Mutations in the gene coding for the NADPH oxidase cause an immunodeficiency syndrome called chronic granulomatous disease, characterized by extreme susceptibility to infection, especially catalase- positive organisms. In phagocytes, superoxide is produced in large quantities by the enzyme NADPH oxidase for use in oxygen-dependent killing mechanisms of invading pathogens. It is generated by the immune system to kill invading microorganisms. Both superoxide and hydroperoxyl are classified as reactive oxygen species. Superoxide and hydroperoxyl ( HO 2) are often discussed interchangeably, although superoxide predominates at physiological pHs. Superoxide salts also decompose in the solid state, but this process requires heating: Superoxide can also be generated in aprotic solvents by cyclic voltammetry. Potassium superoxide is soluble in dimethyl sulfoxide (facilitated by crown ethers) and is stable as long as protons are not available. Given that the hydroperoxyl radical has a p K a of around 4.8, superoxide predominantly exists in the anionic form at neutral pH. The superoxide anion, O − 2, and its protonated form, hydroperoxyl, are in equilibrium in an aqueous solution: O − 2 + H 2O ⇌ HO 2 + OH − In this process, O − 2 acts as a Brønsted base, initially forming the hydroperoxyl radical ( HO 2). Superoxides are also used in firefighters' oxygen tanks to provide a readily available source of oxygen. This reaction (with moisture and carbon dioxide in exhaled air) is the basis of the use of potassium superoxide as an oxygen source in chemical oxygen generators, such as those used on the Space Shuttle and on submarines. Upon dissolution of these salts in water, however, the dissolved O − 2 undergoes disproportionation (dismutation) extremely rapidly (in a pH-dependent manner): 4 O − 2 + 2 H 2O → 3 O 2 + 4 OH − The alkali salts of O − 2 are orange-yellow in color and quite stable, if they are kept dry. The salts sodium superoxide ( NaO 2), potassium superoxide ( KO 2), rubidium superoxide ( RbO 2) and caesium superoxide ( CsO 2) are prepared by the reaction of O 2 with the respective alkali metal. ![]() Superoxide forms salts with alkali metals and alkaline earth metals. Superoxide was historically also known as "hyperoxide". Both dioxygen and the superoxide anion are free radicals that exhibit paramagnetism. Molecular oxygen (dioxygen) is a diradical containing two unpaired electrons, and superoxide results from the addition of an electron which fills one of the two degenerate molecular orbitals, leaving a charged ionic species with a single unpaired electron and a net negative charge of −1. The reactive oxygen ion superoxide is particularly important as the product of the one-electron reduction of dioxygen O 2, which occurs widely in nature. The systematic name of the anion is dioxide(1−). In chemistry, a superoxide is a compound that contains the superoxide ion, which has the chemical formula O − 2.
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