A study of the superoxide radical chemistry by stopped-flow radiolysis and radiation induced oxygen consumption

The chemical reactivity of the superoxide radical has been studied at pH 10 and 23/sup 0/C by absorption spectroscopy in a fast kinetics spectrophotometer and by radiation induced oxygen consumption in a modified stopped-flow radiolysis apparatus on line with a Van de Graaff electron generator. The latter method differentiates between oxidation and reduction reactions and yields information on the corresponding stoichiometry. A number of examples are used to demonstrate the versatility of these techniques. Rate constants were determined for the reaction of superoxide radicals with: ferricytochrome c, k = 2.6 +- 0.2 x 10/sup 5/ M/sup -1/ s/sup -1/ at pH 9.0; ascorbate, k = 1.52 +- 0.1 x 10/sup 5/ M/sup -1/ s/sup -1/ at pH 9.9; nitroblue tetrazolium, k = 5.94 +- 0.5 x 10/sup 4/ M/sup -1/ s/sup -1/ at pH 9.8. Some 19 other compounds (buffers, carboxylic acids, chelating agents, etc.) were shown to be inert toward superoxide radicals.