Hydroxyl radical formation by O-O bond homolysis in peroxynitrous acid.

Peroxynitrite decay in weakly alkaline media occurs by two concurrent sets of pathways which are distinguished by their reaction products. One set leads to net isomerization to NO3- and the other set to net decomposition to O2 plus NO2-. At sufficiently high peroxynitrite concentrations, the decay half-time becomes concentration-independent and approaches a limiting value predicted by a mechanism in which reaction is initiated by unimolecular homolysis of the peroxo O−O bond, i.e., the following reaction:  ONOOH → •OH + •NO2. This dynamical behavior excludes alternative postulated mechanisms that ascribe decomposition to bond rearrangement within bimolecular adducts. Nitrate and nitrite product distributions measured at very low peroxynitrite concentrations also correspond to predictions of the homolysis model, contrary to a recent report from another laboratory. Additionally, (1) the rate constant for the reaction ONOO- → •NO + •O2-, which is critical to the kinetic model, has been confirmed, (2) the app...