Journal of Inclusion Phenomena and Macrocyclic Chemistry 33: 81–97, 1999. © 1999 Kluwer Academic Publishers. Printed in the Netherlands. 81 Inclusion of Enantiomeric Carvones in β -Cyclodextrin: a Variable Temperature 1 H NMR Study in Aqueous Solution AIDA MOREIRA DA SILVA School of Agriculture, Polytechnical Institute of Coimbra, P-3000 Coimbra Portugal JOSÉ EMPIS Department of Chemical Engineering, Instituto Superior Técnico, P-1096 Lisboa Codex Portugal JOSÉ J.C. TEIXEIRA-DIAS  Department of Chemistry, University of Aveiro, P-3810 Aveiro Portugal (Received: 16 October 1997; in final form: 30 January 1998) Abstract. In aqueous solution, the apparent association constant at room temperature for the 1 : 1 inclusion of S-(+)-carvone in β -cyclodextrin is double of that for R-(-)-carvone, whereas, at 45 ◦ C, both enantiomers have association constants two orders of magnitude smaller, with the S- (+) inclusion being then slightly weaker than the R-(-) encapsulation. Calculations carried out at the molecular mechanics, AM1 and STO-3G levels confirm the preferential inclusion of the S-enantiomer and provide important clues for understanding chiral discrimination by β -cyclodextrin. Key words: β -cyclodextrin, carvone enantiomers, molecular inclusion, chiral discrimination, apparent association constants, molecular modelling, molecular mechanics, quantum mechanics 1. Introduction β -Cyclodextrin (cyclomalto-heptaose, β -CD) is a short, hollow, truncated cone shaped molecule, which is formed by seven α(1-4) linked gluco-pyranoses in nor- mal chair conformations (Scheme 1) [1]. As with the other cyclodextrins, β -CD has a positive optical rotation. Both in the crystalline hydrate and in aqueous media, the β -CD molecule interacts with water molecules, some of which are removed when a guest of suitable size enters into the cavity [2]. When β -CD interacts with the enantiomers of a chiral molecule, the difference in chiral properties between host and guest affects the host-guest interaction and the stability of the inclusion, giving rise to chiral discrimination [3–6]. In addition, different degrees of fit be- tween the guest enantiomers and the host may influence the degree of hydration of the inclusion system. Since enantiomers undergo identical solvation processes, the study of the host-guest interactions between β -CD and the enantiomers of a  Author for correspondence.