Reaction of peroxynitrite with carbon dioxide:: intermediates and determination of the yield of CO3•- and NO2•

CO2 catalyses the isomerization of the biological toxin ONOO- to NO3- via an intermediate, presumably ONOOCO2-, which has an absorption maximum near 650 nm. The reflection spectrum of solid NMe4+ ONOO- exposed to CO2 shows a similar band near 650 nm, this absorption decays over minutes. Stopped-flow experiments in which CO2 solutions were mixed with alkaline ONOO- solutions indicate the formation of at least one intermediate. The initial absorption at 302 nm is less than that of ONOO-. which indicates that reactions take place within the mixing time, and this absorption is dependent (but not linearly) on the ONOO- and CO2 concentrations. We found that reaction of peroxynitrite with carbon dioxide forms some trioxocarbonate(.1-) (CO3.-) and nitrogen dioxide (NO2.) radicals via homolysis of the O-O bond in ONOOCO2-. We determined the extent of radical formation by mixing peroxynitrite, carbon dioxide and nitrogen monoxide. The later reacts with CO3.- and NO2. radicals to form, effectively, three NO2- per homolysis; ONOOCO2- that does not undergo homolysis yields NO3- and CO2. Based on the NO3- and NO2- analyses, the extent of conversion to NO3- is 96 +/- 1% and that of homolysis is 3 +/- 1%. respectively, significantly less than that reported in the literature.