Crisostomo, AG, Moreno, RB, Navaratnam, S, Wilkinson, JA and Bisby, RH 2007, 'Generation of superoxide and singlet oxygen from α-tocopherolquinone and analogues.' , Free Radical Research, 41 (6) , pp. 730-737.

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Abstract

Three potential routes to generation of reactive oxygen species from a tocopherolquinone have been identified. The quinone of the water-soluble vitamin E analogue Trolox C (Trol-Q) is reduced by hydrated electron and isopropanol a hydroxyalkyl radical, and the resulting semiquinone reacts with molecular oxygen to form superoxide with a second order rate constant of 1.3 x 108 dm³ mol^-1 s^-1, illustrating the potential for redox cycling. Illumination (UV-A, 355 nm) of the quinone of 2,2,5,7,8-pentamethyl-6-hydroxychromanol (PMHC-Q) leads to a reactive short-lived (ca 10^-6 s) triplet state, able to oxidise tryptophan with a second order rate constant greater than 109 dm³ mol^-1 s^-1. The triplet states of these quinones sensitize singlet oxygen formation with quantum yields of about 0.8. Such potentially damaging reactions of a tocopherolquinone may in part account for the recent findings that high levels of dietary vitamin E supplementation lack any beneficial effect and may lead to slightly enhanced levels of overall mortality.

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