o ona ion o Ia N13 a om, he
b eaking o he bond be ween N13 and C12 in IIb can
p oceed e y easily. Such wo-s ep p ocess could
explain he i e e sible dissocia ion o Iin a s ongly
acidic medium.
In basic solu ion, acco ding o he analysis o he
cha ge dis ibu ion and coe icien s o LUMO, o bi al
a ack o he hyd oxyl g oup a posi ion 2 o he indole
ing o a a om C12 could be expec ed. In bo h cases he
esul is a dec ease in he conjuga ion be ween he indole
ing and he phenyl g oup and a shi in he maximum
abso bance in he UV spec a o he sho e wa eleng hs.
The maximum posi i e ne cha ges unde he skele-
al a oms a e ound on he C2 a om o he indole ing and
on he C12 a om. I is hough ha his pa o he mole-
cule could be di ec ly esponsible o he ion associa ion
o he gi en dye wi h he anion being analy ically de e -
mined.
S uc u e Gas phase In sol en b
Ec[[ha ee]]E el [[kJ/mol]]UVmax [[nm]]Ec[[ha ee]]E el [[kJ/mol]]UVmax [[nm]]
I–960.1113610 0.00 429 –960.1818585 0.00 410
Ia –960.0225070 233.29 406 –960.1298824 136.46 383
Ib –960.0508140 158.97 403 –960.1320537 130.76 372
IIa –960.3321890 0.00 418 –960.5707660 0.00 390
IIb –960.3193670 33.66 692 –960.5691890 4.14 506
IIc –960.3107380 56.32 502 –960.5552075 40.85 440
a Rela i e ene gies ela ed o he minimal ene gy s uc u e o I and II, espec i ely.
b PCM model, wa e , ε= 78.39.
c To al elec onic ene gy wi h co ec ion o ze o poin ene gy (E0+ EZPE).
Scheme 1. Tau ome ic equilib ia o I.
Table 2. Calcula ed o al ene gies and UV abso p ion maxima o he in es iga ed s uc u esa.

556 Ac a Chim. Slo . 2007, 54, 551–557
And uch e al.: In es iga ion o he Acid-base P ope ies ...
4. Conclusion
The acid-base p ope ies o 2-[2-(4-me hoxy-phenyl-
amino)- inyl]-1,3,3- ime hyl-3H-indolium dye we e
in es iga ed. The eagen exis s in a eac i e single
cha ged o m o e a wide acidi y ange, om pH 8 o –2.5
H0. The op imum analy ical wa eleng h o he single
cha ged o m is 412 nm, whe e he mola abso p i i y is
4.06 × 104dm3mol–1 cm–1. The mechanisms o p o ona-
ion and hyd olysis we e discussed. I u ned ou ha he
applied me hods (MS, NMR and quan um chemical cal-
cula ions) a e e y good ools o sea ching o he analy i-
cally ac i e o m o he dye. The esul s sugges ed he ap-
plicabili y o he dye as an e ec i e analy ical eac an .
5. Acknowledgemen s
This wo k has been suppo ed by he Scien i ic
G an Agency o he Minis y o Educa ion o he Slo ak
Republic and he Slo ak Academy o Sciences (G an No.
1/4451/07). A.S. would like hank o he Békésy and he
Va ga/Roh Fellowship. V.A is g a e ul o he Domus
Hunga ica Scien ia ium e A ium ellowship, and Y.R.B.
is hank ul o suppo om APVV G an No. SK-
UA_00806.
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Po ze ek
V p ispe ku so podane kislinsko-bazi~ne las nos i 2-[2-(4-me oksi enilamino)- inil]-1,3,3- ime il-3H-indolnega ba i-
la ko eagen a. Ugo o ljeno je bilo, da obs aja eak i ni, enk a nabi i obliki {i okem obmo~ju, od pH 8 do –2.5 H0.
Op imalna anali ska alo na dol`ina ak{ne oblike ba ila je p i 412 nm, z mola no abso p i nos jo 4.06 × 104dm3
mol–1 cm–1. P eds a ljeni so azli~ni mehanizmi p o onacije in hid olize ba ila. Rezul a i aziska e nakazujejo mo`no
upo abo ba ila ko u~inko i ega anali skega eak an a. P i analizi so bili upo abljeni udi k an no-kemijski iz a~uni
s uk u e in spek oskopskih las nos i ba ila.