Versatile supramolecular gelling agents: Unusual stabilization of physical gels by lithium ions

Article abstract of DOI:10.1002/chem.201002185

Stuck Li-ke glue: Oligo(ethylene oxide)-bridged bis(cyclodipeptides) exhibited remarkable enhancement of gelation ability by the addition of Li ⁺ (see figure). By coordination of metal ions to the oligo(ethylene oxide) chain, terminal cyclodipeptides may move closer and more easily form the hydrogen-bonded-sheet structure of cyclodipeptides.

Full text of DOI:10.1002/chem.201002185

COMMUNICATION
DOI: 10.1002/chem.201002185
Versatile Supramolecular Gelling Agents: Unusual Stabilization of Physical
Gels by Lithium Ions
Jung-A Kim, Young-Hwan Jeong, and Woo-Dong Jang*[a]
Dedicated to the memory of the late Professor Chi Sun Hahn
Supramolecular physical gels,[1–2] which are formed by
noncovalent weak interactions among small organic molecu-
lar gelling agents, have potential for applications[3] in various
fields, such as templates for functional materials,[4] drug de-
livery,[5] sensors,[6] cosmetics,[7,8] matrixes for tissue culture,[9]
separation media,[10] and food processing agents.[8] Hydrogen
bonding[11] is the most common interaction for the formation
of physical gels due to strong and directional characteristics.
Cyclodipeptide moieties[12–14] can be powerful motifs for the
formation of a supramolecular assembly because they can
provide multiple hydrogen-bonding sites with C2 symmetry.
Additionally, the diversity of the amino acid library can pro-
vide structural flexibility for molecular design. Ishida and
Aida reported supramolecular polymers using xylene-
bridged bis(cyclodipeptide), which forms large homochiral
supramolecular polymers in solution.[12] Hanabusa et al. syn-
thesized a wide range of cyclodipeptides and examined gela-
tion behavior for various organic solvents.[13] However, only
limited cyclodipeptides formed physical gels in some organic
solvents with typically a low polarity index. Most cyclodi-
peptides resulted in precipitation or crystallization in polar
solvents due to the hydrophobic side groups. Alternatively,
Feng et al. recently reported that cyclo(l-Tyr-l-Lys) can
form physical gels in several polar organic solvents and
aqueous media, and not with low polarity solvents.[14]
the corresponding dipeptide-conjugated oligo(ethylene
oxides), which were prepared by simple alkali-mediated
coupling reactions between ditosyl oligo(ethylene oxides)
and phenolic OH of the dipeptide moiety and successive de-
protection of tert-butyloxycarbonyl (Boc) groups. Because
cyclodipeptides provide strong and directional hydrogen
bonding sites, compounds 1–3 may form ordered supra-
molecular architectures. In fact, compounds 1–3 exhibited
versatile gelation phenomena. When compounds 1–3 were
dissolved in CHCl3 (20.0 gLÀ1) and incubated for 1 h at
room temperature, the formation of stable physical gels was
observed. The time required for the physical gel formation
was considerably shortened (1 min for 10.0 gLÀ1of 3) with
ultrasonic treatment. Notably, gelation occurred in a wide
range of organic solvents with very low critical gelation con-
centrations (CGCs), when the CGCs were predominately
less than 1 wt% (Table 1). In general, the strength of hydro-
gen bonds decreases under polar conditions, however, com-
pounds 1–3 showed significant gelation abilities in hydro-
philic solvents and polar protic solvents. More interestingly,
compounds 1–3 formed physical gels also in distilled water
Table 1. CGC values [gLÀ1] of 1–3 in various solvents.
Solvent
1
2
3
Herein, we report unique and powerful supramolecular
gelling agents for a wide range of hydrophobic and -philic
solvents, including aqueous media, highlighted by the unusu-
al stabilization of hydrogels with Li+.
A series of oligo(ethylene oxide)-bridged bis(cyclodipep-
tide) (1–3) have been synthesized by cyclization reaction of
CH2Cl2
CHCl3
THF
acetone
acetonitrile
MeOH
EtOH
propanol
butanol
pentanol
hexanol
14.0
9.4
9.0
7.5
5.3
5.5
5.2
5.1
4.7
4.9
4.3
4.0
13.0
9.0
10.6
7.5
10.0
9.8
7.3
4.8
5.6
4.4
4.5
4.2
3.9
3.9
5.0
17.0
10.9
12.0
12.7
8.8
17.0
12.0
6.0
4.6
6.2
4.7
4.9
7.7
7.4
8.0
11.5
12.0
17.5
[a] J.-A. Kim, Y.-H. Jeong, Prof. W.-D. Jang
Department of Chemistry, College of Science
Yonsei University, 262 Seongsanno, Seodaemun-gu
Seoul 120-749 (Korea)
octanol
di(ethylene glycol)
tri(ethylene glycol)
PEG 400
Fax : (+82)2-364-7050
E-mail: wdjang@yonsei.ac.kr
Chem. Eur. J. 2010, 16, 13955 – 13959
ꢀ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
13955

with CGCs of 6.0, 6.0, and 17.0 gLÀ1, respectively. Although
many types of low-molecular-weight gelling agents have
been reported, limited examples have shown hydrogel for-
mation. But those hydrogelators mostly form precipitates in
nonpolar hydrophobic solvents. However, compounds 1–3
exhibited versatile gelation ability, which might be due to
the existence of amphiphilic characteristics in the oligo
(ethylene oxide) chains.
shorter oligo(ethylene oxide) chain length. In contrast to the
small-angle diffraction, the wide-angle diffractions showed
the same peak patterns without dependence on the length
of the oligo(ethylene oxide) chains. Based on the peak pat-
terns, the packing structure of the gelators were oblique
structures (a=0.643 nm, b=0.594 nm, g=66.38), which coin-
cide with crystallographic data from previously reported ex-
amples.[13] The assigned crystallographic structure of com-
pound 3 in the gelled state is shown in Figure 2d. The gela-
tors adopt fully extended conformations, regardless of the
oligo(ethylene oxide) chain length and form fibrous assem-
bly structures through hydrogen-bonding interaction among
cyclodipeptide moieties.
To obtain detailed information on the hydrogen-bonding
interactions, infrared absorption spectra were measured for
To investigate the structures
and morphologies of com-
pounds 1–3, a thin film of the
hydrogels was dried in vacuo
for 1 h, and then the specimens
were examined by field-emis-
sion scanning electron micros-
copy (FE-SEM) and X-ray dif-
fraction (XRD). The FE-SEM
images of the dried gel showed
a three-dimensional network of
nanofibers, in which the aver-
age diameter of the elemental
Figure 1. FE-SEM images of dried gels 1 (a), 2 (b), and 3 (c).
fibrils
were
approximately
60 nm, regardless of the oligo
(ethylene oxide) chain length
(Figure 1). XRD measurements
of dried gels were performed at
258C by using a synchrotron in
transmission mode. As shown
in Figure 2, the three com-
pounds showed similar diffrac-
tion patterns, indicating that
they have very similar self-as-
sembly patterns in the gel state.
In the small-angle region, the
diffraction patterns showed la-
mellar packing of each mole-
cule. For example, compound 3
exhibited three sharp reflection
peaks at d spacings of 1.97,
0.98, and 0.65 nm, correspond-
ing to the 100, 200, and 300
planes, respectively (Figure 2b).
The diffraction of compounds 1
and 2 also showed similar pat-
terns, however, the d spacings
were slightly smaller than those
Figure 2. XRD patterns and proposed packing structure model for xerogels. Xerogels were prepared from hy-
drogels with CGC values of 6.0 (1 and 2) and 17.0 gLÀ1 (3). a) Small-angle X-ray scattering (SAXS) patterns
for 1 (lower), 2 (middle), and 3 (upper). b) Proposed model of 3 from the SAXS pattern. c) Wide-angle X-ray
scattering (WAXS) patterns for 1 (lower), 2 (middle), and 3 (upper). d) Proposed model of 1–3 from WAXS
of compound
3 due to the patterns.
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Chem. Eur. J. 2010, 16, 13955 – 13959

Versatile Supramolecular Gelling Agents
COMMUNICATION
compounds 1–3. Figure 3 shows the FTIR spectra for gels
and solutions of compounds 1–3 in CHCl3. To measure the
FTIR spectrum of each solution state, the concentrations of
surprisingly decreased, as summarized in Table 2. The en-
hancement of gelation by Li+ addition was higher for com-
pound 3 than 1 and 2. The gelation abilities of compounds
Table 2. CGC values [gLÀ1] of 1–3 with various concentrations of Li+.
Li+[a]
1
2
3
0
0.5
1
2
4
6.0
2.5
2.3
2.3
3.2
4.2
4.4
4.3
9.1
6.0
4.8
4.6
4.0
5.2
5.6
6.4
8.0
8.9
17.0
2.9
2.9
2.9
4.8
5.0
5.6
7.0
9.4
8
16
32
64
[a] Li+/gelators (mol/mol).
1–3 were maximized when the stoichiometry of Li+ to each
gelator was 2:1. At higher ratios, the gelation abilities of
compounds 1–3 gradually decreased with increasing Li+,
possibly due to the interference of hydrogen-bond formation
by the coordination of Li+ to the carbonyl groups. The en-
hancement of gelation may be explained by the coordina-
tion of Li+ to oligo(ethylene oxide) chains. As shown in Fig-
ure 2b, the gelators form two distinct layers: lamellar sheets
of cyclodipeptides and oligo(ethylene oxides) within the fi-
brous structures.
Therefore, by coordination of metal ions to the oligo
(ethylene oxide) chain, terminal cyclodipeptides might move
closer and more easily form the hydrogen-bonded-sheet
structure of cyclodipeptides (Figure 4). In fact, the IR spec-
trum of dried gels containing 64 equivalents of Li+ in com-
Figure 3. FTIR absorption spectra of 1–3 in CHCl3 and in the dried state.
compounds 1–3 were adjusted to 10 times the diluted condi-
tions of the CGC, and a 1 mm path-length liquid cell was
utilized. All three dried gels showed similar IR absorption
patterns, regardless of oligo(ethylene oxide) chain length, in-
dicating the packing modes of the gelators were nearly the
same. Solutions of compounds 1–3 in CHCl3 exhibited C=O
À
and N H stretching vibrational bands near 1680 and
3390 cmÀ1, respectively, corresponding to the non-hydrogen
bonded states of a cis-type amide. Alternatively, the absorp-
tion of C=O and N-H stretching vibration appeared near
1672 and 3310 cmÀ1, respectively, when the dried gels were
measured. Gels in CHCl3 exhibited both signals of those ob-
served in solution and dried-state measurements. The strong
shifts of the vibrational bands indicate that the hydrogen-
bonding interactions among amide bonds play a crucial role
for the formation of physical gels.
À
pound 3 (Figure 3) also exhibited C=O and N H stretching
vibrational bands near 1672 and 3310 cmÀ1, respectively;
these values were nearly identical to those obtained from
dried gels without Li+ addition, indicating the efficient for-
mation of hydrogen bonds. As a result, the binding affinity
of Li+ to the oligo(ethylene oxide) chain is much greater
than that to the carbonyl groups of cyclodipeptides.
In conclusion, oligo(ethylene oxide)-bridged bis(cyclodi-
peptide)s were designed as a new type of supramolecular
gelling agents, and exhibited unique and powerful gelation
behavior in a wide range of solvents. Unlike other gelators
containing cyclodipeptide units, they formed physical gels in
nonpolar and polar protic solvents, including aqueous
media. Furthermore, the gelation abilities were remarkably
enhanced by the addition of Li+. Such unusual characteris-
tics offer potential applications in ion conductive materi-
als.[16] We are currently conducting a new project for the
design of ion conductive materials using gel-contained Li+.
Alkali-metal ions, such as Li+, Na+, and K+, can be coor-
dinated to the lone-pair electrons on the carbonyl group of
the amide. The coordination of metal ions onto the carbonyl
group interferes with hydrogen-bonding formation. For ex-
ample, three-dimensional structures of proteins can be easily
denatured upon high ion strength due to the interference in
hydrogen-bonding interactions by ion coordination.[15]
Therefore, the gelation ability of hydrogen-bonding-based
gelators should decrease with the addition of alkali-metal
ions. However, a very interesting phenomenon was observed
in our system, wherein the gelation abilities of compounds
1–3 were greatly enhanced by the addition of Li+. As previ-
ously mentioned, compounds 1–3 have very high gelation
ability in distilled water, in which the CGC values were 6.0,
6.0, and 17.0 gLÀ1, respectively. By adding a small amount
of Li+ to the gelators, the CGC values of compounds 1–3
Experimental Section
Measurements: Melting points were measured by using a Stuart melting
point apparatus SMP3. 1H NMR spectra were recorded from solutions in
Chem. Eur. J. 2010, 16, 13955 – 13959
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www.chemeurj.org
13957

W.-D. Jang et al.
Figure 4. Li+ assisted gelation process.
CDCl3 and DMSO on a Bruker AM 400 spectrometer. Infrared spectra
were obtained on a JASCO FTIR 430 spectrometer by using a CaF2
plate or a CaF2 window liquid cell. SEM images were obtained by using
a Hitachi S-4300 field-emission scanning electron microscope equipped
with a Horiba EMAX 6853-H EDS system (Center for Microcrystal As-
sembly, Sogang University). X-ray scattering measurements were per-
formed in transmission mode with synchrotron radiation at the 10C1 and
3C2 X-ray beam lines at the Pohang Accelerator Laboratory, Korea.
which was dissolved in butyl alcohol/toluene (15 mL/5 mL) and triethyla-
mine (2 mL) was added to the solution. The reaction mixture was heated
at reflux for 12 h and the precipitated mass was separated by filtration
with diethyl ether. The crude products were obtained by recrystallization
with diethyl ether.
Compound 1. Yield 87%; M.p. 2338C (with decomposition); 1H NMR
(400 MHz, [D6]DMSO): d=8.06 (s, 2H; N-H cyclodipeptide), 8.00 (s,
2H; N-H cyclodipeptide), 7.06 (d, 4H; C6H4 in Tyr), 6.85 (d, 4H; C6H4 in
Tyr), 4.07–3.17 (m, 4H; OCH2 in ethylene oxide), 4.00–4.07 (m, 4H;
OCH2 in ethylene oxide), 3.67–3.74 (m, 4H; CH2 in Tyr), 3.49–3.59 (m,
4H; OCH2 in ethylene oxide), 3.06 (m, 2H; -CH in Tyr), 2.79 (m, 2H;
-CH in Ala), 0.55 ppm (d, 6H;-CH3 in Ala); ESI-MS: m/z: 605.39
[M+Na+].
Compound 2. Yield 84%; M.p. 2138C (with decomposition); 1H NMR
(400 MHz, [D6]DMSO): d=8.05 (s, 2H; N-H cyclodipeptide), 7.99 (s,
2H; N-H cyclodipeptide), 7.05 (d, 4H; C6H4 in Tyr), 6.85 (d, 4H; C6H4 in
Tyr), 4.09–4.14 (m, 4H; OCH2 in ethylene oxide), 3.67–3.74 (m, 4H; CH2
in Tyr), 3.63 (d, J=7.63 Hz, 4H; OCH2 in ethylene oxide), 3.47–3.60 (m,
8H; OCH2 in ethylene oxide), 3.06 (m, 2H; -CH in Tyr), 2.78 (m, 2H;
-CH in Ala), 0.54 ppm (d, 6H;-CH3 in Ala); ESI MS: m/z: 649.41
[M+Na+].
Compound 3. Yield 85%; M.p. 2308C (with decomposition); 1H NMR
(400 MHz, [D6]DMSO): d=8.07 (s, 2H; N-H cyclodipeptide), 8.00 (s,
2H; N-H cyclodipeptide), 7.06 (d, 4H; C6H4 in Tyr), 6.85 (d, 4H; C6H4 in
Tyr), 4.07–4.14 (m, 4H; OCH2 in ethylene oxide), 4.03 (t, 4H), 3.69–3.75
(m, 4H; OCH2 in ethylene oxide), 3.58–3.67 (m, 8H; OCH2 in ethylene
oxide), 3.17 (dd, 4H; OCH2 in ethylene oxide), 3.06 (m, 2H; -CH in
Tyr), 2.79 (m, 2H; -CH in Ala), 0.55 ppm (d, 6H; -CH3 in Ala); ESI MS:
m/z: 693.49 [M+Na+].
Determination of CGC: Compounds 1–3 were mixed with various sol-
vents in a 5 mL vial with a screw cap and the mixtures were heated until
the solid was clearly dissolved. The solution was then cooled to room
temperature and the gel was checked visually by inverting the vials.
Synthesis of dipeptide-conjugated oligo(ethylene oxides): The dipeptide-
conjugated oligo(ethylene oxides) were prepared by using the same pro-
cedure. A representative example is described for bis(Boc-l-Tyr-l-Ala-
OMe)tri(ethylene oxide). Di-p-toluenesulfonyl tri(ethylene oxide) (2.4 g,
5.2 mmol), Boc-l-Tyr-l-Ala-OMe (4.0 g, 20.9 mmol), and K2CO3 (3.6 g,
26.0 mmol) were added to acetonitrile (40 mL) and heated at reflux for
24 h. The reaction mixture was poured into water and extracted with
ethyl acetate. The combined extract was dried over anhydrous magnesi-
um sulfate, and the solvent was removed in vacuo. The crude products
were purified by column chromatography (silica gel) using hexane/ethyl
acetate (3:7) as the eluent to yield a colorless liquid (2.7 g, 58%).
Bis(Boc-l-Tyr-l-Ala-OMe)tri(ethylene oxide): Yield 58%; 1H NMR
(400 MHz, CDCl3): d=7.09 (d, J=8.54 Hz, 4H; C6H4 in Tyr), 6.82 (d, J=
8.54 Hz, 4H; C6H4 in Tyr), 6.49 (brs, 1H; NH in Tyr), 4.53 (t, 2H; C-H
in Tyr), 4.24 (m, 2H; C-H in Ala), 4.07–4.14 (m, 4H; OCH2 in ethylene
oxide), 4.03 (t, J=4.35 Hz, 4H; OCH2 in ethylene oxide), 3.69–3.75 (m,
4H; OCH2 in ethylene oxide), 3.58–3.67 (m, 6H; CO2Me), 2.99 (t, J=
5.87 Hz, 4H; C-CH2-Ar in Tyr), 1.41 (s, 18H; Boc), 1.34 ppm (d, 6H;
OCH3).
Bis(Boc-l-Tyr-l-Ala-OMe)tetra(ethylene oxide): Yield 62%; 1H NMR
(400 MHz, CDCl3): d=7.09 (d, J=8.62 Hz, 4H; C6H4 in Tyr), 6.82 (d,
4H; C6H4 in Tyr), 4.52 (t, 2H; C-H in Tyr), 4.24 (m, 2H; C-H in Ala),
3.82–3.87 (m, 6H; CO2Me), 3.67–3.75 (m, 16H; OCH2 in ethylene
oxide), 2.99 (d, J=6.42 Hz, 4H; C-CH2-Ar in Tyr), 1.41 (d, J=1.83 Hz,
18H; Boc), 1.35 ppm (d, J=7.15 Hz, 6H; OCH3).
Bis(Boc-l-Tyr-l-Ala-OMe)penta(ethylene oxide): Yield 59%; 1H NMR
(400 MHz, CDCl3): d=7.09 (d, J=8.54 Hz, 4H; C6H4 in Tyr), 6.82 (d, J=
8.54 Hz, 4H; C6H4 in Tyr), 6.49 (brs, 2H; NH in Tyr), 5.00 (brs, 1H),
4.50 (t, J=7.17 Hz, 2H; C-H in Tyr), 4.20 (m, 2H; C-H in Ala), 3.83 (t,
J=4.81 Hz, 4H; OCH2 in ethylene oxide), 3.69–3.75 (m, 12H; OCH2 in
ethylene oxide), 3.66–3.69 (m, 4H; OCH2 in ethylene oxide), 3.66 (s, 6H;
CO2Me), 2.97 (t, J=5.87 Hz, 4H; C-CH2-Ar in Tyr), 1.41 (s, 18H; Boc),
1.34 ppm (d, 6H; OCH3).
Acknowledgements
This work was supported by the Defense Acquisition Program Adminis-
tration (DAPA), the Agency for Defense Development (ADD) of Korea,
the National Research Foundation (NRF) of Korea (2009-0078174), and
the Center for Bioactive Molecular Hybrids (CBMH), Yonsei University.
We thank the Pohang Accelerator Laboratory for the use of 10C1 and
3C2 X-ray beam lines. J.-A. Kim, Y.-H. Jeong acknowledge fellowships
from the BK21 program of the Ministry of Education, Science and Tech-
nology.
Keywords: cyclodipeptides
·
ethylene glycol
·
gels
·
Synthesis of compounds 1, 2, and 3: Compounds 1, 2, and 3 were synthe-
sized by using the same procedure. A representative example is described
for 1. Trifluoroacetic acid (TFA, 15 mL) was added to a solution of tri-
(ethylene oxide)bis(Boc-l-Tyr-l-Ala-OMe) (2.1 g, 2.6 mmol) in CH2Cl2
(20 mL) at 08C and was stirred for 2 h. The resulting solution was con-
centrated in vacuo to obtain tri(ethylene oxide)bis(l-Tyr-l-Ala-OMe),
hydrogen bonds · self-assembly
[1] a) J.-M. Lehn in Supramolecular Science: Where It Is and Where It
Is Going (Eds.: R. Ungaro, E. Dalcanale), Kluwer Academic, Dor-
13958
www.chemeurj.org
ꢀ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2010, 16, 13955 – 13959

Versatile Supramolecular Gelling Agents
COMMUNICATION
drecht, 1999, p. 287; b) J.-M. Lehn, Science 2002, 295, 2400–2403;
c) J.-M. Lehn, Chem. Soc. Rev. 2007, 36, 151–160.
tuszak, D. Carroll, Glycobiology 2003, 13, 17–27; c) T. Higashiyama,
Pure Appl. Chem. 2002, 74, 1263–1269; d) G. John, G. Zhu, J. Li,
J. S. Dordick, Angew. Chem. 2006, 118, 4890–4893; Angew. Chem.
Int. Ed. 2006, 45, 4772–4775.
[2] a) W.-D. Jang, D.-L. Jiang, T. Aida, J. Am. Chem. Soc. 2000, 122,
3232–3233; b) C. Marmillon, F. Gauffre, T. Gulik-Krzywicki, C.
Loup, A.-M. Caminade J.-P. Majoral, J.-P. Vors, E. Rump, Angew.
Chem. 2001, 113, 2696–2699; Angew. Chem. Int. Ed. 2001, 40, 2626–
2629; c) T. Giorgi, F. Grepioni, I. Manet, P. Mariani, S. Masiero, E.
Mezzina, S. Pieraccini, L. Saturni, G. P. Spada, G. Gottarelli, Chem.
Eur. J. 2002, 8, 2143–2152; d) W.-D. Jang, T. Aida, Macromolecules
2003, 36, 8461–8469; e) G. A. El, F. Gauffre, A.-M. Caminade, J.-P.
Majoral, H. Lannibois-Drean, Langmuir 2004, 20, 9348–9353;
f) K. T. Kim, C. Park, C. Kim, M. A. Winnik, I. Manners, Chem.
Commun. 2006, 1372–1374; g) T. Kato, Y. Hirai, S. Nakaso, M. Mor-
iyama, Chem. Soc. Rev. 2007, 36, 1857–1867; h) S. K. Samanta, A.
Gomathi, S. Bhattacharya, C. N. R. Rao, Langmuir. 2010, 26, 12230–
2236.
[3] a) S. Bhattacharya, U. Maitra, S. Mukhapadhyay, A. Srivastava, Ad-
vances in Molecular Hydrogels, in Molecular Gels: Materials with
Self-Assembled Fibrillar Networks (Eds.: R. G. Weiss, P. Terech),
Springer, Dordrecht, 2005, Chapter 17, p. 605; b) “Low Molecular
Mass Gelators: Design, Self-Assembly, Function”: Top. Curr. Chem.
2005, 256, edited by F. Fages; c) N. M. Sangeetha, U. Maitra, Chem.
Soc. Rev. 2005, 34, 821–836; d) A. R. Hirst, D. K. Smith, Chem. Eur.
J. 2005, 11, 5496–5508; e) M. George, R. G. Weiss, Acc. Chem. Res.
2006, 39, 489–497; f) Y. Ji, G.-C. Kuang, X.-R. Jia, E.-Q. Chen, B.-B.
Wang, W.-S. Li, Y. Wei, J. Lei, Chem. Commun. 2007, 41, 4233–
4235; g) P. Dastidar, Chem. Soc. Rev. 2008, 37, 2699–2715; h) D. K.
Smith, Chem. Soc. Rev. 2009, 38, 684–694.
[4] a) H. Ohno, Electrochemical Aspects of Ionic Liquids, Wiley, New
York, 2005; b) W. Hamley, Introduction to Soft Matter: Synthetic and
Biological Self-Assembling Materials, Wiley-VCH, Weinheim, 2007.
[5] a) D. Gao, H. Xu, M. A. Philibert, R. Kopelman, Angew. Chem.
2007, 119, 2274–2277; Angew. Chem. Int. Ed. 2007, 46, 2224–2227;
b) O. Yamaguchi, L. Zhang, B.-S. Chae, C. S. Palla, E. M. Furst,
K. L. Kiick, J. Am. Chem. Soc. 2007, 129, 3040–3041; c) J. A. Wie-
land, T. L. Houchin-Ray, L. D. Shea, J. Control. Release, 2007, 120,
233–241; d) H. J. Chung, T. G. Park, Nano Today 2009, 4, 429–437.
[6] a) R. Varghese, S. J. George, A. Ajayaghosh, Chem. Commun. 2005,
593–595; b) A. Ghoussoub, J.-M. Lehn, Chem. Commun. 2005,
5763–5765; c) P. Mukhopadhyay, Y. Iwashita, M. Shirakawa, S.-I.
Kawano, N. Fujita, S. Shinkai, Angew. Chem. 2006, 118, 1622–1625;
Angew. Chem. Int. Ed. 2006, 45, 1592–1595; d) J. E. A. Webb, M. J.
Crossley, P. Turner, P. Thordarson, J. Am. Chem. Soc. 2007, 129,
7155–7162; e) H. Maeda, Y. Haketa, T. Nakanishi, J. Am. Chem.
Soc. 2007, 129, 13661–13674; f) H. Maeda, Y. Mihashi, Y. Haketa,
Org. Lett. 2008, 10, 3179–3182; g) M. Teng, G. Kuang, X. Jia, M.
Gao, Y. Li, Y. Wei, J. Mater. Chem. 2009, 19, 5648–5654.
[9] a) K. Y. Lee, D. J. Mooney, Chem. Rev. 2001, 101, 1869–1879;
b) J. L. Drury, D. J. Mooney, Biomaterials 2003, 24, 4337–4351;
c) G. A. Silva, C. Czeisler, K. L. Niece, E. Beniash, D. A. Harring-
ton, J. A. Kessler, S. I. Stupp, Science 2004, 303, 1352–1355; d) R. G.
Ellis-Behnke, Y.-X. Liang, S.-W. You, D. K. C. Tay, S. Zhang, K.-F.
So, G. E. Schneider, Proc. Natl. Acad. Sci. USA 2006, 103, 5054–
5059; e) A. R. Hirst, B. Escuder, J. F. Miravet, D. K. Smith, Angew.
Chem. 2008, 120, 8122–8139; Angew. Chem. Int. Ed. 2008, 47, 8002–
8018; f) P. M. Crapo, Y. Wang, Acta Biomater. 2010, 6, 2091–2096.
[10] a) S. Mizrahi, J. Gun, Z. G. Kipervaser, O. Lev, Anal. Chem. 2004,
76, 5399–5404; b) K. Nakanishi, N. Tanaka, Acc. Chem. Res. 2007,
40, 863–873; c) J. Liu, S. Yang, C. S. Lee, D. L. DeVoe, Electropho-
resis 2008, 29, 2241–2250.
[11] a) J. P. Mathias, C. T. Seto, J. A. Zerkowski, G. M. Whitesides in Mo-
lecular Recognition: Chemical and Biological Problems II (Ed.:
S. M. Roberts), RSC, Cambridge, 1992; b) T. K.-K. Mong, A. Niu,
H.-F. Chow, C. Wu, L. Li, R. Chen, Chem. Eur. J. 2001, 7, 686–699;
c) A. Heeres, C. van der Pol, M. Stuart, A. Friggeri, B. L. Feringa, J.
van Esch, J. Am. Chem. Soc. 2003, 125, 14252–14253; d) W.-D. Jang,
T. Aida, Macromolecules 2004, 37, 7325–7330; e) C. Wang, D.
Zhang, D. Zhu, J. Am. Chem. Soc. 2005, 127, 16372–16373; f) H.-F.
Chow, G.-X. Wang, Tetrahedron 2007, 63, 7407–7418; g) A. Brizard,
M. Stuart, K. van Bommel, A. Friggeri, M. de Jong, J. van Esch,
Angew. Chem. 2008, 120, 2093–2096; Angew. Chem. Int. Ed. 2008,
47, 2063–2066; h) M. Suzuki, M. Yumoto, H. Shirai, K. Hanbusa,
Chem. Eur. J. 2008, 14, 2133–2144; i) A. Pal, S. Shrivastava, J. Dey,
Chem. Commun. 2009, 6997–6999; j) M. Yoshio, Y. Shoji, Y. Tochi-
gi, Y. Nishikawa, T. Kato, J. Am. Chem. Soc. 2009, 131, 6763–6767.
[12] Y. Ishida, T. Aida, J. Am. Chem. Soc. 2002, 124, 14017–14019.
[13] a) K. Hanabusa, Y. Matsumoto, T. Miki, T. Koyama, H. Shirai, J.
Chem. Soc. Chem. Commun. 1994, 1401–1402; b) K. Hanabusa, M.
Matsumoto, M. Kimura, A. Kakehi, H. Shirai, J. Colloid Interface
Sci. 2000, 224, 231–244.
[14] a) Z. Xie, A. Zhang, Z. Feng, Soft Mater. 2009, 5, 1474–1482; b) Z.
Xie, A. Zhang, X. Wang, Z. Feng, J. Mater. Chem. 2009, 19, 6100–
6102.
[15] J. Ello, H. R. Bello, Nature 1962, 194, 681–682.
[16] a) T. Ohtake, M. Ogasawara, K. Ito-Akita, N. Nishina, S. Ujiie, H.
Ohno, T. Kato, Chem. Mater. 2000, 12, 782–789; b) K. Kishimoto,
M. Yoshio, T. Mukai, M. Yoshizawa, H. Ohno, T. Kato, J. Am.
Chem. Soc. 2003, 125, 3196–3197; c) K. Kishimoto, T. Suzawa, T.
Yokota, T. Mukai, H. Ohno, T. Kato, J. Am. Chem. Soc. 2005, 127,
15618–15623.
[7] C. Valenta, E. Nowack, A. Bernkop-Schꢁrch, Int. J. Pharm. 1999,
185, 103–111.
[8] a) J. Kim, D. H. Altreuter, D. S. Clark, J. S. Dordick, J. Am. Oil
Chem. Soc. 1998, 75, 1109–1113; b) A. D. Elbein, Y. T. Pan, I. Pas-
Received: July 30, 2010
Published online: November 4, 2010
Chem. Eur. J. 2010, 16, 13955 – 13959
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