A classic example of synergistic antioxidant interactions can be observed between [alpha]-tocopherol (vitamin E) and ascorbic acid (vitamin C) in cell membranes. This synergism is due to "antioxidant regeneration" via the recycling of a stronger (primary) antioxidant with a weaker (secondary) antioxidant. By this principle, the primary antioxidant ([alpha]-tocopherol) scavenges free radicals in the lipid phase and is then regenerated by the secondary antioxidant (ascorbic acid). From a thermodynamic point of view, the reaction is favorable because the reduction potential of ascorbic add is much lower than a-tocopherol, indicating that ascorbic acid prefers to give an electron to oxidized [alpha]-tocopherol. From a physical property viewpoint, this reaction is also favorable because a-tocopherol is in the membrane where it can inactivate lipid radicals and yet is also at the membrane interface where it can react with ascorbic acid.