Class of chemical compounds, both organic and inorganic, containing sulfur as well as selenium
In
chemistry, a selenosulfide refers to distinct classes of
inorganic and
organic compounds containing sulfur and selenium. The organic derivatives contain Se-S bonds, whereas the inorganic derivatives are more variable.
Selenosulfides have been prepared by the reaction of selenyl halides with thiols:[2]
RSeCl + R'SH → RSeSR' + HCl
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.[3] 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 enzymes, such as
glutathione peroxidase and
thioredoxin reductase. They are formed by the oxidative coupling of
selenocysteine and
cysteine residues.[2] This reaction is powered by the decomposition of cellular peroxides, which can be highly damaging and a source of
oxidative stress. Selenocysteine has a lower
reduction potential than cysteine, making it very suitable for proteins that are involved in
antioxidant activity.[4]
Selenosulfides have been identified in some species of Allium[1] and in roasted coffee.[5] The mammalian version of the protein
thioredoxin reductase contains a
selenocysteine residue which forms a thioselenide (analogous to a
disulfide) upon oxidation.[6]
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
pigmentcadmium red consists of cadmium sulfoselenide. It is a solid solution of
cadmium sulfide, which is yellow, and
cadmium selenide, which is dark brown. It is used as an artist's pigment.[7] Unlike the organic selenosulfides and unlike selenide sulfide itself, no S-Se bond exists in CdS1−xSex or in Sb2S3−xSex.
References
^
abCai, Xiao-Jia; Uden, Peter C.; Block, Eric; Zhang, Xing; Quimby, Bruce D.; Sullivan, James J. (1994). "Allium chemistry: Identification of natural abundance organoselenium volatiles from garlic, elephant garlic, onion, and Chinese chive using headspace gas chromatography with atomic emission detection". Journal of Agricultural and Food Chemistry. 42 (10): 2081–2084.
doi:
10.1021/jf00046a002.
^Meinwald, Jerrold; Dauplaise, David; Clardy, Jon (1977). "Peri-Bridged Naphthalenes. 2. Unsymmetrical Diatomic Chalcogen Bridges". Journal of the American Chemical Society. 99 (23): 7743–7744.
doi:
10.1021/ja00465a074.
^Meija, Juris; Bryson, Joshua M.; Vonderheide, Anne P.; Montes-Bayón, Maria; Caruso, Joseph A. (2003). "Studies of Selenium-Containing Volatiles in Roasted Coffee". Journal of Agricultural and Food Chemistry. 51 (17): 5116–5122.
doi:
10.1021/jf034210h.
PMID12903978.