Peroxynitrous

Peroxynitrous refers to species related to peroxynitrite, most notably the protonated form peroxynitrous acid HOONO and the conjugate base peroxynitrite ONOO−. Peroxynitrite is a reactive nitrogen-oxygen species formed by the rapid reaction of nitric oxide (NO) with superoxide (O2−). In aqueous solution, ONOO− can be protonated: ONOO− + H+ ⇌ HOONO (peroxynitrous acid). The equilibrium lies near neutral pH, so both forms may be present in biological systems.

Peroxynitrite and peroxynitrous acid are strong oxidants and can participate in rapid, damaging reactions. One major pathway is reaction with carbon dioxide (CO2) to form nitrosoperoxocarboxylate ONOOCO2−, which quickly decays to nitrogen dioxide (•NO2) and the carbonate radical (CO3−•). Direct decay of HOONO can yield hydroxyl radical (•OH) and nitrogen dioxide, contributing to oxidative and nitrosative stress in various contexts.

Biological relevance is most noted in inflammation and reperfusion injury, where peroxynitrite species can modify lipids, proteins, and nucleic acids, influencing cell signaling and contributing to tissue damage under high production conditions. At lower, subtoxic levels, peroxynitrous species may participate in signaling pathways, but their short lifetimes and reactive chemistry make precise roles variable and context-dependent. Measurement and interpretation of peroxynitrite-related chemistry are challenging due to rapid transformations and overlapping reactive species.

Safety and handling considerations reflect their high reactivity; peroxynitrite and related species are typically studied under controlled laboratory conditions, with attention to potential hazards from oxidant and radical formation.