Hyperoxides

Dioxide (1−) anion

Hyper oxides or superoxides are chemical compounds from the oxygen -derived dioxide (1-) - anion (O ₂ ^- included). The oxygen in these compounds has an oxidation number of −½.

Compounds with the O ₂ ²⁻ anion, such as H ₂ O ₂ and BaO ₂ , are peroxides , not hyperoxides.

Surname

Hyperoxide is often used as a name in German-language specialist literature. Although "Superoxid" is mentioned in the biochemical nomenclature, it is not recommended in German and instead the use of the systematic name Dioxid (1−) is recommended, as the prefix "Super" does not have the same meaning in all languages. In English, "superoxide" is accepted by the IUPAC as an alternative name to the systematic designation. IUPAC, on the other hand, regards "hyperoxide" as obsolete.

properties

The hyperoxides of the alkali and alkaline earth metals are yellow to orange, crystalline, paramagnetic solids. When heated in the absence of oxygen, they break down, forming the corresponding peroxides and developing oxygen. Hyperoxides disproportionate in the presence of water with evolution of oxygen and formation of hydrogen peroxide and hydroxides:

${\displaystyle \mathrm {2\ O_{2}^{-}\ +\ 2\ H_{2}O\ \longrightarrow \ H_{2}O_{2}\ +\ 2\ OH^{-}\ +\ O_{2}} }$

education

Hyperoxides are formed when the alkali metals potassium , rubidium and cesium are burned in the presence of oxygen. Sodium , on the other hand, burns mainly to form peroxide . Lithium - even with a large excess of oxygen - predominantly turns into oxide . The reason for the different behavior is the increase in the ionic radius with the increasing period of the alkali metal, the increase in the softness of the cations and the gain in lattice energy : while the small, hard lithium cation prefers the equally small and hard oxide anion as a binding partner in the ion crystal , with potassium, but especially with rubidium or cesium, the large, much softer hyperoxide anion takes its place.

biochemistry

Hyperoxides also arise in normal metabolic processes in the course of the reduction of molecular oxygen, e.g. B. in the respiratory chain and may irreversibly destroy cell structures due to their high reactivity. They are therefore assigned to the reactive oxygen species ( RSS or ROS ). The enzyme superoxide dismutase is responsible for the rapid breakdown of such free radicals . The reaction takes place similar to the decomposition in aqueous solution via a disproportionation of the peroxide into oxygen and peroxide. The latter is released as hydrogen peroxide, which is further detoxified into oxygen and water by a catalase . The hydrogen peroxide can also be used in the organism via peroxidases (e.g. breakdown of lignin or aromatics ) and haloperoxidases .

More recent studies write RSS like hyperoxide and hydrogen peroxide, in addition to generating oxidative stress, an important signal function z. B. in the brain in signal transmission, synaptic plasticity and memory formation. They also have a strong vasodilator (vasodilator) effect there and therefore appear to be important for increasing cerebral blood flow and cerebrovascular tone .

history

Linus Pauling found out in 1931 that hyperoxides play a role in the reaction of alkali metals with oxygen and that the previous reaction equations (which assumed the formation of tetroxides) were wrong . Pauling also suggested the name. In 1934 this was confirmed experimentally by Edward W. Neuman (1904–1955) by showing that potassium hyperoxide had the magnetic properties of free radicals.

That hyperoxides also play a role in living beings was first suggested in 1954 by Rebecca Gershman (1903–1986) and Irwin Fridovich suggested in the 1960s that hyperoxides move freely in living cells, but this view was not yet able to prevail. In 1968 Joe Milton McCord (* 1945) identified a well-known, frequently occurring enzyme as a hyperoxide scavenger in cells and named it hyperoxide dismutase.

Individual evidence

1. ↑ Wolfgang Liebscher, Ekkehard Fluck: The systematic nomenclature of inorganic chemistry. Springer, 1998, ISBN 3-540-63097-X , p. 108.
2. ^ IUPAC : Red Book. (PDF; 4.3 MB). Pp. 73 and 320.
3. ^ KT Kishida, E. Klann: Sources and targets of reactive oxygen species in synaptic plasticity and memory. In: Antioxidant Redox Signal . 9, 2007, pp. 233-244. PMID 17115936 .
4. ↑ Derek Lowe, Das Chemiebuch, Librero 2017, p. 296