Relationship between the radical-scavenging activity of selected flavonols and thermodynamic parameters calculated by density functional theory.

ABSTRACT

The relationship between radical-scavenging rate constants (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 (Mor), kaempferol (Kae), 2'-methylquercetin (2'-MeQue), 5'-methylquercetin (5'-MeQue), and 2',5'-dimethylquercetin (Me2Que). 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 flavonols and the corresponding radicals, which equal to the relative O-H bond dissociation energies of the OH groups in the flavonols and ionisation potentials (IP) were calculated by DFT at the B3LYP/6-31++G(d) level with C-PCM solvation model parameterised 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.