Tocopheroxyl Radical

A tocopheroxyl radical is the radical formed when a tocopherol, such as alpha-tocopherol, loses the hydrogen atom from its phenolic hydroxyl group during an oxidation reaction. In biological membranes, this commonly occurs when alpha-tocopherol reacts with a lipid peroxyl radical. By transferring a hydrogen atom to the peroxyl radical, alpha-tocopherol can interrupt the chain reaction of lipid peroxidation and is itself converted into an alpha-tocopheroxyl radical .^1,2

Like other radicals, a tocopheroxyl radical contains an unpaired electron. However, it is relatively stabilized compared with many of the radicals that alpha-tocopherol scavenges because the unpaired electron can be delocalized across its chromanol ring structure. This stabilization reduces its tendency to propagate lipid-peroxidation chain reactions .¹

Formation of the tocopheroxyl radical is therefore an intermediate step in the chain-breaking antioxidant action of vitamin E. The radical can be reduced back to tocopherol by reducing compounds. Ascorbate, the reduced form of vitamin C, can regenerate alpha-tocopherol from the alpha-tocopheroxyl radical in model systems, allowing the tocopherol molecule to participate again in radical-scavenging reactions .²

The tocopheroxyl radical should not be confused with lipid peroxyl radicals. Lipid peroxyl radicals can propagate lipid peroxidation by reacting with additional lipids, whereas the tocopheroxyl radical is a comparatively stabilized product formed when tocopherol intercepts such radicals. Under particular chemical conditions it can participate in further oxidation reactions, but its formation is central to the chain-breaking antioxidant chemistry of tocopherols .^1,2