OXIDATION OF ASCORBIC-ACID AND METAL-IONS AS AFFECTED BY NACL

Ascorbic acid is one of the biological reductants that reduce ferric or cupric ions to ferrous or cuprous forms, inducing in the presence of oxygen a ''metal redox cycle'' which initiates a cascade of reactions producing reactive oxygen species. NaCl inhibits ascorbic acid oxidation and the reactions that produce O-2(.-), H2O2, and HO. by preventing the interaction of the transition metal (Fe, Cu) with oxygen. If the transition metal is liganded by a weak ligand such as acetate or ADP, NaCl prevents the interaction between oxygen and the transition metal. However, if the metal ion is chelated by a strong ligand such as citrate or EDTA, the effect of NaCl on ferrous oxidation is weak or nonexistent. NaCl does not inhibit the interaction of the metal ions (Fe, Cu) with H2O2 and the generation of hydroxyl radicals from preformed H2O2.