Orotic acid as a useful supramolecular synthon for the fabrication of an OPV based hydrogel: Stoichiometry dependent injectable behavior

Article abstract of DOI:10.1039/c5cc01002k

A facile hydrogelation of a p-pyridylenevinylene derivative (PV) bearing oxyethylene chains in the presence of orotic acid (OA) occurs via various non-covalent interactions. Depending on the PV:OA molar ratio, the hydrogel shows vesicle to either cluster-

Full text of DOI:10.1039/c5cc01002k

ChemComm
View Article Online
View Journal | View Issue
COMMUNICATION
Orotic acid as a useful supramolecular synthon
for the fabrication of an OPV based hydrogel:
stoichiometry dependent injectable behavior†
Cite this: Chem. Commun., 2015,
51, 6765
Received 3rd February 2015,
Accepted 10th March 2015
Subham Bhattacharjeea and Santanu Bhattacharya*ab
DOI: 10.1039/c5cc01002k
www.rsc.org/chemcomm
A facile hydrogelation of a p-pyridylenevinylene derivative (PV) gels possessing various fascinating properties, such as stimuli
bearing oxyethylene chains in the presence of orotic acid (OA) occurs responsiveness, self-healing, sensing, catalysis, and white light
via various non-covalent interactions. Depending on the PV : OA molar emission, has emerged as a rapidly expanding area of research for
ratio, the hydrogel shows vesicle to either cluster-type aggregate or their potential applications.5 Although majority of supramolecular
fiber transformation. Visual color tuning, stimuli-responsiveness and gels are formed through entanglement of fibrous networks, a
injectable properties of the hydrogel are also observed.
particularly intriguing class of physical gels include vesicle gels.6
Such vesicular gels might be promising in biomedical applications.
In this communication, an orotic acid (OA) induced two-
component hydrogel of a water-soluble pyridylenevinylene derivative
(PV) is described (Fig. 1a). It is also possible to tune the macroscopic
injectable property of the hydrogel by merely changing the stoichio-
metry of the two components, which is hitherto unknown. Detailed
studies suggest that OA triggers hydrogelation of PV by a synergistic
effect of salt formation (electrostatic), complementary H-bonding
and p–p stacking interactions. At lower concentration, the 1 : 1
Orotic acid (OA) is an intermediate metabolite in the synthetic
pathway of pyrimidine nucleotides.1a An assembly of OA leads
to acidemia and orotic aciduria. At the cellular level, this may
be a symptom of urea cycle disorder.1a Therefore whether OA
is assembled in water by itself or in the presence of other
molecules may be of considerable interest. The chemical structure
of OA encompasses a carboxylic acid group in the para-position
relative to the CO–NH–CO group of the pyrimidine skeleton.
The –COOH group may form a salt with a suitable base while
the CO–NH–CO group could form complementary H-bonds with
appropriate molecular scaffolds.1b These structural parameters
suggest that in principle it could act as a powerful supramolecular
synthon for the design of a robust physical gel in conjunction with
suitable entities. Although there have been several reports on
two-component gels that utilize salt type2 or complementary
H-bonding interactions3 as the primary driving force, to date,
reports on supramolecular gels comprising OA are rare. Only
recently Nandi and co-workers have demonstrated stimuli-
responsive two-component hydrogelation of a melamine–Zn2+–
orotate complex.3b
Oligo ( p-phenylenevinylene) (OPV) based self-assemblies
including gels are widely studied for their potential applica-
tions in various fields as diverse as artificial light harvesting
materials, superhydrophobic coating, supramolecular electro-
nics, liquid crystals, etc.4 Recently the design of supramolecular
Fig. 1 (a) Molecular structures of the PV, OA and 1 : 1 PV : OA gelators.
(b) Yellow-to-red color change in the solution of PV as a result of protonation
by OA and photographs of the 1 : 1 and 1 : 2 PV : OA hydrogels. (c) A schematic
of the possible aggregation of the 1 : 1 PV : OA gelator yielding the 1-D primary
structure in water and further aggregation of the latter into vesicles. (d) A
schematic model of the thixotropic mechanism of the hydrogel through
complementary H-bonding interactions among the vesicles.
a Department of Organic Chemistry, Indian Institute of Science, Bangalore, India.
E-mail: sb@orgchem.iisc.ernet.in; Fax: +91-80-23600529; Tel: +91-80-22932664
b Jawaharlal Nehru Centre for Advanced Scientific Research, Bangalore, India
† Electronic supplementary information (ESI) available: Complete experimental
procedures, compound characterization and Fig. S1–S13. See DOI: 10.1039/
c5cc01002k
This journal is ©The Royal Society of Chemistry 2015
Chem. Commun., 2015, 51, 6765--6768 | 6765

View Article Online
Communication
ChemComm
PV : OA gel produced vesicles, which upon an increase in concen- 2 equiv. of OA, suggesting the completion of protonation of PV
tration led to the formation of a hydrogel via ‘fusion’ of the vesicles (Fig. S3a, ESI†). The 1 : 2 stoichiometry of the PV : OA complex
through complementary H-bonding interactions. In contrast, a was also ascertained from Job plot data analysis (Fig. S3b and c,
fibrous morphology of the 1 : 2 PV : OA gel was observed that has ESI†). The distinct features in the emission spectral properties
probably formed through the fusion of vesicles upon increasing included quenching of the fluorescence of the solution of PV in
the concentration of the gelator. The hydrogel also displayed water along with a significant red-shift in the emission maximum
multi-stimuli responsive properties including molecular recogni- of around B81 nm upon addition of 2 equiv. OA (Fig. 2b).
tion of melamine.
Temperature-dependent fluorescence spectroscopy of the 1 : 2
PV is soluble in water and does not form a gel on its own. PV : OA gel was further carried out at the pre-gelation concen-
However, it has two terminal p-pyridyl N-atoms, suitable to form tration ([PV] = 0.04 mM). At 10 1C, there was a single emission
an organic salt-type interaction with appropriate acidic scaffolds. maximum at 568 nm with a shoulder at 496 nm. With an increase
To verify our hypothesis as discussed so far, we have mixed OA in temperature, the emission maximum at 568 nm, a character-
with a solution of PV in water. Indeed, PV could form a salt with istic of the ‘aggregated’ species, gradually diminished in intensity
OA by simple acid–base interactions when a mixture of both in a with a concomitant increase of the shoulder band, suggesting an
certain molar ratio was heated at 70–75 1C in water followed by a apparent ‘breakdown’ of the aggregates (Fig. S3d, ESI†).
brief bath sonication (Fig. 1b). The protonation of PV by OA was
X-ray diffraction (XRD) studies of the freeze-dried gel of 1 : 1
indicated by a noticeable change in color from yellow-to-red of the and 1 : 2 PV : OA showed a broad first order Bragg reflection
mixture (Fig. 1b). As revealed from NMR, protonation of PV peak at 2y = 4.25 and 3.011 respectively (Fig. S4a, ESI†). The
caused a large downfield shift of Ha and Hb protons, from 8.12 corresponding repetitive distances, i.e., 2.08 and 2.93 nm, were
to 8.65 and 6.96 to 8.10 ppm respectively (Fig. S1, ESI†).
found to be in close agreement with the calculated lengths of a
Interestingly, the hot clear solution of 1 : 1 PV : OA transformed single 1 : 1 and 1 : 2 PV : OA unit along the p-surface of PV
into a robust hydrogel instantaneously upon cooling to room respectively (2.36 and 3.12 nm respectively) (Fig. S4c and d,
temperature with a critical gelator concentration (CGC) of [PV] = ESI†). This observation accounts for the linear growth of the
[OA] = 16.4 mM (Fig. 1b and Table S1, ESI†). Notably, the 1 : 1 gelator units through complementary H-bonding interactions
PV : OA gel remained highly stable over several months. The visual as demonstrated in Fig. 1c and Fig. S5 (ESI†). Furthermore, a
red color of the 1 : 1 PV : OA gel changed to orange color along with weak reflection peak in the wide angle region at 2y = 22.941
reduction in the CGC value to [PV] = 10 mM upon further addition (B0.39 nm) for both the 1 : 1 and 1 : 2 PV : OA xerogels indicates
of the second equivalent of OA to the former (Fig. 1b and Table S1, the presence of p–p stacking interactions among the gelators.
ESI†). Differential scanning calorimetry studies of the 1 : 1 and 1 : 2
Morphological investigations of the 1 : 1 PV : OA ([PV] = 0.1 mM)
PV : OA gels ([PV] = 30 mM) showed a gel melting temperature of gel using atomic force microscopy (AFM) showed the existence of
around 56.5 1C (DH = 5.1 kcal molꢀ1; heating cycle) and 54 1C vesicle-like morphology (diameter B100–250 nm; Fig. 3a and
(DH = 3 kcal molꢀ1; heating cycle) respectively (Fig. S2, ESI†).
Fig. S6a–c, ESI†). Transmission electron microscopy (TEM) of the
An equimolar mixture of either benzoic acid or barbituric solution ([PV] = 0.05 mM) of the same also displayed the presence
acid or tartaric acid with PV, however, did not form gel under of spherical aggregates with an average wall thickness of B14.4 nm
identical conditions. This demonstrates the crucial role of OA (repetitive distances i.e., 2.08 nm ꢁ B7), indicating the formation
towards gelation. The use of the p-pyridylenevinylene derivative of multilayer vesicles (Fig. 3b). Furthermore, the outer periphery
bearing n-butyl chains (BPV; see ESI†) instead of PV only of these aggregates showed intense fluorescence more than in
resulted in precipitation with OA irrespective of the molar ratio the inner portion of the spheres under fluorescence microscopy,
in water indicating the importance of the oxyethylene chain in suggesting the vesicular nature of the aggregates (Fig. S6d and e,
gelation of the PV : OA complexes in water.
ESI†).7 DLS studies showed aggregates with an average hydro-
In order to gain insights into the self-assemblies, UV/Vis dynamic diameter (Dh) of 254 ꢂ 7 nm in the solution of the gelator
absorption spectra were recorded at different molar ratios of PV ([PV] = 0.1 mM) (Fig. S7, ESI†). However, performing AFM of the
and OA. The lmax of PV showed a large bathochromic shift of 1 : 1 PV : OA gel at a relatively higher concentration ([PV] = 2 mM)
around B15 nm upon protonation by OA (Fig. 2a). The plot of revealed the presence of cluster-type aggregates (Fig. 3c and Fig. S6f,
absorbance vs. equivalence of OA showed a break point near ESI†). An analysis of such aggregates suggested that fusion of the
individual vesicles may have created such cluster-type structures.
A schematic model of self-assembly is proposed based on the XRD
and morphological studies (Fig. 1d). Indeed vesicle formation by
similar conjugated scaffolds bearing oxyethylene chains in aqueous
medium has also been reported.7a,8
The 1 : 2 PV : OA gel ([PV] = 0.1 mM) also showed vesicular
morphology (Fig. 3d and e). Interestingly, such vesicular aggregates,
in some cases, fused together to yield fibrous morphology upon
further increasing the concentration of the gelator to [PV] = 0.3 mM
(Fig. S8a and S9, ESI†). Moreover, these fibrous aggregates revealed
of PV : OA at different molar ratios at 25 1C ([PV] = 0.04 mM) respectively. a strong birefringence when viewed under POM, suggesting an
Fig. 2 (a) UV/Vis absorption and (b) fluorescence spectra (lex = 370 nm)
6766 | Chem. Commun., 2015, 51, 6765--6768
This journal is ©The Royal Society of Chemistry 2015

View Article Online
ChemComm
Communication
Interestingly, shaking or vortexing of the 1 : 1 PV : OA gel led to
the formation of a viscous solution, which on resting for a few
seconds again transformed into a stable gel, indicating thixotropic
behavior (Fig. 4b).10 In contrast, the 1 : 2 PV : OA gel was quite
‘brittle’ in nature (Fig. S12, ESI†). Further addition of OA (43 equiv.
relative to PV) into a preformed 1 : 1 or 1 : 2 PV : OA gel also induced
disruption of the gel (Fig. 4d). OA is known to form complementary
H-bonds with melamine.1b Accordingly, melamine was added
gradually to a preformed 1 : 1 or 1 : 2 PV : OA gel. Only half
equivalent of it relative to OA led to complete collapse of the self-
assembly into an insoluble precipitate (Fig. 4c). We believe that the
association of melamine with CO–NH–CO groups of OA of the
gelator prevented efficient 1-D primary structure formation, which
eventually resulted in the disruption of the gel.
Finally, both the 1 : 1 and 1 : 2 PV : OA gels were subjected to
pH variation. The addition of a few drops of dilute HCl solution
on the top of the preformed gel resulted in the formation of a
clear solution (pH 2) instantaneously (Fig. 4e). HCl being a
stronger acid than OA probably replaced the orotate unit from
the gelator, thereby rendering the system water-soluble. The gels
also transformed into an inhomogeneous solution (pH 9) when
few drops of saturated NaHCO3 solution were added to the top of
the preformed gel (Fig. 4f). Addition of NaHCO3 solution prob-
ably deprotonated the pyridyl unit of PV in the gelator.
The hydrogel was further characterized rheologically. Amplitude
sweep experiments suggested that the 1 : 1 PV : OA gel, although less
viscoelastic than the corresponding 1 : 2 PV : OA gel, could tolerate
significantly larger strain (yield strain = 22%) than the latter (yield
strain = 1.84%) (Fig. 5a). The thixotropic nature of the 1 : 1 PV : OA
gel was further probed using a hysteresis loop test, in which the gel
sample was subjected to consecutive low–high strain separated by
enough time to ensure the complete gel-to-sol (G00 4 G0) and sol-to-
gel (G0 4 G00) transitions (Fig. 5b).10b,c Interestingly the sol, which
was obtained under high strain, recovered into the gel state within a
few seconds after the cessation of the high strain, thereby confirm-
ing the thixotropic behavior.10b,c
Indeed, an attempt to destroy the drop-coated gel by a tip-head
was unsuccessful, further suggesting the thixotropic nature of the
gel (see the attached movie in the ESI†). It is noteworthy that OA is
sparingly soluble in water while the oxyethylene chains in PV drive
the solubilization of the PV : OA gelator in water. Therefore, the
1 : 2 PV : OA complex has a lower overall solubility than that of
the 1 : 1 PV : OA complex in water. This is also reflected from the
Fig. 3 AFM and TEM images of the vesicles of (a and b) 1 : 1 PV : OA and
(d and e) 1 : 2 PV : OA gelators respectively ([PV] = 0.1 mM). (c) AFM image
of the cluster-type aggregate of the 1 : 1 PV : OA complex at [PV] = 0.3 mM.
(f) POM image showing the dense fibrous networks of the 1 : 2 PV : OA gel
([PV] = 11 mM).
anisotropic packing of the gelators in the gel matrix (Fig. 3f and
Fig. S8d, ESI†).4a A similar vesicle to fiber transformation upon
increasing concentration has also been reported.6f–h
Additional experiments were performed to gain further evi-
dence of vesicle formation.9 In particular, a mixture of the gelator
solution ([PV] = [OA] = 8.2 mM) and a hydrophilic dye, methylene
blue (MB; 0.8 mM), was co-sonicated for B20 min at 25 1C. The
resultant suspension was centrifuged that allowed sedimentation
of the dye encapsulated vesicular aggregates. The supernatant was
removed and the residue was redispersed in 1 mL of water. The
same procedure was repeated twice to remove any unencapsulated
dye. The residue thus obtained retained significantly dark blue
color (Fig. S10a, ESI†), suggesting an encapsulation of the dye, MB,
inside the vesicular aggregates with an encapsulation efficiency of
B6.1% (Fig. S10b, ESI†).
We also investigated the response of the present gel system
in the presence of various external stimuli. Variable tempera-
ture 1H NMR spectra of the 1 : 1 PV : OA gel in D2O showed
1
gradual evolution of the H-NMR signals from the NMR-silent
condensed state as the gel was heated gradually up to 70 1C,
confirming the thermo-reversibility of the gel–sol transition
(Fig. 4a and Fig. S11, ESI†).6g
Fig. 5 (a) Oscillatory amplitude sweep test of the PV : OA gelator at two
different molar ratios. The inset in (a) shows the injectability of the 1 : 1
PV : OA gel. (b) Thixotropic loop test of the 1 : 1 PV : OA gel ([PV] = 25 mM
for all the cases).
Fig. 4 Responses of the 1 : 1 PV : OA hydrogel in the presence of different
external stimuli ([PV] = 20 mM).
This journal is ©The Royal Society of Chemistry 2015
Chem. Commun., 2015, 51, 6765--6768 | 6767

View Article Online
Communication
ChemComm
(e) B. Adhikari, A. Shah and H.-B. Kraatz, J. Mater. Chem. B, 2014,
2, 4802; ( f ) G. M. Peters, L. P. Skala, T. N. Plank, B. J. Hyman,
G. N. M. Reddy, A. Marsh, S. P. Brown and J. T. Davis, J. Am. Chem.
Soc., 2014, 136, 12596; (g) M. C. Chen, B. J. Cafferty, I. Mamajanov,
comparatively low CGC value of the 1 : 2 PV : OA gel (Table S1,
ESI†). Due to the lower solubility of the 1 : 2 PV : OA gelator, upon
agitation, its entangled fibrous networks probably have collapsed/
broken, which could not ‘heal’ to revert back to the native state
(Fig. S12, ESI†). This fact may account for the brittle nature of the
1 : 2 PV : OA gel despite the presence of CO–NH–CO groups at the
surface of the fibers. In contrast, several reversible H-bonding
interactions among the CO–NH–CO groups at the surface of the
vesicles, which are quite soluble in water, presumably regulate the
thixotropic behavior of the 1 : 1 PV : OA gel (Fig. 1d).
´
I. Gallego, J. Khanam, R. Krishnamurthy and N. V. Hud, J. Am. Chem.
Soc., 2014, 136, 5640; (h) Y. Zhang, Z. Yang, F. Yuan, H. Gu, P. Gao
and B. Xu, J. Am. Chem. Soc., 2004, 126, 15028.
4 (a) S. J. George, A. Ajayaghosh, P. Jonkheijm, A. P. H. J. Schenning and
E. W. Meijer, Angew. Chem., Int. Ed., 2004, 43, 3422; (b) E. W. Meijer and
A. P. H. J. Schenning, Chem. Commun., 2005, 3245; (c) F. J. M. Hoeben,
P. Jonkheijm, E. W. Meijer and A. P. H. J. Schenning, Chem. Rev., 2005,
105, 1491; (d) S. Srinivasan, V. K. Praveen, R. Philip and A. Ajayaghosh,
Angew. Chem., Int. Ed., 2008, 47, 5750; (e) S. Bhattacharya and S. K.
Samanta, Chem. – Eur. J., 2012, 18, 16632; ( f ) S. K. Samanta, A. Pal and
S. Bhattacharya, Langmuir, 2009, 25, 8567; (g) S. K. Samanta and
S. Bhattacharya, J. Mater. Chem., 2012, 22, 25277; (h) S. Bhattacharjee,
S. K. Samanta, P. Moitra, K. Pramoda, R. Kumar, S. Bhattacharya and
C. N. R. Rao, Chem. – Eur. J., 2015, DOI: 10.1002/chem.201405522;
(i) F. J. M. Hoeben, A. P. H. J. Schenning and E. W. Meijer,
ChemPhysChem, 2005, 6, 2337; ( j) F. J. M. Hoeben, M. Wolffs,
The thixotropic nature of the 1 : 1 PV : OA gel enables it to be
injected through a narrow needle of a syringe by applying an
amiable force to fabricate different alphabetical letters (inset in
Fig. 5a).6i The injected material turned into the gel state almost
instantly, which is in accord with the hysteresis loop test data.
In summary, a synergistic combination of electrostatic, comple-
mentary H-bonding and p–p stacking interactions led to the
formation of a robust hydrogel network. Detailed investigations
revealed the formation of vesicular aggregates from the 1 : 1 and
1 : 2 PV : OA systems, which fused into cluster-type and fibrous
aggregates, respectively, upon increasing the concentration of the
two-component gelator complexes, resulting in the gel formation.
The stoichiometry of the PV : OA system was found to be crucial for
the macroscopic thixotropic behavior. The optimum solubility and
stability of the vesicles of the 1 : 1 PV : OA gelators in water allows
fusion of the former in a reversible fashion through complementary
H-bonding interactions more effectively, which is manifested in its
thixotropic behavior. This property makes the 1 : 1 PV : OA hydrogel
injectable, further adding to its practical value. In contrast, the
fibers of the 1 : 2 PV : OA gelators being less soluble in water tend to
phase separate upon agitation, causing damage to the existing gel
and thus fail to show injectable behavior. Furthermore, the OA unit
of the hydrogel can recognize its complementary melamine by
rapid disruption of the gel. The hydrogel also transforms into
solution upon variation of the pH of the system. In a nutshell,
we have described, for the first time, the utilization of a readily
available, biocompatible orotic acid, OA, as a supramolecular
synthon for the fabrication of a smart hydrogel with stoichio-
metry dependent injectable behavior.
`
J. Zhang, S. De Feyter, P. Leclere, A. P. H. J. Schenning and E. W.
Meijer, J. Am. Chem. Soc., 2007, 129, 9819; (k) J. F. Hulvat, M. Sofos,
K. Tajima and S. I. Stupp, J. Am. Chem. Soc., 2005, 127, 366; (l) S. K.
Samanta and S. Bhattacharya, Chem. Commun., 2013, 49, 1425.
5 (a) D. K. Kumar and J. W. Steed, Chem. Soc. Rev., 2014, 43, 2080;
(b) S. S. Babu, V. K. Praveen and A. Ajayaghosh, Chem. Rev., 2014,
114, 1973; (c) G. O. Lloyd and J. W. Steed, Nat. Chem., 2009, 1, 437;
(d) J. M. J. Paulusse, D. J. M. van Beek and R. P. Sijbesma, J. Am. Chem.
Soc., 2007, 129, 2392; (e) R. G. Weiss, J. Am. Chem. Soc., 2014, 136, 7519;
( f ) P. Duan, H. Cao, L. Zhang and M. Liu, Soft Matter, 2014, 10, 5428;
(g) V. K. Praveen, C. Ranjith and N. Armaroli, Angew. Chem., Int. Ed.,
2014, 53, 365; (h) X. Yang, G. Zhang and D. Zhang, J. Mater. Chem.,
2012, 22, 38; (i) J. T. van Herpt, M. C. A. Stuart, W. R. Browne and
B. L. Feringa, Chem. – Eur. J., 2014, 20, 3077; ( j) M. J. M. Munoz and
´
G. Fernandez, Chem. Sci., 2012, 3, 1395; (k) B. N. Ghosh, S. Bhowmik,
P. Mal and K. Rissanen, Chem. Commun., 2014, 50, 734; (l) J. K. Sahoo,
S. K. M. Nalluri, N. Javid, H. Webb and R. V. Ulijn, Chem. Commun.,
2014, 50, 5462; (m) J. Li, I. Cvrtila, M. C. Delsuc, E. Otten and S. Otto,
Chem. – Eur. J., 2014, 20, 15709; (n) J. Seo, J. W. Chung, J. E. Kwon and
S. Y. Park, Chem. Sci., 2014, 5, 4845; (o) F. R. Llansola, J. F. Miravet and
B. Escuder, Chem. Commun., 2009, 7303; (p) W. Li, I. Park, S.-K. Kang
and M. Lee, Chem. Commun., 2012, 48, 8796; (q) V. Stepanenko,
X.-Q. Li, J. Gershberg and F. Wu¨rthner, Chem. – Eur. J., 2013, 19,
4176; (r) E. Krieg, E. Shirman, H. Weissman, E. Shimoni, S. G. Wolf,
I. Pinkas and B. Rybtchinski, J. Am. Chem. Soc., 2009, 131, 14365;
´
´
(s) F. Aparicio, F. Garcıa and L. Sanchez, Chem. – Eur. J., 2013, 19, 3239.
6 (a) F. M. Menger and A. V. Peresypkin, J. Am. Chem. Soc., 2003, 125, 5340;
(b) V. S. Balachandran, S. R. Jadhav, P. Pradhan, S. De Carlo and G. John,
Angew. Chem., Int. Ed., 2010, 49, 9509; (c) C. B. Minkenberg, W. E.
Hendriksen, F. Li, E. Mendes, R. Eelkema and J. H. van Esch, Chem.
Commun., 2012, 48, 9837; (d) P. Long and J. Hao, Soft Matter, 2010,
6, 4350; (e) H. Oh, V. Javvaji, N. A. Yaraghi, L. Abezgauz, D. Danino and
S. R. Raghavan, Soft Matter, 2013, 9, 11576; ( f ) Y. Hisamatsu,
S. Banerjee, M. B. Avinash, T. Govindaraju and C. Schmuck,
Angew. Chem., Int. Ed., 2013, 52, 12550; (g) S. Bhattacharjee and
S. Bhattacharya, J. Mater. Chem. A, 2014, 2, 17889; (h) S. Bhattacharjee
and S. Bhattacharya, Chem. – Asian J., 2015, 10, 572; (i) S. Himmelein,
V. Lewe, M. C. A. Stuart and B. J. Ravoo, Chem. Sci., 2014, 5, 1054.
7 (a) F. J. M. Hoeben, I. O. Shklyarevskiy, M. J. Pouderoijen, H. Engelkamp,
A. P. H. J. Schenning, P. C. M. Christianen, J. C. Maan and E. W. Meijer,
Angew. Chem., Int. Ed., 2006, 45, 1232; (b) P. Rajamalli and E. Prasad, Soft
Matter, 2012, 8, 8896.
Notes and references
1 (a) M. T. McCann, M. M. Thompson, I. C. Gueron and M. Tuchman,
Clin. Chem., 1995, 41, 739; (b) Z.-X. Chen, X.-X. Su and S.-P. Deng,
J. Phys. Chem. B, 2011, 115, 1798.
2 (a) P. Sahoo, R. Sankolli, H.-Y. Lee, S. R. Raghavan and P. Dastidar,
Chem. – Eur. J., 2012, 18, 8057; (b) W. Edwards and D. K. Smith,
J. Am. Chem. Soc., 2013, 135, 5911; (c) S. Bhattacharjee, S. Datta and
S. Bhattacharya, Chem. – Eur. J., 2013, 19, 16672; (d) L. Chen,
T. O. McDonald and D. J. Adams, RSC Adv., 2013, 3, 8714;
(e) H. Maeda, W. Hane, Y. Bando, Y. Terashima, Y. Haketa,
H. Shibaguchi, T. Kawai, M. Naito, K. Takaishi, M. Uchiyama and
´
´
´
8 F. Garcıa, G. Fernandez and L. Sanchez, Chem. – Eur. J., 2009, 15, 6740.
9 J. E. Betancourt, C. Subramani, J. L. S. Velez, E. R. Molinar, V. M.
Rotello and J. M. Rivera, Chem. Commun., 2010, 46, 8537.
A. Muranaka, Chem. – Eur. J., 2013, 19, 16263; ( f ) Y. Yoshii, 10 (a) V. Percec, M. Peterca, M. E. Yurchenko, J. G. Rudick and P. A. Heiney,
´
N. Hoshino, T. Takeda, H. Moritomo, J. Kawamata, T. Nakamura
and T. Akutagawa, Chem. – Eur. J., 2014, 20, 16279; (g) Q. Xia,
Y. Mao, J. Wu, T. Shu and T. Yi, J. Mater. Chem. C, 2014, 2, 1854.
3 (a) B. Roy, P. Bairi and A. K. Nandi, RSC Adv., 2014, 4, 1708;
(b) B. Roy, P. Bairi, P. Chakraborty and A. K. Nandi, Supramol.
Chem., 2013, 25, 335; (c) S. Mahesh, R. Thirumalai, S. Yagai,
A. Kitamura and A. Ajayaghosh, Chem. Commun., 2009, 5984;
(d) J. Cui and A. del Campo, Chem. Commun., 2012, 48, 9302;
Chem. – Eur. J., 2008, 14, 909; (b) S. Saha, J. Bachl, T. Kundu, D. D. Dıaz
and R. Banerjee, Chem. Commun., 2014, 50, 3004; (c) S. Bhattacharjee
and S. Bhattacharya, Chem. Commun., 2014, 50, 11690; (d) H. Wei, S. Du,
Y. Liu, H. Zhao, C. Chen, Z. Li, J. Lin, Y. Zhang, J. Zhang and X. Wan,
Chem. Commun., 2014, 50, 1447; (e) L. Yan, G. Li, Z. Ye, F. Tian and
S. Zhang, Chem. Commun., 2014, 50, 14839; ( f ) M. Zhang, D. Xu, X. Yan,
J. Chen, S. Dong, B. Zheng and F. Huang, Angew. Chem., Int. Ed., 2012,
51, 7011.
6768 | Chem. Commun., 2015, 51, 6765--6768
This journal is ©The Royal Society of Chemistry 2015