Relationship between the Radical-Scavenging Activity of Selected Flavonols and Thermodynamic Parameters Calculated by Density Functional Theory

The relationship between radical-scavenging rate constant (k) in an aprotic medium and thermodynamic parameters calculated by density functional theory (DFT) was investigated for 7 flavonols, which are myricetin (Myr), quercetin (Que), morin (More), kaempferol (Kae), 2'-methylquercetin (2'-MeQue), 5'-methylquercetin (5'-MeQue), and 2',5'-dimethylquercetin (Me(2)Que). The k values were determined for the reaction between the flavonols and galvinoxyl radical used as a reactivity model of reactive oxygen species in deaerated acetonitrile at 298 K. The energy difference values (D(HT), HT: hydrogen transfer) between the flavonoid and the corresponding radicals, which equal to the relative O-H bond dissociation energies of the OH groups in the flavonols and ionization potentials (IP) were calculated by DFT at the B3LYP/6-31++G(d) level with C-PCM salvation model parameterized for acetonitrile. Among the 7 flavonols used in this study, calculated IP values of 4 flavonols exhibited a linear correlation with log k, suggesting that the radical-scavenging reaction of these flavonols may proceed via an electron transfer as the rate determining step.journal articl