Theoretical Investigations and Mechanisms of the Inclusion Processes of bi(3-sulfonatophenyl) (4-tert-butylphenyl) phosphine in the β-cyclodextrin

Abstract

Quantum mechanical calculations on the bi(3-sulfonatophenyl) (4-tert-butylphenyl) phosphine/β-cyclodextrin inclusion complex (TPP/CD) are carried out using semiempirical quantum calculations. Inclusion process pathways described in the present work lead straight to the most probable structures of the 1:1 association. These investigations suggest that the most stable structure obtained is that where the aromatic ring bearing the tert-butyl (tBu) group is included into the hydrophobic cavity of the β-cyclodextrin from the side of the primary hydroxyl groups. Theoretical investigations of the Hartree-Fock level of the inter-proton proximity between the host and guest molecules in the inclusion complex and their corresponding electronic properties suggest a deep insertion of the tBu group into the cavity. The host-guest interaction energy of the complex at different levels of the insertion pathway is reported with the corresponding basis set superposition error (base). The host–guest association is thermodynamically stable when compared to the separated states and the calculated binding energy is 40.6 kcal mol−1.