Oxidation of peroxynitrite by inorganic radicals: A pulse radiolysis study

Reactivity of the peroxynitrite ion toward a number of inorganic radicals was determined by using the pulse radiolysis technique. The rate constants for the oxidation of the ONOO^- ion by CO₃·^-, ·N₃, and ClO₂· radicals were determined from their decay kinetics to be (7.7 ± 1.2) x 10⁶ (I = 0.6 M), (7.2 ± 0.9) x 10⁸, and (3.2 ± 0.3) x 10⁴ M^-1 s^-(l), respectively. For the ·OH radical, the rate constant of (4.8 ± 0.8) x 10⁹ M^-1 s^-1 was obtained by using competition kinetic analysis. The oxidation potential of the ONOO^- ion was estimated as 0.8 V from the kinetic data. Although thermodynamically favorable, oxidation of ONOO^- by the °NO₂ radical was not observed; an upper limit of 2.5 x 10⁴ M^-1 s^-1 could be set for this reaction. Contribution from some of these reactions to the decomposition of peroxynitrite in the presence and absence of CO₂ is discussed.