Selection between Pinching-Type and Supramolecular Polymer-Type
Complexes by r-Cyclodextrin--Cyclodextrin Hetero-Dimer and
Hetero-Cinnamamide Guest Dimers
Hirokazu Takahashi, Yoshinori Takashima, Hiroyasu Yamaguchi, and Akira Harada*
Department of Macromolecular Science, Graduate School of Science, Osaka UniVersity, Toyonaka,
Osaka 560-0043, Japan
harada@chem.sci.osaka-u.ac.jp
ReceiVed March 4, 2006
Novel supramolecular complexes have been prepared from an R-cyclodextrin--cyclodextrin hetero-
dimer (R-CD--CD hetero-dimer) and hetero-cinnamamide guest dimers, G-t-Boc and G-NH
2
, having
adamantyl groups in aqueous solutions. On addition of the competitive guest, the supramolecular structure
formed by a mixture of the R-CD--CD hetero-dimer and G-t-Boc was found to be different from that
of a mixture of the R-CD--CD hetero-dimer and G-NH
2
by the
1
H NMR spectroscopy, the ROESY
NMR spectroscopy, and the circular dichroism spectroscopy. The size of the supramolecular complex
from the mixture of the R-CD--CD hetero-dimer and G-NH
2
is larger than that from the mixture of the
R-CD--CD hetero-dimer and G-t-Boc, which was proved by the pulse field gradient spin-echo NMR
and the atomic force microscopy. These results suggest that the mixture of the R-CD--CD hetero-
dimer and G-t-Boc formed a pinching-type complex, and the mixture of the R-CD--CD hetero-dimer
and G-NH
2
formed a supramolecular polymer-type complex.
Introduction
Biological systems offer several excellent examples of
supramolecular polymers including double- and triple-helical
DNA, as well as protein -sheet and tobacco mosaic virus.
1
Microtubles are supramolecular polymers consisting of hetero-
dimers of R-tubulin and -tubulin with alternating structures.
2
Chemists have challenged the formation of supramolecules
based on host-dimers as supramolecular architectures of artificial
assemblies.
3
Cyclodextrins (CDs) have been used frequently as
a component of supramolecular complexes. CD dimers, used
for molecular recognition and drug delivery, possess the
structural characteristics to completely encapsulate a guest
molecule. CD dimers were prepared by some researchers to
increase the association constants with CDs, because association
constants for complexations of appropriate guests with CDs
show 10
4
M
-1
, whereas the corresponding values for complex-
ations of substrates with antibody are more than 100 times
larger.
4,5
Many researchers are actively working on producing
enzyme models based on CD dimers that strongly bind
appropriate substrates to both CD cavities such as a pinching-
type structure.
6,7
Although there are some papers on the
cooperative binding of guests by CD hetero-dimers,
8,9
there are
* Corresponding author. Tel.: +81-6-6850-5445. Fax: +81-6-6850-5445.
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10.1021/jo0604686 CCC: $33.50 © 2006 American Chemical Society
Published on Web 06/02/2006