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Quinuclidine complex with α-cyclodextrin: a diffusion and 13C NMR relaxation study

✍ Scribed by Sahar Nikkhou Aski; Jozef Kowalewski

Publisher
John Wiley and Sons
Year
2008
Tongue
English
Weight
199 KB
Volume
46
Category
Article
ISSN
0749-1581

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✦ Synopsis

Abstract

The stability of an inclusion complex of quinuclidine with α‐cyclodextrin in solution was investigated by NMR measurements of the translational diffusion coefficient. A 1:1 stoichiometry model yielded an association constant of 35 ± 3 M^−1^. The guest molecules exchange rapidly between the host cavity and the bulk solution. The reorientational dynamics of the guest and host molecules was studied using carbon‐13 NMR relaxation at two magnetic fields. The relaxation of the host nuclei showed very little dependence on the guest‐host concentration ratio, while the ^13^C spins in quinuclidine were sensitive to the solution composition. Using mole‐fraction data, it was possible to extract the relaxation parameters for the bound and free form of quinuclidine. Relaxation rates of the guest molecule, free in solution, were best described by an axially symmetric model, while the data of the complex species were analyzed using the Lipari‐Szabo method. Applying the axially symmetric model to the complexed quinuclidine indicated that the anisotropy of its reorientation in the bound form was increased. Copyright © 2008 John Wiley & Sons, Ltd.

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