Publication costs assisted by Natick Laboratories
The fast-reaction technique of pulse radiolysis and kinetic absorption spectrophotometry was used to generate s 0 2 -and a HO2 radicals in aqueous solution, and follow their one-electron redox reactions. In the presence of electron acceptors A, the one-electron oxidation of these radicals was monitored by following the formation of -Aradicals: -0 2 -+ A * 0 2 + -A-. Similarly, the one-electron reduction of. 0 2 -was monitored in the presence of electron donors: -0 2 -+ AH2 -H202 + -A-. The efficiencies of these electron transfer processes were found to be dependent on the two-electron redox potentials of the electron donor or acceptor compounds used. From the midpoint (50% electron transfer) of these titration curves the kinetic potentials of some redox couples could be derived (at pH 7.0, -25'): E k o l = +0.07 V for the Od -0 2 -couple and Ekol 2 +0.36 V for the -02-1H202 couple. The oxidation of -0 2 -was found to take place under reversible equilibrium conditions, whereas the reduction of -0 2 -was not reversible under the experimental conditions used. The observed rate constants of electron transfer reactions involving 0 2 -, HOz, and 0 2 with a large number of acceptors and donors have been tabulated and found to be in general agreement with the E k o l values derived for the appropriate redox couples.