Ion conducting cholesterol appended pyridinium bisamide-based gel for the selective detection of Ag+ and Cl- ions

Article abstract of DOI:10.1039/c3ra44718a

Cholesterol appended bispyridinium isophthalamide dichloride (1) has been designed and synthesized. While compound 1 forms a gel in CHCl₃, the cholesterol appended bispyridinium isophthalamide dihexafluorophosphate (1a) analogue that results from 1 on anion exchange does not form a gel in any solvent combination. The chloroform gel of 1 is pH responsive and shows thermally activated ionic conductivity. It serves as a medium for the specific detection of Ag⁺ ions over a series of examined cations. Compound 1a, on the other hand, acts as a selective Cl^- ion detector by forming a gel in chloroform in the presence of tetrabutylammonium chloride.

Full text of DOI:10.1039/c3ra44718a

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Ion conducting cholesterol appended pyridinium
bisamide-based gel for the selective detection of
Ag and Cl ions†
Cite this: RSC Adv., 2014, 4, 3798
+
ꢀ
a
a
a
b
Kumaresh Ghosh,* Debasis Kar, Santanu Panja and Subhratanu Bhattacharya
Cholesterol appended bispyridinium isophthalamide dichloride (1) has been designed and synthesized.
While compound 1 forms a gel in CHCl , the cholesterol appended bispyridinium isophthalamide
3
dihexafluorophosphate (1a) analogue that results from 1 on anion exchange does not form a gel in any
solvent combination. The chloroform gel of 1 is pH responsive and shows thermally activated ionic
Received 28th August 2013
Accepted 22nd October 2013
+
conductivity. It serves as a medium for the specific detection of Ag ions over a series of examined
DOI: 10.1039/c3ra44718a
ꢀ
cations. Compound 1a, on the other hand, acts as a selective Cl ion detector by forming a gel in
www.rsc.org/advances
chloroform in the presence of tetrabutylammonium chloride.
(
1) that forms a gel in CHCl (Fig. 1). The gel shows thermally
3
Introduction
activated ionic conductivity. Furthermore, it is pH responsive
+
In recent past, considerable efforts have been focused on the and shis to the sol state selectively in the presence of Ag ion
design and synthesis of low-molecular-weight organogelators due to its strong affinity for Cl ions. A review of the literature
LMOGs) that exhibit responsive properties in the presence of reveals that the majority of Ag -selective gels concern the
certain external stimuli (e.g., temperature, light, pH, solvents, involvement of the Ag ion in gelation through coordination
chemicals and so on). Organogels are formed by assembling between the Ag ion and a donor atom such as nitrogen or
LMOGs into entangled three-dimensional networks containing sulfur. Similarly, examples of organogelators that undergo a gel
solvent molecules trapped via weak interactions such as to sol transition in the presence of Ag ions are reported in the
hydrogen bonding, p–p stacking, coordination, electrostatic literature, where Ag –alkene or Ag –aromatic ring nitrogen
ꢀ
+
(
+
+
1
7
+
+
+
2
8
and van der Waals interactions. Various low-molecular-weight interactions have been exploited in this study.
based organogels that are associated with chemical, photo,
proton, metal, mechanical and redox responsiveness have been
3
recognized in the last few years. In relation to this, the devel-
opment of stimuli responsive gels, whose properties can be
tuned by an external anion or cation is of increasing interest as
both anion and cation are linked to many vital processes in
4
biology, chemistry and the environment. With this in mind,
pyridinium-based compounds are of potential interest as they
5
are easily synthesizable and show good electrophilic character.
They moderately bind to anions through hydrogen bonding and
charge–charge interaction. Exploitation of this motif with suit-
6
able structural modication in gel chemistry is hardly reported.
In this full account, we herein report the synthesis of simple
cholesterol appended bispyridinium isophthalamide dichloride
a
Department of Chemistry, University of Kalyani, Nadia, 741235, India. E-mail:
ghosh_k2003@yahoo.co.in; Fax: +913325828282; Tel: +913325828750
b
Fig. 1 Chemical structures of 1 and 1a.
Department of Physics, University of Kalyani, Nadia, Kalyani, 741235, India
Electronic supplementary information (ESI) available: Figures showing the
change in uorescence and UV-vis titrations of receptor 1a with the halides and
†
ꢀ
1
OH ions, Job plots, binding constant curves, comparison of H NMR of 1 in
ꢀ
ꢀ
Furthermore, it is to be noted that the cholesterol appended
bispyridinium isophthalamide dihexauorophosphate (1a)
(Fig. 1), obtained from anion exchange of 1, forms a gel in
the presence and absence of F and OH ions, FTIR spectral comparison, AFM
1
13
image, Arrhenius plot, experimental procedures, H, C NMR spectra and mass
spectra of the nal compounds are available. See DOI: 10.1039/c3ra44718a
3798 | RSC Adv., 2014, 4, 3798–3803
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CHCl
3
selectively in the presence of tetrabutylammonium Table 1 Results of gelation test for 1 and 1a
chloride (TBACl) in preference to other halides, thereby facili-
a
a
ꢀ
Solvent
CHCl
Result (1)
Result (1a)
tating the recognition of Cl ions by the naked eye. Chloride is
9
one of the most essential anions of biological signicance, and
3
G*
S
S
I
S
S
I
S
P
I
I
10
it is related with cystic brosis. Therefore, the recognition of 1% CH OH in CHCl3
S
S
S
S
I
S
S
P
I
3
this ion is essentially important.
3% DMSO in CHCl
3
CH CN
3
DMSO
DCM
Results and discussion
3
CH OH
DMF
DMF : H
The synthesis of compound 1 was accomplished according to
Scheme 1. Initially, cholesterol was converted to the chloride 2,
2
O (1 : 1, v/v)
1
,2-Dichlorobenzene
CH CN : H O (1 : 1, v/v)
O (1 : 1, v/v)
which on reuxing with isophthaloyl diamide 3 in dry CH CN
3
3
2
I
P
P
P
gave the chloride salt 1. The isophthaloyl diamide 3 was
DMSO : H
2
obtained from the reaction of 3-aminopyridine with iso-
a
S, solution; G, transparent gel; I, insoluble; P, Precipitation, *mgc ¼
phthaloyl dichloride in the presence of Et
3
N in dry CH
2
Cl
2
.
ꢀ1
minimum gelatination concentration ¼ 10 mg mL
.
Anion exchange of the dichloride salt 1 using NH
4
PF gave the
6
desired compound 1a in good yield. All of the compounds were
fully characterized by spectroscopic methods.
ꢀ
solution may form a Cl -templated hydrogen bonded network
into which the solvent molecules are entrapped to form a gel.
Compound 1 contains different segments that play a critical
role in gelation. The cholesterol unit in 1 is hydrophobic in
nature and can interact through van der Waals interaction. This
0
The amide and pyridinium ring protons such as H , H and
, are the possible hydrogen bond donors that complex with
the Cl ions to establish a network in solution. Fig. 3 represents
a suggested mode of hydrogen-bonding in this network. A
similar network of a pyridinium system is reported by Das
o
o
H
p
11a
increases the gelation ability of 1. The pyridinium diamide as
an anion binding site may trigger the arrangement of the
molecules involved in hydrogen bonding and charge–charge
interaction with the anions. Keeping these features in mind, the
gelation propensity of 1 was examined in a wide range of
solvents and solvent mixtures (Table 1). As can be seen from
ꢀ
6b
et al. The cholesterol motif with a large hydrophobic surface
stabilizes the network in the less polar solvent, CHCl
highlights a probable mode of arrangement of the molecules of
considering the ‘Out–Out’ conformation as shown in Fig 2. It
is believed that the replacement of Cl by the larger PF
disrupts the suggested network shown in Fig. 3, by destroying a
number of intermolecular hydrogen bond contacts.
In the FTIR spectrum of 1, while a broad signal appeared at
402 cm , attributable to NH stretching due to hydrogen
bonding effect, the FTIR spectrum of compound 1a exhibited
NH stretching at 3448 cm attributable to free NH (Fig. 4). Even
the amide carbonyl stretching in 1 observed at 1689 cm was
in the spectrum of 1a. This lower
stretching of the amide carbonyl in 1 demonstrates its
involvement in hydrogen bonding. In H NMR, the signals for
the amide NH and the pyridinium ring protons of 1 appeared
further downeld compared to those of 1a (Fig. 5). Thus both
3
. Fig. 3
Table 1, the only ‘instant gel’ of 1 was obtained from CHCl . The
3
1
ꢁ
gel was thermo reversible and upon heating (Tgel ¼ 66 C), was
ꢀ
ꢀ
6
ion
transformed into sol and the resultant solution changed back
into the gel upon cooling to room temperature. In contrast,
ꢀ
compound 1a which is devoid of Cl ions, did not form a gel
ꢀ
under similar conditions. It is assumed that the Cl ions in 1
ꢀ1
3
play a key role in establishing a hydrogen bonded network in
solution, especially in CHCl . It is mentionable that the iso-
ꢀ1
3
phthaloyl diamide moiety can attain different equilibrium
ꢀ1
11b
conformations (In–In, In–Out and Out–Out; see Fig. 2) in
solution. The population of the individual form is dependant
upon the nature of the substituent present in the amide part. To
our belief, in the present case, any one of the conformers in
ꢀ1
shied to 1703 cm
1
1
FTIR and H NMR studies indicate that the dichloride salt 1 is
different from its dihexauorophosphate analogue 1a with
respect to their hydrogen bonding characteristics. Such
ꢀ
ꢀ
6
ions are
different hydrogen bonding behaviours of Cl and PF
well established by us and other groups.
6
a,12
The morphology of the chloroform gel of 1 was characterized
by AFM (ESI, Fig. S11†) and SEM studies. The SEM image in
Fig. 6 shows the aggregation of three dimensional networks with
Scheme 1 (i) Chloroacetyl chloride, pyridine, dry CH
amino pyridine, Et N, dry CH Cl , rt, 24 h; (iii) 2, dry CH
days; (iv) NH PF , DMF : CH OH (1 : 5, v/v), H O.
2
Cl
2
, rt, 10 h; (ii) 3-
3
2
2
3
CN, reflux, 3
4
6
3
2
Fig. 2 The different conformations of isophthaloyl diamide.
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Fig. 6 SEM image of the xerogel from the CHCl
mm).
3
gel of 1 (scale bar: ¼
2
Fig. 3 Schematic representation of the possible arrangement of an uneven surface. Studying the FTIR spectra of the amorphous
molecules during the gelation of 1.
1
and its chloroform gel reveals that there is a small increase in
ꢀ
1
amide carbonyl stretching (ygel ꢀ yamorphous ¼ 6 cm ) in the
gel state (ESI, Fig. S10†). This shi provides the evidence of
the breaking of some intramolecular hydrogen bonds in the
amorphous state to establish some new intermolecular
hydrogen bonds in the gel state. On the other hand, a small
ꢀ
1
decrease in ester carbonyl stretching (yamorphous ꢀ ygel ¼ 7 cm
)
is also an indication of its involvement in intermolecular contact
in the gel state.
It was noted that the gelator 1 composed of the pyridinium-
based cations and chloride anions in the gel state gave a
response in electrical conductivity. It is usual that the dielectric
properties of a medium containing charges are usually
measured by means of the impedance spectroscopy tech-
13
nique. In this technique, the sample is subjected to an
external voltage of the type V (u) ¼ V exp iut, where V is the
t
0
0
amplitude, u ¼ 2pf is the circular frequency, and f is the
frequency. Since dielectric spectroscopy in the frequency
domain covers a broad frequency range, in the present case
from 42 Hz to 5 MHz, this technique allowed the measurement
of ionic conductivity of the chloroform gel of 1. In analogy with
dielectric models that consider the electric polarization of
counter ions induced by an external electric eld, the observed
ionic conductivity can be ascribed to the diffusion processes of
ions, bound to the Columbic potential up to the typical size of
different regions that may characterize the whole system. In this
regard, for a particular temperature the real and imaginary
Fig. 4 Partial FTIR spectra of (a) 1a and (b) 1.
0
00
parts of the complex impedance Z* (u) ¼ Z ꢀ iZ at frequency u
were determined from the measured capacitance C(u) and
conductance G(u) data using the following relations:
GðuÞ
0
Z ¼
(1)
(2)
2
2
2
G ðuÞ þ u ðCðuÞ ꢀ C Þ
0
GðuÞðCðuÞ ꢀ C
0
Þ
00
ꢀ
Z ¼
2
2
2
G ðuÞ þ u ðCðuÞ ꢀ C
0
Þ
where C
electrodes, 3
0
¼ 3
0
A/t is the capacity with a free space between the
0
is the permittivity of the free space, and A is the
0
surface area. Fig. 7a shows the variation of the real (Z ) and
imaginary (Z ) parts of impedance with frequency at two
different temperatures for the cell containing the gel. Indeed,
0
0
0
the magnitude of Z increases with decrease in both frequency
1
Fig. 5 Partial H NMR spectra (400 MHz, d
6
-DMSO) of 1 and 1a.
and temperature, indicating the corresponding decrease in
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simulated curves are shown in Fig. 7a and b using the solid
lines, showing good conformity of the calculated lines with
experimental data. This indicates that the suggested equivalent
circuit describes the gel–electrode interface reasonably well.
Considering the R
tion as the bulk resistance of the system, the dc conductivity was
A (where ‘t’ and ‘A’ are the
b
values obtained from the above simula-
evaluated using the relation sdc ¼ t/R
b
thickness and area of the sample respectively) and is shown in
Fig. S12 (ESI†). The linear plot in Fig. S12 (ESI†) indicates the
thermally activated ionic conductivity (activation energy E ¼
a
ꢂ0.89 eV) that presumably arises from the migration of loosely
ꢀ
bound Cl ions within the gel network. With a decrease in
Fig. 7 (a) The real and imaginary parts of the complex impedance
spectra of the chloroform gel of 1 at two different temperatures; (b) the
Argand diagram of the gel at different measured temperatures. Solid
temperature, the movement of such ions within the gel frame-
work is considered to be slowly restricted, resulting in a
lines in both of the figures are the best fits of the data to eqn (3) and (4) signicant reduction in the conductivity of the system. Thus the
considering the equivalent circuit shown in the inset of (b).
experimental observation reveals that the chloroform gel of 1 is
effectively a good ionic conductor at room temperature.
Apart from ionic conductivity, the gel was also established to
be responsive towards both cationic and anionic substrates. To
ionic conductivity of the gelatinous system. Fig. 7b shows the
study the effect of anions, a concentrated solution of anions was
resultant Argand diagram [imaginary part of complex imped-
0
0
0
added on the top of the chloroform gel of 1 and was kept at room
temperature. Among the different anions tested (taken as their
ance (Z ) versus its real part (Z )] at different measured temper-
atures. As temperature increases, the radius of the arc that
corresponds to the bulk resistance of the gel decreases. This
demonstrates a thermally activated conduction mechanism.
The small tail observed for each semicircle is due to the double
layer capacity of an in-homogeneous electrode surface.
The impedance data was analyzed by considering an equiv-
alent circuit describing the gel–electrode interface as shown in
the inset of Fig. 7b. In this circuit, the parallel combination of
ꢀ
tetrabutylammonium salt), only OH ions disrupted the gel
immediately (Fig. 8). It is interesting to note that uoride being a
basic ion was unable to affect any change in the gel, even when
added in excessive amounts. This is in contrast to our previous
6a
observation on the urea analogue of this pyridinium system.
Such difference of the amide compound from its urea analogue
is attributed to the greater acidic character of the urea protons.
ꢀ
However, the OH ion induced broken gel reappeared only
polarization resistance R
b
(bulk resistance) and a constant
upon the addition of HCl (Fig. 9). Thus the gel in the present
study is pH responsive. It is worth mentioning that the chloro-
form gel of 1 started to disintegrate when the pH of the medium
was raised above 7.0 and it became a clear solution at pH 8.0.
The gel started to appear again when the pH of the medium was
reduced to 7.0 and it became thick at pH 6.0. In our opinion,
phase element (CPE1) accounts for the depression of the
semicircles observed in Fig. 7b. The constant phase element
(
CPE2) in series resembles the effect due to non-ideal electrode
l
geometry. The CPE impedance is ZCPE ¼ Q( ju) where 0 # l # 1
is the measure of the capacitive nature of the element. If l ¼ 1,
the element is an ideal capacitor and if l ¼ 0, it behaves as a
frequency independent Ohmic resistor.
ꢀ
OH abstracts the acidic pyridinium protons in 1 and destroys
the intermolecular hydrogen bond contacts. Protonation arising
from the addition of HCl results in the resetting of the original
structure due to hydrogen bond contacts reforming and gelation
taking place. The deprotonation of amide protons in 1 in the
presence of tetrabutylammonium hydroxide was proved by H
NMR (see ESI†).
The expressions of the real and imaginary components of the
impedance related to the equivalent circuit were calculated
according to the following equations,
ꢀ
ꢁ
1
lp
2
l
u cos
R
b
Q
1
þ R
b
ꢀ
ꢁ
2
ap=2
ua
0
Z ¼
!
! þ cos
ꢀ
ꢁ
2
ꢀ
ꢁ
2
Q
2
lp
lp
l
l
1
þR
b
Q
1
u cos
þ R
b
Q
1
u sin
2
2
(3)
ꢀ
ꢁ
lp
2
l
u sin
R
b
Q
1
ꢀ
ꢁ
2
ap=2
ua
0
0
ꢀ
Z ¼
!
! þ sin
ꢀ
ꢁ
2
ꢀ
ꢁ
2
Q
2
lp
lp
l
l
1
þ R
b
Q
1
u cos
þ R
b 1
Q u sin
2
2
(4)
The resistance R , Q , Q , l and a have been simulated using
a mean square method which consists of minimizing the
difference between the experimental and calculated data. The ꢃ 10 M).
b
1
2
Fig. 8 Photograph showing the changes in the CHCl
3
gel of 1 (10 mg
ꢀ1
mL ) after the addition of 2 equiv. amounts of various anions (c ¼ 2.0
ꢀ2
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ꢀ
1
Fig. 11 The phase changes of the CHCl
3
gel of 1 (10 mg mL ) on
ꢀ1
Fig. 9 The changes of the CHCl
addition of TBAOH (c ¼ 2.0 ꢃ 10 M) and HCl.
3
gel of 1 (10 mg mL ) on successive successive addition of AgClO (2 equiv.) and TBACl (2.5 equiv.). The gel
4
ꢀ2
to sol conversion was completed within 20 min and reappeared upon
the addition of TBACl after 30 min.
In addition to the effects of anions, the effects of cations on
the chloroform gel of 1 were also studied. For this, a series of bonding interaction of the pyridinium-based isophthaloyl
metal ions (taken as their perchlorate salts) were employed. diamide is established and well explored. In spite of that we
+
Among the different metal ions tested, only the Ag ion performed UV-vis and uorescence titrations of 1a (c ¼ 2.25 ꢃ
ꢀ5
destroyed the gel (Fig. 10), which reappeared in the presence of 10 M) in CHCl containing 0.2% DMSO to understand its
3
TBACl (Fig. 11).
affinity for the halides in solution. Halides showed measurable
Upon the breaking of the gel, the stretching frequencies of interaction (see ESI†). Fig. 12a represents the emission prole
ꢀ
the amide and ester carbonyls in the FTIR spectrum reached the where the selective increase in emission in presence of Cl ions
values of the amorphous state of 1 (ESI†). This can be explained is the distinguishing feature from the other halides for its
15
by the silver ions scavenging the chloride ions form the selective detection in the solution phase. Compound 1a binds
16
ꢀ
ꢀ
4
ꢀ1
network, and due to the template effect of Cl ion as proposed Cl ions with K
a
of 1.31 ꢃ 10 M in a 1 : 1 stoichiometric
ꢀ
in Fig. 3, the removal of Cl leads to the breaking down of the fashion. Fluoride initially takes part in hydrogen bonding in the
gel structure. However, externally added Cl ions further cavity and then deprotonates in the presence of its excess con-
resulted in the slow formation of gel (Fig. 11) by establishing the centration. This brought about a greater change in emission.
network as shown in Fig. 3. This process was successfully In contrast, Br and I ions quenched the emission signi-
ꢀ
14b
ꢀ
ꢀ
ꢀ
repeated three times. So, this study is worthwhile in that this gel cantly due to the heavy atom effect (see ESI†). The F induced a
+
is capable of detecting the Ag ion visually.
greater change in the absorption (Fig. 12b) and emission of 1a
It is worth mentioning that although the dihexa- due to hydrogen bonding, and deprotonation was conrmed by
uorophosphate analogue 1a was not responsive in gelation, it recording the same spectra of 1a in the presence of tetrabuty-

produced a transparent gel from CHCl
3
in the presence of lammonium hydroxide which also brought about a marked
TBACl (ESI†). Other halides (taken as their tetrabutylammo- change (Fig. 12c).
nium salt) did not form a gel under similar conditions. In the
ꢀ
presence of Cl ions, compound 1a is supposed to attain the
hydrogen bonding attributes of 1 due to which gelation takes
place. In contrast, other halide ions did not permit a suitable
interaction between pyridinium bisamides, thus preventing gel
formation. Therefore, the dihexauorophosphate analogue 1a
ꢀ
is usable in the visual detection of Cl ions with respect to the
other halides.
In our earlier publication, we have reported that different

uorophore-labeled pyridinium bisamides, built on the iso-
ꢀ
phthaloyl motif, are prone to bind different anions such as F ,
H PO , carboxylates etc. Thus, in solution the hydrogen
ꢀ
14
2
4
ꢀ5
Fig. 12 (a) Fluorescence ratio [I ꢀ I
(10 mg 360 nm upon addition of 6 equiv. of a particular anion (c ¼ 9.0 ꢃ 10
containing 0.2% DMSO, (b) change in absorbance of 1a
0
/I
0
] of 1a (c ¼ 2.25 ꢃ 10 M) at
ꢀ4
Fig. 10 Photograph showing the phase changes of 1 in CHCl
3
ꢀ1
mL ) upon the addition of 2 equiv. amounts of different metal ions M) in CHCl
3
c ¼ 2.0 ꢃ 10ꢀ M).
2
(c ¼ 2.25 ꢃ 10 M) upon addition of F and (c) OH ions.
ꢀ5
ꢀ
ꢀ
(
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3
(a) A. Ajayaghosh and V. K. Praveen, Acc. Chem. Res., 2007, 40,
Conclusion
664; (b) N. M. Sangeetha and U. Maitra, Chem. Soc. Rev., 2005,
In conclusion, we have demonstrated that cholesterol appended
bispyridinium isophthalamide dichloride 1 instantly forms a
gel in chloroform. The gel is stable at room temperature and
exhibits ionic conductivity due to the movement of unrestricted
34, 821; (c) S. K. Samanta and S. Bhattacharya, J. Mater.
Chem., 2012, 22, 25277; (d) X. Cao, Y. Wu, K. Liu, X. Yu,
B. Wu, H. Wu, Z. Gong and T. Yi, J. Mater. Chem., 2012, 22,
2650.
4 U. S. Spichiger-Keller, Chemical Sensors and Biosensors for
Medicinal and Biological Applications, Wiley-VCH,
Weinheim, Germany, 1998.
5 K. Ghosh, G. Masanta and A. P. Chattopadhyay, Eur. J. Org.
Chem., 2009, 4515.
6 (a) K. Ghosh and D. Kar, Org. Biomol. Chem., 2012, 10, 8800;
(b) S. Brahmachari, S. Debnath, S. Dutta and P. K. Das,
Beilstein J. Org. Chem., 2010, 6, 859.
7 (a) S.-I. Kawano, N. Fujita, K. J. C. van Bommel and
S. Shinkai, Chem. Lett., 2003, 32, 12; (b) H.-J. Kim, J.-H. Lee
and M. Lee, Angew. Chem., Int. Ed., 2005, 44, 5810; (c)
J. Son, J. W. Chung, I. Cho and S. Y. Park, So Matter,
2012, 8, 7617; (d) J. Dash, A. J. Patil, R. N. Das,
F. L. Dowdall and S. Mann, So Matter, 2011, 47, 1589; (e)
M. O. M. Piepenbrock, N. Clarke and J. W. Steed, So
Matter, 2011, 7, 2412; (f) P. Casuso, P. Carrasco, I. Loinaz,
H. J. Grande and I. Odriozola, Org. Biomol. Chem., 2010, 8,
ꢀ
Cl ions within the network. Furthermore, the gel is pH
+
responsive and acts as a medium for the recognition of Ag ions
over a series of other cations by exhibiting a gel to sol trans-
formation. Furthermore, the reappearance of the gel in the
selective presence of the chloride salt underlines the revers-
ibility in the process. Notably, we found that the dihexa-

uorophosphate analogue 1a which is obtained from 1 by anion
ꢀ
exchange could allow the selective recognition of Cl over the
other halides by forming a transparent yellow colored gel in
CHCl . In solution, an opposite mode of emission of 1a upon
3
ꢀ
addition of Cl ions further demonstrated this compound’s
ability to distinguish Cl from the other halides examined.
ꢀ
Thus, cholesterol appended pyridinium-based isophthaloyl
diamide exhibits versatile gel chemistry facilitating the visual
detection of both cations and anions. Further exploration in
this direction is underway in our laboratory.
5
455; (g) Q. Liu, Y. Wang, W. Li and L. Wu, Langmuir, 2007,
Acknowledgements
23, 8217.
We thank DST New Delhi, India for the facility under FIST
program in the department. Both D.K. and S.P. thank CSIR, New
Delhi, India for fellowship.
8 (a) W. Edwards and D. K. Smith, Chem. Commun., 2012, 48,
2767; (b) S. Winstein and H. J. Lucas, J. Am. Chem. Soc.,
1938, 60, 836; (c) N. J. Barnett, L. V. Slipchenko and
M. S. Gordon, J. Phys. Chem. A, 2009, 113, 7474; (d)
Z.-G. Tao, X. Zhao, X.-K. Jiang and Z.-T. Li, Tetrahedron
Lett., 2012, 53, 1840.
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