AM1 CALCULATIONS ON INCLUSION COMPLEXES OF CYCLOMALTOHEPTAOSE (BETA-CYCLODEXTRIN) WITH 1,7-DIOXASPIRO[5.5]UNDECANE AND NONANAL, AND COMPARISON WITH EXPERIMENTAL RESULTS

Semiempirical calculations on cyclomaltoheptaose (beta CD), 1,7-dioxas piro[5.5]undecane (1), nonanal (2), and the inclusion complexes of bet a CD with 1 and 2 were carried out using the AM1 method. The structure of beta CD after complete geometry optimization was in very good agre ement with crystallographic structures. Moreover, the calculated dipol e moment of beta CD was found to depend strongly upon the orientation of the primary hydroxyl groups. Different possible positions of the gu est molecules in the beta CD cavity were examined, a few of them resul ting in a gain of energy. These corresponded to partial inclusion of 1 from the secondary side but total inclusion of 2, Conclusions regardi ng the geometries of the complexes were in satisfactory agreement with the dominant structures in aqueous solutions as derived from NMR expe riments. Thermodynamic data (Delta H degrees, Delta S degrees) in aque ous solutions were obtained from van't Hoff plots using H-1 NMR, and w ere compared with the computed heats of formation. The forces responsi ble for host-guest association are discussed in the light of the above results.