ONOOCO2

ONOOCO2 refers to the nitrosoperoxocarboxylate adduct formed when peroxynitrite (ONOO−) reacts with carbon dioxide (CO2) in aqueous solution. In many discussions, the adduct is written as ONOOCO2−, while the neutral shorthand ONOOCO2 is also encountered. This transient species arises in biological contexts where CO2 or bicarbonate is present at millimolar levels.

Formation and structure: The reaction of peroxynitrite with CO2 rapidly yields nitrosoperoxocarboxylate (ONOOCO2−). The adduct is short-lived and can decompose to reactive radicals, notably nitrogen dioxide (NO2•) and carbonate radical (CO3•−). As an intermediate, ONOOCO2− acts as a reservoir that channels the chemistry of reactive nitrogen and oxygen species toward downstream reactions.

Reactivity and biological implications: The decomposition products NO2• and CO3•− are potent oxidants and nitrating agents. They can nitrate tyrosine residues to form 3-nitrotyrosine, initiate lipid peroxidation, and cause oxidative damage to nucleic acids and other biomolecules. The formation of ONOOCO2− thus contributes to nitrosative and oxidative stress in cells, particularly under inflammatory or oxidative conditions where CO2/bicarbonate is abundant.

Detection and kinetics: ONOOCO2− is highly reactive and has a short lifetime that depends on CO2 concentration and solution conditions. Experimental approaches to studying this species include spectroscopic methods and detection of downstream products such as nitrated biomolecules or radical-signature signals captured by EPR spin trapping.

Significance: The ONOOCO2 adduct represents a key intermediate in the interaction of peroxynitrite with carbonate chemistry, linking reactive nitrogen species to nitration and oxidation pathways in biological systems.