Peroxynitrite (sometimes called peroxonitrite) is an ion with the formula ONOO−. It is a structural isomer of nitrate, NO−
3
 Chemical structure of the peroxynitrite anion | |
| Names | |
|---|---|
| IUPAC name Oxido nitrite | |
| Identifiers | |
3D model (JSmol) | |
| ChEBI | |
| KEGG | |
PubChem CID | |
| UNII | |
CompTox Dashboard (EPA) | |
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| Properties | |
| NO3− | |
| Molar mass | 62.005 g·mol−1 |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). | |
Preparation
Peroxynitrite can be prepared by the reaction of superoxide with nitric oxide:[1][2][3]
- NO + O−2 → NO(O2)−
It is prepared by the reaction of hydrogen peroxide with nitrite:[4]
- H2O2 + NO−
2 → 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 (ONOOCO−
2) is by far the predominant pathway for ONOO−. ONOOCO−
2 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.[5][6]