Peroxynitrite (sometimes called peroxonitrite) is an ion with the formula ONOO<sup>âÂÂ</sup>. It is a structural isomer of nitrate, . Peroxynitrite is a potent reactive nitrogen species and is highly cytotoxic.
Peroxynitrite can be prepared by the reaction of superoxide with nitric oxide:
It is prepared by the reaction of hydrogen peroxide with nitrite:
Its presence is indicated by the absorbance at 302 nm (pH 12, õ<sub>302</sub> = 1670 M<sup>âÂÂ1</sup> cm<sup>âÂÂ1</sup>).
Peroxynitrite is weakly basic with a pK<sub>a</sub> of ~6.8.
It is reactive toward DNA and proteins.
ONOO<sup>âÂÂ</sup> reacts nucleophilically with carbon dioxide. In vivo, the concentration of carbon dioxide is about 1 mM, and its reaction with ONOO<sup>âÂÂ</sup> occurs quickly. Thus, under physiological conditions, the reaction of ONOO<sup>âÂÂ</sup> with carbon dioxide to form nitrosoperoxycarbonate () is by far the predominant pathway for ONOO<sup>âÂÂ</sup>. homolyzes to form carbonate radical and nitrogen dioxide, again as a pair of caged radicals. Approximately 66% of the time, these two radicals recombine to form carbon dioxide and nitrate. The other 33% of the time, these two radicals escape the solvent cage and become free radicals. It is these radicals (carbonate radical and nitrogen dioxide) that are believed to cause peroxynitrite-related cellular damage.
Its conjugate acid peroxynitrous acid is highly reactive, although peroxynitrite is stable in basic solutions.