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Free radicals generated during oxidation of green tea polyphenols: Electron paramagnetic resonance spectroscopy combined with density functional theory calculations

Severino, JF; Goodman, BA; Kay, CWM; Stolze, K; Tunega, D; Reichenauer, TG; Pirker, KF; (2009) Free radicals generated during oxidation of green tea polyphenols: Electron paramagnetic resonance spectroscopy combined with density functional theory calculations. FREE RADICAL BIO MED , 46 (8) 1076 - 1088. 10.1016/j.freeradbiomed.2009.01.004.

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Abstract

Electron paramagnetic resonance spectroscopy and density functional theory calculations have been used to investigate the redox properties of the green tea polyphenols (GTPs) (-)-epigallocatechin gallate (EGCG), (-)-epigallocatechin (EGC), and (-)-epicatechin gallate (ECG). Aqueous extracts of green tea and these individual phenols were autoxidized at alkaline pH and oxidized by superoxide anion (O-2(center dot-)) radicals in dimethyl sulfoxide. Several new aspects of the free radical chemistry of GTPs were revealed. EGCG can be oxidized on both the B and the D ring. The B ring was the main oxidation site during autoxidation, but the D ring was the preferred site for O-2(center dot-) oxidation. Oxidation of the D ring was followed by structural degradation, leading to generation of a radical identical to that of oxidized gallic acid. Alkaline autoxidation of green tea extracts produced four radicals that were related to products of the oxidation of EGCG, EGC. ECG, and gallic acid, whereas the spectra from O-2(center dot-) oxidation could be explained solely by radicals generated from EGCG. Assignments of hyperfine coupling constants were made by DFT calculations, allowing the identities of the radicals observed to be confirmed. (C) 2009 Elsevier Inc. All rights reserved.

Type: Article
Title: Free radicals generated during oxidation of green tea polyphenols: Electron paramagnetic resonance spectroscopy combined with density functional theory calculations
DOI: 10.1016/j.freeradbiomed.2009.01.004
Keywords: Green tea, Oxidation, Superoxide anion radicals, Epicatechin gallate, Epigallocatechin, Epigallocatechin gallate, EPR spectroscopy, Density functional theory, Free radicals, CHEMICAL-REACTION DETECTION, ANTIOXIDANT ACTIVITY, GALLIC ACID, (-)-EPIGALLOCATECHIN GALLATE, SPIN-RESONANCE, EPIGALLOCATECHIN GALLATE, CANCER PREVENTION, CATECHINS, SUPEROXIDE, DEGRADATION
UCL classification: UCL > Provost and Vice Provost Offices
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > London Centre for Nanotechnology
URI: http://discovery.ucl.ac.uk/id/eprint/111945
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