Self-assembly studies of a chiral bisurea-based superhydrogelator

Article abstract of DOI:10.1002/chem.201200707

A chiral bisurea-based superhydrogelator that is capable of forming supramolecular hydrogels at concentrations as low as 0.2 mM is reported. This soft material has been characterized by thermal studies, rheology, X-ray diffraction analysis, transmission e

Full text of DOI:10.1002/chem.201200707

FULL PAPER
DOI: 10.1002/chem.201200707
Self-Assembly Studies of a Chiral Bisurea-Based Superhydrogelator
Francisco Rodrꢀguez-Llansola,[a] Daniel Hermida-Merino,[d] Belꢁn Nieto-Ortega,[c]
Francisco J. Ramꢀrez,[c] Juan T. Lꢂpez Navarrete,[c] Juan Casado,[c] Ian W. Hamley,[b]
Beatriu Escuder,*[a] Wayne Hayes,*[b] and Juan F. Miravet*[a]
In memory of Purificaciꢀn Escribano
Abstract: A chiral bisurea-based super-
hydrogelator that is capable of forming
supramolecular hydrogels at concentra-
tions as low as 0.2 mm is reported. This
soft material has been characterized by
thermal studies, rheology, X-ray dif-
fraction analysis, transmission electron
microscopy (TEM), and by various
spectroscopic techniques (electronic
and vibrational circular dichroism and
by FTIR and Raman spectroscopy).
The expression of chirality on the mo-
lecular and supramolecular levels has
been studied and a clear amplification
of its chirality into the achiral analogue
has been observed. Furthermore, ther-
mal analysis showed that the hydrogel-
AHCTUNGTERGaNNUN tion of compound 1 has a high re-
sponse to temperature, which corre-
sponds to an enthalpy-driven self-as-
sembly process. These particular ther-
ACHTUNGTRENNUNG
mal
characteristics
make
these
Keywords: chirality · hydrogels ·
self-assembly · soft materials · su-
pramolecular chemistry
materials easy to handle for soft-appli-
cation technologies.
Introduction
are suited to applications such as regenerative medicine or
organocatalysis.[3]
The study of soft materials that are formed by low-molecu-
lar-weight compounds has attracted great attention over the
last years.[1] Functional materials can be constructed from
simple building blocks that spontaneously self-assemble,
thereby translating their inherent molecular properties onto
the supramolecular level. Of particular interest are com-
pounds, which are not necessarily peptidic in nature,[2] that
are able to form molecular hydrogels with properties that
Within this context, the expression of molecular chirality
through aggregation processes that lead to the formation of
hydrogel networks is of great interest. Examples have been
reported in which molecular chirality is translated onto the
mesoscopic level through the formation of helicoidal
fibers.[4] Moreover, chirality may also be expressed into a
stereoselective transformation or recognition process that
takes place within the hydrogel fibers.[5]
Herein, based upon previous studies within our group,[6]
we report an interesting example of a simple chiral bisurea
compound (1) that is able to form hydrogels at very low
concentrations (Scheme 1). The urea functionality has been
[a] Dr. F. Rodrꢀguez-Llansola, Dr. B. Escuder, Dr. J. F. Miravet
Departament de Quꢀmica Inorgꢁnica i Orgꢁnica
Universitat Jaume I
12071, Castellꢂ (Spain)
Fax : (+34)964728214
E-mail: escuder@uji.es
miravet@uji.es
[b] Prof. I. W. Hamley, Dr. W. Hayes
Department of Chemistry
University of Reading
Whiteknights, Reading, RG6 6AD (UK)
E-mail: w.c.hayes@reading.ac.uk
Scheme 1. Structures of bisurea-based compounds.
[c] B. Nieto-Ortega, Dr. F. J. Ramꢀrez, Prof. J. T. L. Navarrete,
Prof. J. Casado
used widely in low-molecular-weight organogelators because
it provides a convenient 1D directionality and strong inter-
molecular hydrogen-bonding interactions.[7] However, aggre-
gation in water is predominantly governed by hydrophobic
interactions. In this sense, it is well known that molecules
that contain a defined hydrophobic core and peripheral
polar groups allow for their self-assembly into stable colum-
nar aggregates.[8] Furthermore, the effects of the chirality of
the peripheral hydroxy groups on the hydrogelation charac-
teristics of compound 1, as well as of achiral bisurea 2, have
Department of Physical Chemistry
University of Mꢃlaga
Campus de Teatinos s/n, 29071 Mꢃlaga (Spain)
[d] Dr. D. Hermida-Merino
DUBBLE beamline at the ESRF
6 rue Jules Horowitz
BP 220, 38043
CEDEX 9, Grenoble (France)
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201200707.
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also been analyzed at the macroscopic (rheology), micro-
scopic (TEM), and molecular levels (CD, VCD, IR, Raman,
WAXD) and the results from these studies are reported.
Results and Discussion
Gelation studies: Bisureas 1 and 2 were obtained in high
yield by the direct addition of their corresponding amino al-
cohol to 4,4’-methylene diphenyldiisocyanate without the
need to protect the hydroxy groups; these compounds were
subsequently exhaustively characterized (see the Supporting
Information). Compound 1 (R and S) formed transparent
hydrogels at room temperature at concentrations as low as
0.2 mm and it can be considered as a supergelator with one
of the lowest minimum gel concentrations reported in the
literature.[9] In contrast, bisurea 2 was not able to form hy-
drogels, thereby revealing the paramount importance of the
local structural on the self-assembly process.[10]
The thermal stability of the gels was studied by using the
“vial inversion” method (Figure 1). The onset temperature
for gel disassembly (Tgel) shows a typical dependence on
Figure 2. Rheological studies of compound S-1. Top: Plot of oscillation
frequencies for a 2 mm hydrogel; bottom: plot of moduli versus concen-
^
tration ( G’, & G’’).
AHCTUNGTREGdNNNU ent of the oscillation frequency. The G’ values were one
order of magnitude larger than those of G’’, thereby demon-
strating the dominant elastic behavior that is typical of gel
systems. In addition, studies of G’ and G’’ versus the concen-
tration of the hydrogelator revealed (Figure 2B) an increase
in the values of both moduli up to a certain concentration
(about 20 mm), after which the rheological properties de-
creased and the values of G’ and G’’ converged. This behav-
ior can be ascribed to precipitation phenomena that are as-
sociated with a high concentration of the hydrogelator.
Figure 1. Thermal stability of bisureas R-1 and S-1.
concentration, with a plateau at 608C above 6 mm. The rela-
tively high response of this hydrogel to temperature is typi-
cal of enthalpy-driven gels, where weak interactions are
broken by increasing temperature, in contrast to entropy-
driven hydrogelation where the hydrophobicity of the mole-
cule drives the self-assembly process and the hydrogel re-
mains stable over a wide range of temperatures.[11] DSC
measurements of the hydrogels (10 mm) revealed a smooth
second-order transition in the range 60–708C, which is typi-
cal of hierarchically assembled molecular gels (see the Sup-
porting Information).[12a] Notably, this gel-to-sol transition
can be explained by the progressive dissolution of the gela-
tor network into the solvent upon increasing the tempera-
Spectroscopic studies: The transmission of chiral informa-
tion from the molecular level into the supramolecular level
is an issue of great interest.[13] In some cases, intermolecular
interactions force the molecules to adopt helicoidal arrange-
ments in the assemblies and, if the molecule has chiral cen-
ters, such an arrangement may lead to a preferred supramo-
lecular handedness.[14] To investigate this possibility, elec-
tronic and vibrational circular dichroism spectroscopy (CD
and VCD, respectively) were used. As shown in Figure 3,
enantiomeric hydrogels R-1 and S-1 gave CD bands of op-
posite sign. Furthermore, we observed that nonaggregated
solutions of these compounds (Figure 4 and Figure 5) did
not exhibit dichroic bands, thus suggesting that the observed
effects corresponded to the appearance of supramolecular
chirality. Indeed, following the evolution of aggregation with
ACHTUNGTRENNUNG
As evident in Figure 2A, a 2 mm hydrogel exhibited elastic
(G’) and viscous moduli (G’’) that were virtually indepen-
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Self-Assembly of a Chiral Bisurea-Based Superhydrogelator
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Whilst CD spectroscopy has been widely employed to
study chiral supramolecular assemblies, VCD spectrosco-
py[15] is less-frequently utilized.[16] Given that most of these
molecules have 3NÀ6 vibrational modes, where N is the
number of atoms, significant vibrational data can be gained
from VCD measurements,[17] in contrast with the restricted
information (in terms of electronic bands) that is provided
by CD spectroscopy. In addition, VCD spectra can be inter-
preted in terms of structural parameters, which is also ad-
vantageous for structure elucidation. Combined VCD, IR,
and Raman analysis affords a detailed insight into the in-
volvement of specific molecular parts or fragments during
the formation of supramolecular assemblies. However, these
advantages of VCD come at the expense of 1) a smaller
magnitude of the VCD signals, which require longer data
collection; 2) the need for higher concentrations of the
sample; and 3) the requirement for short path-length cells
(and high sample concentrations) because water exhibits
strong IR absorptions at around 1650 cmÀ1.[18] Accordingly,
the VCD measurements were performed on compound 1 at
a concentration of 70 mm. To test that this high concentra-
tion level did not modify the structure of the gel, a gel that
formed at a concentration of 7 mm was studied, which re-
vealed that the IR and VCD patterns were similar to those
recorded at 70 mm (see the Supporting Information).
Figure 3. CD spectra for hydrogels (2 mm) of enantiomers R-1 (solid line)
and S-1 (dotted line).
To obtain further details about the different steps in the
self-assembly process of S-1, IR and VCD spectra were re-
corded at room temperature in solution with different D2O/
[D6]DMSO mixtures (Figure 6) and the spectroscopic region
between 1800 and 1300 cmÀ1 was analyzed.
Figure 4. Time-dependent aggregation of hydrogelator S-1 (2 mm), moni-
tored by CD spectroscopy.
time (Figure 4), an increase in the intensity of the bands
could be observed together with hydrogel formation.
Furthermore,
concentration-dependent
experiments
(Figure 5, R-1) revealed a boost in the CD effect close to
the minimum gel concentration. For both enantiomers, the
spectra showed several zero-crossing points that were coinci-
dent with the maxima in the absorption spectra (205, 210,
and 260 nm). From the shape of the band that was centered
at 205 nm, a relative P configuration of the chromophores in
the aggregates could be assigned for the R-1 enantiomer
and, consequently, an M configuration was assigned to the
S-1 enantiomer.
Figure 5. Concentration-dependent UV and CD spectra of compound
Figure 6. IR (left) and VCD spectra (right) of compound S-1 in various
R-1.
mixtures of D2O/[D6]DMSO.
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B. Escuder, W. Hayes, J. F. Miravet et al.
Significant differences were found when comparing the
IR and VCD behavior with incremental increases in the
D2O concentration. Below 40% D2O, no VCD signals were
evident, thus inferring that chiral aggregates were not
formed. In contrast, noticeable changes were observed in
the IR spectrum. The nACTHUNGTRENNG(U C=O) vibration band of S-1 (com-
monly called the amide I vibrational mode) appeared at
1691 cmÀ1 with a shoulder at 1669 cmÀ1 in pure DMSO. In
the presence of 40% D2O, the most-intense band was mea-
ACHTUNGTRENNUNG
sured at 1656 cmÀ1. Two main phenomena could account for
this shift in wavenumber: 1) H/D exchange of the acidic hy-
drogen atoms and 2) the establishment of hydrogen bonds
with the carbonyl oxygen atom (note: these two phenomena
are absent in pure [D6]DMSO). It is quite reasonable to
assign the displacement in the IR spectrum (1691 to
1656 cmÀ1) to partial deuteration of the sample in D2O,
which provides a clear explanation for the absence of VCD-
signal amplification. To support this explanation, an IR
spectrum in [D6]DMSO was recorded after lyophilization
from D2O (see the Supporting Information), in which the
effect of deuteration on the IR frequencies could be evalu-
ated in the absence of hydrogen-bonding interactions. In
this IR spectrum, the amide I band appeared at 1661 cmÀ1.
The vibrational absorption band of S-1 at 1543 cmÀ1 in
[D6]DMSO was assigned to a bending mode of the NH
bonds on the amide group, mixed (to a certain extent) with
Figure 7. Raman spectra (excitation: 532 nm) of compound S-1 at 40%
(bottom line) and 60% D2O (top line) with respect to [D6]DMSO in sol-
ution.
rings that are co-facially placed in the aggregates and inter-
À
act through aromatic p p-stacking forces, which cause the
shifts in the Raman spectra. These findings exemplify the
cooperative involvement of hydrophobic and hydrophilic
groups to thermodynamically stabilize the structure of the
gel. Our results also indicate that complementary electronic
(CD) and vibrational spectroscopy (VCD, IR, Raman) pro-
vide experimental evidence and structural elucidation of the
effects behind these phenomena.
À
À
the dACHTUNGTRENNUNG(C H) vibrations of the aromatic moiety (dHCATUNGTRNE(NUGN N H),
also called amide II). Given the nature of this IR band, its
frequency will be shifted in D2O given the H/D exchange.
Indeed, this band disappeared in D2O in the region 1600–
1300 cmÀ1.
A further increase in the D2O concentration to 60% is ac-
companied by the net detection of a VCD signal between
1550 and 1650 cmÀ1, with an accompanying further down-
field shift of the amide I band to 1621 cmÀ1. Extensive for-
mation of a hydrogen-bonding network in the gel can be ra-
tionalized, which serves to explain the further shift in the
frequency of the amide I band and the amplification in the
intensity of the VCD peak.
X-ray diffraction: The structure of a dried hydrogel (xero-
gel) of bisurea 1 (R and S) was investigated by wide-angle
X-ray powder diffraction (WAXD). For compound R-1
(Figure 8), the xerogel showed a high degree of crystallinity.
To investigate the structure of the gel in more detail,
Raman spectroscopy was carried out on the same samples
(Figure 7). Raman spectroscopy is a complementary tech-
ACHTUNGTRENNUNGnique to IR spectroscopy because it is sensitive to changes
in molecular polarizability that are especially accentuated in
the vibrational modes of aromatic groups, in particular the
C=C stretches of the benzene moieties at around 1600 cmÀ1.
The Raman spectrum of the nonaggregated form (concen-
trations below 40%) revealed a band at 1615 cmÀ1, which
shifted to high frequencies (1626 cmÀ1) with the formation
of the gel. This upshift in wavenumber can be ascribed to in-
Figure 8. WAXD of the xerogels of bisurea R-1.
À
termolecular aromatic p p-stacking interactions.
Taking all of these spectroscopic data together, we con-
clude that the amplification of the VCD signal at high per-
centages of D2O is a consequence of the chiral aggregates
that are generated by the formation of a network of hydro-
gen bonds. The stability of the gel is also improved by the
formation of hydrophobic interactions between benzene
Sharp peaks were obtained with a periodicity of d, d/2, d/3,
and d/4 (21, 10.6, 7.1, and 5.3 ꢅ, respectively), thus suggest-
ing a lamellar organization. The low-angle peak corresponds
to the extended molecular dimension and a model with the
packing shown in Figure 9 can be proposed in which chiral
columnar stacks are packed into a layered structure. Similar
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Self-Assembly of a Chiral Bisurea-Based Superhydrogelator
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Meijer and co-workers, as well as by other groups.[23] In gen-
eral, the two main amplification effects have been referred
as the “sergeants-and-soldiers” and “majority-rules” princi-
ples. In the first effect, a few chiral molecules (sergeants)
are able to induce supramolecular chirality in a large
number of achiral molecules (soldiers).
In the case of the majority-rules principle, a slight excess
of one enantiomer provokes a bias in the supramolecular
chirality of the quasi-racemic mixture. In this context, we
studied the transmission of chiral information in mixtures of
two enantiomers of hydrogelator 1 (majority-rules experi-
ments) and mixtures of S-1 with compound 2 (sergeants-
and-soldiers experiments).
In the majority-rules experiment, different ratios of R-1
and S-1 were mixed at a total concentration of 2 mm
(10 times higher than the minimum gel concentration). As
shown in Figure 11, an enantiomeric purity of at least 80%
was required to obtain a stable hydrogel. Below this thresh-
old, the minor enantiomer interfered with the aggregation
of the major one. Indeed, WAXD of the solid racemate re-
vealed a higher amorphous character than the enantiomeri-
cally pure xerogel (see the Supporting Information).
Figure 9. Model of the proposed self-assembly process for hydrogelator 1
(C: inter-columnar packing).
results were found for enantiomer S-1 (see the Supporting
Information). Notably, the crystallinity of the xerogel is indi-
rect but strong evidence for the presence of microcrystalline
fibers in the wet gel. For example, several cases of noncrys-
talline xerogels that were obtained from hydrogels have
been reported.[11]
Electron microscopy: The expression of supramolecular
chirality was also observed by TEM (Figure 10). Hydrogels
of S-1 at the minimum gel concentration (0.2 mm) exhibited
the presence of left-handed helicoidal tapes (width: about
10 nm) that further coiled into longer fibers with no expres-
sion of chirality on the mesoscale.
Figure 11. Hydrogelation study of mixtures of bisureas S-1 and R-1:
A) pure S-1, B) 20% R-1, C) racemic mixture, D) 80% R-1, and E) pure
R-1.
In the sergeants-and-soldiers experiments, different mix-
tures of compound R-1 (0.5 mg) and achiral compound 2
were prepared and both hydrogelation-ability (Table 1) and
Table 1. Hydrogelation ability of different mixtures of bisureas R-1 and
2.
Entry
2 [equiv]
Appearance[a]
Figure 10. TEM images of hydrogel S-1 (Pt-shadowing).
1
2
3
4
0.2
0.4
0.6
0.8
G
G
WG
P
Amplification of chirality: The amplification of chirality by
self-assembly, that is, the transmission of chiral information
between chiral molecules and enantiomeric or achiral ana-
logues has been a topic of great interest over the last few
years. Several examples, including polymers,[19] liquid crys-
tals,[20] and gels,[21] have been reported. Following on from
the seminal studies on polyisocyanates reported by Green
et al.,[22] studies that were specifically directed towards dy-
namic supramolecular systems have been reported by
[a] G: gel, WG: weak gel, P: precipitate.
CD spectroscopic features were observed (Figure 12). The
mixtures formed hydrogels up to a ratio of 1:0.6 and further
addition of the achiral compound resulted in precipitation
of the mixture. CD spectra confirmed a clear cooperative
effect after the addition of 0.4 equivalents of bisurea 2.
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B. Escuder, W. Hayes, J. F. Miravet et al.
Figure 13. Demonstration of the application of chiral hydrogels of com-
pound 1 as an injectable material. a) A solution of the gelator is charged
into the syringe at 508C and a gel forms quickly after depositing the solu-
tion onto a surface at room temperature. b) Gels of compounds R-1 and
S-1 can be easily prepared in the same vial by the consecutive addition of
warm solutions of the gelator into the vial at room temperature. The
blue color is due to the addition of methylene blue.
Furthermore, the investigation of the chiral self-assembly
process by using a combination of spectroscopic techniques
and X-ray powder diffraction has provided new information
on the nature of these supramolecular assemblies. In fact, it
has been established that these assemblies are formed by
À
the cooperative effects of p p stacking of the aromatic core
and a hydrogen-bond network that involves the peripheral
polar groups (urea, hydroxy). Remarkably, the final supra-
molecular structure of compound 1 (R and S) shows a
strong enhancement of the chirality and its amplification in
mixtures with achiral partners. Altogether, these features
make the hydrogels of compound 1 of practical use as chiral
gel media.
Figure 12. A) CD spectra of mixtures of compounds R-1 and 2; B) plot of
ellipticity at 220 nm versus the amount of achiral compound 2.
However, the addition of another 0.2 equivalents of com-
pound 2 resulted in a notable decrease in this effect, as well
as a weakening of the hydrogel.
Experimental Section
In summary, hydrogel fibers that contain 40% of achiral
“soldier” compound 2 remain stable and express the chirali-
ty of “sergeant” compound R-1. The main structural differ-
ence between compounds 1 and 2 is the chiral secondary hy-
droxy group, whilst the rest of the molecule is identical,
which, in turn, permits stacking of the aromatic unit, as well
as complementary hydrogen bonding between the urea func-
tions. Presumably, after the inclusion of a high amount of a
compound that lacks hydroxy groups, the peripheral hydro-
gen bonding network becomes disrupted and, as a conse-
quence, the material precipitates out. The role of the sec-
Gelation tests: A given amount of the compound to be studied was
weighed into a screw-capped vial (diameter: 20 mm) and suspended in
water (1 mL). The temperature of the mixture was then increased until
the solid had completely dissolved and the solution was left to cool to
RT. A gel (G) was considered to have formed when gravitational flux
was not observed upon inversion of the vial.
Thermal-stability measurements: Gel samples of different concentrations
were placed in a thermostated bath and the temperature was gradually
raised in 58C steps with 10 min of stabilization in between the tempera-
ture changes.
Circular dichroism (CD): Spectra were collected on a JASCO J-810 spec-
trometer. The samples were prepared in a quartz cuvette (thickness:
1 mm) prior to gelation. The samples were allowed to stabilize for 10 min
at the desired temperature.
ACHTUNGTRENNUNGondACHTUNGTRENNUNGary hydroxy group seems to be critical for the hydrogela-
tion process to occur. In summary, molecular chirality plays
a fundamental role in hydrogelation and expression at the
supramolecular level.
Vibrational circular dichroism (VCD) and IR and Raman Spectroscopy:
Samples of S-1 and R-1 in D2O and [D6]DMSO at a concentration of
70 mm (about 30 mgmLÀ1) were prepared for the vibrational spectroscop-
ic measurements. After thermal treatment, the samples were placed at
RT in a demountable cell A145 (Bruker, Germany) that was supplied
with CaF2 windows. A 25 mm Teflon spacer was used to optimize the vi-
brational signals. IR and VCD spectra were recorded on a Vertex 70
spectrometer that was equipped with a PMA 50 photoelastic modulator
(Bruker, Germany). VCD spectra were obtained by adding 500 scans at a
spectroscopic resolution of 4 cmÀ1, which is equivalent to signal accumu-
lation for 15 min; this is an unusually short time, because the standard ac-
cumulation time to obtain a suitable VCD spectrum is around 8 h. To
ensure the absence of linear dichroism interference, which is caused by
preferential orientation within the gels,[24] spectra on different aliquots of
these compounds were recorded at different angles without observing
any appreciable deviation. As a proof of the quality of the recorded data,
the spectra from pure enantiomeric samples resulted in mirror images
(see the Supporting Information). Raman spectra were recorded on a
Conclusion
In conclusion, we have described a potent hydrogelator with
a very low minimum gel concentration and interesting ther-
mal properties. For instance, the low thermal stability of this
hydrogel and its high temperature-response could be attrac-
tive for its application as an injectable material. For exam-
ple, it is very easy to handle and permits the preparation of
hydrogels with alternated layers of R-1 and S-1, thus yield-
ing materials with potentially interesting chiroptical proper-
ties (Figure 13).
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Self-Assembly of a Chiral Bisurea-Based Superhydrogelator
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Senterra dispersive Raman microscope (Bruker, Germany) with laser ex-
citation at 532 nm and a power of 5 mW.
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Transmission electron microscopy (TEM): Transmission electron micro-
graphs were taken on a JEOL 2100 microscope. Samples of the hydrogels
were prepared by dipping a copper grid that was coated with a formvar
carbon support film into the gels and shadowing with Pt.
Powder X-ray diffraction: Data collection was performed at room tem-
perature on a Bruker D4 Endeavor X-ray powder diffractometer by
using Cu Ka radiation. Samples of the powdered xerogels were placed on
a sample holder and data were collected for 2q values between 28 and
408 with a step size of 0.038 and a step time of 10 s.
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a controlled stress AR-2000 rheometer (TA Instruments). A cone-and-
plate geometry (diameter: 10 mm, gap: 26 mm) was used for all of the
samples. Frequency sweeps were performed in the angular-frequency
range 0.1–100 radsÀ1 with the instrument in oscillatory mode at 258C. To
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Acknowledgements
We thank the Spanish Ministry of Science and Innovation (grants no.
CTQ2009–13961 and CTQ2009–10098), the Junta of Andalucꢀa (grant no.
P09–FQM–4708) and the Universitat Jaume I-Bancaixa (grant no.
P1·1B2009–42) for financial support. F.R.-L. thanks the Generalitat Va-
lenciana for a FPI fellowship. We thank Henkel Adhesives Ltd for a PhD
studentship to D.H.-M.
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ACHTUNGERTNeNUNG r-
U
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Received: March 2, 2012
Revised: July 9, 2012
Published online: && &&, 0000
Chem. Eur. J. 2012, 00, 0 – 0
ꢄ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
&
7
&
ÞÞ
These are not the final page numbers!

B. Escuder, W. Hayes, J. F. Miravet et al.
Chiral Hydrogels
F. Rodrꢁguez-Llansola,
D. Hermida-Merino, B. Nieto-Ortega,
F. J. Ramꢁrez, J. T. L. Navarrete,
J. Casado, I. W. Hamley, B. Escuder,*
W. Hayes,* J. F. Miravet* . . . &&&& — &&&&
Supergelator with a twist: A chiral
bisurea-based compound is capable of
forming supramolecular hydrogels at
concentrations as low as 0.2 mm (see
figure). Molecular chirality is mani-
fested on the supramolecular level and
the soft material is easy to handle.
Self-Assembly Studies of a Chiral
Bisurea-Based Superhydrogelator
&
8
&
www.chemeurj.org
ꢄ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 0000, 00, 0 – 0
ÝÝ
These are not the final page numbers!