Combination of 2D-, 3D-connectivity and quantum chemical descriptors in QSPR.: Complexation of α- and,β-cyclodextrin with benzene derivatives

Quantitative models are found to describe the complexation of alpha- and beta -cyclodextrin with mono- and 1,4-disubstituted benzene derivatives by using combinations of 2D-, 3D-connectivity and quantum chemical molecular descriptors. The association constants (K-a) for the inclusion complexation of cyclodextrins and benzene derivatives are calculated by the models found with a high degree of precision. These models also permit the interpretation of the driving forces of such complexation processes. In the case of the complexation of alpha -cyclodextrin with benzene derivatives these driving forces are mainly the electronic repulsion between frontier orbitals of the host and guest molecules. However, the complexation of beta -cyclodextrin with benzene derivatives is controlled by topological and topographic parameters indicating, the relevance of the van der Waals and hydrophobic interactions. We also carried out molecular modeling studies showing that for a-cyclodextrin complexes the benzene ring is outside the cavity of the cyclodextrin, while in beta -cyclodextrin they penetrate deeply into the apolar and hydrophobic cavity of the host, which explain the differences in the driving forces for both complexation processes.