superoksidiioni

The superoksidiioni, or superoxide ion, is the radical anion derived from molecular oxygen. Its chemical formula is O2−, and it carries one extra electron, giving it an unpaired electron and paramagnetic properties.

Biological and environmental occurrence: Superoxide is produced during normal cellular metabolism and in immune responses. In mitochondria, one-electron reduction of O2 forms superoxide. Enzymes such as NADPH oxidase in phagocytes and xanthine oxidase contribute to its production. It also arises in environmental processes through photochemical reactions and industrial chemistry.

Chemical properties and reactions: In aqueous solution, the hydroperoxyl radical HO2• predominates at low pH, while at physiological pH HO2− is prevalent. The superoxide ion is a weak base and a weak nucleophile. It readily undergoes dismutation to hydrogen peroxide and oxygen: 2 O2− + 2 H+ → H2O2 + O2, a reaction catalyzed by the enzyme superoxide dismutase (SOD). It can react with nitric oxide to form peroxynitrite, a reactive nitrogen species, and participates in redox cycling and Fenton-type chemistry that generate hydroxyl radicals in the presence of transition metals.

Biological significance and safety: Superoxide participates in defense against pathogens and can act in redox signaling at controlled levels. However, excessive production or insufficient detoxification contributes to oxidative stress, damaging lipids, proteins, and DNA. Cells mitigate its effects with SOD and other antioxidants. Salts such as sodium superoxide and potassium superoxide are strong bases that react with water to form hydrogen peroxide and oxygen; they are reactive and used in chemical synthesis, disinfection, and battery technology, requiring careful handling.