chemistry Chemistry is the science, scientific study of the properties and behavior of matter. It is a natural science that covers the Chemical element, elements that make up matter to the chemical compound, compounds made of atoms, molecules and ions ...

, a selenosulfide refers to distinct classes of

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

and

organic compound In chemistry, organic compounds are generally any chemical compounds that contain carbon-hydrogen or carbon-carbon bonds. Due to carbon's ability to catenate (form chains with other carbon atoms), millions of organic compounds are known. The ...

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 compounds are organic compounds that contain sulfur. They are often associated with foul odors, but many of the sweetest compounds known are organosulfur derivatives, e.g., saccharin. Nature abounds with organosulfur compounds—sulfur ...

and

organoselenium 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 ...

compounds. They are hybrids of organic

disulfide In biochemistry, a disulfide (or disulphide in British English) refers to a functional group with the structure . The linkage is also called an SS-bond or sometimes a disulfide bridge and is usually derived by the coupling of two thiol groups. In ...

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 **Diphenyl diselenide, (C6H5)–Se–Se–(C6H5) *Metal ...

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 crystalline solid with a characteristic odor that is detectable at concentrations as low as 0.08 ppm by mass. As an aromati ...

. 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. Functionality Peroxidases typically ca ...

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 h ...

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. In bacteria 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 s ...

and

cysteine Cysteine (symbol Cys or C; ) is a semiessential proteinogenic amino acid with the formula . The thiol side chain in cysteine often participates in enzymatic reactions as a nucleophile. When present as a deprotonated catalytic residue, sometime ...

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 Detoxification, detoxify the reactive intermediates or to repair the resulting damage. Disturbances ...

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

Allium ''Allium'' is a genus of monocotyledonous flowering plants that includes hundreds of species, including the cultivated onion, garlic, scallion, shallot, leek, and chives. The generic name ''Allium'' is the Latin word for garlic,Gledhill, Davi ...

'' 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 In chemistry, a selenosulfide refers to distinct classes of inorganic compound, inorganic and organic compounds containing sulfur and selenium. The organic derivatives contain Se-S bonds, whereas the inorganic derivatives are more variable. Orga ...

compounds are also known. Simplest is the material

selenium sulfide Selenium sulfide can refer to either of the following: * Selenium disulfide, SeS2 * Selenium hexasulfide, Se2S6 {{Short pages monitor