1998Chemical Research in ToxicologyRequires access

Free Radical Formation in the Peroxynitrous Acid (ONOOH)/Peroxynitrite (ONOO-) System

Gábor Merényi, Johan Lind

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Abstract

The rate constant of homolysis of peroxynitrite, ONOO-, into O2- and NO was determined to be 0.017 s-1 at 20 degrees C. In combination with other experimental data taken from the literature, this value yields the Gibbs free energy of formation of ONOO-, delta f G o(ONOO-) = 16.6 kcal/mol. On the basis of this result, we conclude that peroxynitrous acid homolyzes to yield nitrogen dioxide (NO2) and hydroxyl (OH) free radicals and derive delta f G o(ONOOH) = 7.7 kcal/mol. The rate constant of the reaction between NO and ONOO- was found to be 5 x 10(-)2 M-1 s-1 at most. The implications of the two homolysis reactions are discussed.

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The rate constant of homolysis of peroxynitrite, ONOO-, into O2- and NO was determined to be 0.017 s-1 at 20 degrees C. In combination with other experimental data taken from the literature, this value yields the Gibbs free energy of formation of ONOO-, delta f G o(ONOO-) = 16.6 kcal/mol. On the basis of this result, we conclude that peroxynitrous acid homolyzes to yield nitrogen dioxide (NO2) and hydroxyl (OH) free radicals and derive delta f G o(ONOOH) = 7.7 kcal/mol. The rate constant of the reaction between NO and ONOO- was found to be 5 x 10(-)2 M-1 s-1 at most. The implications of the two homolysis reactions are discussed.

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Available abstract

The rate constant of homolysis of peroxynitrite, ONOO-, into O2- and NO was determined to be 0.017 s-1 at 20 degrees C. In combination with other experimental data taken from the literature, this value yields the Gibbs free energy of formation of ONOO-, delta f G o(ONOO-) = 16.6 kcal/mol. On the basis of this result, we conclude that peroxynitrous acid homolyzes to yield nitrogen dioxide (NO2) and hydroxyl (OH) free radicals and derive delta f G o(ONOOH) = 7.7 kcal/mol. The rate constant of the reaction between NO and ONOO- was found to be 5 x 10(-)2 M-1 s-1 at most. The implications of the two homolysis reactions are discussed.

Key concepts: Peroxynitrite, Peroxynitrous acid, Homolysis, Chemistry, Radical, Reaction rate constant, Photochemistry, Yield (engineering)

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