| Abstract
| - The reaction of ONOO- with CO2 at alkaline pH was recently reported to form a transientabsorption with a maximum at 640 nm and a half-life of ca. 4 ms at 10 °C [Meli et al. (1999)Helv. Chim. Acta82, 722−725]. This transient absorption was hardly affected by the presenceof •NO, and therefore was attributed to the adduct ONOOC(O)O-. This conclusion contradictsall current experimental results as it suggests that the decomposition of this adduct viahomolysis of the O−O bond into CO3•- and •NO2 is a minor pathway. In the present work theobservations of Meli et al. will be shown to be artifacts resulting from light coming from theUV region. When these experiments are carried out in the presence of appropriate cutoff filters,the only observable intermediate formed in the reaction of ONOO- with CO2 at alkaline pH isthe carbonate radical ion with a maximum at 600 nm. This transient absorption is not observedin the presence of •NO or ferrocyanide. In the latter case ferricyanide is formed, and its yieldwas determined to be 66 ± 2% of the initial concentration of peroxynitrite. The reaction ofONOO- with 16 mM CO2 with and without ferrocyanide was also studied at pH 5.6−7.7 inthe presence of 0.1 M phosphate, where both the initial pH and [CO2] remain constant. Underthese conditions the rate constant of the decay of peroxynitrite was found to be identical tothat of the formation of ferricyanide, indicating that ONOOC(O)- does not accumulate. Theseresults confirm our earlier observations, i.e., the reaction of peroxynitrite with excess CO2takes place via the formation of about 33% CO3•- and •NO2 radicals in the bulk of the solution.
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