A sulfonyl hydrazone cholesterol conjugate: Gelation, anion interaction and its application in dye adsorption

Article abstract of DOI:10.1039/c8nj05613g

Cholesterol appended sulfonyl hydrazone derivative 1 was designed and synthesized as a supramolecular gelator for anionic sensing and dye adsorption. Gelator 1 forms a stable gel in DMSO-H₂O. The intermolecular H-bonding involving the sulfonamide moieties and the hydrophobic interactions between the cholesterol units encourage gelation. The SEM images of the xerogels show tiny rod-like fibrous structures. The rheological studies of the gel reveal the viscoelastic nature of the material. The gels of 1 exhibit a sharp and selective response toward CN^- and F^- ions causing gel-to-sol transformation. The gels of 1 also show potential for application in adsorption and removal of anionic dyes, such as erythrosine B and uranine, from water. Preparation of a gel column was done with the gel of 1 which shows reasonably high one-time erythrosine B removal efficiency establishing its potential and promising real-life applicability in water purification.

Full text of DOI:10.1039/c8nj05613g

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and K. Ghosh, New J. Chem., 2019, DOI: 10.1039/C8NJ05613G.
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ISSN 1144-0546
PAPER
Jason B. Benedict et al.
The role of atropisomers on the photo-reactivity and fatigue of
diarylethene-based metal–organic frameworks
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DOI: 10.1039/C8NJ05613G
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Sulfonyl Hydrazone Cholesterol Conjugate: Gelation, Anion
Interaction with Application in Dye Adsorption
Received 00th January 20xx,
Accepted 00th January 20xx
DOI: 10.1039/x0xx00000x
Atanu Panja, Sumit Ghosh and Kumaresh Ghosh*
www.rsc.org/
Abstract: Cholesterol appended sulfonyl hydrazone derivative 1 has been designed and synthesized as supramolecular
gelator for anionic sensing and dye adsorption. Gelator 1 forms a stable gel from DMSO-H2O. Intermolecular H-bonding
involving the sulfonamide moieties and hydrophobic interaction between the cholesterol units encourage gelation. SEM
images of the xerogels show tiny rod-like fibrous structures. Rheological studies of the gel reveal the viscoelastic nature of
the material . The gels of 1 exhibit a sharp and selective response toward CN- and F- ions causing gel-to-sol transformation.
The gels of 1 are also potent in adsorption and removal of anionic dyes, such as erythrosine B and uranine, from water.
Preparation of a gel column with the gel of 1 shows reasonably high one time erythrosine B removal efficiency and
establishes its potential and promising real-life applicability in water purification.
However, they are difficult to degrade owing to their inertness
toward photochemical decomposition and oxidation. Direct
discharge of dyes into the environment can be a potent threat
to human and aquatic organisms. Thus there is always a need
of efficient dye adsorbent system. Supramolecular gelators
having the suitable hydrophilic/hydrophobic sites are usually
found to be promising in this event.4c,4f,7a
As part of our ongoing research programme in designing
stimuli responsive LMWGs,4 herein, we report a new LMWG 1
of simple architecture that finds applications in anion sensing
and dye adsorption. Different functional segments of
compound 1 are highlighted in .Figure 1. Sulfonamide moiety is
introduced as anion binding site9 and also to encourage the
formation of molecular-assembly via H-bonding interaction.
Cholesterol motif has been incorporated to assist molecular
aggregation through hydrophobic interaction.1f The large
hydrophobic surface of cholesterol has significant impact in
dye adsorption also.4c,4d,4f
Introduction
Development of new low molecular weight supramolecular
gelators (LMWGs) of simple architectures has become
pertinent over the years owing to their wide potential
applications from medical science to material chemistry.1-7
Supramolecular gels are obtained through self assembly of
small molecules involving several weak forces such as
hydrogen bonding, π-π stacking, van der Waals interactions
etc.2 Non-covalent weak interactions can easily be tuned by
external physical and chemical stimuli (heat, light, redox, pH,
ions etc.) resulting in either weakening (gel-to-sol transition) or
restoring
(sol-to-gel
transition)
the
self-assembled
architectures.3 Such phase transformation in the presence of
chemical analytes is a familiar approach to developing new
sensor devices for naked-eye detection of biologically relevant
metal ions and anionic substrates.2-6
Beside sensing, the use of supramolecular gels as water
cleaning agents is interesting.7,8 Supramolecular gels are often
used in adsorption and removal of heavy metal salts,
nitroaromatic explosives and dyes form water. Removal of
water soluble toxic dyes draws attention as its consumption in
human body leads to serious health damages. Organic dyes are
widely used in various industries like food, textile, lather etc.
H
N
O
H
H
N
S
H
O
O2
O
1
anion binding
site
steroidal group
large hydrophobic surface of cholesterol unit assists molecular
aggregation and favours adsorption of toxic dyes
Department of Chemistry, University of Kalyani, Kalyani-741235, India. Email:
ghosh_k2003@yahoo.co.in, kumareshchem18@klyuniv.ac.in; Fax: +913325828282;
Tel: +913325828750 Extn. 305.
†Electronic Supplementary Information (ESI) available: Gelation tests, gel pics,
binding curves, detection limit, comparative tables, 1H, 13C NMR and HRMS are
available. See http://dx.doi.org/10.1039/b000000x/
Figure 1. Structure of compound 1.
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As anticipated, gelator 1 acts as a good anion sensor as well as engagement of the sulfonamide –NH in hydrogeVniewboArnticdleinOgn.linAe
DOI: 10.1039/C8NJ05613G
an efficient dye adsorbing agent. It forms
a stable small change in stretching frequency of the ester carbonyl
thermoreversible gel from DMSO-H2O and the gel exhibits which could not be ruled out, was possibly due to
visual detection of CN- and F- ions involving gel-to-sol phase intermolecular hydrogen bonding with water of the gelling
transition. In addition, DMSO-H2O gel of 1 was used as a good solvent (Figure S2).
adsorbent of anionic dyes such as erythrosine B and uranine
from water.
Morphology of the gel
The aggregated morphology of the gel was examined by using
scanning electron microscopy (SEM). SEM image of the xerogel
revealed the fibrous structure (Figure 2). Large numbers of tiny
rod-like fibers were in chaotic order to establish a 3D network.
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Results and discussion
Synthesis
Synthesis of compound 1 was achieved according to the
Scheme 1. Initially, cholesteryl-aldehyde 3 was prepared from
the reaction of 4-hydroxy benzaldehyde with compound 2
according to our reported procedure.4a-d p-Toluene sulphonyl
hydrazide 4 was next coupled with compound 3 to have the
Schiff base 1 in reasonable yield. All the compounds were fully
characterized by 1H, 13C NMR and mass spectral analysis.
CHO
O
(iii)
(ii)
(i)
1
R
Cl
R
OH
O
86%
78%
96%
Figure 2. SEM images of the DMSO-H2O (1:1 v/v) gel of 1.
2
O
O
R
Rheological study
R =
SO2
HN NH2
H
H
O
H
3
To evaluate the mechanical behaviour of DMSO-H2O (1:1 v/v)
gel of 1, oscilatory rheology experiment (dynamic amplitude
sweep and frequency sweep) was carried out (Figure 3 and
Table 1). For this, gel was prepared at a concentration of 1.2
4
Scheme 1. (i) Chloroacetyl chloride, pyridine, dry CHCl3, rt, 10h; (ii) 4-
hydroxy benzaldehyde, K2CO3, dry CH3CN, reflux, 5h; (iii) 4, dry
benzene, reflux, 24.
o
wt% of its mgc and the experiment was carried out at 25 C.
Amplitude sweep experiment (at constant frequency of 1 Hz)
determined the linerar viscolelastic region of the gel, which
Gelation study
Gelation study of compound 1 was performed in a wide range
of solvents by means of typical inversion of vial method (Table
S1). While compound 1 was soluble in most of the organic
solvents (toluene, DMF and DMSO etc.), it was insoluble in
water or MeOH due to the presence of cholesterol motif that
provides large hydrophobic surface. So, a better gelation could
be anticipated from solvent mixtures having MeOH or water as
co-solvent. In practice, tosylhydrazone 1 exhibitted excellent
self-aggregation in DMSO-H2O (1:1, v/v) mixture solvent (mgc =
20 mg/mL and Tgel = 44oC). The gel was thermoreversible as
shown in Figure S1.
Figure 3. Rheology study of the DMSO-H2O (1:1 v/v) gel of 1; (a)
However, gelation was unsucessful from other solvent
mixtures including semi-aqueous compositions (Table S1).
amplitude sweep and (b) frequency sweep experiments.
Even the presence of anions, such as F- and AcO-, in toluene- Table 1. Summary of rheological properties of the gel of 1.
MeOH solvent did not bring gelation of compound 1 (Table S1).
Solvent
Crossover
G′av (Pa)
G′′av (Pa)
tan δ
(% of strain)
( G′′av/G′av)
Probable mode of aggregation
The gel formation of 1 in DMSO-H2O (1:1 v/v) occurs due to
functioning of several weak forces. The hydrogen bonding
characteristics of sulfonamide –NH, hydrophobic interactions
DMSO-H2O
(1:1 v/v)
27
175572
54918
0.31
exerted by cholesterol surface are the possible responsible was upto ~2% of strain where both the storage modulus (G′)
forces to induce gelation. In order to understand the hydrogen and the loss modulus (G′′) were independent of strain (Figure
bonding behaviour, FTIR analysis was done. The imine signal 3a). With further increase in strain, both G′ and G′′ were
appeared at 1608 cm-1 in the amorphous state suffered a large decreased. At 27% of strain a crossover between G′ and G′′
shift to 1645 cm-1 in gel state (Figure S2). This is attributed to was noticed indicating demolition of the gel. In frequency
the rigidification of imine bond that arises from the sweep measurement (at constant strain of 0.1%), both G′ and
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G′′ were almost independent of strain in the entire range the gels in the presence of both anions and Fe3+ ions was
View Article Online
DOI: 10.1039/C8NJ05613G
studied (Figure 3b). Higher values of G′ over G′′ suggested the successful (Figure 5A). Thus apart from the gel-to-sol
true gel nature of the gel material.
conversion of 1 in different time frames, use of Ca2+ ions was
important in discriminating CN- from F- ions.
Anion responsive nature of the gel
To be familiar with the case of deprotonation, responsible for
To evaluate the stimuli responsive behaviour of the gel, the gel destruction, the effect of tetrabutylammonium hydroxide
effect of different anions on gel phase of 1 was investigated. (TBAOH) on gelation of 1 was investigated. When aqueous
Since intermolecular H-bonding between the sulfonamide solution of TBAOH was added to a DMSO solution of 1, no gel
groups is one controlling factor in gelation of 1, anions with formation was observed even after 1h, instead it produced a
their basicities and hydrogen bonding capabilities are expected clear solution (Figure 5B). These findings suggested the H-
to influence the gel state via the perturbation of this weak bonding and deprotonation of sulfonamide –NH- in presence
interaction. Accordingly, in the experiment, 2 equiv. amounts of CN- and F- ions for which rupturing of the gels occurred. In
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-
-
of different anions (CN-, F-, Cl-, Br-, I-, AcO-, H2PO4 , HSO4 , and this context, it is also mentionable that DMSO-H2O (1:1 v/v) gel
-
NO3 as their tetrabutylammonium salts, c = 0.2 M in water) of 1 was stable in a wide range of pH (from pH 2-11).
were added to the gel of 1. Both CN- and F- ions caused a Precipitation was noted at pH 11 (Figure 5B).
complete destruction of the gels, whereas other anions were In order to be acquainted with the reason of anion-induced gel
practically non interfering (Figure 4).
breaking, pHs of the broken gels were determined. In the
Both CN- and F- ions interact with the sulfonamide –NH- and study, DMSO-H2O (1:1 v/v) gel of 1 (prepared with or without
1
disrupt the hydrogen bonds to give sol as evident from the H using tris HCl buffer, 10 mM) was destroyed in the presence of
NMR study discussed latter. In the event, the gel state of 1 was 2 equiv. amounts of anions (e.g., F-, CN- and OH-) and pHs of
transformed into sol within 30 min in the presence of CN-. By the sols were found to increase above 11 (Figure 5C). This
contrast, F- ion took almost 2h to bring a similar change. As
optimization, minimum 2 equiv. amounts of F- ion was
necessary to cause such gel to sol conversion. The gel was
virtually stable in the presence of 1.5 equiv. amounts of F- ion
even after 2h. We observed the instant gelation when the gel
was prepared in the presence of 1 equiv. amount of F- ion. On
the other hand, under similar conditions, CN- ion-induced gel
to sol phase transition was noticed in presence of its 1 equiv.
amount. As reason, F- ion being smaller in size is more
hydrated in water compared to CN- ion and remains less free
to interact with gelator 1.10 On contrary, CN- ion being less
hydrated could display its basic nature and thereby caused
deprotonation of sulfonamide –NH- for which gel structure
was destroyed.
Figure 4. Pictorial representation of the phase changes of 1 (c = 20 mg/
ml) in DMSO-H2O (1:1 v/v) upon treatment with 2 equiv. amounts of
the different anions (as tetrabutyl ammonium salt, c = 0.2 M) after 2h.
-
[from left to right: (a) CN-, (b) F-, (c) AcO -, (d) H2PO4 , (e) Cl-, (f) Br-, (g) I-
-
, (h) HSO4- and (i) NO3 ].
To discriminate CN- and F- ions, we prepared the gel of 1 in
Figure 5. (A) and (B) are the photographs to show the effects of
DMSO-H2O (1:1 v/v) separately in presence of these anions
different chemical analytes on sol-to-gel conversion of 1 in DMSO-H2O
and different chelating agents. Under this circumstance, while
the content of the vial containing Ca2+ and CN- ions did not
gelate, gelation was successfully observed in the vial that
contains Ca2+ and F- ions (Figure 5A). This was due to
scavenging of F- ions by Ca2+ ions from the medium.
Importantly, it was very difficult to distinguish between CN-
and F- ions by using Fe3+ ions as chelating agent. Preparation of
(1:1, v/v) (2 equiv. amounts of each analytes were used in the
experiment and the photographs were taken after ~15 min of sample
preparation, Ca2+ and Fe3+ ions were taken as perchlorate and nitrate
salts, respectively); (C) Effects of different stimulus on the gel
formation of 1 in DMSO: H2O (1:1, v/v) and measurement of pH of the
resulting systems (CN-, F- and OH- were taken as TBA-salts, pH of the
final systems (solutions/’precipitations) were measured after
solubilising them in 10 mL of DMSO).
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results indicated that the increasing basicity of the medium DMSO) (Figure 7). Titration with CN- ions caused ratiometric
due to H-bonding followed by deprotonation of sulfonamide – changes in absorption spectra of 1 (Figure 7a). Successive
NH- was reponsible for gel breaking (Figure 5C). Inspite of addition of CN- ions resulted in gradual decrease in initial
having almost identical pH of the sols, externally added absorption band at 282 nm with the simultaneous increase of
chelating agents successfully distinguished F-, CN- from OH- a new absorption band at 330 nm. This new absorption band
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DOI: 10.1039/C8NJ05613G
ions (Figure 5).
at 330 nm progressively reached the plateau region with the
addition of 40 equiv. of CN- ions where a clear isosbestic point
at 312 nm was observed, which clearly indicated the existence
1H NMR study
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To support the mechanism of interaction, H NMR of 1 in the of a new species in the medium. Further addition of CN- ions
presence of anions were recorded in CDCl3 (Figure 6). In did not change the absorption of 1 significantly.
presence of equiv. amount of CN- ions, while the signal for A similar spectral change but to the small extent was observed
sulfonamide –NHa- at 7.67 ppm underwent downfield chemical with F- ions (Figure 7b). Other anions did not induce any
shift by 0.1 ppm, the signal for imine proton (Hb) remained considerable change in the absorption spectrum of 1 (Figure
unchanged in position. However, in the presence of excess of 7c). Such weak interaction was attributed to their poor
CN- ions (2 equiv.), the signal for sulfonamide –NHa- was basicities. By contrast, measurable interactions for CN- and F-
vanished and a small upfield chemical shift of other aromatic ions were due to their marked basicities that caused
protons was observed. This demonstrated the H-bonding deprotonation of sulfonamide –NH-. Importantly, CN- ion is
followed by deprotonation of sulfonamide –NHa- with CN-. easily distinguished from F- ion from the strong ratiometric
Deprotonation induces extensive delocalization of electron nature of the absorption spectra (Figure 7).
density towards the aromatic rings and results in upfield
1
chemical shift of the aromatic protons.
Figure 7. Change in absorbance of 1 [c = 2.50 x 10-5 M, taken in DMSO-
1
Figure 6. Partial H NMR spectra of 1 (c = 0.01 M) (a) in the absence
H2O (1:1 v/v)] upon addition of 40 equiv. amounts of (a) CN-, (b) F- and
and presence of (b) 1 equiv. and (c) 2 equiv. amounts of CN- (c = 0. 3
(c) different anions (c = 1.0 x 10-3 M, taken in DMSO).
M) (left) and F- (c = 0.5 M) (right) ions in CDCl3.
Benesi–Hilderband plot of 1 with the respective anions
Similarly, in the presence of 1 equiv. amount of F- ions, the
reflected linear binding stoichiometry (Figures S3 and S4).12 In
signal of sulfonamide –NHa- was vanished and the imine
this process, detection limits for different anions were also
proton (Hb) underwent a downfield chemical shift by ~0.2 ppm.
calculated (Figures S3 and S4)13. As can be seen from Table S2,
Addition of excess F- ions (2 equiv.) caused upfield chemical
CN- ions display marginally stronger binding than F- ions. Thus
shift of all the aromatic protons including the imine proton.
compound 1 is established as a visual sensor of CN- and F- ions
-
Possibly, HF2 ion, resulting from the deprotonation of
in sol-gel medium.
sulfonamide –NH-, is involved in H-bonding with the imine
Among the different anions, sensing and detection of CN- and
proton (Hb) and induces downfield chemical shift.11 However,
F- ions demand merit because of their biological relevance. CN-
-
the signal for HF2 was difficult to trace possibly due to
is extremely toxic to human body. Accumulation of CN- causes
broadening.
serious damages to health, even can lead to death within few
minutes.14 However, it is extensively used in many industries,
Anion binding in solution
especially in gold and silver extraction processes.15 On the
To understand the host-guest interactions in solution, we
other hand, F- is essential in preventing dental cavities and
recorded UV-vis spectral changes of 1 [c = 2.50 × 10−5 M, taken
osteoporosis whereas presence of excess amount of F- leads to
in DMSO-H2O (1:1 v/v)] upon addition of the different anions
fluorosis.16 In regard to the detection of these two ions,
(as tetrabutylammonium salts; c = 1.0 × 10−3 M, taken in
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although there are various reports on their fluorogenic and the sulfonamide moiety. However, an increase in anionic site
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chromogenic sensing,5i,17 the use of supramolecular gels in this in dye structure had negligible effect during adsorption.
DOI: 10.1039/C8NJ05613G
capacity is limited,5,6 especially LMWGs for CN- ion.6 In this Comparison of normalized UV-vis and FTIR spectra of the dye
capacity, a comparative view is represented in Table S3.
adsorbed gels (erythrosine B was taken as representative
sample) with the pristine gel of 1 undeniably established the
adsorption event. A prominent absorption band at 545 nm in
Dye adsorption experiment
Apart from the exploring of gelator 1 as sensor for CN- and F- the adsorbed gel supported the successful adsorption of ER
ions, DMSO-H2O gel of 1 was further subjected to the (Figure 10). This peak was absent in UV-vis spectrum of the
adsorption and removal of dyes from aqueous solution. pristine gel. The FTIR spectrum of the ER-adsorbed gel showed
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Supramolecular
gelators
having
the
appropriate the presence of characteristic stretching signals of both ER and
hydrophilic/hydrophobic sites find potential application gelator 1 (Figure S5).
toward this event.4c,4d,4f,7a In the present state of art,
sulfonamide moiety of our designed molecule as hydrophilic
unit is expected to initiate the adsorbtion of dyes efficiently on
the hydrophobic cholesteryl surface.
To execute the experiment, a series of aqueous dye solutions
(dianionic dye erythrosine B, monoanionic dye uranine and
monocationic dyes crystal violet and malachite green, 3 mL
each) was separately placed on the top of the gel of 1.
Adsorption of dyes was monitored by UV-vis spectroscopy. The
efficiency of the gel in uptaking dye molecules was determined
by comparing the UV-vis spectral change of respective dye
solutions, recorded before and after the experiment.4f The
outcomes are summarised in Figures 8-9 and in Table 2.
Figure 8. Photograph showing the adsorption of (a) Erythrosine B (ER),
(b) Uranine (UR), (c) Crystal Violet (CV) and (d) Malachite Green (MG)
by the DMSO-H2O (1:1 v/v) gel of 1 (25 mg/mL). In all cases, [dye] = 3.5
x 10-5 M.
Figure 9. Change in absorbance of (a) Erythrosine B (ER), (b) Uranine
It was found that the gel of 1 could remove the anionic dyes
more efficiently than the cationic dyes. About 83% of
erythrosine B (ER), a dianionic dye, was adsorbed by the gel
within 2h (Figures 8-9 and Table 2). A similar situation was
observed with the other monoanionic dye uranine (UR). In this
case, ~82% adsorption of UR was observed within 2h (Figures
8-9 and Table 2). Importantly, adsorption of both these dyes
was very rapid in first few minutes. After 5 min, ~57% and
~70% adsorptions were noted for ER and UR, respectively. On
contrary, adsorption of crystal violet (CV) was moderate
(~28%) and very small adsorption of malachite green (MG,
~4%) was noticed after 2h (Figures 8-9 and Table 2).
The selective removal of anionic dyes over cationic dyes was
attributed due to H-bonding interaction between the anionic
dyes and sulfonamide moiety. Again, relatively better
adsorption of CV over MG was possibly due to extra –NMe2
group in CV that may participate in additional H-bonding with
(UR), (c) Crystal Violet (CV) and (d) Malachite Green (MG) solutions by
the DMSO-H2O (1:1 v/v) gel of 1 (25 mg/mL). In all cases, [dye] = 3.5 x
10-5 M.
Table 2. Summary of adsorption data of the gel 1 using various
dyes.
Dye
( λmax in nm)
Initial conc.
of the dye
(Ci) [mM]
(mgL-1)
Equilibrium
conc. of the
dye (Cf)
Quantity of
the adsorbed
dye (mg per
gram of the
gelator)
[mM] (mgL-1)
Crystal Violet (CV)
(590)
Malachite Green
(MG)
3.5 x 10-2
(14.3)
2.5 x 10-4
(10.3)
480
3.5 x 10-2
(12.8)
3.4 x 10-4
(12.3)
60
(615)
Uranine (UR)
(485)
Erythrosine B (ER)
(525)
3.5 x 10-2
(12.4)
0.6 x 10-4
(2.2)
1224
2928
3.5 x 10-2
(29.3)
0.6 x 10-4
(4.9)
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Finally, to facilitate the practical utility of gel 1 in dye removal reasonable dye removal efficiency.4f,7a,8 A comparVaietwivAertvicileeOwn,linine
and water purification, a gel column was set up by filling a this regard, is highlighted in Table S4.
DOI: 10.1039/C8NJ05613G
plastic syringe with the gel, shown in Figure 11. Aqueous
solution of ER was then passed through it. Interestingly, one
time removal efficiency of the 1-gel column showed ~87%
Conclusions
In conclusion, we have designed and synthesized a simple
cholesterol coupled sulfonyl hydrazone funtionalised LMWG 1
that acts as a sensor both in solution and gel states for
detection of the basic anions, such as CN- and F-. DMSO-H2O
gel of 1 displays sharp and selective interaction toward CN- and
F- ions causing gel-to-sol phase transition. In the presence of
CN- the gel state of 1 undergoes fast conversion to sol
compared to F-. Moreover, in solution, a high ratiometric
change in absorption was another distinctive feature for
selective detection of CN- over F-.
Gelator 1 forms a stable and thermoreversible gel from DMSO-
H2O as confirmed by rheological studies. Intermolecular H-
bonding involving the sulfonamide moieties and the
hydrophobic interaction exerted by the cholesterol units are
the possible driving forces, responsible for gelation. The
morphology of the gel reveals tiny rod-like fibrillar structure.
The DMSO-H2O gel of 1 has been explored in dye adsorption.
The gel exhibits excellent efficiency towards adsorption and
removal of the anionic dyes, such as erythrosine B and
uranine, from water. Finally, demonstration of adsorption of
erythrosine B by a gel column corroborates its high one-time
removal efficiency. This establishes the potential and
adsorption of ER and the resulting solution appeared to be
light in color. The efficiency of the gelator in adsorption was
significantly increased with gelator concentration. When a
similar experiment was conducted by preapring the gel column
with a higher amount of gelator, one-time dye removal
efficiency reached upto ~95% (Figure S6).
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Figure 10. Comparision of normalized UV-vis spectra of DMSO-H2O
(1:1, v/v) gel of 1 before and after adsorption of Erythrosine B (ER).
promising real-life application of gelator
purification.
1 in water
Experimental
Materials and methods
All the chemicals and reagents were purchased from Spectrochem,
India. Tetrabutylammonium salts of the anions were purchased
from Sigma-Aldrich. Solvents used in the synthesis were purified,
dried and distilled before use. Solvents used in NMR experiments
were obtained from Aldrich. 1H and 13C NMR spectra were recorded
using Bruker 400 MHz instrument using TMS as internal standard.
FTIR measurements of the compounds were carried out using
Perkin-Elmer L120-00A spectrometer (max in cm-1) using KBr pellet.
UV-vis studies were performed using Shimadzu UV-2450
spectrophotometer.
Synthesis
Compound 1:
Compounds 3 (1.0 g, 1.82 mmol) and 4 (0.68 g, 3.64 mmol) were
taken in 20 ml of dry benzene and refluxed for 24h. Progression of
the reaction was monitored by checking TLC. After completion of
the reaction, benzene was evaporated and the reaction mixture was
repeatedly washed with MeOH to have the pure compound 1 in
appreciable yield (1.12 g, yield 86%, mp 134 oC). 1H NMR (400 MHz,
CDCl3):  8.59 (s, 1H), 7.77 (d, J = 8 Hz, 2H), 7.63 (s, 1H), 7.44 (d, J = 8
Hz, 2H), 7.23 (d, J = 8 Hz, 2H), 6.79 (d, J = 8 Hz, 2H), 5.31 (s, 1H),
4.72-4.68 (m, 1H), 4.53 (s, 2H), 2.33 (s, 3H), 2.27–0.68 (43H,
cholesteryl protons); 13C NMR (100 MHz, CDCl3):  168.0, 159.5,
147.7, 144.1, 139.1, 135.3, 129.6, 128.9, 127.9, 126.9, 123.1, 114.7,
75.4, 65.3, 56.6, 56.1, 49.9, 42.3, 39.6, 39.5, 37.9, 36.8, 36.5, 36.1,
Figure 11. (a) Removal of Erythrosine B (ER) from its aqueous solution
using gel column and (b) change in absorbance of Erythrosine B (ER)
solution during purification using the gel column [for the gel column
[1] = 25 mg/mL and [ER] = 3.5 x 10-5 M].
These observations established the gelator 1 as an excellent
water purifing agent for toxic anionic dyes. Specific removal of
anionic dyes with high efficiency in short response time makes
it unique in comparision to other reported supramolecular gels
which usually take several hours even a day to achieve a
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35.8, 31.89, 31.82, 28.2, 28.0, 27.6, 24.2, 23.8, 22.8, 22.5, 21.6, efficiency of the dye via the equation as: RE = (Ci – Cf)V/Cieiw, iAnrtiwclehOicnhlinCei
21.0, 19.3, 18.7, 11.8; FTIR (KBr, cm-1): 3445, 3214, 2949, 1766, represents the initial concentration of the dye in solution; Cf is the
DOI: 10.1039/C8NJ05613G
1608, 1440, 1363, 1213, 1163; HRMS (TOF MS ES+): calcd. 717.4301 final concentration of dye in the presence of adsorbing gel.
(M+H)+, found 717.4385 (M+H)+; calcd. 739.4121 (M+Na)+, found For the gel column, gel of 1 (50 mg) was prepared in 2 mL DMSO-
739.4122 (M+Na)+.
General procedure for gelation test
H2O (1:2, v/v) in the syringe. Then aqueous solution of ER solution
(5 mL, c = 3.5 x 10-5 M) was passed through it. The removal
The required amount of compound 1 was dissolved in desired efficiency (RE) of ER from its aqueous solution (2 mL) was estimated
solvent (1 mL) by slight warming and then cooled to room according to the procedure as described above.
temperature to form a gel. For solvent mixtures, compound 1 was
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first dissolved in a solvent and then the co-solvent was added as per
requirement. The gel was tested via the usual inversion of vial
method. The gel-to-sol transition temperature (Tgel) was measured
by dropping ball method. Sample of gel for SEM imaging was dried
under vacuum and then coated with a thin layer of gold metal.
Acknowledgements
AP thanks CSIR, New Delhi, India for a fellowship. SG thanks
University of Kalyani for providing University Research
Fellowship. KG thanks SERB, DST, New Delhi, for financial
support (File No. EMR/2016/008005/OC). We also
acknowledge DST, Govt. of India for financial assistance in
PURSE-II program.
General procedures for UV-vis titrations
Stock solution of the compound 1 (c = 2.50 × 10−5 M) was prepared
in DMSO-H2O (1:1 v/v). Stock solutions of anions (c = 1.0 × 10−3 M)
were prepared in DMSO. Then 2 mL solution of the compound was
taken in the cuvette and different amounts of various anions were
sequentially added to it. Upon addition of anions, change in
absorbance of the compound was recorded.
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4
Dye adsorption experiment4f
For this experiment, gel of 1 [25 mg/ml] was prepared in DMSO-H2O
(1:1 v/v). Dye solutions were prepared in the concentration of c =
3.5 x 10-5 M in pure water. Then an amount of 3 ml of different dye
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changes of respective dye solutions, recorded before and after the
experiment. The final concentration of the dye in solution was
calculated according to the Beer-Lambert law (A = cl, A is the
absorbance of the dye at a certain absorption wavelength in
solution,  is the molar extinction coefficient and l is the path length
of the incident light) which ultimately determined the removal
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GRAPHICAL ABSTRACT
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Sulfonyl Hydrazone Cholesterol Conjugate: Gelation, Anion Interaction with
Application in Dye Adsorption
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Atanu Panja, Sumit Ghosh and Kumaresh Ghosh*
Cholesterol appended sulfonyl-hydrazone derivative 1
has been designed and synthesized as supramolecular
gelator for anionic sensing and dye adsorption.
Gelator 1 forms strong gel from DMSO-H2O and the
morphology of xerogel shows tiny rod-like fibrous
network. The gel of 1 shows selective response toward
CN- and F- ions causing gel-to-sol transformation. The
gel of 1 acts as efficient matrix for adsorption and
removal of anionic dyes such as erythrosine B and
uranine from water.
.
.
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