SPIN TRAPPING STUDY ON THE KINETIC OF FE-2+ AUTOXIDATION - FORMATION OF SPIN ADDUCTS AND THEIR DESTRUCTION BY SUPEROXIDE

The oxidation of Fe2+ was investigated by electron spin resonance spin trapping techniques with N-t-butyl-α-phenylnitrone (PBN) and dimethyl sulfoxide. Under pure oxygen, the spin adduct PBN/·OCH3 was rapidly generated by the addition of Fe2+ (0.2-1.2 mm) into phosphate buffer containing ethylenediaminetetraacetate (EDTA), dimethyl sulfoxide, and PBN at pH 7.4, but it decayed. The decay process of PBN/·OCH3 consists of two components. The fast decay was dependent on Fe2+ concentration. Another was due to destruction of the spin adduct by superoxide anion (·O2-), because superoxide dismutase (SOD) markedly prevented the decay. Catalase decreased the yield of PBN/·OCH3. When EDTA was replaced by diethylenetriaminepentaacetic acid (DTPA), both the generation and decay process of PBN/·OCH3 were slow. SOD and catalase effects were similar to those in EDTA. Fe2+ produced PBN/·OCH3 even in the absence of chelators. We could estimate the kinetic parameters by computer simulation, comparing the Fe2+ oxidation in EDTA with that in DTPA. These results demonstrate that Fe2+ reacts with O2 to generate ·O2- and then H2O2, which produces ·CH3 by reaction with Fe2+ and dimethyl sulfoxide. ·OCH3 results from the reaction between ·CH3 and O2. The adduct PBN/·OCH3 decays by reaction with Fe2+ and ·O2-. © 1992.