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Title: The dependence of alpha-tocopheroxyl radical reduction by hydroxy-2,3-diarylxanthones on structure and micro-environment
Authors: Morlière, Patrice
Patterson, Larry K.
Santos, Clementina M.M.
Silva, Artur
Marzière, Jean-Claude
Filipe, Paulo
Gomes, Ana
Fernandes, Eduarda
Garcia, Beatriz
Santus, René
Keywords: Pulse-radiolysis
Redox potentials
Issue Date: 2012
Publisher: Royal Society of Chemistry
Citation: Morlière, Patrice; Patterson, Larry K.; Santos, Clementina M.M.; Silva, Artur; Marzière, Jean-Claude; Filipe, Paulo; Gomes, Ana; Fernandes, Eduarda; Garcia, Beatriz; Santus, René (2012) - The dependence of alpha-tocopheroxyl radical reduction by hydroxy-2,3-diarylxanthones on structure and micro-environment. Organic & Biomolecular Chemistry. ISSN 1477-0539. 10, p. 2068-2076
Abstract: The flavonoid quercetin is known to reduce the α-tocopheroxyl radical (˙TocO) and reconstitute α-tocopherol (TocOH). Structurally related polyphenolic compounds, hydroxy-2,3-diarylxanthones (XH), exhibit antioxidant activity which exceeds that of quercetin in biological systems. In the present study repair of ˙TocO by a series of these XH has been evaluated using pulse radiolysis. It has been shown that, among the studied XH, only 2,3-bis(3,4-dihydroxyphenyl)-9H-xanthen-9-one (XH9) reduces ˙TocO, though repair depends strongly on the micro-environment. In cationic cetyltrimethylammonium bromide (CTAB) micelles, 30% of ˙TocO radicals are repaired at a rate constant of ∼7.4 × 106 M−1 s−1 by XH9 compared to 1.7 × 107 M−1 s−1 by ascorbate. Water-soluble Trolox (TrOH) radicals (˙TrO) are restored by XH9 in CTAB (rate constant ∼3 × 104 M−1 s−1) but not in neutral TX100 micelles where only 15% of ˙TocO are repaired (rate constant ∼4.5 × 105 M−1 s−1). In basic aqueous solutions ˙TrO is readily reduced by deprotonated XH9 species leading to ionized XH9 radical species (radical pKa ∼10). An equilibrium is observed (K = 130) yielding an estimate of 130 mV for the reduction potential of the [˙X9,H+/XH9] couple at pH 11, lower than the 250 mV for the [˙TrO,H+/TrOH] couple. A comparable value (100 mV) has been determined by cyclic voltammetry measurements.
Peer review: yes
ISSN: 1477-0539
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Appears in Collections:PTV - Artigos em Revistas Indexados ao ISI/Scopus

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