STRUCTURE AND DYNAMIC STABILITY OF CYCLODEXTRIN INCLUSION COMPLEXES WITH 1,4-DISUBSTITUTED BICYCLO- [2.2.2]OCTANES ULF BERG,* MARCIA BERGLUND, NINA BLADH, ANETTE SVENSSON AND MAGNUS STODEMAN$ Division of Organic Chemistry 1 and Division of Thermochemistry$, Chemical Center, Lund University, P.O.Box 124, S-221 00, Lund, Sweden ABSTRACT The properties of inclusion complexes of 1,4-di-R-bicyclo[2.2.2]octanes (R = H (1), Me (2), C1 (3), Br (4), and OH (5)) with cyclodextrins have been studied by NMR, microcalorimetry, and force-field computations. The compounds 2 and 3 (but not the other compounds) give dynamically stable 1:2 guest-host complexes with c~-cyclodextrin. Microcalorimetry of 5 in water indicates a moderately strong 1:1 complex with 13- but weak complexes with c~- or 7-cyclodextrin. The behaviour depends on the subtle interplay of size, polarity, hydrophobicity and type of solvent. 1. INTRODUCTION Cyclodextrins (CD) act as hosts for a variety of small molecules in water solution and have found use in many fields, such as chromatography, pharmaceutical industry and as potential enzyme mimics, 1 and the phenomenon has proven to be an excellent model system for studying the nature of noncovalent bonding in aqueous solution. In order to study the structure and dynamic stability of such inclusion complexes 1,4-disubstituted bicyclo[2.2.2]octane turned out to possess interesting properties as guest molecules. Thus, the 1,4-dimethyl derivative was found to give a 1:2 complex with ~x-cyclodextrin in D20/CD3OD/DMF-d 7, which exchanges with "free" species with remarkably high barrier. 2 We here present an extended study of a series of analogues in order to gain information of the origin of the unusual dynamic stability of the complexes. The complexes of the analogues, shown in the Scheme, with c~-, 13- and y-cyclodextrin have been examined by both experimental and computational methods. Journal oflnclusion Phenomena and Molecular Recognition in Chemistry 25: 73-76, 1996. 73 © 1996 Kluwer Academic Publishers. Printed in the Netherlands.