Peroxynitrite: A tale of two radicals

The published syntheses of peroxynitrite from azide, nitrite, amylnitrite, hydroxylamine, nitrogen monoxide, and ammonia are discussed. With one exception, all of these syntheses yield peroxynitrite contaminated with nitrate and nitrite as well as reactants. The rate constant for the reaction of nitrogen monoxide with superoxide has been determined by pulse radiolysis and flash photolysis. In pulse radiolysis studies, the formation of the reactants may be rate-limiting and could lead to underestimation of the second-order rate constant. The conditions of flash photolysis experiments can be chosen to minimize conflict between reactant formation and the reaction half-life, thus the rate constant of 1.6 × 10¹⁰ M⁻¹ s⁻¹ determined by flash photolysis is preferred. The toxicity of peroxynitrite can be attributed mainly to its rapid reaction with carbon dioxide to yield the oxidizing trioxidocarbonate(•1−) and nitrogen dioxide radicals.