MECHANISM FOR BINDING TO THE FLEXIBLE CAVITY OF PERMETHYLATED ALPHA-CYCLODEXTRIN

Citation
K. Kano et al., MECHANISM FOR BINDING TO THE FLEXIBLE CAVITY OF PERMETHYLATED ALPHA-CYCLODEXTRIN, Journal of inclusion phenomena and molecular recognition in chemistry, 22(4), 1995, pp. 285-298
Citations number
19
Categorie Soggetti
Chemistry,Crystallography
ISSN journal
09230750
Volume
22
Issue
4
Year of publication
1995
Pages
285 - 298
Database
ISI
SICI code
0923-0750(1995)22:4<285:MFBTTF>2.0.ZU;2-4
Abstract
The cavity of alpha-cyclodextrin (alpha-CDx) is too small to include o -toluic acid (o-TA) while it is filled by p-toluic acid (p-TA) to form a relatively stable inclusion complex. Such strict selectivity is asc ribed to a rigid structure of the alpha-CDx cavity which is stabilized by intramolecular hydrogen bonds between the O(2) hydroxyl groups and the O(3) hydroxyl groups of adjacent glucopyranose units. Meanwhile, the substrate selectivity of hexakis(2,3,6-tri-O-methyl)-alpha-CDx (TM e-alpha-CDx) remains somewhat obscure because of the flexible nature o f its cavity. The absence of the intramolecular hydrogen bonds seems t o cause the flexible nature of the TMe-alpha-CDx cavity leading to an induced-fit type inclusion. The structures of the inclusion complexes have been presented on the basis of the H-1 NMR data. The thermodynami c parameters indicate that the complexation of TMe-alpha-CDx with o-TA or p-TA is the entropically favorable process. The entropically favor able complexation of TA with TMe-alpha-CDx seems to occur through dehy dration from the CO2H group of TA which is situated at the hydrophobic CDx cavity. The dipole-dipole interaction has been regarded as the fo rce which dominates the orientation of the polar guest molecule in the CDx cavity.