PULSE-RADIOLYSIS STUDY OF THE REACTION OF NITRIC-OXIDE WITH SUPEROXIDE

Using the pulse-radiolysis technique, nitric oxide (NO) was produced by the reaction of an hydrated electron with NO2-. This was verified by the formation of the NO complex of iron(II) myoglobin (Mb) after pulse radiolysis of iron(III) myoglobin in the presence of NO2- under anaerobic conditions. By employing this technique. the reaction of superoxide (O-2(-)) with NO was followed directly in an oxygen-saturated solution containing NO2-. It was found that O-2(-) reacted with NO with a second-order rate constant of 3.8 x 10(9) dm(3) mol(-1) s(-1) at pH 7.5 to form oxoperoxonitrate(III) [NO(O-2)(-)] which has an absorption maximum around 300 nm. Oxoperoxonitrate(III) thus formed decomposed with a first-order rate constant of 0.8 s(-1) at pH 7.5. A similar decay process was observed in the reaction of O-2(-) with NO by monitored stopped-flow. where one part KO2 in dimethyl sulfoxide was mixed with nine parts of a NO-saturated solution in water. The formation of oxoperoxonitrate(III) was complete within the dead-time of the stopped-flow system.