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Information about Superoxide

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Lewis electron configuration of superoxide. The six outer shell electrons of each oxygen atom are shown in black; one electron pair is shared (middle); the unpaired electron is shown in the upper left and the additional electron conferring a negative charge is shown in red.


Superoxide is the anion O2−. It is important as the product of the one-electron reduction of dioxygen, which occurs widely in nature.[1] With one unpaired electron, the superoxide ion is a free radical, and, like dioxygen, it is paramagnetic.

Synthesis, basic reactions, and structure

Superoxides are compounds in which the oxidation number of oxygen is -1/2. The O-O bond distance in O2− is 1.33 Ã…, vs. 1.21 Ã… in O2 and 1.49 Ã… in O22−.

The salts CsO2, RbO2, KO2, and NaO2 are prepared by the direct reaction of O2 with the respective alkali metal.[2] The overall trend corresponds to a reduction in the bond order from 2 (O2), to 1.5 (O2−), to 1 (O22−).

The alkali salts of O2− are orange-yellow in color and quite stable, provided they are kept dry. Upon dissolution of these salts in water, however, the dissolved O2− undergoes disproportionation (dismutation) extremely rapidly:
2 O2− + 2 H2O → O2 + H2O2 + 2 OH−
In this process O2− acts as a strong Brønsted base, initially forming HO2. The pKa of its conjugate acid, hydrogen superoxide (HO2, also known as "hydroperoxyl" or "perhydroxy radical"), is 4.88 so that at neutral pH 7 the vast majority of superoxide is in the anionic form, O2−.

Salts also decompose in the solid state, but this process requires heating:
2NaO2 → Na2O2 + O2
This reaction 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.

Biology and superoxide

Superoxide is biologically quite toxic and is deployed by the immune system to kill invading microorganisms. In phagocytes, superoxide is produced in large quantities by the enzyme NADPH oxidase for use in oxygen-dependent killing mechanisms of invading pathogens. Mutations in the gene coding for the NADPH oxidase cause an immunodeficiency syndrome called chronic granulomatous disease, characterized by extreme susceptibility to infection. Superoxide is also deleteriously produced as a byproduct of mitochondrial respiration (most notably by Complex I and Complex III), as well as several other enzymes, for example xanthine oxidase.

The biological toxicity of superoxide is due to its capacity to inactivate iron-sulfur cluster containing enzymes (which are critical in a wide variety of metabolic pathways), thereby liberating free iron in the cell, which can undergo Fenton chemistry and generate the highly reactive hydroxyl radical. In its HO2 form, superoxide can also initiate lipid peroxidation of polyunsaturated fatty acids. It also reacts with carbonyl compounds and halogenated carbons to create toxic peroxy radicals. Superoxide can also react with nitric oxide (NO) to form ONOO−. As such, superoxide is one of the main causes of oxidative stress.

Because superoxide is toxic, nearly all organisms living in the presence of oxygen contain isoforms of the superoxide scavenging enzyme, superoxide dismutase, or SOD. SOD is an extremely efficient enzyme; it catalyzes the neutralization of superoxide nearly as fast as the two can diffuse together spontaneously in solution. Genetic inactivation ("knockout") of SOD produces deleterious phenotypes in organisms ranging from bacteria to mice. The latter species dies around 21 days after birth if the mitochondrial variant of SOD (Mn-SOD) is inactivated, and suffers from multiple pathologies, including reduced lifespan, liver cancer, muscle atrophy, cataracts and female infertility when the cytoplasmic (Cu,Zn-SOD) variant is inactivated.

Superoxide may contribute to the pathogenesis of many diseases, and perhaps also to aging by the oxidative damage that it inflits in cells. In model organisms (yeast, the fruit fly Drosophila and mice), knocking out CuZnSOD shortens lifespan and accelerates certain features of aging, but the converse, increasing the levels of CuZnSOD, does not seem (except in Drosophila), to consistently increase lifespan.

References

1. ^ Sawyer, D. T. Superoxide Chemistry, McGraw-Hill, doi:10.1036/1097-8542.669650
2. ^ Holleman, A. F.; Wiberg, E. "Inorganic Chemistry" Academic Press: San Diego, 2001. ISBN 0-12-352651-5.

Further reading

  • McCord, J. M.; Fridovich, I. Superoxide dismutase. An enzymic function for erythrocuprein (hemocuprein). J. Biol. Chem. 244:6049-6055.; 1969.
  • Li, Y. et al. Dilated cardiomyopathy and neonatal lethality in mutant mice lacking manganese superoxide dismutase. Nat. Genet. 11:376-381; 1995.
  • Elchuri, S. et al. CuZnSOD deficiency leads to persistent and widespread oxidative damage and hepatocarcinogenesis later in life. Oncogene 24:367-380; 2005.
  • Muller, F. L.; et al. Absence of CuZn superoxide dismutase leads to elevated oxidative stress and acceleration of age-dependent skeletal muscle atrophy. Free Radic. Biol. Med. 40:1993-2004; 2006.
  • Muller, F. L., Lustgarten, M. S., Jang, Y., Richardson, A. and Van Remmen, H. (2007) Trends in oxidative aging theories. Free Radic. Biol. Med. 43, 477-503

See also

2, −1
(neutral oxide)
Electronegativity 3.44 (Pauling scale)
Ionization energies
(more) 1st: 1313.9 kJmol−1
2nd: 3388.3 kJmol−1
3rd: 5300.5 kJmol−1

Atomic radius 60 pm
Atomic radius (calc.
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Electron

Theoretical estimates of the electron density for the first few hydrogen atom electron orbitals shown as cross-sections with color-coded probability density
Composition: Elementary particle
Family: Fermion
Group: Lepton
Generation: First
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ion is an atom or molecule which has lost or gained one or more electrons, making it positively or negatively charged. A negatively charged ion, which has more electrons in its electron shells than it has protons in its nuclei, is known as an anion
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radicals (often referred to as free radicals) are atomic or molecular species with unpaired electrons on an otherwise open shell configuration. These unpaired electrons are usually highly reactive, so radicals are likely to take part in chemical reactions.
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Paramagnetism is a form of magnetism which occurs only in the presence of an externally applied magnetic field. Paramagnetic materials are attracted to magnetic fields, hence have a relative magnetic permeability greater than one (or, equivalently, a positive magnetic
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Not to be confused with oxidation state.
The oxidation number of an element in a molecule or complex is the charge that it would have if all the ligands (basically, atoms that donate electrons) were removed along with the electron pairs that were shared
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Potassium superoxide is the chemical compound with the formula KO2. This rare salt of the superoxide ion is produced by burning molten potassium in pure oxygen.
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Sodium superoxide has the formula: NaO2.

Sodium Superoxide is formed when sodium is burned in oxygen at elevated temperature and pressure.

Sodium superoxide is hydrolyzed by water to form sodium hydroxide plus oxygen.
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Disproportionation or dismutation is used to describe two particular types of chemical reaction:[1]
  • A chemical reaction of the type: 2A → A' + A" where A, A' and A" are different chemical species.

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    An acid-base reaction is a chemical reaction that occurs between an acid and a base. Several concepts exist which provide alternative definitions for the reaction mechanisms involved and their application in solving related problems.
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    PKA or pKa may be:
    • PKA, an acronym for Previously Known As, or Professionally Known AS
    • PKA, an acronym for protein kinase A
    • pKa, the symbol for Acid dissociation constant
    • Pi Kappa Alpha
    • PKA, an acronym for Public Key Authentication

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    conjugate acid is the acid member, HX, of a pair of two compounds that transform into each other by gain or loss of a proton. A conjugate acid can also be seen as the chemical substance that releases a proton in the backward chemical reaction. Thus, the term acid.
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    The introduction to this article provides insufficient context for those unfamiliar with the subject matter.
    Please help [ improve the introduction] to meet Wikipedia's layout standards.

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      pH is a measure of the acidity or alkalinity of a solution. Aqueous solutions at 25 ℃ with a pH less than seven are considered acidic, while those with a pH greater than seven are considered basic (alkaline). The pH of 7.
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      Potassium superoxide is the chemical compound with the formula KO2. This rare salt of the superoxide ion is produced by burning molten potassium in pure oxygen.
      ..... Click the link for more information.
      2, −1
      (neutral oxide)
      Electronegativity 3.44 (Pauling scale)
      Ionization energies
      (more) 1st: 1313.9 kJmol−1
      2nd: 3388.3 kJmol−1
      3rd: 5300.5 kJmol−1

      Atomic radius 60 pm
      Atomic radius (calc.
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      A chemical oxygen generator is a device that releases oxygen created by a chemical reaction. The oxygen source is usually an inorganic superoxide, chlorate or perchlorate. A promising group of oxygen sources are ozonides.
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      Space Shuttle

      Space Shuttle Atlantis on the launch pad prior to the STS-115 mission.
      Fact sheet
      Function Manned partially re-usable launch and reentry system
      Manufacturer United Space Alliance:
      Thiokol/Boeing (SRBs)
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      submarine is a watercraft that can operate underwater. Military submarines were first widely used in World War I and are used by all major navies today. Civilian submarines and submersibles are used for scientific work at depths too great for human divers.
      ..... Click the link for more information.
      immune system is a collection of mechanisms within an organism that protects against disease by identifying and killing pathogens and tumor cells. It detects a wide variety of agents, from viruses to parasitic worms, and needs to distinguish them from the organism's own healthy
      ..... Click the link for more information.
      microorganism (also spelled as microrganism) or microbe is an organism that is microscopic (too small to be seen by the human eye). The study of microorganisms is called microbiology.
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      A phagocyte is a cell that ingests and destroys foreign matter such as microorganisms or debris by a process known as phagocytosis.

      Types of Phagocytes

      There are three main categories of phagocytes: [1]
      • macrophages (and monocytes)

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      Enzymes are proteins that catalyze (i.e. accelerate) chemical reactions.[1] In enzymatic reactions, the molecules at the beginning of the process are called substrates, and the enzyme converts them into different molecules, the products.
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      The NADPH oxidase (nicotinamide adenine dinucleotide phosphate-oxidase) complex is an enzyme complex

      Subunits

      It is made up of six subunits. These subunits are:

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      2, −1
      (neutral oxide)
      Electronegativity 3.44 (Pauling scale)
      Ionization energies
      (more) 1st: 1313.9 kJmol−1
      2nd: 3388.3 kJmol−1
      3rd: 5300.5 kJmol−1

      Atomic radius 60 pm
      Atomic radius (calc.
      ..... Click the link for more information.
      MeSH D006105 Chronic granulomatous disease (CGD) is a diverse group of hereditary diseases in which certain cells of the immune system have difficulty forming the reactive oxygen compounds (most importantly, the superoxide radical) used to kill certain ingested pathogens.
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      Cellular respiration describes the metabolic reactions and processes that take place in a cell or across the cell membrane to obtain biochemical energy from fuel molecules and the release of the cells' waste products.
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      NADH dehydrogenase (EC 1.6.5.3 ) is an enzyme located in the inner mitochodrial membrane that catalyzes the transfer of electrons from NADH to coenzyme Q (CoQ). It is also called the NADH:quinone oxidoreductase.
      ..... Click the link for more information.
      The coenzyme Q : cytochrome c — oxidoreductase, sometimes called the cytochrome bc1 complex, and at other times complex III, is the third complex in the electron transport chain (EC 1.10.2.
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