A DFT Study on the Kinetics of HOO(•), CH(3)OO(•), and O(2)(•−) Scavenging by Quercetin and Flavonoid Catecholic Metabolites

Reaction kinetics have been theoretically examined to ascertain the potency of quercetin (Q) and flavonoid catecholic metabolites 1–5 in the inactivation of HOO(•), CH(3)OO(•), and O(2)(•−) under physiological conditions. In lipidic media, the [Formula: see text] rate constants for the proton-coupled electron transfer (PCET) mechanism indicate the catecholic moiety of Q and 1–5 as the most important in HOO(•) and CH(3)OO(•) scavenging. 5-(3,4-Dihydroxyphenyl)-γ-valerolactone (1) and alphitonin (5) are the most potent scavengers of HOO(•) and CH(3)OO(•), respectively. The [Formula: see text] rate constants, representing actual behavior in aqueous media, reveal Q as more potent in the inactivation of HOO(•) and CH(3)OO(•) via single electron transfer (SET). SET from 3-O(−) phenoxide anion of Q, a structural motif absent in 1–5, represents the most contributing reaction path to overall activity. All studied polyphenolics have a potency of O(2)(•−) inactivation via a concerted two-proton–coupled electron transfer (2PCET) mechanism. The obtained results indicate that metabolites with notable radical scavenging potency, and more bioavailability than ingested flavonoids, may contribute to human health-promoting effects ascribed to parent molecules.