Generation of superoxide and singlet oxygen from α-tocopherolquinone and analogues

Three potential routes to generation of reactive oxygen species (ROS) from α-tocopherolquinone (α-TQ) have been identified. The quinone of the water-soluble vitamin E analogue Trolox C (Trol-Q) is reduced by hydrated electron and isopropanol α-hydroxyalkyl radical, and the resulting semiquinone reac...

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Bibliographic Details
Published in:Free radical research 2007-01, Vol.41 (6), p.730-737
Main Authors: Crisostomo, Ana G., Moreno, Raphael B., Navaratnam, Suppiah, Wilkinson, James A., Bisby, Roger H.
Format: Article
Language:English
Subjects:
Antioxidants - chemistry
Antioxidants - metabolism
Chromans - chemistry
Chromans - metabolism
Lasers
Oxidation-Reduction
Pulse Radiolysis
radical
Reactive Oxygen Species - metabolism
redox cycling
singlet oxygen
Singlet Oxygen - metabolism
superoxide
Superoxides - metabolism
Tocopherolquinone
triplet
Tryptophan - chemistry
Vitamin E - analogs & derivatives
Vitamin E - chemistry
Vitamin E - metabolism
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Summary:Three potential routes to generation of reactive oxygen species (ROS) from α-tocopherolquinone (α-TQ) have been identified. The quinone of the water-soluble vitamin E analogue Trolox C (Trol-Q) is reduced by hydrated electron and isopropanol α-hydroxyalkyl radical, and the resulting semiquinone reacts with molecular oxygen to form superoxide with a second order rate constant of 1.3 × 108 dm3/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 109 dm3/mol/s. The triplet states of these quinones sensitize singlet oxygen formation with quantum yields of about 0.8. Such potentially damaging reactions of α-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.
ISSN:1071-5762
1029-2470
DOI:10.1080/10715760701324075