C O M M U N I C A T I O N S
Scheme 1
Figure 3. Concentration dependence of the diffusion coefficient values
(D) of free CD dimer guest (solid line) and 1-1 mixtures of guest C3 dimer
with host CD dimer (dash line) in D2O at 30 °C by NMR. The cis and
trans isomers of the guest are respectively represented in blue and red lines.
In conclusion, we prepared a stilbene bis(â-CD) dimer and
controlled its trans-cis conformation by photoirradiation in aqueous
solutions. With a ditopic adamantyl guest molecule, in trans
conformation, it formed dimer or small supramolecular assemblies
(oligomers), whereas in cis conformation, supramolecular linear
polymers with high molecular weight were observed. The control
of the structure of the supramolecular polymers by an external
stimulus may open the way to various applications. Now we are
studying the properties of the supramolecular polymers and the
interaction of the stilbene CD dimer with different guests.
the concentration, and this value was comparable to that of the
host alone, indicative of the formation of 1:1 complexes or small
assemblies (hydrodynamic radius, Rh ) 1.51 nm at 6.0 mM).
However, D of the guest and cis host mixture was significantly
lower than that with the trans isomer at high concentration,
indicating a higher Rh (2.39 nm at 6.0 mM)6 and that cis stilbene
bis(â-CD) dimer and C3 guest formed a supramolecular polymer.
Acknowledgment. P.K. gratefully acknowledges the Japanese
Society for the Promotion of Science (JSPS) for a JSPS Postdoctoral
Fellowship for Foreign Researchers (Grant PE07064). This work
has been partially supported by Grant in-Aid No. A19205014 for
Scientific Research and has been conducted with financial support
from the “Stress and Symbiosis on Supramolecules” program of
the Ministry of Education, Culture, Sports, Science and Technology,
Japan.
1
In the H NMR spectra, broad proton signals also indicated the
formation of supramolecular structure. Remarkably, the upfield shift
of the C3 pyridinium protons when mixed with trans host pointed
out electron donor-acceptor type interactions and supported the
formation of a dimer-type structure. (see Supporting Information,
Figure S5)
Association constants between host and guest dimers are in
agreement with the PFG NMR measurements. Isothermal titration
calorimetry (ITC) experiments have been carried out in aqueous
solutions. With three monotopic model guest molecules,4b it was
shown that the trans and cis CD dimers have similar affinity for
these adamantyl derivatives. But concerning the ditopic C3 guest,
the association constants were (1.45 ( 0.2) × 106 M-1 and (4.18
( 0.3) × 105 M-1, respectively, for the trans and cis stilbene dimer
(see Supporting Information, Table S3). The higher constant for
the trans isomer (about three times higher) resulted from a
cooperative effect:7 the ditopic guest is complexed simultaneously
by both CD residues of the same host dimer, forming a 1:1 complex.
In the case of the cis isomer, a ditopic guest is complexed by two
cyclodextrins belonging to two dimers, and it forms a linear and
higher-order supramolecular entity with a lower association con-
stant.
To confirm the nanometer-sized molecular assembly, supramo-
lecular dimer or polymer, atomic force microscopy (AFM) mea-
surements were performed. When the sample was made from a
1:1 mixture of trans host and C3 guest, only small objects that were
approximately 30 nm in overall length could be detected. In contrast,
nanometer-sized supramolecular wires, that were about 350 nm in
overall length, were observed on mica substrate in the case of the
cis isomer (see Supporting Information, Figure S2). Therefore, the
AFM measurements also pointed out different supramolecular
structures for the trans and cis stilbene bis(â-CD) dimer mixed with
C3 guest. Consequently, the proposed conformation change of
cis stilbene bis(â-CD) dimer and C3 adamantyl dimer in aqueous
solutions stimulated by light was illustrated schematically in
Scheme 1.
Supporting Information Available: Synthesis, UV-vis spectra,
ITC titrations, and AFM measurements. This material is available free
References
(1) (a) Koumura, N.; Zijlstra, R. W. J.; van Delden, R. A.; Harada, N.; Feringa,
B. L. Nature 1999, 401, 152-155. (b) Brouwer, A. M.; Frochot, C.; Gatti,
F. G.; Leigh, D. A.; Mottier, L.; Paolucci, F.; Roffia, S.; Wurpel, G. W.
H. Science 2001, 291, 2124-2128. (c) Shinkai, S.; Nakaji, T.; Nishida,
Y.; Ogawa, T.; Manabe, O. J. Am. Chem. Soc. 1980, 102, 5860-5865.
(d) Murakami, H.; Kawabuchi, A.; Kotoo, K.; Kunitake, M.; Nakashima,
N. J. Am. Chem. Soc. 1997, 119, 7605-7606. (e) Muraoka, T.; Kinbara,
K.; Kobayashi, Y.; Aida, T. J. Am. Chem. Soc. 2003, 125, 5612-5613.
(f) Inoue, Y.; Kuad, P.; Okumura, Y.; Takashima, Y.; Yamaguchi, H.;
Harada, A. J. Am. Chem. Soc. 2007, 129, 6396-6397. (g) Yu, Y.; Nakano,
M.; Ikeda, T. Nature 2003, 425, 145-145. (h) Tomatsu, I.; Hashidzume,
A.; Harada, A. J. Am. Chem. Soc. 2006, 128, 2226-2227.
(2) Aoyagi, T.; Ueno, A.; Fukushima, M.; Osa, T. Macromol. Rapid. Commun.
1998, 19, 103-105.
(3) Lui, Y.; Kang, S.; Chen, Y.; Yang, Y.-W.; Huskens, J. J. Inclusion
Phenom. Macrocyclic Chem. 2006, 56, 197-201.
(4) (a) Takahashi, H.; Takashima, Y.; Yamaguchi, H.; Harada, A. J. Org.
Chem. 2006, 71, 4878-4883. (b) Ohga, K.; Takashima, Y.; Takahashi,
H.; Kawaguchi, Y.; Yamaguchi, H.; Harada, A. Macromolecules 2005,
38, 5897-5904. (c) Hasegawa, Y.; Miyauchi, M.; Takashima, Y.;
Yamaguchi, H.; Harada, A. Macromolecules 2005, 38, 3724-3730.
(5) Lott, P. F.; Millich, F. J. Chem. Educ. 1966, 43, A191.
(6) The moderate value for the supramolecular polymer is due to the relatively
low concentration of the measurement and to the dynamic exchange in
solutions. Indeed, in solutions, the supramolecular structure is constantly
in fast equilibrium between the polymer and the monomers in the NMR
time scale (as confirmed by the broad signals). This explains the relatively
high measured diffusion coefficient.
(7) (a) Soto Tellini, V. H. S.; Jover, A.; Garcia, J. C.; Galantani, L.; Meijide,
F.; Tato, J. V. J. Am. Chem. Soc. 2006, 128, 5728-5734. (b) Zhang, B.;
Breslow, R. J. Am. Chem. Soc. 1993, 115, 9353-9354.
JA075139P
9
J. AM. CHEM. SOC. VOL. 129, NO. 42, 2007 12631