| Abstract
| - Peroxynitrite is formed when •NO is added tooxygenated solutions of hydrogen-peroxide. The formationratesand the yields of peroxynitrite were determined using the stopped-flowtechnique at pH 7.5−11.7. Thestoichiometry of this process has been determined, and is given by4•NO + O2 +2H2O2 → 2ONOO- +2NO2-+ 4H+. Kinetic studies show that the rate law ofthe nitrosation process is given by -d[O2]/dt =k1[•NO]2[O2]with k1 = (2.4 ± 0.3) × 106M-2 s-1. Thekinetic results are identical to those obtained for the autoxidationof•NO, indicating that the rate determining step ofthe nitrosation process is the formation of ONOONO (orONONO2or O2NNO2), which is the precursor of•NO2 and ofN2O3. The stoichiometry of the nitrosationprocess suggeststhat •NO2 and/orN2O3 are the reactive species. Competitivekinetic studies demonstrate that the yield ofperoxynitrite is independent of •NO concentrations,indicating that the reactive intermediate isN2O3. The rateconstant of the reaction of N2O3 withHO2- was determined to be (1.0 ± 0.6) ×109 M-1s-1, whereas that withH2O2 is at least 4 orders of magnitude lower.The nitrosation of H2O2 by•NO takes place only in the presenceof oxygen, and under the conditions of this study, we found no evidencefor the direct nitrosation of H2O2by•NO.
- Nitrosation ofH2O2 by •NO takes place onlyin the presence of oxygen. The rate-determining step of thisprocess is the formation of ONOONO which is the precursor of•NO2 and ofN2O3. The stoichiometry of this process isgiven by the equation below. The nitrosating species isN2O3. The rate constant of its reactionwith HO2- has been determined to be (1.0 ±0.6) × 109 M-1s-1, whereas that withH2O2 is lower than 1 × 105M-1s-1.
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