The effect of pH on the conversion of superoxide to hydroxyl free radicals.
The conversion of superoxide (O-.2) to the hydroxyl (HO.) free radical by superoxide-driven Fenton reactions was measured by the formation of hydroxylated derivatives from benzoate. Among a range of catalysts required for the conversion, the Fe3+EDTA complex was the most effective. The effect of superoxide dismutase and catalase indicated that O-.2 and H2O2 were essential reactants, while the formation of authentic HO. was confirmed by the inhibiting capacities of formate, t-butanol, and mannitol. The conversion of O-.2 to HO. was tested over a broad pH range, and was found to be highest at pH 4.8 whether Fe3+EDTA or free Fe3+ were used as the catalysts. When Fe3+EDTA was used at the optimum pH, every HO. produced required 3.7 O-.2 radicals, close to the theoretical limit of one HO. from every three O-.2 radicals generated.
D002384:Catalysis; D055598:Chemical Phenomena; D002621:Chemistry; D002712:Chlorides; D004492:Edetic Acid; D005290:Ferric Compounds; D005609:Free Radicals; D006863:Hydrogen-Ion Concentration; D006878:Hydroxides; D062385:Hydroxybenzoates / Q000528:radiation effects; D017665:Hydroxyl Radical; D007536:Isomerism; D013050:Spectrometry, Fluorescence; D013481:Superoxides
D002712:Chlorides; D005290:Ferric Compounds; D005609:Free Radicals; D006878:Hydroxides; D062385:Hydroxybenzoates; D013481:Superoxides; D017665:Hydroxyl Radical; D004492:Edetic Acid; C024555:ferric chloride