Premium
Antioxidant stoichiometry and the oxidative fate of vitamin E in peroxyl radical scavenging reactions
Author(s) -
Liebler Daniel C.,
Burr Jeanne A.
Publication year - 1995
Publication title -
lipids
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.601
H-Index - 120
eISSN - 1558-9307
pISSN - 0024-4201
DOI - 10.1007/bf02533953
Subject(s) - chemistry , antioxidant , acetonitrile , liposome , stoichiometry , vitamin e , hexane , radical , autoxidation , phosphatidylcholine , organic chemistry , photochemistry , medicinal chemistry , phospholipid , biochemistry , membrane
Oxidation of R,R,R ‐α‐tocopherol (vitamin E; TH) by peroxyl radicals generated from the azo initiator azo bis (2,4‐dimethylvaleronitrile) in acetonitrile, hexane, or in phospholipid liposomes yields 8a‐(alkyldioxy)tocopherone adducts, 8a‐(hydroxy)tocopherone, and their hydrolysis product α‐tocopherolquinone TH oxidation also yields 4a,5‐epoxy‐ and 7,8‐epoxy‐8a‐(hydroperoxy)tocopherones and their respective hydrolysis products 2,3‐epoxy‐α‐tocopherolquinone and 5,6‐epoxy‐α‐tocopherolquinone. Previous work indicates that the distribution of TH oxidation products varies with reaction environment. We investigated the dependence of antioxidant stoichiometry on TH oxidation product distribution for reactions in hexane, acetonitrile, and in phosphatidylcholine liposomes. Yields of 8a‐substituted tocopherones were highest in hexane and lowest in phosphatidylcholine liposomes. In contrast, yields of epoxide products were highest in the liposome system and lowest in hexane. Yields of α‐tocopherolquinone were similar in all three systems. Antioxidant stoichiometry, measured by the inhibited autoxidation method, was approximately 2.0 peroxyl radicals trapped per TH consumed in acetonitrile and in liposomes. In hexane, a slightly larger stoichiometric factor of approximately 2.5 was measured. This may, in part, reflect the generation of more reactive alkoxyl radicals in hexane. The reaction environment thus markedly affects the balance between competing TH oxidation pathways but produces comparatively little effect on antioxidant stoichiometry. These results imply that competing reaction pathways contribute similarly to the antioxidant chemistry of TH.