A quantum-chemical study on the molecular recognition of beta-cyclodextrinwith ground and excited xanthones

PM3 and density function theory B3LYP/3-21G(d) calculations in vacuo and in water were performed on the inclusion complexation of beta -cyclodextrin ( CD) with the ground singlet and excited triplet xanthones. It revealed that the complex of beta -CD with the singlet xanthone was significantly more s table than that with the triplet one, which agreed with the experimental ob servation. Calculations on the model system at the level of B3LYP/6-311G(p, d) supported the above result, which indicated that the repulsion between the oxygens of xanthone and the oxygens of the secondary hydroxyls of beta -CD constituted the origin for the above behavior. Hence, caution should be given when extrapolating excited state behavior to the supramolecular syst ems in their ground state. (C) 2001 Elsevier Science B.V. All rights reserv ed.