FREE-RADICAL FORMATION IN THE PEROXYNITROUS ACID (ONOOH) PEROXYNITRITE (ONOO-) SYSTEM

The rate constant of homolysis of peroxynitrite, ONOO-, into O-2(.-) a nd NO. was determined to be 0.017 s(-1) at 20 degrees C. In combinatio n with other experimental data taken from the literature, this value y ields the Gibbs free energy of formation of ONOO-, Delta(f)G degrees(O NOO-) = 16.6 kcal/mol. On the basis of this result, we conclude that p eroxynitrous acid homolyzes to yield nitrogen dioxide (NO2.) and hydro xyl (OH.) free radicals and derive Delta(f)G degrees(ONOOH) = 7.7 kcal /mol. The rate constant of the reaction between NO. and ONOO- was foun d to be 5 x 10(-2) M-1 s(-1) at most. The implications of the two homo lysis reactions are discussed.