Mechanism of Decomposition of Peroxynitric Ion (O2NOO-): Evidence for the Formation of O2•- and •NO2 Radicals

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Abstract
The rate constant of the self-decomposition of O(2)NOO(-) was determined to be 1.35 +/- 0.03 s(-)(1) at 25 degrees C. The decomposition rate constant of O(2)NOO(-) in the presence of C(NO(2))(4), CuSO(4), SOD, and Fe(CN)(6)(4)(-) was found to be 2.4 +/- 0.2 s(-)(1), independent of the concentration of these substrates. The oxidation yields of C(NO(2))(3)(-) and ferricyanide were measured to be 47 +/- 5 and 83 +/- 9% of added peroxynitrate, respectively, where the latter decreased to 54 +/- 6% in the presence of SOD. We therefore suggest that ca. 50% of O(2)NOO(-) homolyses into O(2)(*)(-) and (*)NO(2) (k = 1.05 +/- 0.23 s(-)(1)). The equilibrium constant of the homolysis of O(2)NOO(-) into (*)NO(2) and O(2)(*)(-) and the reduction potential of the couple O(2)NOOH,H(+)/NO(3)(-) were calculated to be 2.3 x 10(-)(10) M and 1.83 V, respectively.