Direct and Indirect Oxidations by Peroxynitrite

The mechanism of oxidation of iodide, Ni^IIcyclam, and ferrocyanide by peroxynitrite has been studied in detail. The results demonstrate that the oxidative chemistry of peroxynitrite is highly pH dependent and can take place either directly by the peroxynitrous acid, as in the case of iodide and Ni^IIcyclam, or indirectly by secondary reactive intermediates formed via the self-decomposition of peroxynitrous acid, as in the case of ferrocyanide. The rate constants of the oxidation of I⁻ and Ni^IIcyclam by ONOOH have been determined to be (2.3 ±0.1) × 10⁴ M^‒1 s^‒1 and (3.25 ± 0.15) × 10⁴ M^‒1 s^‒1, respectively. In the indirect pathway, about 60% of ONOOH isomerizes to nitric acid and about 40% is converted into a highly reactive oxidant which directly oxidized ferrocyanide via the formation of NO₂• as an intermediate without the involvement of hydroxyl radicals in this process.