Multiple-stimulus-responsive supramolecular gels and regulation of chiral twists: The effect of spacer length

Article abstract of DOI:10.1002/chem.201500097

Abstract A new class of homologous gelators, LG₁₂-(CH₂)_n-BSA, composed of bipyridinyl groups, L-glutamic moieties having double dodecyl chains, and linked alkyl spacers with different lengths were synthesized. It was found that these gelators could immobilize medium-polarity solvents readily and the behaviors of these gels showed a dependence on the spacer length. Of all the gels, the LG₁₂-(CH₂)₁₁-BSA gels exhibited self-healing property and multiple-stimulus responsibility, such as heating, shaking, and sonication. The investigation of CD spectra indicated that the supramolecular chirality, which was attributed to the chiral transfer from the chiral center to the assemblies, was also closely related to the length of methylene spacers. The longer the alkyl spacers, the weaker the transmitted supramolecular chirality. Only LG₁₂-(CH₂)₁-BSA gelators, which had the shortest spacers, formed right-handed nanoscale chiral twists owing to crowded hydrogen bonding interactions. Moreover, the high-polarity solvent DMF was found to be able to regulate the chiral twist as well as its pitch length readily. A new twist on healing: Self-healing supramolecular gels that are responsive to multiple stimuli were developed. The formation of nanoscale twists could be controlled by the length of the methylene spacers of the gelator molecules. The pitch of these twists could be regulated by DMF.

Full text of DOI:10.1002/chem.201500097

DOI: 10.1002/chem.201500097
Full Paper
&
Supramolecular Chirality
Multiple-Stimulus-Responsive Supramolecular Gels and
Regulation of Chiral Twists: The Effect of Spacer Length
Wangen Miao,*[a] Dong Yang,[b] and Minghua Liu*[b]
Abstract: A new class of homologous gelators, LG12-(CH2)n-
BSA, composed of bipyridinyl groups, l-glutamic moieties
having double dodecyl chains, and linked alkyl spacers with
different lengths were synthesized. It was found that these
gelators could immobilize medium-polarity solvents readily
and the behaviors of these gels showed a dependence on
the spacer length. Of all the gels, the LG12-(CH2)11-BSA gels
exhibited self-healing property and multiple-stimulus re-
sponsibility, such as heating, shaking, and sonication. The in-
vestigation of CD spectra indicated that the supramolecular
chirality, which was attributed to the chiral transfer from the
chiral center to the assemblies, was also closely related to
the length of methylene spacers. The longer the alkyl
spacers, the weaker the transmitted supramolecular chirality.
Only LG12-(CH2)1-BSA gelators, which had the shortest
spacers, formed right-handed nanoscale chiral twists owing
to crowded hydrogen bonding interactions. Moreover, the
high-polarity solvent DMF was found to be able to regulate
the chiral twist as well as its pitch length readily.
perature, pH, Ca2+, and light.[7a] Huang’s group provided
a crown ether appended super gelator and found its acetoni-
trile gels could be triggered by stimuli of heating, acid/base,
ion and redox reactions, and so on.[8f] Ihara et al. presented
some combination logic gates in an organogelator owing to
its response to multiple chemical stimuli and multiple output
signals.[8g] The development of multiple-stimulus-responsive
supramolecular gels would facilitate the preparation of multi-
functional materials.[9]
Introduction
Supramolecular gels, in which small gelator molecules self-as-
sembled into entangled nanostructures to immobilize the sol-
vents, are apt to show responsiveness to stimuli because the
driving forces of the gel formation originate from non-covalent
intermolecular interactions, such as hydrogen bonding, p–p
stacking, hydrophobic interactions, van der Waals forces, and
so forth.[1] All kinds of stimuli, such as light,[2] ultrasound,[3] me-
chanical stress,[4] ionic strength,[5] electric or magnetic fields,[6]
and pH[7] have been used to stimulate the reversible gel–sol
phase transition by introducing suitable responsive units into
the gelator molecules. Among these, the multiple-stimulus re-
sponsibility of organogel has attracted more and more atten-
tion.[8] For example, Fang et al. reported cyclohexane organo-
gels with several cholesterol–ferrocene appended gelators that
presented multiple response to shaking, sonication, heating,
and redox reaction.[8c] Hamachi et al. prepared a supramolecular
hydrogel of the phosphate-type hydrogelator that exhibited
macroscopic gel–sol behavior in response to four stimuli: tem-
On the other hand, the supramolecular gels provided an ex-
cellent environment for chiral gelator molecules to self-assem-
ble into chiral nanostructures.[10] Of all of these, chiral nano-
helices or twists have attracted more and more interest owing
to the similarity to the double helix in DNA and the a-helix in
proteins. The mimicking and tuning of chiral helical or twists
nanostructures would lead to a comprehensive understanding
of the mechanism of their formation. In the past two decades,
many chiral or achiral molecules have been extensively devel-
oped for the simulation of chiral helices or twists.[11] Moreover,
the self-assembled chiral nanostructures could be regulated
when the temperature, pH, light, cooling rate, additives, metal
ions, and even the solvents are changed.[12] For instance, Stupp
and co-workers reported a peptide amphiphile having a bulky
photolabile 2-nitrobenzyl group and found that the formed
quadruple helical fiber would dissociate into single fibrils in re-
sponse to light.[12a] We have found that water was able to tune
the self-assembled nanostructures of a cationic amphiphile in
organic solvents from nanofibers to helical tapes, helical tubes
and chiral nanotwists with various pitch lengths depended on
water content.[12i] Besides, we have also found that a glycine-
based achiral molecule could self-assemble into different nano-
structures from fibers to chiral twists along with the elevation
of temperature.[12e] Despite these reports, in situ tuning of heli-
[a] Dr. W. Miao
School of Chemistry and Chemical Engineering
Institute of Physical Chemistry, Lingnan Normal University
Development Centre for New Materials Engineering & Technology
in Universities of Guangdong, Zhanjiang, 524048 (P. R. China)
E-mail: miaowangen@iccas.ac.cn
[b] Dr. D. Yang, Prof. Dr. M. Liu
Beijing National Laboratory for Molecular Science
CAS Key Laboratory of Colloid, Interface and Chemical Thermodynamics
Institute of Chemistry, Chinese Academy of Sciences
Beijing, 100190 (P. R. China)
E-mail: liumh@iccas.ac.cn
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/chem.201500097.
Chem. Eur. J. 2015, 21, 7562 – 7570
7562
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Paper
cal structures through external stimulators and controlling
over the expression of chirality at supramolecular levels re-
mained a challenge.
Table 1. Gelation properties of LG12-(CH2)n-BSA in various solvents.[a]
Solvent
LG12-(CH2)n-BSA
n=1
3
5
11
We have now prepared a new class of homologous gelators
(abbreviated as LG12-(CH2)n-BSA, n=1, 3, 5, and 11), the molec-
ular structure of which is shown in Scheme 1. These gelator
n-hexane
I
I
I
I
I
I
I
I
I
I
I
I
cyclohexane
carbon tetrachloride
toluene
PG
PG
4
5
4
3
I
5
I
P
P
P
P
PG
PG
3
5
3
3
PG
4
I
P
4
PG
3
4
3
2
PG
4
2, SG
3, SG
2, SG
3, SG
1, SG
0.8, SG
PG
benzene
dichloromethane
chloroform
1,4-dioxane
tetrahydrofuran
acetonitrile
2-propanol
ethyl acetate
ethanol
2, SG
PG
I
Scheme 1. Molecular structure of LG12-(CH2)n-BSA.
P
P
P
P
P
P
P
P
methanol
DMF
DMSO
P
P
P
molecules were composed of bipyridinyl groups and l-gluta-
mic moieties having double dodecyl chains and linked alkyl
spacers with different length. It was found that these homolo-
gous gelators could immobilize medium-polarity solvents
easily. Of all, the LG12-(CH2)11-BSA gels exhibited self-healing
properties and multiple-stimulus responsibility, such as heat-
ing, shaking, and sonication. And the investigation of CD spec-
tra indicated that the supramolecular chirality induced by self-
assemblies of chiral gelator molecules in gels was closely relat-
ed to the length of methylene spacers. The longer the alkyl
spacers, the weaker the transmitted supramolecular chirality.
Moreover, we found that the length of spacers played impor-
tant role in the formation of nano structures assembled from
gels. Only the LG12-(CH2)1-BSA gelators, which had the shortest
spacers, formed right-handed nanoscale chiral twists. Interest-
ingly, the high-polarity solvent, DMF, was found to be able to
regulate such chiral twist as well as its pitch length readily.
However, similar phenomena were not observed in the other
three homologous gels.
[a] P-precipitate, I-insoluble, PG-partial gel, SG-thixotropical and self-heal-
ing gel. The number is the critical gelation concentration in mgmLÀ1
.
1 mgmLÀ1, suggesting strong gelation abilities. Interestingly,
we found that LG12-(CH2)11-BSA gels were thixotropic with fast-
recovery capability. Under shaking by hand, the gels changed
into sols immediately. Subsequent resting resulted in gelation
again rapidly. The self-healing time was less than 1 min. Such
thixotropical and self-healing properties had been reported by
many research groups.[4b,8f,13] Besides, LG12-(CH2)11-BSA gels also
exhibited a responsiveness to sonication. The gels would turn
into sols under sonication. And the consequent resting would
recover the gel again. Thus, a multiple-responsive supramolec-
ular gel was prepared successfully. Figure 1 showed the reversi-
Results and Discussion
Gel formation
The gelation abilities were tested in various solvents by using
the “stable to the inversion of a test tube” method. The gela-
tors and solvents were added into a screw-capped sample
tube and heated until the solid was dissolved. The solution
was then cooled to room temperature, and the sample was in-
verted to determine whether the solution flowed. The gelation
test (Table 1) indicated that these homologous gelators, LG12-
(CH2)n-BSA (n=1, 3, 5, and 11), could only immobilize medium
polarity solvents, such as dicholoromethane, chloroform, tetra-
hydrofuran, and 1,4-dioxane, and so forth. In most weakly
polar solvents, these gelators were insoluble. While in strong
polarity solvents (methanol, DMF, and DMSO), precipitates
were obtained when the heated transparent solutions were
cooled to room temperature. Moreover, it was found that the
critical gelation concentration (CGC) of these gelators was less
than 5 mgmLÀ1 in all gels. In particular, In the LG12-(CH2)11-BSA
gels from THF and 1,4-dioxane, the CGCs were even less than
Figure 1. Reversible gel–sol transitions of LG12-(CH2)11-BSA gels from THF
triggered by temperature, sonication, and shear stress.
ble sol–gel phase transition of LG12-(CH2)11-BSA gels from THF
triggered by shear stress, sonication, and temperature.
Thixotropic properties
Of all the gels from homologous LG12-(CH2)n-BSA gelators, only
LG12-(CH2)11-BSA gels exhibited the thixotropic property
Chem. Eur. J. 2015, 21, 7562 – 7570
www.chemeurj.org
7563
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Paper
(Table 1). It indicated that the methylene spacer played an im-
portant role in the thixotropy of gels. To obtain more informa-
tion of mechanical properties of the self-healing gels, rheologi-
cal measurements were performed. As shown in the Support-
ing Information, Figure S3A, the frequency sweep results re-
vealed that both the storage modulus (G’) and the loss modu-
lus (G’’) exhibited less frequency dependence in the range of
0.1–100 radsÀ1. The G’ values showed a substantial elastic re-
sponse, which were larger than the values of G’’ over the
entire range of frequencies, suggesting that the gels were
a typical elastic rather than viscous soft matter. The G’ and G’’
depended on time (Supporting Information, Figure S3B), show-
ing no change, indicating the stability of the gel once it was
formed.
thixotropy process might be attributed to the easy variation of
supramolecular assemblies in gels under the outer shear stress
due to the longer flexible methylene spacer of LG12-(CH2)11-BSA
molecules.
Analysis of spectra
The driving forces of gel formation were further investigated
by UV/Vis, FTIR, and 1H NMR spectra. Figure 3A showed the
Strain amplitude sweeps, as shown in Figure 2A, indicated
that the G’ began to decrease at the critical strain about 50 Pa,
Figure 3. A) UV/Vis absorption and B) FTIR spectra of LG12-(CH2)11-BSA from
CHCl3/CH3OH (1:1, v/v) solution (a) and THF gel (b).
UV/Vis spectra of LG12-(CH2)11-BSA both in the solution and gel
state. It could be seen that an absorption appeared at 293 nm
in solution, which was attributed to the p–p* transition of aro-
matic cycle. When gels formed, this absorption took an obvi-
ous red-shift to 302 nm. Moreover, a shoulder peak at 318 nm
emerged. These suggested that J-aggregates formed in the
gels. The similar UV spectra of all four homologous gels from
THF, as shown in the Supporting Information, Figure S4B, re-
vealed the same type of the aromatic stacking in these gels.
The FTIR technique is an important tool for studies of gel
formation. Figure 3B shows FTIR spectra of the cast film of
LG12-(CH2)11-BSA from CHCl3/CH3OH (1:1, v/v) solution and its
xerogel from THF. In the case of FTIR spectra of the cast film,
asymmetric and symmetric methylene stretching vibrations
were found in 2921 and 2852 cmÀ1, respectively, indicating
that the alkyl chains were packed in both all-trans zigzag and
Figure 2. Rheological studies of LG12-(CH2)11-BSA gels from THF: A) oscillate
stress sweeps; B) continuous step strain measurement.
which implied a partial breakup of the gel that begins to flow.
Above 60 Pa, the G’ decreased rapidly. As the value of strain
was larger than 110 Pa, the value of G’ would become lower
than that of G’’, suggesting the gel had been transformed into
viscous sol completely. However, when the amplitude oscilla-
tion decreased, the G’ would recover almost the initial value in
1 min. And the system returned to a gel state. These indicated
a very smart thixotropic property. Moreover, the thixotropic
process could be repeated for many cycles (Figure 2B). The
Chem. Eur. J. 2015, 21, 7562 – 7570
www.chemeurj.org
7564
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Paper
gauche fashions.[14] The NÀH stretching mode was composed
ture. Simultaneously, the signal intensity decreased obviously.
On the contrary, those protons neighboring to amide, such as
aromatic proton (8.82, 8.66, and 7.80 ppm) and alkyl protons
(3.59, 3.43, and 3.33 ppm), showed a downfield shift. Moreover,
the intensities of these protons increased as temperature was
elevated. This suggested the disruption of the hydrogen bonds
upon heating. Therefore, the investigation from UV/Vis, FTIR,
and NMR spectra confirmed that hydrogen-bonding interac-
tions, p–p stacking of aromatic rings, and hydrophobic interac-
tions of alkyl chains were main driving forces in the formation
of gels. These results were further evidenced by the following
investigation of SEM and the XRD measurements.
of two vibrations. The main absorption band was situated at
3295 cmÀ1, while a shoulder peak appeared around 3468 cmÀ1
.
Two absorptions at 1643 and 1541 were ascribed to amide I
(the stretching vibration of carbonyl in amide groups) and ami-
de II (the NÀH bending mode in amide groups) bands, respec-
tively. Moreover, the CH2 scissoring vibration is at 1462 cmÀ1
,
suggesting no or less packing of the alkyl chains in solution.[15]
However, the FTIR spectra of xerogels showed obvious
changes. The split NÀH stretching vibrations were combined
into a single band near 3292 cmÀ1, which showed a red-shift in
comparison with that from solution.[16] Furthermore, amide I
also took a red-shift from 1643 to 1639 cmÀ1. On the contrary,
the amide II indicated a blue-shift from 1541 to 1548 cmÀ1.
These confirmed that hydrogen bonding were one of the main
driving forces for the gel formation. As for the vibrations con-
cerned with CH2 chains, obvious change could also be ob-
served in xerogels. For example, the asymmetric and symmet-
ric CH2 stretching vibrations shifted to 2919 and 2850 cmÀ1, in-
dicating that alkyl chains are highly ordered with almost all-
trans conformations. And the CH2 scissoring vibration, located
at 1467 cmÀ1, implied that a hexagonal packing of alkyl chains
was formed, which demonstrated that alkyl chains formed
well-ordered packing in gels. Furthermore, the FTIR spectra of
the other LG12-(CH2)n-BSA (n=1, 3 and 5) xerogels from THF
were similar to that of LG12-(CH2)11-BSA, as shown in the Sup-
porting Information, Figure S5, indicating that the same pack-
ing mode from self-assembly in all four gels.
Morphological studies
The microscopic structures of gels were investigated by SEM.
Figure 5a–d shows representative SEM images of LG12-(CH2)n-
To confirm the gelation formation, and in particular the hy-
drogen-bonding interactions, temperature-dependent NMR
measurement of LG12-(CH2)11-BSA gels from [D6]benzene was
performed (Figure 4). It could be seen that the gel were NMR
Figure 5. SEM images and XRD patterns of LG12-(CH2)n-BSA xerogels from
THF, a) n=1; b) n=3; c) n=5, and d) n=11. Bottom right: Models for the ar-
rangements of LG12-(CH2)n-BSA molecules in THF gels.
BSA xerogels obtained from THF. Slightly twisted belts with
a width of 1 mm were observed for LG12-(CH2)1-BSA xerogels. In
the case of LG12-(CH2)3-BSA xerogels, a nanorod structure was
formed. While for LG12-(CH2)5-BSA and LG12-(CH2)11-BSA xero-
gels, intertwined fibrous structures with a width of 100-200 nm
were obtained. To gain the information of stacking mode of
the gelator molecules in gels, XRD patterns of LG12-(CH2)n-BSA
xerogels from THF were performed. As shown in Figure 5, it in-
dicated that a lamellar structure existed in all gels. As for the
LG12-(CH2)1-BSA xerogels, a diffraction peak at a 2q value of
2.098 was detected, suggesting 4.22 nm of the d-spacing. How-
1
Figure 4. Temperature-dependent H NMR spectra of LG12-(CH2)11-BSA gels
from [D6]benzene.
silent at room temperature. Upon heating, the signals ap-
peared, indicating the disassembly and dissolution of gelator
molecules in gels. Furthermore, chemical shifts of NÀH protons
in the amide moieties, which were located at 8.29 and
5.35 ppm respectively, shifted upfield with increasing tempera-
Chem. Eur. J. 2015, 21, 7562 – 7570
www.chemeurj.org
7565
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Paper
ever, the extended length of a LG12-(CH2)1-BSA molecule was
about 5.60 nm based on CPK molecular modeling. The d-spac-
ing was less than the extended length of a single LG12-(CH2)1-
BSA molecule, indicating that the space lattice was composed
of a single molecule with interdigitated layer of the alkyl
chains for the assemblies in gels.[17] Such packing mode of
alkyl chains was displayed in Figure 5. Similarly, the results of
XRD patterns from LG12-(CH2)n-BSA xerogels (n=3, 5, and 11)
also supported such conclusions, which suggested that the
similar packing occurred in all four LG12-(CH2)n-BSA gels from
THF.
structures in THF gels. Thus, we tried to regulate the nano-
structures by adjusting the polarity of solvents. However, in
pure solvent, only medium-polarity solvent could induce the
gel formation. The LG12-(CH2)1-BSA gelators were insoluble and
precipitated in weak and strong polarity solvents, respectively.
So we chose mixed solvents for the attempt to regulation of
nanostructures. Fortunately, it was found that DMF could be
employed to tune the supramolecular nanostructures. Fig-
ure 7a–f exhibited the photos and of SEM images of the gels
fabricated from the mixed THF–DMF solvents. The amount of
DMF was regulated from 5% to 50%, where the stable gels
could be formed. Beyond this range, the precipitates instead
of the gels were obtained (see SEM image in the Supporting
Information, Figure S6). With the addition of 5% DMF, obvious
Supramolecular chirality
The designed LG12-(CH2)n1-BSA gelators containing different
length of spacer have chiral centers lied at the l-glutamide
moiety. In solution, no CD signal was detected because the
chirality could not be transferred into aromatic chromophore.
However, the molecular chirality might be transferred to the
chromophore due to the assemblies from gelation. Figure 6
showed the CD spectra of all four LG12-(CH2)n-BSA gels in THF.
Figure 6. CD spectra of LG12-(CH2)n-BSA gels from THF, a) n=1, b) n=3,
c) n=5, and d) n=11.
In the case of LG12-(CH2)1-BSA gels, a negative Cotton effect at
323 nm and a positive band at 253 nm with a crossover at
296 nm was observed. This was in accordance with the UV ab-
sorption of the gels, indicating that the chirality was trans-
ferred to the chromophore of aromatic rings. However, when
the length of alkyl chain spacer was increased, the intensity of
CD signal decreased obviously, such as in LG12-(CH2)3-BSA or
LG12-(CH2)5-BSA gels from THF. As for LG12-(CH2)11-BSA gels, the
CD signal almost disappeared. Therefore, it was suggested that
flexible methylene spacer would weaken the supramolecular
chirality induced from chiral gelator molecules in the gel.
Figure 7. Photographs and SEM images of LG12-(CH2)1-BSA assembly at dif-
ferent content of DMF in THF (vol%): a) 5%; b) 10%; c) 20%; d) 30%;
e) 40%; and f) 50%. XRD patterns of corresponding xerogels (bottom, left)
Regulation of chiral twists
The above investigation of SEM results showed that LG12-
(CH2)1-BSA molecules self-assembled into slightly twisted nano-
&
*
and correlative plots of d-spacing ( ) of nanostructure and pitch ( ) of
nanostructure against DMF content (bottom, right).
Chem. Eur. J. 2015, 21, 7562 – 7570
www.chemeurj.org
7566
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Paper
right-handed twists with the pitch of around 4.5 mm were ob-
served (Figure 7a). Upon further addition of DMF, twisted
structures increased and some of pitches changed to around
2 mm at 10% DMF (Figure 7b). The uniform right-handed
twists would be obtained once the content of DMF reached
40%. At the same time, the pitch were limited in the range of
0.9–1.0 mm. Herein, it is shown that by simply changing the
DMF content, regulation of the chiral twist as well as its pitch
length could be easily achieved. To investigate the effect of
DMF on the packing mode and supramolecular chirality from
self-assemblies of the gels, XRD patterns and CD spectra of
these gels were recorded. As shown in Figure 7, the results of
XRD measurements revealed a slight increase of d-spacing
from 4.22 to 4.35 nm that depended on the content of DMF,
suggesting that the interdigitated layer of LG12-(CH2)1-BSA mol-
ecules underwent no or less changes regardless of whether
nanoscale twists were formed. We plotted the layer distances
and the pitch for each of the xerogels as a function of the
DMF/THF ratio in the bottom of Figure 7. It is clearly seen the
pitch decreased while the d-spacing became a little lager
along with an increase of the DMF content in gels. CD spectra
of LG12-(CH2)1-BSA gels from different DMF/THF ratio (Support-
ing Information, Figure S7) suggest that the supramolecular
chirality sense was almost the same regardless of chiral nano-
structures from different solvents.
ality of LG12-(CH2)1-BSA gelators, the assembled nanostructures
were more twisted. Therefore, regulation of the chiral twist as
well as its pitch length could be easily achieved by introducing
DMF, as shown in Figure 8. However, when the spacer became
Discussion
Figure 8. LG12-(CH2)n-BSA molecules self-assembled into supramolecular gels
by hydrogen bonding, hydrophobic interaction, and p–p stacking. Of them,
the formed LG12-(CH2)11-BSA gels showed thixotropic and self-healing prop-
erties owing to flexibility of longer methylene spacers. However, the LG12-
(CH2)1-BSA molecules, which had the shortest spacers, formed right-handed
nanoscale twists because of crowded hydrogen bonding. Furthermore, the
pitch of chiral twists could be regulated by DMF. While for those gels with
the middle spacer length, LG12-(CH2)n-BSA (n=3 and 5), none of these two
properties appeared.
From above results, it is clear that the LG12-(CH2)n-BSA gelator
molecules formed supramolecular gels through three non-co-
valent intermolecular interactions, such as hydrogen bonding,
hydrophobic interactions, and p–p stacking from aromatic
rings. Each LG12-(CH2)n-BSA gelator molecule based on l-gluta-
mic acid had eight hydrogen bonding sites from amide
groups. Of these, six hydrogen bonding sites originated from
of glutamic amide while the other two sites were from biisoni-
cotinic amide. A alkyl chain spacer with different length was
used to link these two types of hydrogen bonding sites.
Through hydrophobic interaction from interdigitated alkyl
chains, LG12-(CH2)n-BSA molecules aggregated into a layer
structure. These layer subunits were further stacked in a layer-
by-layer fashion and then self-assemble into nanostructures.
Subsequently, the nano structures become woven into 3D net-
works, which could trap organic solvent molecules, thereby
leading to supromolecular gels. Notably, if the spacer was very
short, such as LG12-(CH2)1-BSA gelator molecules, all four hydro-
gen bonding sites on the same side were neighboring and
crowded. Therefore, the chiral transferring occurred easily. Ac-
cordingly, the formed nanostructure self-assembled in gels ex-
hibited chirally twisted properties. Furthermore, when the
strong polarity solvent, DMF, was introduced, the torsion was
enhanced because the DMF molecules containing two hydro-
gen bonding sites were also involved into the formation of hy-
drogen bonding for assemblies. Furthermore, all hydrogen
bonding sites of both DMF and LG12-(CH2)1-BSA molecules
were close, which would give rise to the more crowded hydro-
gen bonding interactions. Upon induced by the molecular chir-
longer, such as LG12-(CH2)n-BSA (n=3, 5 and 11) molecules, the
steric hindrance from crowded hydrogen bonding sites de-
creased. Thus, not chiral twists but nanorods or fibers were ob-
served. The corresponding SEM images of LG12-(CH2)n-BSA (n=
3, 5, and 11) gels from different ratios of THF-DMF solvents
(Supporting Information, Figure S8) confirmed such specula-
tion.
On the other hand, the longer methylene spacers of LG12-
(CH2)11-BSA molecules exhibited flexible abilities, which could
adjust self-assembled structures in the gel for the adaption to
external stress, such as shaking and sonication. Once the stress
disappeared, supramolecular gels would recover the initial
status. Therefore, the LG12-(CH2)11-BSA gels had thixotropic and
self-healing properties (Figure 8). Moreover, it is known in LG12-
(CH2)n-BSA molecules that the chiral center located in l-gluta-
mic moiety was linked to aromatic chromophore by alkyl
spacer. In gels, the chirality on molecular level could be trans-
ferred into the chromophore as supramolecular chirality owing
to self-assembly through alkyl spacers. Obviously, if the spacer
became longer, the increasing flexibility would lead to hard-
ness for the transmission of supramolecular chirality on the
Chem. Eur. J. 2015, 21, 7562 – 7570
www.chemeurj.org
7567
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Paper
condition of the same packing modes. Therefore, we detected
the weaker CD signals as the length of spacer were increased.
Furthermore, the formed suparmolecular chirality from gels
was closely related to the packing of the gelator molecules re-
gardless of the nanostructures, which would show fewer
changes unless the different packing modes of the gelator
molecules occurred in gels.
To sum up, it was found the spacer length between the aro-
matic ring and the amphiphilic l-glutamide played an impor-
tant role in regulating the formation of the gels as well as their
properties. For the spacer length of one methylene, the
formed gel showed strong chiral transfer from the chiral center
to the assemblies, thus leading to chiral twist structures. When
the spacer was long enough, the gel showed self-healing prop-
erties. For those gels with the middle spacer length, none of
these two properties appeared.
Scheme 2. Synthetic route for LG12-(CH2)n-BSA gelator molecules, n=1, 3, 5,
and 11.
Conclusion
We have designed a new class of l-glutamic gelators, which
were composed of bipyridinyl groups, l-glutamic moieties
having double dodecyl chains, and linked alkyl spacers with
different length. It was found that all these homologous com-
pounds could immobilize medium polarity solvents more read-
ily. In low-polarity solvents, these gelators were insoluble,
while in high-polarity solvents, precipitates were obtained. The
investigation of XRD, FTIR, UV, and temperature-dependent
1H NMR spectra indicated that self-assemblies of supramolec-
ular gels were induced by hydrogen bonding, hydrophobic in-
teractions, and p–p stacking. Of all, the LG12-(CH2)11-BSA gels
exhibited self-healing properties owing to flexibility of longer
methylene spacers and multiple-stimulus responsibility, such as
heating, shaking, and sonication. The results of CD spectra re-
vealed that the supramolecular chirality induced by self-assem-
bled chiral gelator molecules in gels was also closely related to
the length of methylene spacers. The longer the alkyl spacers,
the weaker the transmitted supramolecular chirality. Further-
more, we found that the length of spacers also played impor-
tant role in the formation of nanostructures in gels. Only LG12-
(CH2)1-BSA gelators, which had the shortest spacers, formed
right-handed nanoscale chiral twists owing to crowded hydro-
gen-bond interactions. Moreover, the high-polarity solvent,
DMF, was found to be able to regulate such chiral twist as well
as its pitch length readily. The results revealed that the spacer
length between the aromatic ring and the amphiphilic l-gluta-
mide played a key role in regulating the formation of the gels
as well as their properties.
Boc-12-aminododecanoic acid (Boc-NH2-(CH2)11COOH): The synthet-
ic method was modified from preparation of Boc-glycine.[18] The
main procedures were as follows: A mixture of di-tert-butyl dicar-
bonate (6.55 g, 30 mmol) in 90 mL of THF/H2O (1:2, v/v) was added
dropwise to a stirred solution of 12-aminododecanoic acid (5.4 g,
25 mmol) in THF/H2O (1:2, v/v, 90 mL) containing 3.2 g of Na2CO3
under ice bath during half an hour. Then, the mixture was allowed
to warm to room temperature and stirred for 12 h. Afterwards, the
mixture was adjusted to pH 4–5 by 1 molLÀ1 of HCl aqueous solu-
tion carefully. The obtained white precipitate was collected by fil-
tration and dried in vacuum. Recrystallization from methanol (3”
1
200 mL) to give 6.3 g of white pure product, yield: 80%. H NMR
(400 MHz, CDCl3; Supporting Information, Figure S1): 1.22–1.32 (m,
16H), 1.45 (s, 9H), 1.62 (m, 2H), 2.34 (t, J=7.2 Hz, 2H), 3.09 (t, J=
6.8 Hz, 2H), 4.51 (s, 1H). Elemental analysis calcd for C17H33NO4:
C 64.73, H 10.54, N 4.44; found: C 64.65, H 10.41, N 4.52.
Synthesis of LG12-(CH2)n-NH2-Boc (2a–d): 2.41 g of LG12 (1, 5 mmol),
whose synthetic method was elucidated in our recent report,[13l]
and 5.02 mmol of Boc-NH2-(CH2)nCOOH (n=1, 3, 5, and 11) was dis-
solved in dichloromethane (100 mL). Then, 1-ethyl-3-(3-dimethylla-
minopropyl)carbodiimide hydrochloride (EDC·HCl; 1.15 g) and 1-hy-
droxybenzotrizole (HOBt; 0.81 g) were added. The mixture was
stirred at room temperature for 24 h. After removal of the solvents,
the remained substance was dissolved in 100 mL of ethanol and
then poured into the 0.5% Na2CO3 aqueous solution (1 L). The ob-
tained white solid was filtered and dried in vacuum to give crude
products 2a–d, which was not further purified for next step.
Synthesis of LG12-(CH2)n-NH2 (3a–d): The crude products 2a–d
(4 mmol), respectively, were dissolved in dichloromethane (20 mL).
Afterwards, trifluoroacetic acid (4 mL) was added. The formed
transparent solution was stirred at room temperature for 6 h. After
removal of the solvents, the remained substance was dissolved in
100 mL of THF and then poured into 0.5% Na2CO3 aqueous solu-
tion (1 L). The obtained white solid was filtered and dried in
vacuum. Recrystallization from ethanol (3”80 mL) afforded the
pure products, LG12-(CH2)n-NH2 (3a–d). All of these four com-
Experimental Section
Materials and synthesis: All starting materials, including Boc-gly-
cine, Boc-4-aminobutyric acid, and Boc-6-aminohexanoic acid (Boc-
NH2-(CH2)nCOOH, n=1, 3, and 5; Boc=tert-butoxycarbonyl) were
obtained from commercial suppliers and used as received. Solvents
were purified and dried according to standard methods. The syn-
thetic route is shown in Scheme 2.
1
pounds were not characterized by H NMR, MALDI-TOF MS, or ele-
mental analysis before the next synthesis.
Synthesis of LG12(CH2)n-BSA (n=1, 3, 5, and 11): 2,2’-biisonicotinic
acid (366 mg, 1.5 mmol) and LG12-(CH2)n-NH2 (3a–d; 3 mmol) were
Chem. Eur. J. 2015, 21, 7562 – 7570
www.chemeurj.org
7568
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Paper
dissolved in a solution of THF/CH2Cl2 (100 mL, 2:1, v/v). Then
EDC·HCl (740 mg, 3.75 mmol) and HOBT (506 mg, 3.69 mmol) were
added. The reaction mixture was stirred at 508C for 12 h. After re-
moval of solvents, the remained solids were dissolved in THF
(50 mL) and then poured into 0.5% Na2CO3 aqueous solution (1 L).
The collected precipitate were recrystallized from 3”100 mL of
CH3OH/CHCl3 (8:1, v/v) to obtain the pure products, LG12(CH2)n-
BSA. Yield: LG12(CH2)1-BSA, 1.32 g, 68%; LG12(CH2)3-BSA, 1.51 g,
75%; LG12(CH2)5-BSA, 1.64 g, 78%; and LG12(CH2)11-BSA, 1.88 g, 80%.
LG12(CH2)1-BSA: 1H NMR (600 MHz, CDCl3:CD3OD=1:1, v/v): 0.86–
0.90 (t, J=6.0 Hz, 12H), 1.26–1.47 (m, 66H), 1.43–1.45 (m, 8H),
1.47–1.53 (m, 4H), 1.90–1.92 (m, 2H), 2.07–2.10 (m, 2H), 2.23–2.30
(m, 4H), 3.07–3.13 (m, 4H), 3.21 (t, J=7.2 Hz, 4H), 3.36 (s, 2H), 4.11
(m, 4H), 4.36 (m, 2H), 7.89 (d, J=4.8 Hz, 2H), 8.84 (d, J=5.4 Hz,
2H), 8.91 (s, 2H). MALDI-TOF-MS: calcd for C74H128N10O8: 1285.9
Found: 1308.3 (M+Na)+, 1324.3 (M+K)+. Elemental analysis calcd
for C74H128N10O8: C 69.12, H 10.03, N 10.89; found: C 68.95, H 10.00,
a Carlo-Erba-1106 instrument. SEM was carried out on a Hitachi
S4300 FE-SEM microscope. The fully aging gels were cast onto
single-crystal silica plates (Pt coated), and any trapped solvent in
the gels was evaporated first under ambient conditions and then
under vacuum for 12 h for SEM measurements. Cast films or xero-
gel on silica plate were prepared for the measurement of FTIR
spectra on a Bruker Tensor 27 FTIR spectrometer at room tempera-
ture. Glass-sustained xerogel films were used for X-ray diffraction
(XRD) measurements on a Rigaku D/Max-2500 X-ray diffractmeter
(Japan) with CuKa radiation (l=1.5406 Š), which was operated at
45 kV, 100 mA. UV and circular dichroism (CD) spectra were ob-
tained on JASCO UV-550 and JASCO J-810 CD spectrophotometers,
respectively. Rheological measurements were carried out with
a stress-controlled rheometer (TA Instruments, AR-G2) equipped
with steel parallel-plate geometry (40 mm diameter) at room tem-
perature. Strain sweep at a constant frequency (6.28 rad·sÀ1) was
performed in the 0.05–200% range. The frequency sweep was ob-
tained from 0.1 to 100 radsÀ1 at a constant strain of 0.1%. The con-
tinuous step stain measurement was conducted when 50 seconds
were allowed for the recovery of gels after the strain sweep.
1
N 10.73. LG12(CH2)3-BSA: H NMR (600 MHz, CDCl3:CD3OD=1:1, v/v):
0.86–0.90 (t, J=6.0 Hz, 12H), 1.24–1.30 (m, 68H), 1.48–1.50 (m,
8H), 1.90–2.06 (m, 8H), 2.26 (t, J=6.4 Hz, 4H), 2.37 (t, J=7.2 Hz,
4H), 3.18 (m, 8H), 3.36 (s, 4H), 3.49 (t, J=6.6 Hz, 4H), 4.35 (m, 2H),
7.85 (s, 2H), 8.78 (s, 2H), 8.82 (d, J=4.2 Hz, 2H). MALDI-TOF-MS:
calcd for C78H136N10O8: 1342.0. Found: 1364.2 (M+Na)+, 1380.3
(M+K)+. Element analysis calcd for C78H136N10O8: C 69.81, H 10.22,
N 10.44; found: C 69.95, H 10.21, N 10.25. LG12(CH2)5-BSA: 1H NMR
(600 MHz, CDCl3:CD3OD=1:1, v/v): 0.86–0.90 (t, J=6.6 Hz, 12H),
1.24–1.35 (m, 70H), 1.40–1.53 (m, 12H), 1.69 (m, 8H), 1.87 (m, 2H),
2.02 (m, 2H), 2.20–2.30 (m, 8H), 3.17 (t, J=7.2 Hz, 8H), 3.36 (s, 2H),
3.47 (m, 4H), 4.30 (m, 2H), 7.81 (d, J=4.2 Hz, 2H), 8.41 (s, 1H), 8.71
(s, 2H), 8.81 (d, J=4.8 Hz, 2H). MALDI-TOF-MS: calcd for
C82H144N3O5: 1398.1. Found: 1420.3 (M+Na)+, 1435.3 (M+K)+. Ele-
mental analysis calcd for C82H144N3O5: C 70.44, H 10.38, N 10.02;
found: C 70.58, H 10.29, N 10.09. LG12(CH2)11-BSA: 1H NMR
(600 MHz, CDCl3:CD3OD=1:1, v/v): 0.86–0.90 (t, J=6.6 Hz, 12H),
1.24–1.55 (m, 108H), 1.61–1.66 (m, 8H), 1.87 (m, 2H), 2.00 (m, 2H),
2.23 (m, 8H), 3.17 (m, 8H), 3.36 (s, 2H), 3.45 (t, J=7.2 Hz, 4H), 4.30
(m, 2H), 7.82 (d, J=4.8 Hz, 2H), 8.66 (s, 2H), 8.80 (d, J=4.8 Hz, 2H).
MALDI-TOF-MS: calcd for C94H168N10O8: 1566.4. Found: 1588.6 (M+
Na)+, 1604.6 (M+K)+. Elemental analysis calcd for C94H168N10O8:
C 72.08, H 10.81, N 8.94; found: C 71.98, H 10.99, N 9.09.
Acknowledgements
This work was supported by the Natural Science Foundation
of Guangdong Province, China (Nos. S2013010011844), the
Basic Research Development Program (2010CB833305,
2013CB834504), and the National Natural Science Foundation
of China (Nos. 91027042, 21021003, 21227802, 21321063).
Keywords: chiral twists · gels · l-glutamic gelators · self-
assembly · supramolecular chirality
[1] a) J. H. van Esch, B. L. Feringa, Angew. Chem. Int. Ed. 2000, 39, 2263–
2266; Angew. Chem. 2000, 112, 2351–2354; b) O. Gronwald, E. Snip, S.
Shinkai, Curr. Opin. Colloid Interface Sci. 2002, 7, 148–156; c) N. Sangee-
tha, U. Maitra, Chem. Soc. Rev. 2005, 34, 821–836; d) M. George, R.
Weiss, Acc. Chem. Res. 2006, 39, 489–497; e) R. Weiss, Langmuir 2009,
25, 8369–8369; f) P. Dastidar, Chem. Soc. Rev. 2008, 37, 2699–2715;
g) M. Piepenbrock, G. Lloyd, N. Clarke, J. Steed, Chem. Rev. 2010, 110,
1960–2004; h) A. Dawn, T. Shiraki, S. Haraguchi, S. Tamaru, S. Shinkai,
Chem. Asian J. 2011, 6, 266–282; i) G. Yu, X. Yan, C. Han, F. Huang,
Chem. Soc. Rev. 2013, 42, 6697–6722.
[2] a) S. Yagai, T. Iwashima, K. Kishikawa, S. Nakahara, T. Karatsu, A. Kita-
mura, Chem. Eur. J. 2006, 12, 3984–3994; b) S. Matsumoto, S. Yamagu-
chi, S. Ueno, H. Komatsu, M. Ikeda, K. Ishizuka, Y. Iko, K. Tabata, H. Aoki,
S. Ito, H. Noji, I. Hamachi, Chem. Eur. J. 2008, 14, 3977–3986; c) S. Tame-
sue, Y. Takashima, H. Yamaguchi, S. Shinkai, A. Harada, Angew. Chem. Int.
Ed. 2010, 49, 7461–7464; Angew. Chem. 2010, 122, 7623–7626; d) M.
Ikeda, T. Yoshii, T. Matsui, T. Tanida, H. Komatsu, I. Hamachi, J. Am. Chem.
Soc. 2011, 133, 1670–1673; e) R. Du, J. Wu, L. Chen, H. Huang, X.
Zhang, J. Zhang, small 2014, 10, 1387–1393.
[3] a) K. Isozaki, H. Takay, T. Naota, Angew. Chem. Int. Ed. 2007, 46, 2855–
2857; Angew. Chem. 2007, 119, 2913–2915; b) J. Wu, T. Yi, T. Shu, M. Yu,
Z. Zhou, M. Xu, Y. Zhou, H. Zhang, J. Han, F. Li, C. Huang, Angew. Chem.
Int. Ed. 2008, 47, 1063–1067; Angew. Chem. 2008, 120, 1079–1083;
c) D. Bardelang, F. Camerel, J. Margeson, D. Leek, M. Schmutz, M.
Zaman, K. Yu, D. Soldatov, R. Ziessel, C. Ratcliffe, J. Ripmeester, J. Am.
Chem. Soc. 2008, 130, 3313–3315; d) X. Hou, D. Gao, J. Yan, Y. Ma, K.
Liu, Y. Fang, Langmuir 2011, 27, 12156–12163; e) J. Malicka, A. Sandeep,
F. Monti, E. Bandini, M. Gazzano, C. Ranjith, V. Praveen, A. Ajayaghosh,
N. Armaroli, Chem. Eur. J. 2013, 19, 12991–13001.
Self-assembly experiments: A weighed sample of a homologous
LG12-(CH2)n-BSA gelator was mixed with
a solvent (1 mL) in
a septum-capped vial and heated in an oil bath until the solid was
dissolved. Then the sample vial was cooled to room temperature.
The aggregation state was then assessed. If no flow was observed
when inverting the vial, a stable gel was formed and noted as gela-
tion (G). If part of the mixture formed a gel but flow was still ob-
served, the phenomenon was recorded as partial gelation (PG). If
precipitation occurred, P was noted. And if the compound was
unable to dissolve, it was noted as insoluble (I). Repeated heating
and cooling confirmed the thermo-reversibility of the gelation pro-
cess. The critical gelation concentration (CGC) of the gelators was
determined by measuring the minimum amount of gelator re-
quired for the formation of a stable gel at room temperature.
0.001 mmol of each LG12-(CH2)n-BSA gelator was used to form gels
in 1 mL of THF or mixed THF/DMF for the measurements of UV,
FTIR, XRD, and CD spectra. Accordingly, the concentration of CHCl3
solution from LG12-(CH2)n-BSA gelator for the UV and FTIR measure-
ments was also fixed as 0.001 mmolmLÀ1
.
Instruments and methods: 1H NMR spectra were recorded on
a Bruker AV400 or AV600 spectrometer. Matrix-assisted laser de-
sorption ionization time-of-flight (MALDI-TOF) MS was measured
on a BIFLEIII instrument. Elemental analysis was performed on
[4] a) M. Shirakawa, N. Fujita, S. Shinkai, J. Am. Chem. Soc. 2005, 127, 4164–
4165; b) X. Huang, S. Raghavan, P. Terech, R. Weiss, J. Am. Chem. Soc.
2006, 128, 15341–15352; c) W. Weng, J. B. Beck, A. Jamieson, S. Rowan,
Chem. Eur. J. 2015, 21, 7562 – 7570
www.chemeurj.org
7569
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Paper
J. Am. Chem. Soc. 2006, 128, 11663–11672; d) L. Fang, H. Zhang, Z. Li, Y.
Zhang, Y. Zhang, H. Zhang, Macromolecules 2013, 46, 7650–7660; e) P.
Xing, X. Chu, S. Li, M. Ma, A. Hao, Chemphyschem 2014, 15, 2377–2385;
f) Z. Qi, C. Schalley, Acc. Chem. Res. 2014, 47, 2222–2233.
D. Amabilino, N. Avarvari, J. Am. Chem. Soc. 2011, 133, 8344–8353; d) J.
Wang, H. Lu, R. Kamat, S. Pingali, V. Urban, J. Cheng, Y. Lin, J. Am. Chem.
Soc. 2011, 133, 12906–12909; e) E. Lee, B. Hammer, J. Kim, Z. Page, T.
Emrick, R. Hayward, J. Am. Chem. Soc. 2011, 133, 10390–10393; f) Y. Fu,
B. Li, Z. Huang, Y. Li, Y. Yang, Langmuir 2013, 29, 6013–6017; g) Y. Oka-
zaki, J. Cheng, D. Dedovets, G. Kemper, M. Delville, M. Durrieu, H. Ihara,
M. Takafuji, E. Pouget, R. Oda, ACS Nano 2014, 8, 6863–6872.
[5] a) J. Webb, M. Crossley, P. Turner, P. Thordarson, J. Am. Chem. Soc. 2007,
129, 7155–7162; b) H. Maeda, Y. Haketa, T. Nakanishi, J. Am. Chem. Soc.
2007, 129, 13661–13674; c) Z. Zhang, N. Krishna, M. Lettinga, J. Verm-
ant, E. Grelet, Langmuir 2009, 25, 2437–2442; d) J. Liu, Y. Yang, C. Chen,
J. Ma, Langmuir 2010, 26, 9040–9044; e) C. Bowerman, W. Liyanage, A.
Federation, B. Nilsson, Biomacromolecules 2011, 12, 2735–2745; f) B.
Nieto-Ortega, V. Nebot, J. Miravet, B. Escuder, J. López Navarrete, J.
Casado, F. Ramírez, J. Phys. Chem. Lett. 2012, 3, 2120–2124.
[6] a) J. Puigmartí-Luis, V. Laukhin, A. del Pino, J. Vidal-Gancedo, C. Rovira,
V. Laukhina, D. Amabilino, Angew. Chem. Int. Ed. 2007, 46, 238–241;
Angew. Chem. 2007, 119, 242–245; b) J. Puigmartí-Luis, E. Laukhina, J.
Esquena, V. Laukhin, C. Rovira, J. Vidal-Gancedo, A. Kanaras, R. Nichols,
M. Brust, D. Amabilino, Angew. Chem. Int. Ed. 2008, 47, 1861–1865;
Angew. Chem. 2008, 120, 1887–1891; c) M. Yoshio, Y. Shiko, Y. Tochigi, Y.
Nishikawa, T. Kato, J. Am. Chem. Soc. 2009, 131, 6763–6767; d) C. Wang,
Q. Chen, F. Sun, D. Zhang, G. Zhang, Y. Huang, R. Zhao, D. Zhu, J. Am.
Chem. Soc. 2010, 132, 3092–3096.
[7] a) H. Komatsu, S. Matsumoto, S. Tamaru, K. Kaneko, M. Ikeda, I. Hamachi,
J. Am. Chem. Soc. 2009, 131, 5580–5585; b) Z. Ge, J. Hu, F. Huang, S.
Liu, Angew. Chem. Int. Ed. 2009, 48, 1798–1802; Angew. Chem. 2009,
121, 1830–1834; c) F. Zhao, Y. Gao, J. Shi, H. Browdy, B. Xu, Langmuir
2011, 27, 1510–1512; d) S. Dong, Y. Luo, X. Yan, B. Zheng, X. Ding, Y.
Yu, Z. Ma, Q. Zhao, F. Huang, Angew. Chem. Int. Ed. 2011, 50, 1905–
1909; Angew. Chem. 2011, 123, 1945–1949; e) D. Mandal, T. Kar, P. Das,
Chem. Eur. J. 2014, 20, 1349–1358; f) Z. Sun, Q. Huang, T. He, Z. Li, Y.
Zhang, L. Yi, Chemphyschem 2014, 15, 2421–2430.
[8] a) M. George, R. Weiss, J. Am. Chem. Soc. 2001, 123, 10393–10394; b) S.
Kawano, N. Fujita, S. Shinkai, J. Am. Chem. Soc. 2004, 126, 8592–8593;
c) J. Liu, P. He, J. Yan, X. Fang, J. Peng, K. Liu, Y. Fang, Adv. Mater. 2008,
20, 2508–2511; d) G. Lloyd, J. Steed, Nat. Chem. 2009, 1, 437–442; e) H.
Komatsu, S. Tsukiji, M. Ikeda, I. Hamachi, Chem. Asian J. 2011, 6, 2368–
2375; f) S. Dong, B. Zheng, D. Xu, X. Yan, M. Zhang, F. Huang, Adv.
Mater. 2012, 24, 3191–3195; g) P. Xue, R. Lu, J. Jia, M. Takafuji, H. Ihara,
Chem. Eur. J. 2012, 18, 3549–3558; h) X. Yan, D. Xu, X. Chi, J. Chen, S.
Dong, X. Ding, Y. Yu, F. Huang, Adv. Mater. 2012, 24, 362–369; i) S.
Chen, L. Chen, H. Yang, H. Tian, W. Zhu, J. Am. Chem. Soc. 2012, 134,
13596–13599; j) Z. Liu, Y. Feng, Z. Zhao, Z. Yan, Y. He, X. Luo, C. Liu, Q.
Fan, Chem. Eur. J. 2014, 20, 533–541; k) Z. Li, Y. Zhang, C. Zhang, L.
Chen, C. Wang, H. Tan, Y. Yu, X. Li, H. Yang, J. Am. Chem. Soc. 2014, 136,
8577–8589; l) T. He, K. Li, N. Wang, Y. Liao, X. Wang, X. Yu, soft Matter
2014, 10, 3755–3761; m) K. Fan, J. Yang, X. Wang, J. Song, soft Matter
2014, 10, 8370–8375; n) C. Yuan, J. Guo, M. Tan, M. Guo, L. Qiu, F. Yan,
ACS Macro Lett. 2014, 3, 271–275; o) S. Dong, J. Yuan, F. Huang, Chem.
Sci. 2014, 5, 247–252.
[12] a) T. Muraoka, H. Cui, S. Stupp, J. Am. Chem. Soc. 2008, 130, 2946–2947;
b) D. Kurouski, R. Lombardi, R. Dukor, I. Lednev, L. Nafie, Chem.
Commun. 2010, 46, 7154–7156; c) M. Mukai, H. Minamikawa, M.
Aoyagi, M. Asakawa, T. Shimizu, M. Kogiso, Soft Matter 2012, 8, 11979–
11981; d) A. Gopal, M. Hifsudheen, S. Furumi, M. Takeuchi, A. Ajaya-
ghosh, Angew. Chem. Int. Ed. 2012, 51, 10505–10509; Angew. Chem.
2012, 124, 10657–10661; e) H. Cao, Q. Yuan, X. Zhu, Y. Zhao, M. Liu,
Langmuir 2012, 28, 15410–15417; f) T. Qi, V. Maurizot, H. Noguchi, T.
Charoenraks, B. Kauffmann, M. Takafuji, H. Ihara, I. Huc, Chem. Commun.
2012, 48, 6337–6339; g) Q. Jin, L. Zhang, M. Liu, Chem. Eur. J. 2013, 19,
9234–9241; h) J. Li, K. Fan, X. Guan, Y. Yu, J. Song, Langmuir 2014, 30,
13422–13429; i) C. Liu, Q. Jin, K. Lv, L. Zhang, M. Liu, Chem. Commun.
2014, 50, 3702–3705; j) R. Tamoto, N. Daugey, T. Buffeteau, B. Kauff-
mann, M. Takafuji, H. Ihara, R. Oda, Chem. Commun. 2014, DOI: 10.1039/
c4cc07972h; k) H. Cao, X. Zhu, M. Liu, Angew. Chem. Int. Ed. 2013, 52,
4122–4126; Angew. Chem. 2013, 125, 4216–4220; l) X. Wang, P. Duan,
M. Liu, Chem. Commun. 2012, 48, 7501–7503.
[13] a) P. Mukhopadhyay, N. Fujita, A. Takada, T. Kishida, M. Shirakawa, S.
Shinkai, Angew. Chem. Int. Ed. 2010, 49, 6338–6342; Angew. Chem.
2010, 122, 6482–6486; b) T. Hamilton, D. Bucar, J. Baltrusaitis, D. Flana-
gan, Y. Li, S. Ghorai, A. Tivanski, L. MacGillivray, J. Am. Chem. Soc. 2011,
133, 3365–3371; c) M. Nakahata, Y. Takashima, H. Yamaguchi, A. Harada,
Nat. Commun. 2011, 2, 511 –517; d) A. Dawn, T. Shiraki, H. Ichikawa, A.
Takada, Y. Takahashi, Y. Tsuchiya, L. Lien, S. Shinkai, J. Am. Chem. Soc.
2012, 134, 2161–2171; e) M. Zhang, D. Xu, X. Yan, J. Chen, S. Dong, B.
Zheng, F. Huang, Angew. Chem. Int. Ed. 2012, 51, 7011–7015; Angew.
Chem. 2012, 124, 7117–7121; f) Y. Liu, T. Wang, M. Liu, Chem. Eur. J.
2012, 18, 14650–14659; g) W. Fang, Z. Sun, T. Tu, J. Phys. Chem. C 2013,
117, 25185–25194; h) T. Kakuta, Y. Takashima, M. Nakahata, M. Otsubo,
H. Yamaguchi, A. Harada, Adv. Mater. 2013, 25, 2849–2853; i) D. Liu, D.
Wang, M. Wang, Y. Zheng, K. Koynov, G. Auernhammer, H. Butt, T. Ikeda,
Macromolecules 2013, 46, 4617–4625; j) A. Harada, Y. Takashima, M. Na-
kahata, Acc. Chem. Res. 2014, 47, 2128–2140; k) S. Dong, B. Zheng, F.
Wang, F. Huang, Acc. Chem. Res. 2014, 47, 1982–1994; l) W. Miao, L.
Qin, D. Yang, X. Jin, M. Liu, Chem. Eur. J. 2014, DOI: 10.1002/
chem.201405406; m) X. Yan, D. Xu, J. Chen, M. Zhang, B. Hu, Y. Yu, F.
Huang, Polym. Chem. 2013, 4, 3312–3322.
[14] a) D. Allara, R. Nuzzo, Langmuir 1985, 1, 45–52; b) D. Allara, R. Nuzzo,
Langmuir 1985, 1, 52–66.
[15] a) D. Moore, M. Rerek, J. Phys. Chem. B 1997, 101, 8933–8940; b) T. Le B-
ihan, M. Pezolet, Chem. Phys. Lipids 1998, 94, 13–33.
[9] a) E. Schçn, E. MarquØs-López, R. Herrera, C. Alemµn, D. Díaz Díaz,
Chem. Eur. J. 2014, 20, 10720–10731; b) Y. Feng, Y. He, Q. Fan, Chem.
Asian J. 2014, 9, 1724–1750.
[16] a) L. Zhang, C. Liu, Q. Jin, X. Zhu, M. Liu, soft Matter 2013, 9, 7966–
7973; b) X. Wang, M. Liu, Chem. Eur. J. 2014, 20, 10110–10116.
[17] a) P. Duan, Y. Li, L. Li, J. Deng, M. Liu, J. Phys. Chem. B 2011, 115, 3322–
3329; b) W. Miao, L. Zhang, X. Wang, H. Cao, Q. Jin, M. Liu, Chem. Eur. J.
2013, 19, 3029–3036.
[10] a) C. Cameron, C. Lee, E. Meijer, A. Schenning, Chem. Soc. Rev. 2009, 38,
671–683; b) J. Crassous, Chem. Soc. Rev. 2009, 38, 830–845; c) P. Duan,
H. Cao, L. Zhang, M. Liu, Soft Matter 2014, 10, 5428–5448; d) L. Zhang,
L. Qin, X. Wang, H. Cao, M. Liu, Adv. Mater. 2014, 26, 6959–6964.
[11] a) A. Ajayaghosh, P. Chithra, R. Varghese, Angew. Chem. Int. Ed. 2007, 46,
230–233; Angew. Chem. 2007, 119, 234–237; b) C. Li, K. Deng, Z. Tang,
L. Jiang, J. Am. Chem. Soc. 2010, 132, 8202–8209; c) I. Danila, F. RiobØ, F.
Piron, J. Josep Puigmartí-Luis, J. Wallis, M. Linares, H. Šgren, D. Beljonne,
[18] R. Houssin, J. Bernier, J. HØnichard, Synthesis 1988, 259–261.
Received: January 9, 2015
Revised: February 10, 2015
Published online on April 1, 2015
Chem. Eur. J. 2015, 21, 7562 – 7570
www.chemeurj.org
7570
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim