A superoxide is a compound containing superoxide anion, which has the chemical formula O - 2 . The systematic name of anions is dioxide (1-). Reactive superoxide oxygen is essential as a one-electron reduction product of the O 2 dioxygen, which occurs extensively in nature. While molecular oxygen (dioxygen) is a diradical containing two unpaired electrons, the addition of a second electron fills one of its two degenerating molecular orbitals, leaving a charged ionic species with an unpaired electron and a net negative charge of -1. Both dioxygen and superoxide anions are free radicals that exhibit paramagnetism.
Video Superoxide
Derivatives
Anion superoxide, O 2 - , and the hydroperoxyl radicals are in equilibrium in an aqueous solution:
- O 2 - H 2 O? HO 2 OH -
Thus at a neutral pH, superoxides are primarily present in protonated form, called hydroperoxyl.
Superoxides form salts with alkali metals and alkaline earth metals. CsO 2 , RbO 2 , KO 2 , and NaO 2 /sub> with their respective alkali metals..
Alkaline Salt O - 2 orange-yellow and fairly stable, provided it remains dry. After dissolution of these salts in water, however, -
2 has disproportioned very quickly (in a pH- depending how):
- 4 O - 2 2 H 2 O -> 3 O 2 4 OH -
This reaction (with water vapor and carbon dioxide in exhaled air) is the basis of the use of potassium superoxide as a source of oxygen in chemical oxygen generators, such as those used in spacecraft and on submarines. Superoxide is also used in the fire suppression oxygen tank to provide a source of available oxygen.
In this process O - 2 act as the base of BrÃÆ'¸nsted, originally formed a radical HO 2 . But p K a of conjugate acid, hydrogen superoxide (HO 2 Ã, Â ·, also known as "hydroperoxyl" or "perhydroxy radical" ), is 4.88 so that at neutral pH 7 all except 0.3% superoxide in anionic form, O -
2 .
Superoxide potassium dissolves in dimethyl sulfoxide (facilitated by ether crown) and is stable as long as protons are not available. Superoxide can also be produced in aprotic solvents by cyclic voltammetry.
Salt also decomposes in a solid state, but this process requires heating:
- 2 NaO 2 -> Na 2 O 2 O 2
Maps Superoxide
Biology
Superoxide and hydroperoxyl (HO 2 ) are discussed alternately, although hydroperoxyl dominates at physiological pH. Both are classified as reactive oxygen species. This is produced by the immune system to kill invading microorganisms. In phagocytes, superoxide is produced in large quantities by the enzyme NADPH oxidase to be used in the oxygen-dependent killing mechanism of the invading pathogens. Mutations in genes encoding NADPH oxidase cause an immunodeficiency syndrome called chronic granulomatous disease, characterized by extreme susceptibility to infection, especially positive catalase organisms. In turn, genetically engineered micro-organisms to superoxide dismutase (SOD) lose virulence. Superoxide is also damaging when it is produced as a byproduct of mitochondrial respiration (mainly by Complex I and Complex III), as well as several other enzymes, such as xanthine oxidase.
Because superoxide is toxic at high concentrations, almost all organisms living in the presence of oxygen contain superoxide enzymes called superoxide dismutase (SOD). SOD efficiently catalyzes superoxide disproportionation:
- 2 HO 2 -> O 2 H 2 O 2
Other proteins that can be oxidized and reduced by superoxide (eg, hemoglobin) have weak SOD activity. The genetic inactivation ("knockout") of SOD results in a destructive phenotype in organisms ranging from bacteria to mice and has provided important clues about the mechanism of superoxide toxicity in vivo.
Yeast that lacks SOD of mitochondria and cytosol grows very badly in the air, but good enough under anaerobic conditions. The absence of SOD cytosol causes a dramatic increase in mutagenesis and genomic instability. Mice deprived of mitochondrial SOD (MnSOD) die about 21 days after birth due to neurodegeneration, cardiomyopathy, and lactic acidosis. Mice lacking SOD cytosol (CuZnSOD) can live but suffer from several pathologies, including a reduced lifespan, liver cancer, muscle atrophy, cataracts, thymic involution, haemolytic anemia and very rapid decline in female fertility.
Superoxide can contribute to the pathogenesis of many diseases (very strong evidence for radiation poisoning and hyperoxic injury), and possibly aging through the oxidative damage it causes to cells. While superoxide action in the pathogenesis of some conditions is strong (eg, mice and mice overexpressed CuZnSOD or MnSOD more resistant to stroke and heart attack), the role of superoxide in aging should be considered unproven for now. In model organisms (yeast, Drosophila fruit flies and mice), genetically breaking down CuZnSOD shortens life and accelerates certain aging features (cataract, muscle atrophy, macular degeneration, thymic involution). But instead, it increases CuZnSOD levels, not visible (except perhaps in Drosophila ), to consistently improve lifespan. The most widely accepted view is that oxidative damage (caused by many causes, including superoxide) is just one of several life-limiting factors.
The O 2 bonding of the heme protein involved the formation of superoksida complex Fe (III).
Testing in biological systems
Superoxide tests generated in biological systems are a difficult task because of their high reactivity and short half-lives. One approach that has been used in quantitative testing turns superoxide into hydrogen peroxide, which is relatively stable. Hydrogen peroxide was then tested using the fluorimetric method. As free radicals, superoxide has a strong EPR signal, and it is possible to detect superoxide directly using this method when its abundance is high enough. For practical purposes, this can only be achieved in vitro in nonphysychological conditions, such as high pH (which slows spontaneous termination) with the xanthine oxidase enzyme. Researchers have developed a set of tools called "spin traps" that can react with superoxide, forming a stable meta radical (part-time of 1-15 minutes), which can be more easily detected by EPR. Superoxide spin traps were originally done with DMPO, but, more recently, phosphorus derivatives with increasing half-lives, such as DEPPMPO and DIPPMPO, have become more widely used.
Bonding and structure
Superoxide is a compound in which the oxidation number of oxygen - 1 / 2 . While molecular oxygen (dioxygen) is a diradical containing two unpaired electrons, the addition of a second electron fills one of its two degenerating molecular orbitals, leaving a charged ionic species with an unpaired electron and a net negative charge of -1. Both dioxygen and superoxide anions are free radicals that exhibit paramagnetism.
The derivative of dioxygen has the O-O distance characteristics correlated with the O-O bond sequence.
See also
- Oxygen, O 2
- Ozonide, -
3 - Peroxide, 2 - 2
- Oxide, O 2 -
- Dioxygenyl, O 2
- Antimycin A - used in fisheries management, this compound generates large amounts of these free radicals.
- Paraquat - used as a herbicide, this compound generates large amounts of these free radicals.
- Xanthine oxidase - This form of xanthine dehydrogenase enzyme produces many superoxides.
References
Source of the article : Wikipedia
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