Everything about Peroxynitrite totally explained
Peroxynitrite is the
anion with the formula ONOO
−. It is an unstable "valence isomer" of
nitrate, NO
3−, which has the same formula but a different structure. Although peroxynitrous acid is highly reactive, its
conjugate base peroxynitrite is stable in basic solution. It is prepared by the reaction of
hydrogen peroxide with
nitrite:
» H
2O
2 + NO
2− → ONOO
− + H
2O
Peroxynitrite is an
oxidant and
nitrating agent. Because of its oxidizing properties, peroxynitrite can damage a wide array of molecules in
cells, including
DNA and
proteins. Formation of peroxynitrite
in vivo has been ascribed to the reaction of the free radical
superoxide with the free radical
nitric oxide:
» ·O
2− + ·NO → ONO
2−
The resultant paring of these two free radicals results in peroxynitrite, a molecule which is itself
not a free radical, but which
is a powerful oxidant.
In the laboratory, a solution of peroxynitrite can be prepared by treating acidified hydrogen peroxide with a solution of sodium nitrite, followed by rapid addition of NaOH. Its concentration is indicated by the
absorbance at 302
nm (pH 12, λ
302 = 1670 M
−1 cm
−1).
As a nucleophile
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
The
conjugate acid of ONOO
− is peroxynitrous acid (ONOOH) (or phonetically "HOONO," pronounced "hoo-noh"), which has a p
Ka of ~6.8. HOONO can
homolyze to form
nitrogen dioxide and
hydroxyl radical as a pair of
caged radicals. Approximately 66% of the time, these two radicals undergo
electron transfer to form
nitronium ion and
hydroxide. The other 33% of the time, the two species escape the solvent cage as free radicals.
» OH· + NO
2 ← HOONO → OH
− + NO
2+
HOONO is thought to be important in
atmospheric chemistry.
Further Information
Get more info on 'Peroxynitrite'.
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