Indirect Oxidation of Ferrocyanide by Peroxynitrite—Evidence against the Formation of Hydroxyl Radicals

Abstract

Thermodynamic calculations by different assumptions for arriving to the standard entropy of the formation of peroxynitrite anion in water lead to opposite conclusions considering the feasibility of the homolysis of ONOOH to•OH and•NO2(Koppenolet al.(1992).Chem. Res. Toxicol.5, 834–832; Merenyi (1997). The First International Conference on the Chemistry and Biology of Peroxynitrite). Nevertheless, the formation of hydroxyl radicals is not guaranteed even if it is feasible on thermodynamic grounds. To test the role of hydroxyl radicals during the isomerization of ONOOH, the indirect oxidation of ferrocyanide by peroxynitrite was studied in the presence of formate ions and methanol, where all the relevant rate constants of the primary and secondary reactions involving hydroxyl radicals are known. The oxidation rates were unaffected by these scavengers, while the decrease in the oxidation yields was not correlated with the known rate constants of these scavengers with hydroxyl radicals. It is concluded that the indirect oxidation of ferrocyanide by peroxynitrite takes place through an unidentified intermediate (ONOOH*), which is not a cage of•OH and•NO2.