Characterization of π-stacking interactions between aromatic amino acids and quercetagetin

In the present study, the pi-stacking interactions between quercetagetin (QUE), which is one of the most representatiVe flavonol compounds with biological and chemical activities, and some aromatic amino acid (AA) residues has been investigated by the quantum mechanical calculations. The trend in the absolute value of stacking interaction energy IDES with respect to AAs is HIS > PHE > TYR > TPR. The results show that the sum of donor-acceptor interaction energy between AAs and QUE (Sigma(E2)) and the sum of electron densities p calculated at BCPs and CCPs between the rings (Sigma rho BCPs and Sigma rho CCP can be useful descriptors for prediction of the Delta E values of the complexes. The O-H bond dissociation enthalpy (BDE) slightly decreases by the pi-stacking interaction, which confirms the positive effect of that interaction on the antioxidant activity of QUE. A reverse trend is observed for BDE when is compared with the vertical bar Delta E vertical bar values. A reliable relationship is also observed between the Muliken spin density (MSD) distributions of the radical species and the most convenient O-H bond dissociations. In addition, reactivity is in good correlation with the antioxidant activity of the complexes. (C) 2016 Elsevier B.V. All rights reserved.