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

•The π-stacking interactions of QUE and some amino acids containing five and six-membered aromatic rings have been investigated at the M06-2X/6-311++G(d,p) level of theory.•A broader understanding of the effects of charge on both the preferred geometries and the magnitude of the binding energies has been revealed in the AA||QUE-X complexes.•The interaction energies of the most stable complexes (AA||QUE-C) with respect to AAs decrease as TRP > TYR > PHE > HIS.•The results show that the sum of donor-acceptor interaction energy between AAs and QUE (∑E2) and the sum of electron densities ρ calculated at BCPs and CCPs between the rings (∑ρBCPs and ∑ρCCP) can be useful descriptors for prediction of the ΔE values of the complexes.•The OH bond dissociation enthalpy (BDE) slightly decreases by the π-stacking interaction, which confirms the positive effect of that interaction on the antioxidant activity of QUE.

In the present study, the π-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 |ΔE| with respect to AAs is HIS > PHE > TYR > TPR. The results show that the sum of donor-acceptor interaction energy between AAs and QUE (∑E2) and the sum of electron densities ρ calculated at BCPs and CCPs between the rings (∑ρBCPs and ∑ρCCP) can be useful descriptors for prediction of the ΔE values of the complexes. The OH bond dissociation enthalpy (BDE) slightly decreases by the π-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 |ΔE| values. A reliable relationship is also observed between the Muliken spin density (MSD) distributions of the radical species and the most convenient OH bond dissociations. In addition, reactivity is in good correlation with the antioxidant activity of the complexes.

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