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A peroxide is a compound containing an oxygen–oxygen single bond or the peroxide anion, O. The O−O group is called the peroxide group or peroxo group. In contrast to oxide ions, the oxygen atoms in the peroxide ion have an oxidation state of −1. The simplest stable peroxide is hydrogen peroxide. Superoxides, dioxygenyls, ozones and ozonides are considered separately. Peroxide compounds can be roughly classified into organic and inorganic. Whereas the inorganic peroxides have an ionic, salt-like character, the organic peroxides are dominated by the covalent bonds. The oxygen-oxygen chemical bond of peroxide is unstable and easily split into reactive radicals via homolytic cleavage. For this reason, peroxides are found in nature only in small quantities, in water, atmosphere, plants, and animals. Peroxide ion formation has recently been highlighted as one of the main mechanisms by which oxides accommodate excess oxygen in ionic crystals and may have a large impact on a range of industrial applications including solid oxide fuel cells.〔 〕 Peroxides have a bleaching effect on organic substances and therefore are added to some detergents and hair colorants. Other large-scale applications include medicine and chemical industry, where peroxides are used in various synthesis reactions or occur as intermediate products. With an annual production of over 2 million tonnes, hydrogen peroxide is the most economically important peroxide. Many peroxides are unstable and hazardous substances; they cannot be stored and therefore are synthesized ''in situ'' and used immediately. ==In biochemistry== Peroxides are usually very reactive and thus occur in nature only in a few forms. These include, in addition to hydrogen peroxide, a few vegetable products such as ascaridole and a peroxide derivative of prostaglandin. Hydrogen peroxide occurs in surface water, groundwater and in the atmosphere. It forms upon illumination or natural catalytic action by substances containing in water. Sea water contains 0.5 to 14 ug/L of hydrogen peroxide, freshwater 1 to 30 ug/L and air 0.1 to 1 parts per billion.〔 Hydrogen peroxide is formed in human and animal organisms as a short-lived product in biochemical processes and is toxic to cells. The toxicity is due to oxidation of proteins, membrane lipids and DNA by the peroxide ions.〔Löffler G. and Petrides, P. E. ''Physiologische Chemie''. 4 ed., p. 288, Springer, Berlin 1988, ISBN 3-540-18163-6 (in German)〕 The class of biological enzymes called SOD (superoxide dismutase) is developed in nearly all living cells as an important antioxidant agent. They promote the disproportionation of superoxide into oxygen and hydrogen peroxide, which is then rapidly decomposed by the enzyme catalase to oxygen and water.〔Löffler G. and Petrides, P. E. ''Physiologische Chemie''. 4 ed., pp. 321–322, Springer, Berlin 1988, ISBN 3-540-18163-6 (in German)〕 : : Formation of hydrogen peroxide by superoxide dismutase (SOD) Peroxisomes are organelles found in virtually all eukaryotic cells. They are involved in the catabolism of very long chain fatty acids, branched chain fatty acids, D-amino acids, polyamines, and biosynthesis of plasmalogens, etherphospholipids critical for the normal function of mammalian brains and lungs. Upon oxidation, they produce hydrogen peroxide in the following process:〔Nelson, David; Cox, Michael; Lehninger, Albert L. and Cox, Michael M. (Lehninger Biochemie ), pp. 663–664, Springer, 2001, ISBN 3-540-41813-X (in German)〕 : : FAD = flavin adenine dinucleotide Catalase, another peroxisomal enzyme, uses this H2O2 to oxidize other substrates, including phenols, formic acid, formaldehyde, and alcohol, by means of the peroxidation reaction: :, thus eliminating the poisonous hydrogen peroxide in the process. This reaction is important in liver and kidney cells, where the peroxisomes neutralize various toxic substances that enter the blood. Some of the ethanol humans drink is oxidized to acetaldehyde in this way.〔Riley, Edward P. ''et al.'' (ed.) (Fetal Alcoholspectrum Disorder Fasd: Management and Policy Perspectives ), Wiley-VCH, 2010, ISBN 3-527-32839-4 p. 112〕 In addition, when excess H2O2 accumulates in the cell, catalase converts it to H2O through this reaction: : Another origin of hydrogen peroxide is the degradation of adenosine monophosphate which yields hypoxanthine. Hypoxanthine is then oxidatively catabolized first to xanthine and then to uric acid, and the reaction is catalyzed by the enzyme xanthine oxidase:〔Nelson, David; Cox, Michael; Lehninger, Albert L. and Cox, Michael M. (Lehninger Biochemie ), p. 932, Springer, 2001, ISBN 3-540-41813-X (in German)〕 The degradation of guanosine monophosphate yields xanthine as an intermediate product which is then converted in the same way to uric acid with the formation of hydrogen peroxide.〔 Eggs of sea urchin, shortly after fertilization by a sperm, produce hydrogen peroxide. It is then quickly dissociated to OH· radicals. The radicals serve as initiator of radical polymerization, which surrounds the eggs with a protective layer of polymer. The bombardier beetle has a device which allows it to shoot corrosive and foul-smelling bubbles at its enemies. The beetle produces and stores hydroquinone and hydrogen peroxide, in two separate reservoirs in the rear tip of its abdomen. When threatened, the beetle contracts muscles that force the two reactants through valved tubes into a mixing chamber containing water and a mixture of catalytic enzymes. When combined, the reactants undergo a violent exothermic chemical reaction, raising the temperature to near the boiling point of water. The boiling, foul-smelling liquid partially becomes a gas (flash evaporation) and is expelled through an outlet valve with a loud popping sound. Hydrogen peroxide is a signaling molecule of plant defense against pathogens.〔(Wie Pflanzen sich schützen ), Helmholtz-Institute of Biochemical Plant Pathology (in German)〕 In firefly, oxidation of luciferins, which is catalyzed by luciferases, yields a peroxy compound 1,2-dioxetane. The dioxetane is unstable and decays spontaneously to carbon dioxide and excited ketones, which release excess energy by emitting light (bioluminescence).〔Aldo Roda (Chemiluminescence and Bioluminescence: Past, Present and Future ), p. 57, Royal Society of Chemistry, 2010, ISBN 1-84755-812-7〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「peroxide」の詳細全文を読む スポンサード リンク
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