KINETIC-ANALYSIS AND DOUBLE QUENCHING EXPERIMENTS AS TOOLS TO ELUCIDATE THE ACTION MECHANISM OF ANTIOXIDANTS

The dependence of the oxidation rate with the concentration of an addi tive that reduces the rate of the process can be employed to determine if its effect is due to trapping of active radicals (chain-breaking a ntioxidant) or to its ability to chelate active metals (metal-chelatin g antioxidant). Kinetic expressions are deduced for metal-chelating an tioxidants of high or low efficiency and for chain-breaking antioxidan ts. In particular, it is proposed that chain-breaking antioxidants mus t provide lineal SternVolmer's like relationships, while efficient pri mary antioxidants will give plots with a strong upward curvature. A se cond procedure is proposed that could allow a determination of the mai n mechanism of action of the additive based on double quenching experi ments. The effect of the simultaneous addition of two antioxidant will depend of their mechanism of action. Two strong metal-chelating antio xidants will present a synergic behavior, while two chain-breaking ant ioxidants acting on the same species will present antagonic behavior. Antioxidants acting by different mechanisms will present an indifferen t behavior, its efficiency being independent of the presence of the se cond antioxidant. Several different situations are contrasted with dat a obtained in the autoxidation of brain homogenates employing propyl g allate, desferrioxamine and BHT as antioxidants.