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Biomimetics 2017, 2(3), 9;

The Antioxidant Activity of Quercetin in Water Solution

University of Bologna, Department of Chemistry “G. Ciamician”, Via S. Giacomo 11, 40126 Bologna, Italy
School of Chemistry (Rm 267), University of Edinburgh, West Mains Road, Edinburgh EH9 3FJ, UK
Authors to whom correspondence should be addressed.
Academic Editor: Daniel Ruiz-Molina
Received: 30 May 2017 / Revised: 19 June 2017 / Accepted: 22 June 2017 / Published: 27 June 2017
(This article belongs to the Special Issue Bioinspired Catechol-Based Systems: Chemistry and Applications)
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Despite its importance, little is known about the absolute performance and the mechanism for quercetin’s antioxidant activity in water solution. We have investigated this aspect by combining differential oxygen-uptake kinetic measurements and B3LYP/6311+g (d,p) calculations. At pH = 2.1 (30 °C), quercetin had modest activity (kinh = 4.0 × 103 M−1 s−1), superimposable to catechol. On raising the pH to 7.4, reactivity was boosted 40-fold, trapping two peroxyl radicals in the chromen-4-one core and two in the catechol with kinh of 1.6 × 105 and 7.0 × 104 M−1 s−1. Reaction occurs from the equilibrating mono-anions in positions 4′ and 7 and involves firstly the OH in position 3, having bond dissociation enthalpies of 75.0 and 78.7 kcal/mol, respectively, for the two anions. Reaction proceeds by a combination of proton-coupled electron-transfer mechanisms: electron–proton transfer (EPT) and sequential proton loss electron transfer (SPLET). Our results help rationalize quercetin’s reactivity with peroxyl radicals and its importance under biomimetic settings, to act as a nutritional antioxidant. View Full-Text
Keywords: catechol; peroxyl radicals; proton-coupled electron transfer; kinetics; thermodynamics; mechanisms catechol; peroxyl radicals; proton-coupled electron transfer; kinetics; thermodynamics; mechanisms

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Amorati, R.; Baschieri, A.; Cowden, A.; Valgimigli, L. The Antioxidant Activity of Quercetin in Water Solution. Biomimetics 2017, 2, 9.

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