A DFT Study on the Kinetics of HOO•, CH3OO•, and O2•− Scavenging by Quercetin and Flavonoid Catecholic Metabolites

Abstract

Reaction kinetics have been theoretically examined to ascertain the potency of quercetin (Q) and flavonoid catecholic metabolites 1–5 in the inactivation of HOO•, CH3OO•, and O2•− under physiological conditions. In lipidic media, the koverallTST/Eck 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 CH3OO• scavenging. 5-(3,4-Dihydroxyphenyl)-γ-valerolactone (1) and alphitonin (5) are the most potent scavengers of HOO• and CH3OO•, respectively. The koverallMf rate constants, representing actual behavior in aqueous media, reveal Q as more potent in the inactivation of HOO• and CH3OO• 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 O2•− 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.