Vitamin E models. Can the anti-oxidant and pro-oxidant dichotomy of α-tocopherol be related to ionic ring closing and radical ring opening redox reactions?

Abstract

The free radical scavenging mechanism, leading to a quinodal structure via an oxidative ring opening is exothermic. However, the ionic oxidative ring opening is endothermic. Consequently, the ionic reductive ring closing must be exothermic. This leads to the suggestion that Vitamin E may be recovered, unchanged, thus effectively acts as a catalyst for the following reaction 2 HOO + H 3 O (+)+ NADH→2 HOOH+ H 2 O+ NAD (+), ΔE≈−120 kcal mol −1. As Vitamin E is biologically recycled, a single α-tocopherol molecule may convert numerous HOO radical to H 2O 2 which is accumulated if not removed at the same rate, enzymatically, with the participation of catalase (Fe) or glutathione peroxidase, GP x (Se). This accumulation of peroxide, which may be referred to as a ‘peroxide traffic jam’, may well be the reason of the pro-oxidant effect of Vitamin E.