The dependence of alpha-tocopheroxyl radical reduction by hydroxy-2,3-diarylxanthones on structure and micro-environment

• Type: Article in International Scientific Journal
• Date: 2012

Authors

Patrice Morliere (Author) Other; Larry K Patterson (Author) Other; Clementina M M Santos (Author) Other; Artur M S Silva (Author) Other; Jean Claude Maziere (Author) Other; Paulo Filipe (Author) Other; Ana Gomes (Author) Other; Eduarda Fernandes (Author) FFUP; Beatriz B Q Garcia (Author) FFUP; Rene Santus (Author) Other

Journal

Title: Organic and Biomolecular Chemistry

Vol. 10

Pages: 2068-2076

ISSN: 1477-0520

Publisher: Royal Society of Chemistry

Indexing

ISI Web of Knowledge - 6 Citations

Scopus - 5 Citations

Scientific classification

FOS: Natural sciences > Chemical sciences

Other information

Authenticus ID: P-002-H00

DOI: 10.1039/c2ob06612b

Abstract (EN): The flavonoid quercetin is known to reduce the alpha-tocopheroxyl radical ((center dot)TocO) and reconstitute alpha-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 (center dot)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 (center dot)TocO, though repair depends strongly on the micro-environment. In cationic cetyltrimethylammonium bromide (CTAB) micelles, 30% of (center dot)TocO radicals are repaired at a rate constant of similar to 7.4 x 10(6) M-1 s(-1) by XH9 compared to 1.7 x 10(7) M-1 s(-1) by ascorbate. Water-soluble Trolox (TrOH) radicals ((TrO)-Tr-center dot) are restored by XH9 in CTAB (rate constant similar to 3 x 10(4) M-1 s(-1)) but not in neutral TX100 micelles where only 15% of (center dot)TocO are repaired (rate constant similar to 4.5 x 10(5) M-1 s(-1)). In basic aqueous solutions (TrO)-Tr-center dot is readily reduced by deprotonated XH9 species leading to ionized XH9 radical species (radical pK(a) similar to 10). An equilibrium is observed (K = 130) yielding an estimate of 130 mV for the reduction potential of the [(center dot)X9, H+/XH9] couple at pH 11, lower than the 250 mV for the [(TrO)-Tr-center dot,H+/TrOH] couple. A comparable value (100 mV) has been determined by cyclic voltammetry measurements.

Language: English

Type (Professor's evaluation): Scientific

No. of pages: 9