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

The inclusion process involving β-cyclodextrin (β-CD) and quercetin has been investigated by using the PM3 quantum-mechanical semi-empirical method. In the β-CD quercetin inclusion complex, a large portion of the flavonoid skeleton is included in the β-CD cavity and the bond connected ring B with ring C is inclined to the molecular axis of β-CD. The orientation in which the B ring of the guest molecule located near the secondary hydroxyls of the β-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 1 atm and 298.15 K by PM3 demonstrate that 1:1 quercetin/β-CD complex is favored by a negative enthalpy change.