Radical Scavenging Activity of Myricetin

Density functional theory (DFT) calculations have been performed to explore the molecular structure, electronic structure, and O-H bond dissociation enthalpy of myricetin. Possible antioxidation mechanisms between lipid peroxide radical CH3OO center dot and myricetin have been discussed. DFT calculations at the M06-2X/6-31++G(d, p) level indicated that the 4 '-OH group of myricetin is the most active site on the basis of the stability of dehydrogenated myricetin radicals, O-H bond dissociation enthalpy, and hydrogen abstraction activation barrier, as well as kinetic data for myricetin determined at different temperatures. The relatively high activity of the 4 '-OH site can be ascribed to weak hydrogen- bonding interactions between the oxygen radical of the reactive OH group and the adjacent OH group in the B- ring, which is retained upon going from free myricetin to reactant complex to product according to atoms in molecule (AIM) analysis. The hydrogen- bond helps to stabilize the electronic deficiency generated on the oxygen radical during the hydrogen abstraction reaction. All calculations are in agreement with the structure- activity relationship previously established for myricetin by considering its antioxidant activity. Present calculations provide theoretical basis for the designing new antioxidants.