A quantum-mechanical study on the complexation of β-cyclodextrin with quercetin

The inclusion process involving beta-cyclodextrin (beta-CD) and quercetin has been investigated by using the PM3 quantum-mechanical semi-empirical method. In the beta-CD quercetin inclusion complex, a large portion of the flavonoid skeleton is included in the beta-CD cavity and the bond connected ring B with ring C is inclined to the molecular axis of beta-CD. The orientation in which the B ring of the guest molecule located near the secondary hydroxyls of the beta-CD cavity is preferred in energy. One intermolecular hydrogen bond is formed. The molecular modeling results are in agreement with the NMR observations and molecular dynamics (MD) simulations. The statistical thermodynamic calculations at I atm and 298.15 K by PM3 demonstrate that 1:1 quercetin/beta-CD complex is favored by a negative enthalpy change. (c) 2006 Elsevier B.V. All rights reserved.