A selenenic acid is an

organoselenium compound Organoselenium compounds (or seleno-organic) are chemical compounds containing carbon-to-selenium chemical bonds. Organoselenium chemistry is the corresponding science exploring their properties and reactivity. Selenium belongs with oxygen and sulf ...

and an

oxoacid An oxyacid, oxoacid, or ternary acid is an acid that contains oxygen. Specifically, it is a compound that contains hydrogen, oxygen, and at least one other element, with at least one hydrogen atom bonded to oxygen that can dissociate to produce ...

with the general formula RSeOH, where R ≠ H. It is the first member of the family of organoselenium oxoacids, which also include

seleninic acid A seleninic acid is an organoselenium compound and an oxoacid with the general formula , where R ≠ H. Its structure is . It is a member of the family of organoselenium oxoacids, which also includes selenenic acids and selenonic acid A selenoni ...

s and

selenonic acid A selenonic acid is an organoselenium compound containing the SeO3H functional group. Selenonic acids are the selenium analogs of sulfonic acids. Examples of the acid are rare. Benzeneselenonic acid is a white solid. It can be prepared by the o ...

s, which are RSeO₂H and RSeO₃H, respectively. Selenenic acids derived from selenoenzymes are thought to be responsible for the

antioxidant Antioxidants are compounds that inhibit oxidation, a chemical reaction that can produce free radicals. This can lead to polymerization and other chain reactions. They are frequently added to industrial products, such as fuels and lubricant ...

activity of these enzymes. This functional group is sometimes called SeO-selenoperoxol.

Properties

In contrast to selenonic and seleninic acids, selenenic acids are unstable with respect to a self-

condensation reaction In organic chemistry, a condensation reaction is a type of chemical reaction in which two molecules are combined to form a single molecule, usually with the loss of a small molecule such as water. If water is lost, the reaction is also known as a ...

to form the corresponding selenoseleninates or

disproportionation In chemistry, disproportionation, sometimes called dismutation, is a redox reaction in which one compound of intermediate oxidation state converts to two compounds, one of higher and one of lower oxidation states. More generally, the term can b ...

into corresponding seleninic acids and

diselenide Diselenide may refer to: *Diselane, H-Se-Se-H *Carbon diselenide, CSe2, a yellow-orange oily liquid with pungent odor * Any organic chemical compound with a selenium-selenium bond, R-Se-Se-R **Diphenyl diselenide, (C6H5)–Se–Se–(C6H5) *Metal ...

s: :2 RSeOH → RSe(O)SeR + H₂O :2 RSeOH → RSeO₂H + 1/2 RSeSeR Even the very bulky 2,4,6-tri-''tert''-butylbenzeneselenenic acid disproportionates readily. A stable selenenic acid was synthesized by burying the SeOH functional group within the cavity of a ''p''-''tert''-butyl alix[6rene macrocycle"><_a>rene_macrocycle.html" ;"title="alix[6rene macrocycle">alix[6rene macrocycle X-ray crystallography">X-ray crystallographic analysis revealed the Se-O bond length to be 1.763 Å. The Se-O absorbs in the IR spectrum at 680–700 cm⁻¹. In a stable selenenic acid prepared by oxidizing a highly hindered selenol, BmtSeH, the Se-O bond length was found to be 1.808 Å while the O-Se-C angle was 96.90°. Oxidation of BmtSeOH gave BmtSeO₂H. Selenenic acids are believed to be transient intermediates in a number of redox reactions involving

s. One notable example is the ''syn''-elimination of selenoxides. Selenenic acids are also transient intermediates in the reduction of seleninic acids as well as the oxidation of diselenides. The reasoning for postulating selenenic acids as reactive intermediates is based in part on analogy with their more extensively studied sulfenic acid analogs.

Biology

Selenenic acids derived from selenocysteine are involved in cell signaling and certain enzymatic processes. The best known selenoenzyme, glutathione peroxidase (GPx), catalyzes the reduction of peroxides by

glutathione Glutathione (GSH, ) is an antioxidant in plants, animals, fungi, and some bacteria and archaea. Glutathione is capable of preventing damage to important cellular components caused by sources such as reactive oxygen species, free radicals, pero ...

(GSH). The selenenic acid intermediate (E-SeOH) is formed upon oxidation of the catalytically active selenol (E-SeH) by hydrogen peroxide. This selenenic acid derivative of the peroxidase then reacts with a thiol-containing cofactor (GSH) to generate the key intermediate selenenyl sulfide (E-SeSG). This intermediate is subsequently attacked by a second GSH to regenerate the selenol and the glutathione cofactor is released in its oxidized form, GSSG. The catalytic mechanism of GPx, involves selenol (R-SeH), selenenyl sulfide (R1-SeS-R2), and selenenic acid intermediates. :RSeH + H₂O₂ → RSeOH + H₂O :RSeOH + GSH → GS-SeR + H₂O :GS-SeR + GSH → GS-SG + RSeH In the absence of thiols, selenols tend to overoxidize to produce seleninic acids. Many organoselenium compounds (selenenamides, diaryl diselenides) contain "interesting" biological activities. Their activity is attributed to their mimicry of glutathione peroxidase activity. They reduce

hydroperoxide Hydroperoxides or peroxols are Chemical compound, compounds containing the hydroperoxide functional group (ROOH). If the R is organic, the compounds are called organic hydroperoxides. Such compounds are a subset of organic peroxides, which have t ...

s that otherwise convert to toxic byproducts and/or reactive oxygen species that can cause further damage to the cell.K. P. Bhabak, G. Mugesh, "Functional Mimics of Glutathione Peroxidase: Bioinspired Synthetic Antioxidants" ''Acc. Chem. Res.'', 2010, 43, 1408–1419.

References

{{Functional group Functional groups Organoselenium compounds