Peroxynitrite

Peroxynitrite (sometimes called peroxonitrite) is an ion with the formula ONOO−. It is a structural isomer of nitrate,

Preparation
Peroxynitrite can be prepared by the reaction of superoxide with nitric oxide:
 * NO + O2-  ->  NO(O2)-

It is prepared by the reaction of hydrogen peroxide with nitrite:
 * H2O2 +   →  ONOO−  +  H2O

Its presence is indicated by the absorbance at 302 nm (pH 12, ε302 = 1670 M−1 cm−1).

Reactions
Peroxynitrite is weakly basic with a pKa of ~6.8.

It is reactive toward DNA and proteins.

ONOO− reacts nucleophilically with carbon dioxide. In vivo, the concentration of carbon dioxide is about 1 mM, and its reaction with ONOO− occurs quickly. Thus, under physiological conditions, the reaction of ONOO− with carbon dioxide to form nitrosoperoxycarbonate is by far the predominant pathway for ONOO−. 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.

Peroxynitrous acid
Its conjugate acid peroxynitrous acid is highly reactive, although peroxynitrite is stable in basic solutions.