Peroxynitrite (sometimes called peroxonitrite) is an ion with the formula ONOO−. It is an unstable structural isomer of nitrate, . Although its conjugate acid is highly reactive, peroxynitrite is stable in basic solutions.Holleman, A. F.; Wiberg, E. Inorganic Chemistry Academic Press: San Diego, 2001. . W. H. Koppenol It is prepared by the reaction of hydrogen peroxide with nitrite: H2O2 + → ONOO− + H2O 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:Pacher, P.; Beckman, J. S.; Liaudet, L.; "Nitric Oxide and Peroxynitrite: in Health and disease" Physiological Reviews 2007, volume 87(1), page 315–424. Csaba Szabó, Harry Ischiropoulos and Rafael Radi; "Peroxynitrite: biochemistry, pathophysiology and development of therapeutics" Nature Reviews Drug Discovery; 6, 662–680 (August 2007) • + •NO → The resultant pairing of these two free radicals results in peroxynitrite, a molecule that is itself not a free radical, but that 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, ε302 = 1670 M−1 cm−1).Beckman, J. S.; Koppenol, W. H. "Nitric Oxide, Superoxide, and Peroxynitrite: the Good, the Bad, and Ugly" American Journal of Physiology – Cell Physiology 1996, volume 271, page C1424–C1437.