title: Oxidation of flavonoids by hypochlorous acid: reaction kinetics and antioxidant activity studies.
abstract: Flavonoids, plant polyphenols, ubiquitous components of human diet, are excellent antioxidants. Hypochlorous acid (HOCl), produced by activated neutrophils, is highly reactive chlorinating and oxidizing species. It has been reported earlier that flavonoids are chlorinated by HOCl. Here we show that flavonoids from flavonol subclass are also oxidized by HOCl, but only if the latter is in a large molar excess (≥ 10). The kinetics of this reaction was studied by stopped-flow spectrophotometry, at different pH. We found that flavonols were oxidized by HOCl with the rate constants of the order of 10(4)-10(5) M(-1) s(-1) at pH 7.5. Antioxidant activity of HOCl-modified flavonoids was measured by 2,2'-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) method. Slightly higher antioxidant activity, compared to parent compounds, was observed for flavonols after their reaction with equimolar or moderate excess of HOCl whereas flavonols treated with high molar excess of HOCl exhibited decrease in antioxidant activity. The mechanism of flavonoid reaction with HOCl at physiological pH is proposed, and biological consequences of this reaction are discussed.
authors.affiliation: a Faculty of Chemistry , Institute of Applied Radiation Chemistry, Lodz University of Technology (TUL) , Lodz , Poland.
authors.forename: Justyna
authors.initials: J
authors.lastname: Krych-Madej
authors.affiliation: a Faculty of Chemistry , Institute of Applied Radiation Chemistry, Lodz University of Technology (TUL) , Lodz , Poland.
authors.forename: Katarzyna
authors.initials: K
authors.lastname: Stawowska
authors.affiliation: a Faculty of Chemistry , Institute of Applied Radiation Chemistry, Lodz University of Technology (TUL) , Lodz , Poland.
authors.forename: Lidia
authors.initials: L
authors.lastname: Gebicka
mesh_terms: D000975:Antioxidants / Q000737:chemistry*; D005419:Flavonoids; D006801:Humans; D006997:Hypochlorous Acid / Q000737:chemistry*; D007700:Kinetics
chemical_list: D000975:Antioxidants; D005419:Flavonoids; D006997:Hypochlorous Acid
keywords: ABTS; flavonoid; hypochlorous acid