Supramolecular polymers formed by bifunctional cyclodextrin derivatives

Article abstract of DOI:10.1246/cl.2007.828

The mixture of monofunctional and bifunctional cyclodextrin derivatives formed branched supramolecular polymers, which showed an increase in the viscosity of aqueous solution. However, a monofunctional cyclodextrin derivative did not form viscous solution

Full text of DOI:10.1246/cl.2007.828

828
Chemistry Letters Vol.36, No.7 (2007)
Supramolecular Polymers Formed by Bifunctional Cyclodextrin Derivatives
Atsuhisa Miyawaki, Yoshinori Takashima, Hiroyasu Yamaguchi, and Akira Haradaꢀ
Department of Macromolecular Science, Graduate School of Science,
Osaka University, Toyonaka, Osaka 560-0043
(Received April 10, 2007; CL-070387; E-mail: harada@chem.sci.osaka-u.ac.jp)
The mixture of monofunctional and bifunctional cyclodex-
trin derivatives formed branched supramolecular polymers,
which showed an increase in the viscosity of aqueous solution.
However, a monofunctional cyclodextrin derivative did not
form viscous solutions. It is caused by the crosslinking of
linear supramolecular polymers through hetero-type inclusion
and some intermolecular interactions.
Preparation of supramolecular structures in aqueous envi-
ronments is one of the most versatile approaches for developing
new dynamic systems.1 Many kinds of supramolecular polymers
linked by appropriate interactions including metal coordinations,
hydrogen bonds, and/or hydrophobic interactions have been
reported by the efforts of synthetic chemists in recent years.2
Previously, we reported preparations and structures of water-
soluble cyclic tri[2]rotaxanes (daisy chain necklaces) and linear
supramolecular polymers formed by cyclodextrins (CDs) having
a cinnamoyl group and a cinnamamide group as a guest part.3
However, the viscosity of supramolecular polymers is lower
than that excepted from the molecular weight of supramolecular
polymers. Herein, we have prepared 3-cinnamoylaminohexan-
ꢀ
amide-ꢀ-CD (1) bearing a pentyl group and 3-N -cinnamoly-
aminohexancarbonyl-N -cinnamoyl-lysinamide-ꢀ-CD (2) bear-
ing two guest parts and have investigated the formation of linear
and hyperbranched supramolecular polymers, respectively. This
is the first example of the formation of fibrous supramolecular
polymers by cyclodextrin-based host–guest systems.
Figure 1. (a) Chemical structures of compounds 1 and 2. (b)
Reduced viscosity of ꢀ-CD (triangle), compound 1 (rhombic),
and mixtures of 1 and 2 (circle) in H2O at 25 ꢂC.
"
The physical properties of supramolecular polymers formed
by each mono-substituted CD (1 and 2) were investigated by
viscosity measurements under dilute conditions (Figure 1). The
ꢁsp=C value of compound 1 moderately increased with an
increase in the concentration and reached 3.9 cm3 gꢁ1 at 80
mM. However, the ꢁsp=C value of compound 2 was too low to
be measured4 because of the low solubility in aqueous solutions,
whereas compound 2 was easily solubilized in 20 mM aqueous
solutions of compound 1, which reached the saturated concentra-
tion at 14.1 mM. Mixtures of 1 and 2 showed a dramatic increase
in the viscosity with an increase in the molar ratio of compound
2. The ꢁsp=C value of the mixture of 1 and 2 (2/1 = 0.7) is 1.4
times larger than that of compound 1 at 34.1 mM. Compound
2 affects the elevation of viscosity of aqueous solutions, which
was caused by the formation of branched supramolecular
polymer. These results are in agreement with the self-diffusion
coefficients of supramolecular complexes determined from
pulsed field gradient spin-echo (PFG) NMR measurements.5
1H NMR spectra of mixtures of 1 and 2 were measured to
verify the formation of branched supramolecular polymer
(Figure 2). Mixtures of 1 and 2 showed that protons of the
cinnamoyl group of compound 2 shifted to upfield significantly
with an increase in the molar ratio of compound 2. The electro-
Figure 2. 1H NMR spectra of mixtures of 1 and 2 at various
ratios in D2O at 30 ꢂC.
Copyright Ó 2007 The Chemical Society of Japan

Chemistry Letters Vol.36, No.7 (2007)
829
of supramolecular polymers from mixtures of 1 and 2 transcend
the estimated results from association constants of model
system.8 These results suggested that the other interactions as
well as inclusion effects of CD cavities have an influence on
the formation of supramolecular polymers.
The proposed structures of supramolecular polymers are
represented in Figure 4. We supposed that supramolecular poly-
mers were formed through not only the formation of intermolec-
ular inclusion complexes but also aggregations by intermolecu-
lar interactions such as hydrophobic interactions and/or hydro-
gen bonds. Supramolecular polymers are able to interact
with other polymer chains through nonincluded guest parts
in aqueous solutions especially at high concentrations since
compound 2 consists of one host moiety and two guest moieties.
In conclusion, novel supramolecular polymer has been pre-
pared from the complex of 1 and 2. Their properties were caused
by crosslinking of linear supramolecular polymer through
hetero-type inclusion and some intermolecular interactions.
Now, the mechanical properties of these supramolecular poly-
mers are under investigation.
Figure 3. Photographs for the mixture of 1 and 2 (a) thread-
forming property (40 wt %) (b) freestanding fiber.
This work has been partially supported by the Center of
Excellence (21COE) Program ‘‘Creation of Integrated Eco-
Chemistry’’ of Osaka University.
References and Notes
1
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Weinheim, Germany, 1995. b) J. L. Atwood, J. E. D.
Davis, D. M. MacNicol, F. Vogtle, J.-M. Lehn, in
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Pergamon, Oxford, 1996, Vol. 3. c) J.-M. Lehn, Angew.
Chem., Int. Ed. Engl. 1990, 29, 1304. d) C. Fouquey,
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See Supporting Information. It is available electronically
on the CJS-Journal web site; http://www.csj.jp/journals/
chem-lett/.
a) T. Hoshino, M. Miyauchi, Y. Kawaguchi, H. Yamaguchi,
A. Harada, J. Am. Chem. Soc. 2000, 122, 9876. b) A. Harada,
Y. Kawaguchi, T. Hoshino, J. Inclusion Phenom. Macrocycl.
Chem. 2001, 41, 115. c) M. Miyauchi, Y. Kawaguchi, A.
Harada, J. Inclusion Phenom. Macrocycl. Chem. 2004, 50,
57.
Figure 4. Schematic illustration of fibrous supramolecular
polymers formed by 1–2 complexes in aqueous solution.
spray ionization (ESI) mass spectra of the mixture of 1 and 2
showed the species of potassium cation adducts of 1 with 2
([M1 + M2 + K]þ and [2M1 + M2 + K]þ). These results
indicate that mixtures of 1 and 2 formed hetero-type supramolec-
ular complexes. Compounds 1 and 2 were also found to form
supramolecular polymers, respectively, by ESI mass spectrome-
try, 1H NMR spectroscopy, and ROESY NMR spectroscopy.
The ESI spectra of compounds 1 and 2 showed the species of
supramolecular complexes with at least 5 mer. Considering their
chemical structures, we suppose that compound 1 formed linear
type and compound 2 formed hyperbranched type supramolecu-
lar polymers.
2
3
4
5
6
The saturated concentration of compound 2 was 2.3 mM.
O. E. Stejskal, J. E. Tanner, J. Chem. Phys. 1965, 42, 288.
K. A. Connors, A. Paulson, D. Toledo-Velasquez, J. Org.
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See Supporting Information. It is available electronically
on the CJS-Journal web site; http://www.csj.jp/journals/
chem-lett/.
a) N. Yamaguchi, L. M. Hamilton, H. W. Gibson, Angew.
Chem., Int. Ed. Engl. 1998, 37, 3275. b) N. Yamaguchi,
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Figure 3 shows photographs of a mixture of 1 and 2 in a
concentrated solution. The mixture exhibits the thread-forming
property (Figure 3a) and freestanding fiber was formed by
wet spinning (Figure 3b). In contrast, compound 1 did not
exhibit such properties. The powder X-ray diffraction (XRD)
pattern of compounds 1 and 2 exhibited two broad reflections
around 2ꢂ ¼ 13 and 20ꢂ, respectively. However, the mixture
of 1 and 2 had fewer reflections, indicating the amorphous state.
We suppose that supramolecular polymers from mixtures
of 1 and 2 mainly consist of compound 1. Compound 2 was
solubilized in the solution of compound 1, then compound 1
forms branched supramolecular polymer including guest groups
of compound 2. The association constants were determined
by UV–vis absorption spectroscopy.6 The mod0el system of
7
8
0
compound 1 and compound 2 has K1, K1 , and K2 , which were
determined to be 5:7 ꢃ 102 Mꢁ1, 5:8 ꢃ 10 Mꢁ2, and 5.6 Mꢁ1
,
0
0
respectively (K1 > K1 , K2 ).7 It should be noted that viscosity
Published on the web (Advance View) May 31, 2007; doi:10.1246/cl.2007.828