Search results
Results from the WOW.Com Content Network
Selenium in biology. Selenocysteine is the main organic molecule involving selenium in humans. Selenium is an essential micronutrient for animals, though it is toxic in large doses. In plants, it sometimes occurs in toxic amounts as forage, e.g. locoweed. Selenium is a component of the amino acids selenocysteine and selenomethionine.
Selenium is a chemical element; it has the symbol Se and atomic number 34. It has various physical appearances, including a brick-red powder, a vitreous black solid, and a grey metallic-looking form. It seldom occurs in this elemental state or as pure ore compounds in Earth's crust.
The selenium cycle is a biological cycle of selenium similar to the cycles of carbon, nitrogen, and sulfur. Within the cycle, there are organisms which reduce the most oxidized form of the element and different organisms complete the cycle by oxidizing the reduced element to the initial state. In the selenium cycle it has been found that ...
Selenocysteine is an analogue of the more common cysteine with selenium in place of the sulfur. Selenocysteine is present in several enzymes (for example glutathione peroxidases , tetraiodothyronine 5′ deiodinases , thioredoxin reductases , formate dehydrogenases , glycine reductases , selenophosphate synthetase 2 , methionine- R -sulfoxide ...
Organoselenium chemistry. Organoselenium chemistry is the science exploring the properties and reactivity of organoselenium compounds, chemical compounds containing carbon -to- selenium chemical bonds. [ 1][ 2][ 3] Selenium belongs with oxygen and sulfur to the group 16 elements or chalcogens, and similarities in chemistry are to be expected.
At higher pH, selenide forms. Solutions of hydrogen selenide and selenide are oxidized by air to give elemental selenium: 2 SeH − + O 2 → 2 Se + 2 OH −. Most elements form selenides. They sometimes have salt-like properties, e.g. sodium selenide, but most exhibit covalent bonding, e.g. molybdenum diselenide. Their properties are diverse ...
Selenium compounds are compounds containing the element selenium (Se). Among these compounds, selenium has various oxidation states , the most common ones being −2, +4, and +6. Selenium compounds exist in nature in the form of various minerals, such as clausthalite , guanajuatite , tiemannite , crookesite etc., and can also coexist with ...
Selenate is the form required by organisms that need selenium as a micronutrient. These organisms have the ability to acquire, metabolize and excrete selenium. [ 7 ] The level at which selenium becomes toxic varies from species to species and is related to other environmental factors like pH and alkalinity that influence the concentration of ...