Journal Article (Refereed)
Generation of reactive oxygen species from a-tocopherolquinone and analogues
AG, C & RB, M & S, N & Wilkinson, J A & Bisby, R H 2007, 'Generation of reactive oxygen species from a-tocopherolquinone and analogues', Free Radical Research, 41, pp.730-737.
Three potential routes to generation of reactive oxygen species (ROS) from alpha- tocopherolquinone (alpha-TQ) have been identified. The quinone of the water-soluble vitamin E analogue Trolox C (Trol-Q) is reduced by hydrated electron and isopropanol alpha-hydroxyalkyl radical, and the resulting semiquinone reacts with molecular oxygen to form superoxide with a second order rate constant of 1.3 x 10(8) dm(3)/mol/s, 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 10(9) dm(3)/mol/s. The triplet states of these quinones sensitize singlet oxygen formation with quantum yields of about 0.8. Such potentially damaging reactions of alpha-TQ 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.
Free Radical Research