Multidrug-Containing, Salt-Based, Injectable Supramolecular Gels for Self-Delivery, Cell Imaging and Other Materials Applications

Article abstract of DOI:10.1002/chem.201602429

Both molecular and crystal-engineering approaches were exploited to synthesize a new class of multidrug-containing supramolecular gelators. A well-known nonsteroidal anti-inflammatory drug, namely, indomethacin, was conjugated with six different l-amino a

Full text of DOI:10.1002/chem.201602429

DOI: 10.1002/chem.201602429
Full Paper
&
Imaging Agents
Multidrug-Containing, Salt-Based, Injectable Supramolecular Gels
for Self-Delivery, Cell Imaging and Other Materials Applications
[
a]
Rajdip Roy and Parthasarathi Dastidar*
Abstract: Both molecular and crystal-engineering ap-
proaches were exploited to synthesize a new class of multi-
drug-containing supramolecular gelators. A well-known non-
steroidal anti-inflammatory drug, namely, indomethacin, was
conjugated with six different l-amino acids to generate the
corresponding peptides having free carboxylic acid function-
ality, which reacted further with an antiviral drug, namely,
amantadine, a primary amine, in 1:1 ratio to yield six primary
ammonium monocarboxylate salts. Half of the synthesized
salts showed gelation ability that included hydrogelation, or-
ganogelation and ambidextrous gelation. The gels were
characterized by table-top and dynamic rheology and differ-
ent microscopic techniques. Further insights into the gela-
tion mechanism were obtained by temperature-dependent
1
H NMR spectroscopy, FTIR spectroscopy, photoluminescence
and dynamic light scattering. Single-crystal X-ray diffraction
studies on two gelator salts revealed the presence of 2D hy-
drogen-bonded networks. One such ambidextrous gelator
(capable of gelling both pure water and methyl salicylate,
which are important solvents for biological applications) was
promising in both mechanical (rheoreversible and injectable)
and biological (self-delivery) applications for future multi-
drug-containing injectable delivery vehicles.
Introduction
it can deliver itself (hence the name “self-delivery”) to the
target site via an invasive (subcutaneous) or non-invasive (topi-
cal) route.
Smart soft materials such as supramolecular gels having both
[
1,2]
[3]
biomedical
terest because they are emerging as promising biomaterials
and rheoreversible behaviour are of great in-
Supramolecular gelators, which are usually derived from
small molecules having molecular weight less than 3000, also
[
1,4]
[19–21]
for developing injectable self-delivery systems.
In conven-
known as low molecular weight gelators or LMWGs,
are
tional drug-delivery techniques, the drug is loaded on a carrier
capable of immobilizing a large amount of liquid within the
gel network through capillary forces to result in gels. LMWGs
have drawn keen attention of the materials research communi-
ty because of their various potential applications such as in de-
[
5]
[6]
[7]
[8]
(e.g., vesicles, reverse micelles, polymer gel matrix, virus
etc.) and then delivered at the target site. Non-trivial synthetic
impediments pertaining to the accessibility of the carrier mole-
cule, efficient loading (physical or chemical) of the drug into
the carrier, subsequent release of the drug at the target site,
and cytotoxicity, biodegradability and biostability of the carrier
molecule along with the consequential side effects are some
of the crucial challenges associated with such conventional ap-
proaches.
[22]
[23]
veloping templates for crystallization,
sensors,
cosmet-
[24]
[25]
[26]
ics,
electrooptics/photonics,
oxygen-storage materials,
[27]
[28]
[29]
catalysis,
conservation of art,
regenerative medicine,
[30]
[31]
structure-directing agents, biomineralization, wound heal-
[32]
[33]
[34]
ing,
enzyme mimics,
[35]
medical diagnostics,
tissue engi-
[36]
neering, inhibitors of cancer cells, immunosuppressive ma-
[
37]
[38]
To overcome these problems, an alternative drug-delivery
terials,
3D cell cultures
and so on. However, designing
[
9,10]
system known as self-delivery is becoming popular.
One of
LMWGs a priori is a daunting task because of the lack of mo-
lecular-level understanding of the gelation mechanism. Never-
the approaches to developing self-delivery systems involves
converting the drug/prodrugs or biogenic molecules them-
theless, several groups are actively involved in developing
[
11–18]
[39–43]
selves to supramolecular gelators,
either by chemical (co-
methodologies for designing new gelators.
It is believed
valent) or supramolecular (non-covalent) modifications, so that
widely that the gelator molecules form 1D networks sustained
by various non-covalent interactions (hydrogen bonding, p–p,
hydrophobic, van der Waals, charge-transfer, donor–acceptor,
metal coordination, etc.). Such 1D networks are then entangled
to form a 3D assemblies known as self-assembled fibrillar net-
[a] R. Roy, Prof. P. Dastidar
Department of Organic Chemistry
Indian Association for the Cultivation of Science (IACS)
[44]
2
A and 2B, Raja S. C. Mullick Road
works, the surface of which, if conducive, is able to immobi-
lize the gelling solvent by capillary-force action to give a gel.
We have contributed significantly to the understanding and
Jadavpur, Kolkata 700032, West Bengal (India)
E-mail: ocpd@iacs.res.in
parthod123@rediffmail.com
[
45–47]
subsequent design of LMWGs.
In this endeavour, we have
Supporting information for this article can be found under http://
dx.doi.org/10.1002/chem.201602429.
[48]
successfully employed supramolecular synthons in the con-
Chem. Eur. J. 2016, 22, 1 – 12
1
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
&
&
These are not the final page numbers! ÞÞ

Full Paper
[
49]
[61,62]
text of crystal engineering to design LMWGs capable of dis-
gate salts could be used for cell imaging.
Indeed, 50% of
[
50–52]
playing various functional properties
including self-deliv-
the PAM salts thus prepared turned out to be good to moder-
ate gelators.
[
53,54]
ery applications.
We recently exploited primary ammonium
monocarboxylate (PAM) synthons, which are among the most
successful gel-inducing supramolecular synthons developed by
us, to develop supramolecular topical gels for combination
Remarkably, one such gelator salt, namely, IND·LEU·AMN,
was found to be biocompatible, anti-inflammatory and capable
of cell imaging, and its hydrogel was injectable and thus suita-
ble for self-delivery applications. Its methyl salicylate (MS) gel
displayed interesting load-bearing and self-healing properties.
To the best of our knowledge, salt-based, multidrug-containing
supramolecular gels exhibiting both biological (self-delivery/
cell imaging) and other materials properties (self-healing, load-
bearing and shape-sustaining) have never been explored so
far.
[
55]
therapy.
While hydrogen-bonding among the gelator molecules is
the key interaction for gel-network formation in organogels,
such a self-assembly process involving gelator molecules is ex-
pected to be highly compromised in hydrogels, because the
target solvent water molecules, which are both hydrogen-
bond donors and acceptors, take part in hydrogen bonding
and are very much part of the gel network. Thus, a critical bal-
ance between hydrophobic and hydrophilic interactions is the
[
56]
Results and Discussion
key to hydrogelation.
Recently, we demonstrated that or-
[
57,58]
thogonal hydrogen bonding
involving amide functionality
Monocarboxylic acid peptide conjugates of IND were prepared
and PAM synthons played a crucial role in designing PAM salt-
based hydrogelators capable of displaying various material be-
haviours, such as sensing ammonia and purification of dyes
by following a literature procedure (see the Supporting Infor-
[63]
mation, Scheme S1). The corresponding AMN salts were pre-
pared by treating the peptide conjugates with AMN in 1:1
molar ratio in MeOH at room temperature (Scheme 2). FTIR
[
59]
from water.
In the present study, we aimed to exploit such orthogonal
hydrogen bonding together with hydrophobic/hydrophilic in-
teractions to develop hydrogels/organogels for multidrug self-
delivery via non-invasive (topical) and invasive (subcutaneous)
routes. To this end, we considered exploiting PAM synthons
with additional hydrogen-bonding functionality (amide) and
hydrophilic/hydrophobic moiety on a drug scaffold (Scheme 1).
Scheme 2. Various salts derived from the NSAIDs indomethacin (IND) and
amantadine (AMN).
Scheme 1. Design of PAM salt-based gelators.
For this purpose, we first made peptide conjugates of a well-
known nonsteroidal anti-inflammatory drug (NSAID), namely,
indomethacin (IND), with some selected l-amino acids having
hydrophilic [trans-3-hydroxy l-proline (HYP) and l-threonine
data provided evidence of salt formation. The absence of the
À1
COOH stretching band (1735–1712 cm ) of the peptide conju-
gates in the spectra of the resulting salts indicated proton
transfer, that is, salt formation (for a specific salt, see the Sup-
porting Information, Figure S1). All the peptide salts thus pre-
pared were scanned for gelation with various polar, nonpolar
and aqueous solvents. Remarkably, 50% of the peptide salts,
namely, IND·PHE·AMN, IND·HYP·AMN and IND·LEU·AMN,
turned out to be gelators. Gelation was confirmed by the test-
tube inversion method, whereby no gravitational flow of the
gel was seen when the container was inverted. All the gels
were thermoreversible over several cycles. Gelation data (for
(
(
THR)] and hydrophobic [l-phenylalanine (PHE), l-leucine
LEU), l-valine (VAL) and l-alanine (ALA)] side chains. The mon-
ocarboxylic acid peptide conjugates thus synthesized reacted
further with the primary amine antiviral drug amantadine
(
AMN) to generate PAM salts as potential supramolecular gela-
tors for self-delivery applications, as described above. We de-
liberately chose to work with IND because its emission proper-
[
60]
ty is well known, and therefore the corresponding bioconju-
&
&
Chem. Eur. J. 2016, 22, 1 – 12
www.chemeurj.org
2
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ÝÝ These are not the final page numbers!

Full Paper
detailed gelation studies, see the Supporting Information,
Table S1 and Figures S8–S10) revealed that the amino acid side
chain of the peptide conjugate salts had a profound effect on
gelation. The gradual increase in the number of C atoms and
consequent hydrophobicity of the amino acid side chain in
these salts on going from IND·ALA·AMN to IND·PHE·AMN
seemed to be influencing the gelation ability of the salts. It ap-
peared that the critical balance between hydrophobicity and
hydrophilicity was best achieved in IND·LEU·AMN, as is evident
from its ambidextrous ability to gel both organic solvents and
pure water.
nearly frequency-invariant, indicative of the viscoelastic nature
of the gels (see the Supporting Information, Figures S13–S29
and Table S6). The rheological behaviour of the MS gel and the
hydrogel of IND·LEU·AMN turned out to be nearly identical (G’
5
ꢀ10 ), which suggests a remarkable ability of this ambidex-
trous gelator to self-assemble equally efficiently in both organ-
ic and aqueous solvents (Figure 2). The rheological behaviour
The minimum gelator concentrations (MGCs) of many orga-
nogels and the hydrogel of this salt were less than 1.0 wt%
and thus indicate remarkable gelation efficiency of IN-
D·LEU·AMN. The fact that IND·PHE·AMN was able to gel
mainly aromatic solvents indicated that p–p interactions per-
haps helped the gelation process. The peptide conjugate salt
IND·HYP·AMN having a polar amino acid side chain turned out
be the least versatile gelator, and was able to gel only MS. On
the other hand, the peptide conjugate salts having less hydro-
phobic side chains (IND·ALA·AMN and IND·VAL·AMN) turned
out to be non-gelators, whereas the higher hydrophilicity of
IND·THR·AMN compared to IND·HYP·AMN proved to be detri-
mental to gelation. The gels were characterized by table-top
Figure 2. Frequency-sweep experiments on the hydro and MS gels.
[
64]
rheology; a steady increase in the Tgel value with increasing
concentration of the gelator indicated the importance of vari-
ous supramolecular interactions such as hydrogen bonding in
gel-network formation. The table-top rheology data also
showed that the gels derived from IND·LEU·AMN were ther-
mally more stable than those derived from the other two gela-
tors (Figure 1).
of the hydrogel of IND·LEU·AMN with temperature was also
evaluated under dynamic shear, and the data were in good
agreement with the expected behaviour of a viscoelastic gel-
like material; with increasing temperature the corresponding
moduli G’/G’’ gradually decreased and crossed each other at
68.58C, indicating gel–sol transition. The complex viscosity was
also found to decrease, as expected for a more fluid-like state
(
see the Supporting Information, Figure S31).
We focused further rheological studies on the MS gel and
the hydrogel of IND·LEU·AMN, because both solvents (MS and
water) are important in biological applications and the gelator
salt is a supergelator. Since our goal is to develop self-delivery
systems for delivering the drug via invasive (subcutaneous)
and non-invasive (topical) routes, and rheoreversibility of the
resulting gel is an important criterion for achieving such goals,
we carried out further rheological studies. For this purpose, we
first evaluated the critical strains g for both the MS gel and
c
hydrogel (4 wt%) of the supergelator, which turned out to be
5
.3 and 25.1%, respectively. In separate experiments, both gels
2 mL, 4.0 wt%) were sheared at high strain (above the critical
strain, 10 and 30% for MS gel and hydrogel, respectively) for
00 s and then returned to the low strain of the LVE region.
(
1
Viscous response (G’’>G’) was observed at high strain with
subsequent instantaneous recovery to elastic response (G’>
G’’) for both samples over several cycles, and this demonstrates
clearly that the behaviour of the gels is rheoreversible
(Figure 3).
Figure 1. Tgel versus [gelator] plots for the gels.
Dynamic rheological experiments were carried out to evalu-
ate the viscoelastic nature of all the gels studied herein. For
this purpose, we first carried out amplitude-sweep experiments
to determine the linear viscoelastic (LVE) range, which suggest-
ed the corresponding strain required for the frequency-sweep
experiments. Remarkably, in all cases, the elastic modulus G’
was found to be larger than the viscous modulus G’’ and was
Thus, high plateau modulus (G’ꢀ1000 KPa), high yield stress
(10 KPa) and instantaneous recovery under shear for both gels
indicated that they can be used for self-delivery applications as
proposed. To evaluate further the suitability of the hydrogel
for invasive (subcutaneous) delivery, the injectability of the hy-
drogel was assessed. Preloaded hydrogel in a 5 mL hypodermic
Chem. Eur. J. 2016, 22, 1 – 12
www.chemeurj.org
3
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
&
&
These are not the final page numbers! ÞÞ

Full Paper
The rheoreversible behaviour of the MS gel also encouraged
us to evaluate its self-healing, load bearing and shape-sustain-
ing properties. A block of MS gel (4 mL, 4 wt%) was able to
sustain its shape outside a container. The same block was able
to hold thirteen Indian five Rupee coins (each weighing 6.7 g)
amounting to 1.3 psi (8.72 kPa), beyond which the gel col-
lapsed. Five such gel blocks, obtained by cutting a single large
piece and dyed alternatingly with rhodamine B, were brought
into contact without applying any extra force; within a few mi-
nutes, all the pieces were found to have self-healed, and the
integrity of the self-healed gel block was evident from its
shape sustainability when placed between two bars. These re-
sults corroborated well with the rheoreversible property de-
scribed above (see the Supporting Information, Figure S35).
We believe that such load-bearing, self-healing properties will
be conducive to homogenous spreading of the gel in topical
application.
The morphology of the gel network of some of the selected
gels was studied by high-resolution TEM (HRTEM). Since MS
and water are important solvents for the main focus of the
present study, we selected both the MS gels and the hydrogels
of IND·HYP·AMN and IND·LEU·AMN. For the other gelator
IND·PHE·AMN, we chose to study the gels derived from
chlorobenzene and o-xylene. For this purpose, the sample
was prepared by smearing the gel (4 wt%) on a carbon-coated
copper grid. 1D tapes several micrometres long, apparently
composed of thin fibres, were seen for both chlorobenzene
and o-xylene gels of IND·PHE·AMN. In the case of the MS gel
of IND·HYP·AMN, a 3D network of highly entangled 1D fibres
was observed. On the other hand, shorter fibres forming a 3D
network by complex entanglement were observed in the case
of the MS gel derived from IND·LEU·AMN. Interestingly, the hy-
drogel of the same gelator showed a 3D network composed of
the thinnest fibres among the studied samples (Figure 5).
To understand the self-assembly process of hydrogelation in
Figure 3. A 4 wt% IND·LEU·AMN gel in MS and in water was cycled be-
tween high and low oscillatory shear strains. First, the sample was sheared
for 100 s at low amplitude of g=0.05% (proposed LVE strain) with an angu-
lar frequency of w=10 rads , which is within its LVE. For the next 100 s,
the sample was transferred to high strain amplitude of g=10% and 30%
À1
for MS gel and hydrogel, respectively, with the same angular frequency of
À1
w=10 rads which is well beyond the yield stress or LVE range. This cycle
was then repeated once more.
1
more detail, we carried out temperature-dependent H NMR
syringe could be injected into a container as a sol, which
turned into gel within a few minutes (Figure 4; for video, see
the Supporting Information).
spectroscopy, which was established to be effective in explain-
[65]
ing the role of CÀH···p and p···p interactions
in gelation
1
mechanisms. Thus, variable-temperature H NMR spectra were
recorded for the hydrogel of IND·LEU·AMN (10 mg in 0.6 mL
of D O). The upfield shift of both the aromatic and aliphatic
2
protons on going from high temperature (858C, sol) to low
temperature (258C, gel) revealed that in the gel state the self-
assembled molecules were in close proximity, so that both the
aromatic and aliphatic protons experience shielding by the
neighbouring aromatic p-electron clouds, suggestive of
CÀH···p and p···p interactions involving the aromatic/aliphatic
moieties of the salt (Figure 6). To rule out the possibility of
proton shifts due to effects unrelated to the self-assembly pro-
cess, we performed a control experiment wherein a D O solu-
2
tion of IND·LEU·AMN at a concentration of 0.3 wt% (well
below the MGC of 0.5 wt%) was subjected to variable-temper-
1
ature H NMR spectroscopy. The data clearly showed that there
was no significant shift of any of the protons (see the Support-
ing Information, Figure S42), which indicated that no specific
self-assembly of the molecules in the sol state occurred.
Figure 4. A) Preloaded hydrogel of IND·LEU·AMN in a 5 mL hypodermic sy-
ringe. B) Hydrogel flowing freely through the needle of the syringe. C) Hy-
drosol after passing through the syringe. D) Formation of hydrogel after
a few minutes.
&
&
Chem. Eur. J. 2016, 22, 1 – 12
www.chemeurj.org
4
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ÝÝ These are not the final page numbers!

Full Paper
À1
Table 1. FTIR C=O stretching frequencies [cm ].
Compound
COOH CON
CONH
(
tertiary amide) (secondary amide)
IND
IND·LEU
IND·LEU·AMN
IND·LEU·AMN (D
1716 1691
1733 1683
absent 1683
absent 1620
not applicable
1652
1649
2
O gel)
1606
IND·LEU.AMN ([D
6
]DMSO sol) absent 1687
1637
wherein NÀH can be amide NÀH or ammonium NÀH. Interest-
ingly, the absence of the hydrogen-bonded amide band (1620
À1
and 1606 cm in the gel) in the molecularly dissolved gelator
salt in [D ]DMSO clearly indicated that the C=O groups of the
6
amides were no longer involved in NÀH···O hydrogen bonding;
instead, the S=O group of [D ]DMSO now took part in hydro-
6
gen bonding with the NÀH group of the amide and ammoni-
um moieties (see the Supporting Information, Figure S33).
To probe the aggregation process during gelation, we car-
ried out concentration-dependent dynamic light scattering
(
DLS) experiments on the hydrogelator salt. For this purpose,
we scanned an aqueous solution of the gelator salt having var-
ious concentrations ranging from below and much above the
MGC. The particle sizes of the scatterers at the MGC and at
a much higher concentration (2 wt%) were about 5 and about
Figure 5. HRTEM images: A) MS gel of IND·HYP·AMN. B) MS gel of IN-
D·LEU·AMN. C) Chlorobenzene gel of IND·PHE·AMN. D) o-Xylene gel of IN-
D·PHE·AMN. E) Hydrogel of IND·LEU·AMN.
8
mm, respectively. The data indicated that the size of the scat-
tering particles in such solutions increased with increasing con-
centration, an observation commensurate with the expected
self-assembly process during gelation (Figure 7).
1
Figure 6. Variable-temperature H NMR spectra of IND·LEU·AMN in D
2
O.
Figure 7. DLS studies on IND·LEU·AMN in water (mean with +/À standard
To understand the supramolecular process of hydrogelation
by IND·LEU·AMN, we undertook detailed FTIR studies. For this
purpose, we considered monitoring the C=O stretching fre-
quency of various hydrogen-bond functionalities such as
COOH, CON (tertiary amide) and CONH (secondary amide)
present in the drug IND, the peptide conjugate IND·LEU and
the gelator salt IND·LEU·AMN (Table 1). The data clearly indi-
cated that both amide moieties in the gelator salt were in-
volved in hydrogen-bonding interactions in the corresponding
deviation error bar).
Since the design aspect of the peptide conjugate salts was
based on the assumption that various hydrogen-bond func-
tionalities such as amide and ammonium carboxylate would
display orthogonal hydrogen bonding, it was necessary at this
stage to determine the single-crystal structure of the gelators
studied herein. We obtained X-ray-quality single crystals of IN-
D·PHE·AMN and IND·HYP·AMN. We could not, however, crys-
tallize the hydrogelator salt. As expected, both salts crystallized
in a chiral space group (see the Supporting Information,
D O gel. It is, however, difficult to propose the exact details of
2
the hydrogen bonding. In most likelihood, both amide C=O
groups were involved in NÀH···O-type hydrogen bonding,
Chem. Eur. J. 2016, 22, 1 – 12
www.chemeurj.org
5
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
&
&
These are not the final page numbers! ÞÞ

Full Paper
Table S2) because of the inherent chirality of the amino acid
moiety. Unfortunately, both the crystals picked up lattice-oc-
cluded water molecules of solvation and, since water is an ex-
cellent hydrogen-bond donor and acceptor, it participated in
hydrogen-bonding and thereby disrupted the expected or-
thogonal hydrogen bonding. In both salts, the 38 amide part
of the drug moiety did not participate in hydrogen bonding,
whereas the peptide moiety took part in hydrogen bonding
tide-conjugate salt in water. The hydrogelator salt was 78
times more soluble than the parent drug IND (see the Sup-
porting Information, Table S5).
Before performing an MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-
[66]
diphenyltetrazolium bromide) assay, the stability of the hy-
drogelator was checked in PBS (pH 7.4) at 378C by incubation
for 48 h. No degradation in the incubated soup was detected
by UV/Vis spectroscopy (see the Supporting Information, Fig-
ure S39).
+
with NH3 /OMe/water in IND·PHE·AMN and water/OH(hy-
À
droxyproline) in IND·HYP·AMN. The COO group in both salts
Biocompatibility of the hydrogelator (IND·LEU·AMN) as well
as of the parent drug (IND) is important for determining the
concentration of the drug for treating mouse macrophage
cells. It was determined by an MTT assay in which the hydroge-
lator was incubated with mouse macrophage cells (RAW 264.7
cell line) for 24, 48 and 72 h at 378C. Both the parent drug and
the hydrogelator salt have IC50 values greater than 0.50 mm,
and the hydrogelator showed better biocompatibility than the
parent drug (Figure 9).
+
was found to be involved in hydrogen bonding with NH3
/water, which prevents PAM-synthon formation. Interestingly,
CÀH···p interactions (see the Supporting Information, Fig-
ures S36 and S37) involving both aromatic and non-aromatic
moieties were observed in these salts. Overall, both salts dis-
played 2D hydrogen-bonded networks (Figure 8).
Figure 8. Single-crystal structures of A) IND·PHE·AMN and B) IND·HYP·AMN.
Since IND·LEU·AMN was found to be an ambidextrous gela-
tor and was able to gel efficiently solvents useful in bio-appli-
cations (MS and water), we concentrated our focus on this ge-
lator salt. First, we evaluated the ability of this gelator salt to
form gels under physiological conditions, which is important
for using this modified drug salt for self-delivery applications.
The hydrogelator IND·LEU·AMN was examined for gelation in
saline water (0.9 wt% NaCl solution) and phosphate buffer so-
lution (PBS) at physiological pH 7.4, and in both the cases it
was able to form gel with slightly higher MGC (0.75 wt% for
Figure 9. MTT assay of A) IND and B) IND·LEU·AMN in RAW 264.7 cells for
24, 48 and 72 h at 378C. 1D, 2D and 3D stand for 1, 2 and 3 d, respectively.
0.9 wt% NaCl solution and 1 wt% for PBS). This could be at-
tributed to the fact that the salts (NaCl and PBS) increased the
polarity of the medium and thus resulted in a higher MGC of
the gelator by increasing its solubility.
After determining the biocompatibility of the hydrogel, the
anti-inflammatory activity was evaluated by prostaglandin E
2
[67]
assay (PGE assay) in the RAW 264.7 cell line. In this experi-
2
Since the solubility of NSAIDs is a major concern regarding
their delivery, we assessed the solubility of the modified pep-
ment, the maximum inflammation response, which was deter-
mined by monitoring the production of PGE in the cell culture
2
&
&
Chem. Eur. J. 2016, 22, 1 – 12
www.chemeurj.org
6
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ÝÝ These are not the final page numbers!

Full Paper
medium, was found by adjusting the amount of inflammation-
drug. The most conclusive evidence came from Z-stacking (see
the Supporting Information for a video). Thus, it was clear that
the gelator salt indeed penetrated the cell membrane and ade-
quately accumulated within the cells to give emission in the
green region (Figure 11).
inducing agents such as lipopolysaccharide (LPS) and interfer-
À1
on gamma (IFN-g). Concentrations of 1 mgmL
LPS and
À1
À1
1
00 ngmL IFN-g produced the maximum of 2012.3 pgmL
PGE in the RAW 264.7 cell culture medium, which was re-
2
À1
duced significantly to 138.7 and 147.6 pgmL in the presence
of 0.3 mm (<IC ) of IND and IND·LEU·AMN, respectively.
50
These reductions in PGE levels (6.8 and 7.3% for IND and IN- Conclusion
2
D·LEU·AMN respectively) signified that the hydrogelator
showed an anti-inflammatory response almost comparable to
By exploiting covalent and supramolecular approaches, a new
series of organic salt based supramolecular gelators derived
from two different drugs (indomethacin and amantadine) was
designed. Half of the organic salts thus synthesized showed
versatile gelation ability. One such ambidextrous gelator,
namely, IND·LEU·AMN, was found to be biocompatible (MTT
that of the parent drug IND (Figure 10).
assay), anti-inflammatory (PGE assay) and capable of cell imag-
2
ing. The hydrogel of this salt was injectable and hence could
possibly be used for self-delivery purposes via invasive (subcu-
taneous) and non-invasive (topical) routes. The MS organogel
of this salt exhibited intriguing materials properties, which in-
cluded shape sustaining, load-bearing and self-healing behav-
iour. The results clearly indicated that the strategy adopted
herein could be used in developing multidrug-based supra-
molecular gelators for combination therapy.
2
Figure 10. PGE assay of IND and IND·LEU·AMN. In=indomethacin, L=lipo-
polysaccharide, Y=interferon-g and S=IND·LEU·AMN.
Experimental Section
Materials: All chemicals were commercially available and used
To establish the multidrug self-delivery capability of the hy-
drogelator in drug-delivery applications, a leaching experiment
on the hydrogel of IND·LEU·AMN was performed under phys-
iological conditions (PBS, pH 7.4 at 378C) by placing 100 mL of
PBS (pH 7.4) over 100 mL of a 4 wt% hydrogel in a test tube.
Five such test tubes were incubated at 378C for various time
intervals (3, 6, 9, 12 and 24 h) in each case. The concentration
of the gelator in the PBS layer was determined in triplicate by
UV spectrophotometry. The hydrogel showed a maximum
leaching of 36% after 24 h. Thus, it can be concluded that the
hydrogel could be used as a useful tool in self-delivery applica-
tions (see the Supporting Information, Figure S40).
without further purification. Solvents were of analytical-reagent
grade and used without further distillation. PGE assay was per-
2
formed by using Prostaglandin E2 EIA Kit - Monoclonal (Cayman
Chemicals, Ann Arbor, MI).
Methods: Melting points of all the salts were determined with
a programmable melting point apparatus (Veego, India). The ele-
mental analyses of the salts were carried out with a PerkinElmer
2
400 Series II CHNO/S Elemental Analyzer. The mass spectra were
collected with a QTOF Micro YA263 instrument. FTIR spectra were
1
13
obtained with a Shimadzu FTIR-8300 instrument. H and C NMR
spectra were recorded with a 300 MHz spectrometer (Bruker Ultra-
shield Plus-300). TEM images were recorded with a JEOL instru-
ment on 300 mesh copper TEM grids. SEM images were recorded
with a JEOL JMS-6700F field-emission scanning electron micro-
scope. Rheology studies were carried out with an Anton Paar Mod-
ular Compact Rheometer MCR 102. Emission spectra were recorded
with a Fluorolog Horiba Jobin Yvon Fluoromax 4C Fluorescence
Spectrometer. A JASCO J-815 CD spectrometer was used to carry
out circular dichroism experiments. Differential scanning calorime-
try was done with a PerkinElmer Pyris Diamond DSC. Dynamic light
scattering experiments were executed with a Malvern Particle Size
Analyzer (Model No. ZEN 3690 ZETASIZER NANO ZS 90 version
To carry out cell imaging, it was necessary to evaluate the
emission behaviour of IND·LEU·AMN in aqueous solution. The
emission spectra of the sol and gel of IND·LEU·AMN in
double-distilled water (4.0 wt% for both sol and gel) showed
a significant increase in the emission intensity on going from
sol to gel at approximately 450 nm (l=329 nm), which could
be attributed to aggregation-induced emission (see the Sup-
[
68,69]
porting Information, Figure S34).
This result encouraged us
7
.03). A VARIAN CARY 50 Bio UV-Visible Spectrophotometer was
to further explore the possibility of using the drug gelator salt
for cell imaging. For this purpose, we chose to work with the
RAW 264.7 cell line (see the Experimental Section for details).
Figure 11 shows the bright-field, fluorescence and overlay
images of cells exposed to the gelator drug. The considerable
background in Figure 11B could be due to weak autofluores-
cence (see the Supporting Information, Figure S41) and also
used to measure the concentration of the hydrogelator in biosta-
bility and leaching experiments. MTT and PGE assays were con-
ducted by using a multiplate ELISA reader (Varioskan Flash Elisa
Reader, Thermo Fisher).
2
X-ray diffraction: Single-crystal X-ray diffraction data were collect-
ed by using MoKa (l=0.7107 ꢁ) radiation with a Bruker APEX II dif-
fractometer equipped with CCD area detector. A Bruker AXS D8
Advance powder diffractometer equipped with super speed LYN-
XEYE detector (CuKa1 radiation, l=1.5406 ꢁ, scan speed=
[
70]
because of phagocytosis.
However, localization of fluores-
cence in Figure 11C clearly indicated penetration of the gelator
Chem. Eur. J. 2016, 22, 1 – 12
www.chemeurj.org
7
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
&
&
These are not the final page numbers! ÞÞ

Full Paper
À1
0
.3 sstep , step size=0.028) was used to collect powder XRD
data.
Synthesis of salts: All the salts were prepared by reaction of the
corresponding acids and amines in 1:1 molar ratio in methanol at
room temperature followed by evaporation of the solvent in
a rotary evaporator (see the Supporting Information, Scheme S2).
The resultant solid was isolated as the salt in near-quantitative
yield. FTIR spectra (KBr) of the salts showed the presence of
stretching band of the carboxylate group (COO) at 1683–
À1
1
680 cm and the absence of the carbonyl stretching band (C=O)
À1
of the COOH group at 1735–1712 cm indicating complete salt
formation (see the Supporting Information, Figure S1).
Synthesis of peptides: Indomethacin (3.0 mmol, 1073.37 mg) and
N-hydroxysuccinimide (3.3 mmol, 379.797 mg) were placed in
a two-neck round-bottom flask and dissolved in dry THF (50 mL) to
form a homogeneous solution. The reaction mixture was stirred for
1
0 min in an ice bath (0–58C) under argon atmosphere, and then
a solution of dicyclohexylcarbodiimide (4.5 mmol, 928.485 mg) in
dry THF (20 mL) was added dropwise. The reaction mixture was
stirred overnight at room temperature. The white precipitate ob-
tained was filtered off and the filtrate was concentrated under re-
duced pressure. After evaporation of the solvent, the residue was
again dissolved in 60 mL THF and then corresponding l-amino
acid (3.0 mmol) dissolved in aqueous sodium carbonate (2.4 mmol,
2
54.372 mg) was added and the mixture stirred for 24 h. THF was
removed under reduced pressure and then the solution was acidi-
fied with cold aqueous HCl (1N) in a dropwise manner to obtain
a white precipitate. The precipitate was collected by filtration and
washed with distilled water to remove the excess acid. The solid
product thus obtained was dried in a vacuum desiccator and puri-
fied by column chromatography (2% MeOH in CH Cl ) to give 73–
2
2
8
2% of pure product (see the Supporting Information, Scheme S1).
Physicochemical Data
IND·PHE·AM: Light yellow solid, m.p. 173–1748C; elemental analy-
sis calcd (%) for C H ClN O : C 69.55, H 6.45, N 6.40; found: C
38
42
1
3
5
6
9.91, H 6.25, N 6.76; H NMR (300 MHz, [D ]methanol, 258C): d=
4
7
.63–7.55 (d, J=8.6 Hz, 2H), 7.55–7.48 (d, J=8.7 Hz, 2H), 7.10–7.04
(d, J=9.0 Hz, 1H), 7.04–6.98 (s, 5H), 6.98–6.94 (d, J=2.6 Hz, 1H),
6
3
1
6
1
1
1
.74–6.66 (dd, J=2.9, 2.6 Hz, 1H), 4.54–4.41 (t, J=5.7 Hz, 1H),
.84–3.72 (s, 3H), 3.63–3.50 (m, 2H), 3.20–3.07 (dd, J=5.9, 4.9 Hz,
H), 3.07–2.90 (dd, J=6.0, 6.4 Hz, 1H), 2.18–2.02 (d, J=12.7 Hz,
13
H), 1.86–1.60 ppm (m, 11H); C NMR (75 MHz, [D ]methanol): d=
4
70.5, 170.4, 168.4, 156.3, 138.6, 137.5, 136.3, 135.4, 134.2, 131.0,
30.9, 130.6, 129.1, 128.7, 127.6, 127.5, 125.7, 114.5, 113.2, 111.6,
00.8, 55.5, 54.7, 51.2, 48.1, 40.0, 37.3, 34.9, 31.0, 28.9, 12.2 ppm
À1
(Supporting Information, Figure S2); FTIR (KBr pellet): 1680 cm (s,
salt carboxylate C=O stretch).
IND·HYP·AMN: Light yellow solid, m.p. 177–1788C; elemental anal-
ysis calcd (%) for C H ClN O ·CH OH: C 64.26, H 6.78, N 6.42;
3
4
40
3
6
3
1
found: C 64.81, H 6.29, N 6.76; H NMR (300 MHz, [D ]methanol,
4
2
7
1
2
58C): d=7.78–7.61 (dd, J=8.4, 9.0 Hz, 2H), 7.61–7.44 (m, 2H),
.10–6.98 (dd, J=3.0, 2.6 Hz, 1H), 6.99–6.86 (m, 1H), 4.65–4.44 (m,
H), 3.91–3.73 (m, 4H), 3.73–3.48 (m, 3H), 2.45–2.29 (m, 1H), 2.28–
.16 (d, J=8.1 Hz, 3H), 2.16–2.06 (m, 4H), 1.91–1.58 ppm (m, 13H);
13
C NMR (75 MHz, [D ]methanol): d=172.7, 171.1, 167.0, 155.9,
4
1
35.1, 134.5, 132.2, 130.8, 130.7, 130.6, 128.7, 128.4, 123.7, 123.3,
114.3, 110.4, 109.5, 103.4, 100.9, 98.9, 69.4, 54.9, 54.7, 51.1, 40.2,
Figure 11. Fluorescent microscopy images of the RAW 264.7 cells incubated
with the hydrogelator IND·LEU·AMN. A) bright field, B) fluorescence and
C) overlay images.
&
&
Chem. Eur. J. 2016, 22, 1 – 12
www.chemeurj.org
8
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ÝÝ These are not the final page numbers!

Full Paper
3
7.6, 35.0, 28.9, 12.2, 10.3 ppm (Supporting Information, Figure S3);
ensure uniform heating. The temperature at which the ball
touched the bottom of the test tube was noted (see the Support-
ing Information, Figures S11 and S12).
À1
FTIR (KBr pellet): 1683 cm (s, salt carboxylate C=O stretch).
IND·LEU·AMN: Light yellow solid, m.p. 167–1688C; elemental anal-
ysis calcd (%) for C H ClN O : C 67.56, H 7.13, N 6.75; found: C
3
5
44
1
3
5
Organogel gelation and Tgel experiments: To prepare organogels,
we first dissolved the gelator in organic solvent by heating, and
the hot clear solution was then allowed to cool to room tempera-
ture to afford a stable organogel within a few minutes. Organogel
formation was confirmed by test-tube inversion. The Tgel values of
the organogels were measured by the dropping-ball method at
various gelator concentrations. A glass ball weighing 205.50 mg
was placed on 0.5 mL of organogel (at the MGC) in a test tube
6
8.01, H 6.68, N 6.79; H NMR (300 MHz, [D ]methanol, 258C): d=
4
7
.78–7.62 (d, J=8.3 Hz, 2H), 7.62–7.44 (d, J=8.4 Hz, 2H), 7.14–6.86
(
m, 2H), 6.76–6.55 (dd, J=3.0, 2.6 Hz, 1H), 4.44–4.24 (dd, J=3.0,
3
2
0
1
.9 Hz, 1H), 3.89–3.71 (s, 3H), 3.71–3.56 (d, J=2.2 Hz, 2H), 2.38–
.20 (s, 3H), 2.20–2.00 (t, J=3.4 Hz, 3H), 1.94–1.36 (m, 16H), 1.02–
13
.66 ppm (d, J=5.8 Hz, 6H); C NMR (75 MHz, [D ]methanol): d=
4
70.7, 170.1, 168.4, 156.2, 138.6, 138.0, 135.5, 134.3, 130.9, 128.7,
114.5, 113.5, 111.5, 100.8, 54.6, 53.5, 51.0, 42.0, 40.2, 35.0, 33.3, 31.0,
(15ꢂ100 mm).The test tube was then immersed in an oil bath
2
8.9, 24.7, 22.3, 20.9, 12.2 ppm (Supporting Information, Figure S4);
placed on a magnetic stirrer to ensure uniform heating. The tem-
perature at which the ball touched the bottom of the test tube
was noted (see the Supporting Information, Figures S11 and S12).
À1
FTIR (KBr pellet): 1683 cm (s, salt carboxylate C=O stretch).
IND·VAL·AMN: Light yellow solid, m.p. 161–1628C; elemental anal-
ysis calcd (%) for C H ClN O : C 67.15, H 6.96, N 6.91; found: C
3
4
42
1
3
5
SEM and TEM sample preparation: Dilute (0.1 wt%) solutions of
the gelators were drop cast on a glass plate with attached stan-
dard metallic SEM stub and dried under ambient conditions. The
samples were coated with platinum, and the SEM images were re-
corded. Dilute (0.1 wt%) solutions of the gelators were drop cast
on a carbon-coated Cu TEM grid (300 mesh) for each sample. The
grid was dried under vacuum at room temperature for 1 d and
used for recording TEM images at an accelerating voltage of
6
7.66, H 7.34, N 7.19; H NMR (300 MHz, [D ]methanol, 258C): d=
4
7
.78–7.61 (d, J=8.4 Hz, 2H), 7.61–7.45 (d, J=8.6 Hz, 2H), 7.13–7.01
(
d, J=2.5 Hz, 1H), 7.01–6.87 (d, J=9.1 Hz, 1H), 6.77–6.58 (dd, J=
3
3
1
.0, 2.6 Hz, 1H), 4.33–4.09 (d, J=4.8 Hz, 1H), 3.87–3.72 (s, 3H),
.72–3.54 (d, J=3.2 Hz, 2H), 2.40–2.20 (s, 3H), 2.21–2.04 (m, 3H),
.94–1.55 (m, 9H), 0.96–0.86 (d, J=6.9 Hz, 3H), 0.87–0.75 ppm (d,
1
3
J=6.9 Hz, 3H); C NMR (75 MHz, [D ]methanol): d=171.0, 170.9,
4
1
70.0, 156.2, 138.6, 135.5, 134.3, 130.9, 130.6, 128.7, 125.0, 114.5,
2
00 kV without staining.
113.5, 112.8, 111.6, 100.7, 59.9, 54.7, 51.2, 40.1, 34.9, 31.3, 31.1, 28.9,
1
8.7, 16.8, 12.2 ppm (Supporting Information, Figure S5); FTIR (KBr
Rheology studies: Rheology studies were carried out with an
Anton Paar Modular Compact Rheometer MCR 102 on 4 wt% gels
at 258C in parallel-plate geometry (25 mm diameter, 1 mm gap).
À1
pellet): 1683 cm (s, salt carboxylate C=O stretch).
IND·ALA·AMN: Light yellow solid, m.p. 158–1598C; elemental anal-
ysis calcd (%) for C H ClN O ·H O: C 64.26, H 6.74, N 7.03; found:
C 63.94, H 7.14, N 7.22; H NMR (300 MHz, [D ]methanol, 258C): d=
3
2
38
3
5
2
1
Single crystal X-ray diffraction: Single crystals of IND·PHE·AMN
and IND·HYP·AMN were grown from pure methanol as solvent by
slow evaporation at room temperature. Data were collected by
using MoKa (l=0.7107 A) radiation with a Bruker APEX II diffrac-
tometer equipped with CCD area detector. Data collection, data re-
duction and structure solution/refinement were carried out with
the SMART APEX-II software package. All structures were solved by
direct methods and refined in a routine manner. Non-hydrogen
atoms were treated anisotropically. All hydrogen atoms were geo-
metrically fixed. CCDC 1480781 (IND·PHE·AMN), and 1480782 (IN-
D·HYP·AMN) contain the supplementary crystallographic data for
this paper. These data are provided free of charge by The Cam-
bridge Crystallographic Data Centre.
4
7
.75–7.65 (d, J=8.5 Hz, 2H), 7.61–7.51 (d, J=8.5 Hz, 2H), 7.06–7.00
(
d, J=2.6 Hz, 1H), 7.00–6.93 (d, J=9.0 Hz, 1H), 6.71–6.63 (dd, J=
2
3
1
.4, 2.5 Hz, 1H), 4.32–4.13 (q, J=7.1 Hz, 1H), 3.85–3.73 (s, 3H),
.69–3.58 (s, 2H), 2.33–2.23 (s, 3H), 2.22–2.04 (d, J=2.8 Hz, 3H),
13
.92–1.56 (m, 9H), 1.41–1.27 ppm (d, J=7.0 Hz, 3H); C NMR
(
75 MHz, [D ]methanol): d=177.2, 174.2, 168.5, 156.0, 138.4, 134.6,
4
1
5
34.3, 131.5, 130.9, 130.8, 128.6, 115.9, 114.3, 110.9, 108.9, 101.3,
8.4, 54.6, 51.2, 40.0, 36.1, 34.9, 32.3, 28.9, 12.2 ppm (Supporting In-
À1
formation, Figure S6); FTIR (KBr pellet): 1683 cm (s, salt carboxyl-
ate C=O stretch).
IND·THR·AMN: Yellow solid, m.p. 171–1728C; elemental analysis
calcd (%) for C H ClN O ·CH OH: C 63.59, H 6.91, N 6.54; found: C
3
3
40
3
1
6
3
6
3.94, H 7.14, N 7.22; H NMR (300 MHz, [D ]methanol, 258C): d=
4
MTT assay: The cytotoxicity of the gelator salt was evaluated in
RAW 264.7 cells by standard MTT assay. The mouse macrophage
RAW 264.7 cells were purchased from American Type Culture Col-
lection (ATCC) and maintained by following its guidelines. The cells
were grown in Dulbecco’s modified Eagle’s medium (DMEM) sup-
plemented with 10% fetal bovine serum (FBS), 1% penicillin and
7
.79–7.62 (d, J=8.5 Hz, 2H), 7.62–7.44 (d, J=8.5 Hz, 2H), 7.12–6.92
(
m, 2H), 6.74–6.60 (dd, J=2.4, 2.5 Hz, 1H), 4.33–4.24 (d, J=3.3 Hz,
1
2
1
H), 4.24–4.12 (m, 1H), 3.90–3.75 (s, 3H), 3.75–3.61 (d, J=2.9 Hz,
H), 2.43–2.22 (s, 3H), 2.22–2.01 (t, J=3.1 Hz, 3H), 1.97–1.53 (m,
13
0H), 1.17–0.95 (d, J=6.3 Hz, 3H) ppm;
C NMR (75 MHz,
[
D ]methanol): d=173.5, 172.3, 168.7, 156.2, 138.6, 135.5, 134.4,
4
streptomycin in a humidified incubator at 378C and 5% CO . The
2
1
5
30.9, 130.6, 128.7, 128.4, 114.8, 111.7, 108.2, 100.7, 67.5, 56.0, 54.7,
0.4, 40.2, 35.0, 31.0, 28.9, 18.6, 12.2 ppm (Supporting Information,
4
cells were seeded in 96-well plates at a density of 1ꢂ10 cells/well
for 24 h. After 24 h of seeding, the cells were treated with various
concentrations (up to 2 mm) of the salt or DMEM alone for 72 h in
À1
Figure S7); FTIR (KBr pellet): 1681 m (s, salt carboxylate -C=O
stretch).
a humidified incubator at 378C and 5% CO . Then, the culture
2
Hydrogel gelation and Tgel experiments: to prepare hydrogels,
we first dissolved the gelator in pure water by heating, and the
hot clear solution was then allowed to cool to room temperature
to afford a stable hydrogel within a few minutes. Hydrogel forma-
tion was confirmed by test-tube inversion. The Tgel values of the
four hydrogels were measured (only for pure-water gels) by the
dropping-ball method at various gelator concentrations. A glass
ball weighing 205.50 mg was placed on 0.5 mL of hydrogel (at the
respective MGC) in a test tube (15ꢂ100 mm). The test tube was
then immersed in an oil bath placed on a magnetic stirrer to
medium was replaced with 100 mg of MTT per well and kept for
4 h at 378C. To dissolve the formazan produced by mitochondrial
reductase from live cells, DMSO (100 mL/well) was added and the
medium incubated for 30 min at room temperature. The colour in-
tensity of the formazan solution, which is positively correlated to
the cell viability, was measured with a multiplate ELISA reader at
570 nm (Varioskan Flash Elisa Reader, Thermo Fisher). The percent-
age of live cells in salt-treated samples was calculated by consider-
ing the DMEM-treated sample as 100%. This experiments were
done in triplicate.
Chem. Eur. J. 2016, 22, 1 – 12
www.chemeurj.org
9
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
&
&
These are not the final page numbers! ÞÞ

Full Paper
PGE assay: Production of PGE was estimated according to a pub-
[14] Z. Yang, K. Xu, L. Wang, H. Gu, H. Wei, M. Zhang, B. Xu, Chem. Commun.
2
2
[67]
2
005, 4414–4416.
[15] R. Lin, A. G. Cheetham, P. Zhang, Y. Lin, H. Cui, Chem. Commun. 2013,
9, 4968–4970.
lished protocol by using six-well plates and the RAW 264.7 cell
6
line. Approximately 1ꢂ10 cells/well were seeded in four wells of
4
six-well plates for 24 h. One of the wells was treated with 2 mL of
[
[
[
16] H. Wang, Z. Yang, Soft Matter 2012, 8, 2344–2347.
17] R. V. Ulijn, A. M. Smith, Chem. Soc. Rev. 2008, 37, 664–675.
18] P. K. Vemula, U. Aslam, V. A. Mallia, G. John, Chem. Mater. 2007, 19, 138–
DMEM alone as control experiment, and the remaining three wells
À1
were treated with 1 mgmL
1
lipopolysaccharide (LPS) and
À1
00 ngmL interferon gamma (IFN-g); two of these LPS/IFN-g-
140.
treated wells were treated with 0.3 mm IND and IND·LEU·AMN, re-
spectively, in such a way that the total medium (DMEM) volume in
each well was 2 mL, and all the wells were further incubated for
[
[
19] J. W. Steed, Chem. Soc. Rev. 2010, 39, 3686–3699.
20] P. Terech, R. G. Weiss, Chem. Rev. 1997, 97, 3133–3160.
[21] D. J. Abdallah, R. G. Weiss, Adv. Mater. 2000, 12, 1237–1247.
[22] J. A. Foster, M. M. Piepenbrock, G. O. Lloyd, N. Clarke, J. A. K. Howard,
J. W. Steed, Nat. Chem. 2010, 2, 1037–1043.
2
4 h. The culture medium was diluted to 1:100 or 1:500 for meas-
uring PGE2 with Prostaglandin E2 EIA Kit - Monoclonal (Cayman
Chemicals, Ann Arbor, MI). This experiment was done in triplicate.
[
[
[
23] J. J. D. de Jong, L. N. Lucas, R. M. Kellogg, J. H. van Esch, B. L. Feringa,
Science 2004, 304, 278–281.
24] A. Wynne, M. Whitefield, A. J. Dixon, S. Anderson, J. Dermatol. Treat.
Cell imaging: Having successfully established the biocompatibility
of the hydrogel, it was applied in cell imaging. RAW 264.7 cells
were cultured by using DMEM supplemented with 10% FBS and
2
002, 13, 61–66.
25] S. S. Babu, V. K. Praveen, A. Ajayaghosh, Chem. Rev. 2014, 114, 1973–
129.
1
3
% penicillin/streptomycin on ethanol-etched cover slips kept in
5 mm tissue-culture dishes. These were kept in a humidified incu-
2
[26] A. P. Piccionello, A. Guarcello, A. Calabrese, I. Pibiri, A. Pace, S. Buscemia,
Org. Biomol. Chem. 2012, 10, 3044–3052.
[27] B. Escuder, F. Rodrguez-Llansola, J. F. Miravet, New J. Chem. 2010, 34,
bator at 378C overnight. Then the medium was removed and fresh
hydrogelator-containing medium was added (5 mm). The medium
was incubated for 30 min. Then, the medium was removed and
fresh medium was added. The cells were mounted on a confocal
Petri dish, and a Carl Zeiss Axio Observer Z1 microscope fitted with
a Hamamatsu Orca-Flash4.0 digital camera was used to acquire the
images.
1
044–1054.
28] E. Carretti, E. Fratini, D. Berti, L. Dei, P. Baglioni, Angew. Chem. Int. Ed.
009, 48, 8966–8969; Angew. Chem. 2009, 121, 9128–9131.
29] R. N. Shah, N. A. Shah, M. M. D. R. Lim, C. Hsieh, G. Nuber, S. I. Stupp,
Proc. Natl. Acad. Sci. USA 2010, 107, 3293–3298.
[
[
[
[
[
[
[
2
30] K. J. C. van Bommel, A. Friggeri, S. Shinkai, Angew. Chem. Int. Ed. 2003,
4
2, 980–999; Angew. Chem. 2003, 115, 1010–1030.
31] Z. A. C. Schnepp, R. Gonzalez-McQuire, S. Mann, Adv. Mater. 2006, 18,
1869–1872.
Acknowledgements
32] Z. Yang, G. Liang, M. Ma, A. S. Abbah, W. W. Lu, B. Xu, Chem. Commun.
2
007, 843–845.
P.D. thanks DBT, DST and IACS New Delhi for financial support
33] Q. Wang, Z. Yang, X. Zhang, X. Xiao, C. K. Chang, B. Xu, Angew. Chem.
Int. Ed. 2007, 46, 4285–4289; Angew. Chem. 2007, 119, 4363–4367.
34] S. Kiyonaka, K. Sada, I. Yoshimura, S. Shinkai, N. Kato, I. Hamachi, Nat.
Mater. 2004, 3, 58–64.
(CEIB project BT/01/CEIB/V/13). R.R. thanks CSIR, New Delhi, for
SRF (CSIR grant no. 09/080(0802)/2012-EMR-I). SXRD data were
collected at the DBT-funded X-ray diffraction facility under the
CEIB program in the Department of Organic Chemistry, IACS,
Kolkata. We thank Mahesh Agarwal of Department of Biologi-
cal Chemistry, IACS for fluorescence microscopy images; Biplab
Kumar Patra of Department of Materials Science, IACS for col-
lecting the PL data; and Dr. Ahmad Husain and Dr. Suman
Bhattacharya of Department of Organic Chemistry for crystallo-
graphic discussions.
[
[
35] K. Y. Lee, D. J. Mooney, Chem. Rev. 2001, 101, 1869–1879.
36] S. M. Standley, D. J. Toft, H. Cheng, S. Soukasene, J. Chen, S. M. Raja, V.
Band, H. Band, V. L. Cryns, S. I. Stupp, Cancer Res. 2010, 70, 3020–3026.
37] F. Zhao, B. A. Heesters, I. Chiu, Y. Gao, J. Shi, N. Zhou, M. C. Carroll, B.
Xu, Org. Biomol. Chem. 2014, 12, 6816–6819.
[
[
[
38] V. Jayawarna, M. Ali, T. A. Jowitt, A. F. Miller, A. Saiani, J. E. Gough, R. V.
Ulijn, Adv. Mater. 2006, 18, 611–614.
39] Y. Lan, M. G. Corradini, X. Liu, T. E. May, F. Borondics, R. G. Weiss, M. A.
Rogers, Langmuir 2014, 30, 14128–14142.
[
[
40] M. Suzuki, K. Hanabusa, Chem. Soc. Rev. 2009, 38, 967–975.
41] L. Meazza, J. A. Foster, K. Fucke, P. Metrangolo, G. Resnati, J. W. Steed,
Nat. Chem. 2013, 5, 42–47.
42] O. Lebel, M. Perron, T. Maris, S. F. Zalzal, A. Nanci, J. D. Wuest, Chem.
Mater. 2006, 18, 3616–3626.
Keywords: drug delivery · gels · hydrogen bonds · imaging
agents · supramolecular chemistry
[
[
43] M. L. Muro-Small, J. Chen, A. J. McNeil, Langmuir 2011, 27, 13248–
[1] F. Zhao, M. L. Ma, B. Xu, Chem. Soc. Rev. 2009, 38, 883–891.
[2] X. Du, J. Zhou, J. Shi, B. Xu, Chem. Rev. 2015, 115, 13165–13307.
[3] E. Carretti, L. Dei, R. G. Weiss, Soft Matter 2005, 1, 17–22.
[4] L. Yu, J. Ding, Chem. Soc. Rev. 2008, 37, 1473–1481.
[5] V. Gujrati, S. Kim, S.-H. Kim, J. J. Min, H. E. Choy, S. C. Kim, S. Jon, ACS
Nano 2014, 8, 1525–1537.
13253.
[
[
[
44] M. George, R. G. Weiss, Acc. Chem. Res. 2006, 39, 489–497.
45] P. Dastidar, Chem. Soc. Rev. 2008, 37, 2699–2715.
46] T. K. Adalder, U. K. Das, J. Majumder, R. Roy, P. Dastidar, J. Indian Inst. Sci.
2
014, 94:1, 9–24.
[
47] U. K. Das, T. K. Adalder, J. Majumder, R. Roy, P. Dastidar in Hydrogen
Bonded Supramolecular Materials (Eds.: Z.-T. Li, L.-Z. Wu) 2015, , Chap-
ter 4, pp. 101–131.
[
[
[
6] B. Lukanov, A. Firoozabadi, Langmuir 2016, 32, 3100–3109.
7] B. S. Bolu, E. M. Gecici, R. Sanyal, Mol. Pharm. 2016, 13, 1482–1490.
8] Z. Zhang, X. Zhang, X. Xu, Y. Li, Y. Li, D. Zhong, Y. He, Z. Gu, Adv. Funct.
Mater. 2015, 25, 5250–5260.
[48] G. R. Desiraju, Angew. Chem. Int. Ed. Engl. 1995, 34, 2311–2327; Angew.
Chem. 1995, 107, 2541–2558.
[
9] R. Langer, Nature 1998, 392, 5–10.
[
[
[
[
10] K. E. Uhrich, S. M. Cannizzaro, R. S. Langer, K. M. Shakesheff, Chem. Rev.
999, 99, 3181–3198.
11] M. J. Webber, J. B. Matson, V. K. Tamboli, S. I. Stupp, Biomaterials 2012,
3, 6823–6832.
12] J. Li, Y. Gao, Y. Kuang, J. Shi, X. Du, J. Zhou, H. Wang, Z. Yang, B. Xu, J.
Am. Chem. Soc. 2013, 135, 9907–9914.
[49] G. R. Desiraju, J. J. Vittal, A. Ramanan, Crystal Engineering–A Textbook,
World Scientific, Singapore, 2011.
[50] P. Sahoo, R. Sankolli, H.-Y. Lee, S. R. Raghavan, P. Dastidar, Chem. Eur. J.
2012, 18, 8057–8063.
[51] T. K. Adalder, D. P. Kumar, P. Dastidar, Cryst. Growth Des. 2014, 14, 11–
14.
[52] D. R. Trivedi, A. Ballabh, P. Dastidar, B. Ganguly, Chem. Eur. J. 2004, 10,
5311–5322.
1
3
13] H. Wang, J. Wei, C. Yang, H. Zhao, D. Li, Z. Yin, Z. Yang, Biomaterials
2012, 33, 5848–5853.
&
&
Chem. Eur. J. 2016, 22, 1 – 12
www.chemeurj.org
10
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ÝÝ These are not the final page numbers!

Full Paper
[
53] J. Majumder, J. Deb, M. R. Das, S. S. Jana, P. Dastidar, Chem. Commun.
[64] S. R. Raghavan, B. H. Cipriano, R. G. Weiss, P. Terech, Molecular Gels: Ma-
terials with Self-Assembled Fibrillar Networks, 2005, Springer, Dordrecht,
Chapter 8, pp. 233–244.
[65] J. H. Jung, S. Shinkai, T. Shimizu, Chem. Eur. J. 2002, 8, 2684–2690.
[66] Q.-S. Wang, Y. Xiang, Y.-L. Cui, K.-M. Lin, X.-F. Zhang, PLoS One 2012, 7,
e34122.
2014, 50, 1671–1674.
[
[
54] R. Roy, J. Deb, S. S. Jana, P. Dastidar, Chem. Asian J. 2014, 9, 3196–3206.
55] R. Roy, J. Deb, S. S. Jana, P. Dastidar, Chem. Eur. J. 2014, 20, 15320–
15324.
[
[
56] L. A. Estroff, A. D. Hamilton, Chem. Rev. 2004, 104, 1201–1217.
57] A. Das, S. Ghosh, Angew. Chem. Int. Ed. 2014, 53, 1092–1097; Angew.
Chem. 2014, 126, 1110–1115.
[67] E. Heiss, C. Herhaus, K. Klimo, B. Bartsch, C. Gerhauser, J. Biol. Chem.
2001, 276, 32008–32015.
[
58] A. Heeres, C. van der Pol, M. Stuart, A. Friggeri, B. L. Feringa, J. van Esch,
[68] Y. Hong, J. W. Y. Lam, B. Z. Tang, Chem. Soc. Rev. 2011, 40, 5361–5388.
[69] M. R. Molla, S. Ghosh, Chem. Eur. J. 2012, 18, 1290–1294.
[70] R. J. Anand, S. C. Gribar, J. Li, J. W. Kohler, M. F. Branca, T. Dubowski,
C. P. Sodhi, D. J. Hackam, J. Leukocyte Biol. 2007, 82, 1257–1265.
J. Am. Chem. Soc. 2003, 125, 14252–14253.
[
[
[
[
59] J. Majumder, P. Dastidar, Chem. Eur. J. 2015 in press.
60] M. Frenette, G. Cosa, T. Fri sˇ cˇ ic, CrystEngComm 2013, 15, 5100–5106.
61] K. Y. Zhang, K. K.-W. Lo, Inorg. Chem. 2009, 48, 6011–6025.
62] L. R. Palmera, T. Chen, A. M. I. Lam, D. B. Fenske, K. F. Wong, I. MacLa-
chlan, P. R. Cullis, Biochim Biophys. Acta 2003, 1611, 204–216.
63] X. Li, Y. Kuang, H. Lin, Y. Gao, J. Shi, B. Xu, Angew. Chem. Int. Ed. 2011,
[
Received: May 21, 2016
50, 9365–9369; Angew. Chem. 2011, 123, 9537–9541.
Published online on && &&, 0000
Chem. Eur. J. 2016, 22, 1 – 12
www.chemeurj.org
11
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
&
&
These are not the final page numbers! ÞÞ

Full Paper
FULL PAPER
Smart gelators: Organic salts derived
from peptide conjugates of the non-
steroidal anti-inflammatory drug indo-
methacin (IND) and the antiviral drug
amantadine (AMN) exhibit remarkable
gelation ability that makes them suita-
ble for multidrug-self-delivery, cell imag-
ing and other materials applications
&
Imaging Agents
R. Roy, P. Dastidar*
& – &&
&
Multidrug-Containing, Salt-Based,
Injectable Supramolecular Gels for
Self-Delivery, Cell Imaging and Other
Materials Applications
(
see figure; LEU=l-leucine).
&
&
Chem. Eur. J. 2016, 22, 1 – 12
www.chemeurj.org
12
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ÝÝ These are not the final page numbers!