chemistry Chemistry is the scientific study of the properties and behavior of matter. It is a physical science within the natural sciences that studies the chemical elements that make up matter and chemical compound, compounds made of atoms, molecules a ...

, a selenosulfide refers to distinct classes of

inorganic An inorganic compound is typically a chemical compound that lacks carbon–hydrogen bonds⁠that is, a compound that is not an organic compound. The study of inorganic compounds is a subfield of chemistry known as '' inorganic chemistry''. Inor ...

and

organic compound Some chemical authorities define an organic compound as a chemical compound that contains a carbon–hydrogen or carbon–carbon bond; others consider an organic compound to be any chemical compound that contains carbon. For example, carbon-co ...

s containing sulfur and selenium. The organic derivatives contain Se-S bonds, whereas the inorganic derivatives are more variable.

Organic selenosulfides

These species are classified as both

organosulfur Organosulfur chemistry is the study of the properties and synthesis of organosulfur compounds, which are organic compounds that contain sulfur. They are often associated with foul odors, but many of the sweetest compounds known are organosulfur der ...

and organoselenium compounds. They are hybrids of organic

disulfide In chemistry, a disulfide (or disulphide in British English) is a compound containing a functional group or the anion. The linkage is also called an SS-bond or sometimes a disulfide bridge and usually derived from two thiol groups. In inorg ...

s and organic

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 (see Organoselenium chemistry) ** Diphenyl diselenide ...

Preparation, structure, and reactivity

Selenosulfides have been prepared by the reaction of selenyl halides with thiols: : The equilibrium between diselenides and disulfides lies on the left: :RSeSeR + R'SSR' 2 RSeSR' Because of the facility of this equilibrium, many of the best characterized examples of selenosulfides are cyclic, whereby S-Se bonds are stabilized intramolecularly. One example is the 1,8-selenosulfide of

naphthalene Naphthalene is an organic compound with formula . It is the simplest polycyclic aromatic hydrocarbon, and is a white Crystal, crystalline solid with a characteristic odor that is detectable at concentrations as low as 0.08 Parts-per notation ...

. The selenium-sulfur bond length is about 220 picometers, the average of a typical S-S and Se-Se bond.

Occurrence

Selenosulfide groups can be found in almost all living organisms as part of various

peroxidase Peroxidases or peroxide reductases ( EC numberbr>1.11.1.x are a large group of enzymes which play a role in various biological processes. They are named after the fact that they commonly break up peroxides, and should not be confused with other ...

enzymes, such as

glutathione peroxidase Glutathione peroxidase (GPx) () is the general name of an enzyme family with peroxidase activity whose main biological role is to protect the organism from oxidative damage. The biochemical function of glutathione peroxidase is to reduce lipid ...

and

thioredoxin reductase Thioredoxin reductases (TR, TrxR) () are enzymes that reduce thioredoxin (Trx). Two classes of thioredoxin reductase have been identified: one class in bacteria and some eukaryotes and one in animals. Bacterial TrxR also catalyzes the reduction ...

. They are formed by the oxidative coupling of

selenocysteine Selenocysteine (symbol Sec or U, in older publications also as Se-Cys) is the 21st proteinogenic amino acid. Selenoproteins contain selenocysteine residues. Selenocysteine is an analogue of the more common cysteine with selenium in place of the ...

and

cysteine Cysteine (; symbol Cys or C) is a semiessential proteinogenic amino acid with the chemical formula, formula . The thiol side chain in cysteine enables the formation of Disulfide, disulfide bonds, and often participates in enzymatic reactions as ...

residues. This reaction is powered by the decomposition of cellular peroxides, which can be highly damaging and a source of

oxidative stress Oxidative stress reflects an imbalance between the systemic manifestation of reactive oxygen species and a biological system's ability to readily detoxify the reactive intermediates or to repair the resulting damage. Disturbances in the normal ...

. Selenocysteine has a lower

reduction potential Redox potential (also known as oxidation / reduction potential, ''ORP'', ''pe'', ''E_'', or E_) is a measure of the tendency of a chemical species to acquire electrons from or lose electrons to an electrode and thereby be reduced or oxidised respe ...

than cysteine, making it very suitable for proteins that are involved in

antioxidant Antioxidants are Chemical compound, compounds that inhibit Redox, oxidation, a chemical reaction that can produce Radical (chemistry), free radicals. Autoxidation leads to degradation of organic compounds, including living matter. Antioxidants ...

activity. Selenosulfides have been identified in some species of ''

Allium ''Allium'' is a large genus of monocotyledonous flowering plants with around 1000 accepted species, making ''Allium'' the largest genus in the family Amaryllidaceae and among the largest plant genera in the world. Many of the species are edible, ...

'' and in roasted coffee. The mammalian version of the protein

contains a

residue which forms a thioselenide (analogous to a

) upon oxidation.

Inorganic selenosulfides

Some inorganic selenide sulfide compounds are also known. Simplest is the material selenium sulfide, which has medicinal properties. It adopt the diverse structures of elemental sulfur but with some S atoms replaced by Se. Other inorganic selenide sulfide compounds occur as minerals and as pigments. One example is antimony selenosulfide. The

pigment A pigment is a powder used to add or alter color or change visual appearance. Pigments are completely or nearly solubility, insoluble and reactivity (chemistry), chemically unreactive in water or another medium; in contrast, dyes are colored sub ...

cadmium red consists of cadmium sulfoselenide. It is a solid solution of

cadmium sulfide Cadmium sulfide is the inorganic compound with the formula CdS. Cadmium sulfide is a yellow salt.Egon Wiberg, Arnold Frederick Holleman (2001''Inorganic Chemistry'' Elsevier It occurs in nature with two different crystal structures as the rare min ...

, which is yellow, and

cadmium selenide Cadmium selenide is an inorganic compound with the formula Cd Se. It is a black to red-black solid that is classified as a II-VI semiconductor of the n-type. It is a pigment, but applications are declining because of environmental concerns. ...

, which is dark brown. It is used as an artist's pigment.Hugo Müller, Wolfgang Müller, Manfred Wehner, Heike Liewald "Artists' Colors" in Ullmann's Encyclopedia of Industrial Chemistry 2002, Wiley-VCH, Weinheim. Unlike the organic selenosulfides and unlike selenide sulfide itself, no S-Se bond exists in CdS_1−xSe_x or in Sb₂S_3−xSe_x.

References

{{Selenides Organoselenium compounds Organosulfur compounds Cadmium compounds Selenides Semiconductor materials Optical materials Mixed anion compounds Sulfides