The intermolecular interactions of α- and β-cyclodextrin (CD) as hosts with o-methoxyphenol (o-Mop) as guest in aqueous solution were investigated by UV-Vis spectroscopy. The stability constants K_s of the two inclusion complexes were calculated via Hildebrand-Benesi equation. Semi-empirical PM3 calculations were performed on the inclusion complexations of α-, β-CD with o-Mop and its analogs. The energy changes involved in these host-guest inclusion processes were clearly observed. Possible structures of the supramolecular complexes were presented and discussed. The stabilization energies (ΔE_s) of the inclusion complexes were also obtained. The value of ΔE_s of an inclusion system increased with increasing numbers of the substituents present on the phenyl ring of the guests selected in this study upon inclusion into the same host. The optimized host-guest supramolecular structures at energy minima, obtained by PM3 method in vacuo, were just accorded with the structures measured in aqueous solution.

Key words: cyclodextrin, supermolecule, PM3, stabilization energy, stability constant, inclusion complex