Competition between Ascorbate and Glutathione for the Oxidized Form of Methylated Quercetin Metabolites and Analogues: Tamarixetin, 4'O-Methylquercetin, Has the Lowest Thiol Reactivity

M. Moalin, G.P. van Strijdonck, A. Bast, G.R.M.M. Haenen

Research output: Contribution to journalArticleAcademicpeer-review

Abstract

Quercetin (Q) is a bioactive compound with excellent antioxidant activity. However, the thiol reactivity of its oxidation product (oxQ) forms a disadvantage. The aim of the present study was to decrease this thiol toxicity. We found that methylated Q metabolites displayed lower thiol reactivity than Q. The most effective was tamarixetin, 4'O-methylquercetin (4'MQ), that has a corresponding oxidation product (ox4'MQ) with thiol reactivity 350 times lower than oxQ. The endogenous metabolism of Q to 4'MQ might be a physiological way to safely benefit from the antioxidant potential of Q in vivo. Our results were explained with Pearson's HSAB concept and corroborated by quantum molecular calculations that revealed a strong correlation between the relative thiol reactivity and the lowest unoccupied molecular orbital (LUMO). The polarity of the molecule and the pi-pi interaction between the AC- and the B-ring appeared to determine the LUMO and the thiol reactivity of the oxidation product.
Original languageEnglish
Pages (from-to)9292-9297
JournalJournal of Agricultural and Food Chemistry
Volume60
Issue number36
DOIs
Publication statusPublished - 1 Jan 2012

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