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Encyclopedia > Selenium
34 arsenicseleniumbromine
S

Se

Te
General
Name, Symbol, Number selenium, Se, 34
Chemical series nonmetals
Group, Period, Block 16, 4, p
Appearance gray-black, metallic luster
Standard atomic weight 78.96(3) g·mol−1
Electron configuration [Ar] 3d10 4s2 4p4
Electrons per shell 2, 8, 18, 6
Physical properties
Phase solid
Density (near r.t.) (gray) 4.81 g·cm−3
Density (near r.t.) (alpha) 4.39 g·cm−3
Density (near r.t.) (vitreous) 4.28 g·cm−3
Liquid density at m.p. 3.99 g·cm−3
Melting point 494 K
(221 °C, 430 °F)
Boiling point 958 K
(685 °C, 1265 °F)
Critical point 1766 K, 27.2 MPa
Heat of fusion (gray) 6.69 kJ·mol−1
Heat of vaporization 95.48 kJ·mol−1
Heat capacity (25 °C) 25.363 J·mol−1·K−1
Vapor pressure
P(Pa) 1 10 100 1 k 10 k 100 k
at T(K) 500 552 617 704 813 958
Atomic properties
Crystal structure hexagonal
Oxidation states ±2, 4, 6
(strongly acidic oxide)
Electronegativity 2.55 (scale Pauling)
Ionization energies
(more)
1st: 941.0 kJ·mol−1
2nd: 2045 kJ·mol−1
3rd: 2973.7 kJ·mol−1
Atomic radius 115 pm
Atomic radius (calc.) 103 pm
Covalent radius 116 pm
Van der Waals radius 190 pm
Miscellaneous
Magnetic ordering no data
Thermal conductivity (300 K) (amorphous)
0.519 W·m−1·K−1
Thermal expansion (25 °C) (amorphous)
37 µm·m−1·K−1
Speed of sound (thin rod) (20 °C) 3350 m/s
Young's modulus 10 GPa
Shear modulus 3.7 GPa
Bulk modulus 8.3 GPa
Poisson ratio 0.33
Mohs hardness 2.0
Brinell hardness 736 MPa
CAS registry number 7782-49-2
Selected isotopes
Main article: Isotopes of selenium
iso NA half-life DM DE (MeV) DP
72Se syn 8.4 d ε - 72As
γ 0.046 -
74Se 0.87% Se is stable with 40 neutrons
75Se syn 119.779 d ε - 75As
γ 0.264, 0.136,
0.279
-
76Se 9.36% Se is stable with 42 neutrons
77Se 7.63% Se is stable with 43 neutrons
78Se 23.78% Se is stable with 44 neutrons
79Se syn 2.95×105 y β- 0.151 79Br
80Se 49.61% Se is stable with 46 neutrons
82Se 8.73% 1.08×1020 y β-β- 2.995 82Kr
References
Elemental selenium in different allotropic forms: black, gray, and red
Elemental selenium in different allotropic forms: black, gray, and red

Selenium (IPA: /səˈliːniəm/) is a chemical element with atomic number 34, with the chemical symbol Se. Selenium occurs only rarely in the free state in nature. It is a nonmetal that is chemically related to sulfur and tellurium. It is toxic in large amounts, but trace amounts of it, forming the active center of certain enzymes, are necessary for the function of all cells in (probably) all animals. Selenium requirements in plants differ by species, with some plants apparently requiring none. [1] Selenium can refer to: Selenium, a chemical element Selenium (software), a test tool for web applications Selenium (company), a loudspeaker manufacturer Category: ... SE could mean: Ferrocarriles Unidos del Sureste (AAR reporting mark SE) Southeast (the ordinal direction) Sweden (ISO country code SE) Societas Europaea the European Public Company Software engineering Selenium the chemical element This is a disambiguation page — a navigational aid which lists other pages that might otherwise share the... The se ç‘Ÿ (pinyin: sè) is an ancient Chinese stringed instrument. ... General Name, Symbol, Number arsenic, As, 33 Chemical series metalloids Group, Period, Block 15, 4, p Appearance metallic gray Standard atomic weight 74. ... General Name, Symbol, Number bromine, Br, 35 Chemical series halogens Group, Period, Block 17, 4, p Appearance gas/liquid: red-brown solid: metallic luster Atomic mass 79. ... General Name, Symbol, Number sulfur, S, 16 Chemical series nonmetals Group, Period, Block 16, 3, p Appearance lemon yellow Standard atomic weight 32. ... General Name, Symbol, Number tellurium, Te, 52 Chemical series metalloids Group, Period, Block 16, 5, p Appearance silvery lustrous gray Standard atomic weight 127. ... File links The following pages link to this file: Selenium User:Femto/elements e3 Categories: GFDL images ... This is a standard display of the periodic table of the elements. ... An extended periodic table was suggested by Glenn T. Seaborg in 1969. ... This is a list of chemical elements, sorted by name and color coded according to type of element. ... A table of chemical elements ordered by atomic number and color coded according to type of element. ... A group, also known as a family, is a vertical column in the periodic table of the chemical elements. ... Together with the metals and metalloids, a nonmetal is one of three categories of chemical elements as distinguished by ionization and bonding properties. ... A group, also known as a family, is a vertical column in the periodic table of the chemical elements. ... In the periodic table of the elements, a period is a horizontal row of the table. ... A block of the periodic table of elements is a set of adjacent groups. ... The chalcogens are the name for the periodic table group 16 (old-style: VIB or VIA) in the periodic table. ... A period 4 element is one of the chemical elements in the fourth row (or period) of the periodic table of the elements. ... The p-block of the periodic table of elements consists of the last six groups. ... Color is an important part of the visual arts. ... Selenium sample. ... The atomic mass (ma) is the mass of an atom at rest, most often expressed in unified atomic mass units. ... To help compare different orders of magnitude we list here masses between 60. ... Hydrogen = 1 List of Elements in Atomic Number Order. ... Electron atomic and molecular orbitals In atomic physics and quantum chemistry, the electron configuration is the arrangement of electrons in an atom, molecule, or other physical structure (eg, a crystal). ... General Name, Symbol, Number argon, Ar, 18 Chemical series noble gases Group, Period, Block 18, 3, p Appearance colorless Standard atomic weight 39. ... e- redirects here. ... [[Image:Valence shell 011 Sodiumup of one or more electron subshells, or sublevels, which have two or more orbitals with the same angular momentum quantum number l. ... In the physical sciences, a phase is a set of states of a macroscopic physical system that have relatively uniform chemical composition and physical properties (i. ... For other uses, see Solid (disambiguation). ... In physics, density is mass m per unit volume V. For the common case of a homogeneous substance, it is expressed as: where, in SI units: ρ (rho) is the density of the substance, measured in kg·m-3 m is the mass of the substance, measured in kg V is... Room temperature describes a certain temperature within enclosed space that is uses for various purposes by human beings. ... In physics, density is mass m per unit volume V. For the common case of a homogeneous substance, it is expressed as: where, in SI units: ρ (rho) is the density of the substance, measured in kg·m-3 m is the mass of the substance, measured in kg V is... Room temperature describes a certain temperature within enclosed space that is uses for various purposes by human beings. ... In physics, density is mass m per unit volume V. For the common case of a homogeneous substance, it is expressed as: where, in SI units: ρ (rho) is the density of the substance, measured in kg·m-3 m is the mass of the substance, measured in kg V is... Room temperature describes a certain temperature within enclosed space that is uses for various purposes by human beings. ... In physics, density is mass m per unit volume V. For the common case of a homogeneous substance, it is expressed as: where, in SI units: ρ (rho) is the density of the substance, measured in kg·m-3 m is the mass of the substance, measured in kg V is... The melting point of a crystalline solid is the temperature at which it changes state from solid to liquid. ... The melting point of a crystalline solid is the temperature at which it changes state from solid to liquid. ... The kelvin (symbol: K) is a unit increment of temperature and is one of the seven SI base units. ... Celsius is, or relates to, the Celsius temperature scale (previously known as the centigrade scale). ... Fahrenheit is a temperature scale named after the German-Dutch physicist Daniel Gabriel Fahrenheit (1686–1736), who proposed it in 1724. ... Italic text This article is about the boiling point of liquids. ... The kelvin (symbol: K) is a unit increment of temperature and is one of the seven SI base units. ... Celsius is, or relates to, the Celsius temperature scale (previously known as the centigrade scale). ... Fahrenheit is a temperature scale named after the German-Dutch physicist Daniel Gabriel Fahrenheit (1686–1736), who proposed it in 1724. ... In physical chemistry, thermodynamics, chemistry and condensed matter physics, a critical point, also called a critical state, specifies the conditions (temperature, pressure) at which the liquid state of the matter ceases to exist. ... The kelvin (symbol: K) is a unit increment of temperature and is one of the seven SI base units. ... Standard enthalpy change of fusion of period three. ... The joule per mole (symbol: J·mol-1) is an SI derived unit of energy per amount of material. ... The standard enthalpy change of vaporization, ΔvHo, also (less correctly) known as the heat of vaporization is the energy required to transform a given quantity of a substance into a gas. ... The joule per mole (symbol: J·mol-1) is an SI derived unit of energy per amount of material. ... To meet Wikipedias quality standards, this article or section may require cleanup. ... In chemistry and physics, Vapor pressure is the pressure of a vapor in equilibrium with its non-vapor phases. ... Enargite crystals In mineralogy and crystallography, a crystal structure is a unique arrangement of atoms in a crystal. ... The oxidation number of an element in a molecule or complex is the charge that it would have if all the ligands (basically, atoms that donate electrons) were removed along with the electron pairs that were shared with the central atom[1]. It means that the oxidation number is the... Acidity redirects here. ... Electronegativity is a measure of the ability of an atom or molecule to attract electrons in the context of a chemical bond. ... The ionization energy (IE) of an atom or of a molecule is the energy required to strip it of an electron. ... These tables list the ionization energy in kJ/mol necessary to remove an electron from a neutral atom (first energy), respectively from a singly, doubly, etc. ... Kilojoule per mole are an SI derived unit of energy per amount of material, where energy is measured in units of 1000 joules, and the amount of material is measured in mole units. ... Atomic radius: Ionic radius Covalent radius Metallic radius van der Waals radius edit Atomic radius, and more generally the size of an atom, is not a precisely defined physical quantity, nor is it constant in all circumstances. ... You have big harry skanky balls ... One picometre is defined as 1x10-12 metres, in standard units. ... You have big harry skanky balls ... Atomic radius: Ionic radius Covalent radius Metallic radius van der Waals radius edit The covalent radius, rcov, is a measure of the size of atom which forms part of a covalent bond. ... You have big harry skanky balls ... The van der Waals radius of an atom is the radius of an imaginary hard sphere which can be used to model the atom for many purposes. ... You have big harry skanky balls ... For other senses of this word, see magnetism (disambiguation). ... In physics, thermal conductivity, k, is the intensive property of a material that indicates its ability to conduct heat. ... During heat transfer, the energy that is stored in the intermolecular bonds between atoms changes. ... Sound is a vibration that travels through an elastic medium as a wave. ... Metre per second (U.S. spelling: meter per second) is an SI derived unit of both speed (scalar) and velocity (vector), defined by distance in metres divided by time in seconds. ... In solid mechanics, Youngs modulus (E) is a measure of the stiffness of a given material. ... In materials science, shear modulus, G, or sometimes S or μ, sometimes referred to as the modulus of rigidity, is defined as the ratio of shear stress to the shear strain:[1] where = shear stress; force acts on area ; = shear strain; length changes by amount . ... The bulk modulus (K) of a substance essentially measures the substances resistance to uniform compression. ... Figure 1: Rectangular specimen subject to compression, with Poissons ratio circa 0. ... This article or section does not cite any references or sources. ... The Brinell scale characterises the indentation hardness of materials through the scale of penetration of an indenter, loaded on a material test-piece. ... CAS registry numbers are unique numerical identifiers for chemical compounds, polymers, biological sequences, mixtures and alloys. ... Selenium (Se) Standard atomic mass: 78. ... Isotopes are any of the several different forms of an element each having different atomic mass (mass number). ... Natural abundance refers to the prevalence of different isotopes of an element as found in nature. ... Half-Life For a quantity subject to exponential decay, the half-life is the time required for the quantity to fall to half of its initial value. ... Radioactive decay is the process in which an unstable atomic nucleus loses energy by emitting radiation in the form of particles or electromagnetic waves. ... The decay energy is the energy released by a nuclear decay. ... The electronvolt (symbol eV) is a unit of energy. ... In nuclear physics, a decay product, also known as a daughter product, is a nuclide resulting from the radioactive decay of a parent or precursor nuclide. ... A Synthetic radioisotope is a radionuclide that is not found in nature: no natural process or mechanism exists which produces it, or it is so unstable that it decays away in a very short period of time. ... Look up day in Wiktionary, the free dictionary. ... Electron capture is a decay mode for isotopes that will occur when there are too many protons in the nucleus of an atom, and there isnt enough energy to emit a positron; however, it continues to be a viable decay mode for radioactive isotopes that can decay by positron... General Name, Symbol, Number arsenic, As, 33 Chemical series metalloids Group, Period, Block 15, 4, p Appearance metallic gray Standard atomic weight 74. ... This article is about electromagnetic radiation. ... This article needs to be cleaned up to conform to a higher standard of quality. ... This article or section does not adequately cite its references or sources. ... A Synthetic radioisotope is a radionuclide that is not found in nature: no natural process or mechanism exists which produces it, or it is so unstable that it decays away in a very short period of time. ... Look up day in Wiktionary, the free dictionary. ... General Name, Symbol, Number arsenic, As, 33 Chemical series metalloids Group, Period, Block 15, 4, p Appearance metallic gray Standard atomic weight 74. ... This article needs to be cleaned up to conform to a higher standard of quality. ... This article or section does not adequately cite its references or sources. ... This article needs to be cleaned up to conform to a higher standard of quality. ... This article or section does not adequately cite its references or sources. ... This article needs to be cleaned up to conform to a higher standard of quality. ... This article or section does not adequately cite its references or sources. ... A Synthetic radioisotope is a radionuclide that is not found in nature: no natural process or mechanism exists which produces it, or it is so unstable that it decays away in a very short period of time. ... A year (from Old English gÄ“r) is the time between two recurrences of an event related to the orbit of the Earth around the Sun. ... In nuclear physics, beta decay (sometimes called neutron decay) is a type of radioactive decay in which a beta particle (an electron or a positron) is emitted. ... General Name, Symbol, Number bromine, Br, 35 Chemical series halogens Group, Period, Block 17, 4, p Appearance gas/liquid: red-brown solid: metallic luster Atomic mass 79. ... This article needs to be cleaned up to conform to a higher standard of quality. ... This article or section does not adequately cite its references or sources. ... A year (from Old English gÄ“r) is the time between two recurrences of an event related to the orbit of the Earth around the Sun. ... In the process of beta decay unstable nuclei decay by converting a neutron in the nucleus to a proton and emitting an electron and anti-neutrino. ... General Name, Symbol, Number krypton, Kr, 36 Chemical series noble gases Group, Period, Block 18, 4, p Appearance colorless Standard atomic weight 83. ... Recommended values for many properties of the elements, together with various references, are collected on these data pages. ... Image File history File links Selen_1. ... Image File history File links Selen_1. ... Articles with similar titles include the NATO phonetic alphabet, which has also informally been called the “International Phonetic Alphabet”. For information on how to read IPA transcriptions of English words, see IPA chart for English. ... The periodic table of the chemical elements A chemical element, or element for short, is a type of atom that is defined by its atomic number; that is, by the number of protons in its nucleus. ... It has been suggested that List of elements by atomic number be merged into this article or section. ... Together with the metals and metalloids, a nonmetal is one of three categories of chemical elements as distinguished by ionization and bonding properties. ... General Name, Symbol, Number sulfur, S, 16 Chemical series nonmetals Group, Period, Block 16, 3, p Appearance lemon yellow Standard atomic weight 32. ... General Name, Symbol, Number tellurium, Te, 52 Chemical series metalloids Group, Period, Block 16, 5, p Appearance silvery lustrous gray Standard atomic weight 127. ...


Selenium is an essential component of the enzyme glutathione peroxidase(GSH-Px) which catalyzes the reaction: Glutathione peroxidase (PDB 1GP1, EC 1. ...


2 GSH+ H2O2---------GSH-Px → GSSG + 2 H2O


Isolated selenium occurs in several different forms, but the most stable of these is a dense purplish-gray semimetal (semiconductor) form that is structurally a trigonal polymer chain. It conducts electricity better in the light than in the dark, and is used in photocells (see allotropic section below). Selenium also exists in many nonconductive forms: a black glass-like substance, as well as several red crystalline forms built of eight-membered ring molecules, like its lighter cousin sulfur. Lightning strikes during a night-time thunderstorm. ... A photoresistor is an electronic component whose resistance decreases with increasing incident light intensity. ... Look up ring in Wiktionary, the free dictionary. ...


Selenium is found in economic quantities partially replacing sulfur in sulfide ores such as pyrite. Minerals that are selenide or selenate compounds are also known, but all are rare. General Name, Symbol, Number sulfur, S, 16 Chemical series nonmetals Group, Period, Block 16, 3, p Appearance lemon yellow Standard atomic weight 32. ... Formally, sulfide is the dianion, S2−, which exists in strongly alkaline aqueous solutions formed from H2S or alkali metal salts such as Li2S, Na2S, and K2S. Sulfide is exceptionally basic and, with a pKa > 14, it does not exist in appreciable concentrations even in highly alkaline water. ... The mineral pyrite, or iron pyrite, is iron sulfide, FeS2. ...

Contents

Occurrence

Selenium occurs naturally in a number of inorganic forms, including selenide, selenate and selenite. In soils, selenium most often occurs in soluble forms like selenate (analogous to sulfate), which are leached into rivers very easily by runoff. The selenide ion is Se2-. A selenide is a chemical compound in which selenium serves as a anion with oxidation number of -2, much as sulfur does in a sulfide. ... The selenate ion is SeO42-. Selenates are analogous to sulfates and have similar chemistry. ... Sodium selenite, Na2SeO3, is a selenium compound. ...


Selenium has a biological role, and is found in organic compounds such as dimethyl selenide, selenomethionine and selenocysteine. In these compounds selenium plays an analogous role to sulfur. Selenomethionine: chemical structure Selenomethionine is an amino acid containing selenium. ... Skeletal formula of L-selenocysteine Space-filling model of L-selenocysteine Selenocysteine is an amino acid that is present in several enzymes (for example glutathione peroxidases, tetraiodothyronine 5 deiodinases, thioredoxin reductases, formate dehydrogenases, glycine reductases and some hydrogenases). ...


Selenium is most commonly produced from selenide in many sulfide ores, such as those of copper, silver, or lead. It is obtained as a byproduct of the processing of these ores, from the anode mud of copper refineries and the mud from the lead chambers of sulfuric acid plants. These muds can be processed by a number of means to obtain free selenium. The selenide ion is Se2-. A selenide is a chemical compound in which selenium serves as a anion with oxidation number of -2, much as sulfur does in a sulfide. ... Formally, sulfide is the dianion, S2−, which exists in strongly alkaline aqueous solutions formed from H2S or alkali metal salts such as Li2S, Na2S, and K2S. Sulfide is exceptionally basic and, with a pKa > 14, it does not exist in appreciable concentrations even in highly alkaline water. ... An ore is a mineral deposit containing a metal or other valuable resource in economically viable concentrations. ... General Name, Symbol, Number copper, Cu, 29 Chemical series transition metals Group, Period, Block 11, 4, d Appearance metallic pinkish red Standard atomic weight 63. ... General Name, Symbol, Number silver, Ag, 47 Chemical series transition metals Group, Period, Block 11, 5, d Appearance lustrous white metal Standard atomic weight 107. ... For Pb as an abbreviation, see PB. General Name, Symbol, Number lead, Pb, 82 Chemical series Post-transition metals or poor metals Group, Period, Block 14, 6, p Appearance bluish gray Standard atomic weight 207. ... Diagram of a zinc anode in a galvanic cell. ... Sulfuric (or sulphuric) acid, H2SO4, is a strong mineral acid. ...


Natural sources of selenium include certain selenium-rich soils, and selenium that has been bioconcentrated by certain toxic plants such as locoweed. Anthropogenic sources of selenium include coal burning and the mining and smelting of sulfide ores[2]. If the input of a toxic substance to an organism is greater than the rate at which the substance is lost, the organism is said to be bioaccumulating that substance. ... Locoweed is a term used to describe plants from two different genera of legumes most commonly found in the midwest and Joe LoConte. ...


See also Selenide minerals.


Isotopes

Main article: isotopes of selenium

Selenium has six naturally-occurring isotopes, five of which are stable: 74Se, 76Se, 77Se, 78Se, and 80Se. The last three also occur as fission products, along with 79Se which has a halflife of 295,000 years, and 82Se which has a very long half life (~1020 yr, decaying via double beta decay to 82Kr) and for practical purposes can be considered to be stable. 23 other unstable isotopes have been characterized. Selenium (Se) Standard atomic mass: 78. ... Isotopes are any of the several different forms of an element each having different atomic mass (mass number). ... Fission products are the residues of fission processes. ... 79Se is a radioisotope of selenium present in spent nuclear fuel and the wastes resulting from reprocessing this fuel. ... Half-Life For a quantity subject to exponential decay, the half-life is the time required for the quantity to fall to half of its initial value. ... General Name, Symbol, Number krypton, Kr, 36 Chemical series noble gases Group, Period, Block 18, 4, p Appearance colorless Standard atomic weight 83. ...


History and changing global demand for selenium

Selenium (Greek σελήνη selene meaning "Moon") was discovered in 1817 by Jöns Jakob Berzelius who found the element associated with tellurium (named for the Earth). 1817 was a common year starting on Wednesday (see link for calendar). ... Friherre Jöns Jakob Berzelius (August 20, 1779 – August 7, 1848) was a Swedish chemist. ... General Name, Symbol, Number tellurium, Te, 52 Chemical series metalloids Group, Period, Block 16, 5, p Appearance silvery lustrous gray Standard atomic weight 127. ...


Growth in selenium consumption was historically driven by steady development of new uses, including applications in rubber compounding, steel alloying, and selenium rectifiers. By 1970, selenium in rectifiers had largely been replaced by silicon, but its use as a photoconductor in plain paper copiers had become its leading application. During the 1980s, the photoconductor application declined (although it was still a large end-use) as more and more copiers using organic photoconductors were produced. Presently, the largest use of selenium world-wide is in glass manufacturing, followed by uses in chemicals and pigments. Electronic use, despite a number of continued applications, continues to decline.[1] The steel cable of a colliery winding tower. ... General Name, Symbol, Number silicon, Si, 14 Chemical series metalloids Group, Period, Block 14, 3, p Appearance as coarse powder, dark grey with bluish tinge Standard atomic weight 28. ...


In 1996, continuing research showed a positive correlation between selenium supplementation and cancer prevention in humans, but widespread direct application of this important finding would not add significantly to demand owing to the small doses required. In the late 1990s, the use of selenium (usually with bismuth) as an additive to plumbing brasses to meet no-lead environmental standards, became important. At present, total world selenium production continues to increase modestly. Cancer is a class of diseases or disorders characterized by uncontrolled division of cells and the ability of these to spread, either by direct growth into adjacent tissue through invasion, or by implantation into distant sites by metastasis (where cancer cells are transported through the bloodstream or lymphatic system). ... General Name, Symbol, Number bismuth, Bi, 83 Chemical series poor metals Group, Period, Block 15, 6, p Appearance lustrous reddish white Atomic mass 208. ... A plumber wrench for working on pipes and fittings Plumbing, from the Latin for lead (plumbum), is the skilled trade of working with pipes, tubing and plumbing fixtures for potable water systems and the drainage of waste. ... For other uses, see Brass (disambiguation). ...


Selenium and health

Although it is toxic in large doses, selenium is an essential micronutrient for animals. In plants, it occurs as a bystander mineral, sometimes in toxic proportions in forage (some plants may accumulate selenium as a defense against being eaten by animals, but other plants such as locoweed require selenium, and their growth indicates the presence of selenium in soil).[3] It is a component of the unusual amino acids selenocysteine and selenomethionine. In humans, selenium is a trace element nutrient which functions as cofactor for reduction of antioxidant enzymes such as glutathione peroxidases and thioredoxin reductase. It also plays a role in the functioning of the thyroid gland by participating as a cofactor for thyroid hormone deiodinases [4]. Dietary selenium comes from nuts, cereals, meat, fish, and eggs. Brazil nuts are the richest ordinary dietary source (though this is soil-dependent, since the Brazil nut does not require high levels of the element for its own needs). High levels are found in meats found in kidney, crab and lobster, in that order.[2][3] In the USA, the recommended dietary allowance for adults is 55 micrograms per day. Dietary minerals are the chemical elements required by living organisms, other than the four elements carbon, hydrogen, nitrogen, and oxygen which are present in common organic molecules. ... Locoweed is a term used to describe plants from two different genera of legumes most commonly found in the midwest and Joe LoConte. ... Phenylalanine is one of the standard amino acids. ... Skeletal formula of L-selenocysteine Space-filling model of L-selenocysteine Selenocysteine is an amino acid that is present in several enzymes (for example glutathione peroxidases, tetraiodothyronine 5 deiodinases, thioredoxin reductases, formate dehydrogenases, glycine reductases and some hydrogenases). ... Selenomethionine: chemical structure Selenomethionine is an amino acid containing selenium. ... Dietary minerals are the chemical elements required by living organisms, other than the four elements carbon, hydrogen, nitrogen, and oxygen which are present in common organic molecules. ... A cofactor is the following: In mathematics a cofactor is the minor of an element of a square matrix. ... Illustration of a redox reaction Redox (shorthand for oxidation/reduction reaction) describes all chemical reactions in which atoms have their oxidation number (oxidation state) changed. ... Space-filling model of the antioxidant metabolite glutathione. ... Glutathione peroxidase (PDB 1GP1, EC 1. ... Thioredoxin Reductase (TR, TrxR) are the only known enzymes to reduce thioredoxin (Trx). ... A cofactor is any substance that needs to be present in addition to an enzyme to catalyze a certain reaction. ... The thyroid hormones, thyroxine (T4) and triiodothyronine (T3), are tyrosine-based hormones produced by the thyroid gland. ... Deiodinase (eg. ... Binomial name Bertholletia excelsa Humb. ... The kidneys are organs that filter wastes (such as urea) from the blood and excrete them, along with water, as urine. ... Superfamilies Dromiacea Homolodromioidea Dromioidea Homoloidea Eubrachyura Raninoidea Cyclodorippoidea Dorippoidea Calappoidea Leucosioidea Majoidea Hymenosomatoidea Parthenopoidea Retroplumoidea Cancroidea Portunoidea Bythograeoidea Xanthoidea Bellioidea Potamoidea Pseudothelphusoidea Gecarcinucoidea Cryptochiroidea Pinnotheroidea * Ocypodoidea * Grapsoidea * An asterisk (*) marks the crabs included in the clade Thoracotremata. ... Subfamilies and Genera Neophoberinae Acanthacaris Thymopinae Nephropsis Nephropides Thymops Thymopsis Nephropinae Homarus Nephrops Homarinus Metanephrops Eunephrops Thymopides Clawed lobsters comprise a family (Nephropidae, sometimes also Homaridae) of large marine crustaceans. ... It has been suggested that this article or section be merged with Daily values. ...


Toxicity

Although selenium is an essential trace element it is toxic if taken in excess. Exceeding the Tolerable Upper Intake Level of 400 micrograms per day can lead to selenosis.[4] Symptoms of selenosis include a garlic odour on the breath, gastrointestinal disorders, hair loss, sloughing of nails, fatigue, irritability and neurological damage. Extreme cases of selenosis can result in cirrhosis of the liver, pulmonary edema and death.[5] Dietary minerals are the chemical elements required by living organisms, other than the four elements carbon, hydrogen, nitrogen, and oxygen which are present in common organic molecules. ... Dietary Reference Intake is a set of guidelines set up in 1997 to give more detailed guidance than the RDA system which preceded it. ... Cirrhosis of the liver is a consequence of chronic liver disease characterized by replacement of liver tissue by fibrotic scar tissue as well as regenerative nodules, leading to progressive loss of liver function. ... Pulmonary edema is swelling and/or fluid accumulation in the lungs. ...


Elemental selenium and most metallic selenides have relatively low toxicities because of their low bioavailability. By contrast, selenate and selenite are very toxic, and have modes of action similar to that of arsenic. Hydrogen selenide is an extremely toxic, corrosive gas.[6] Selenium also occurs in organic compounds such as dimethyl selenide, selenomethionine and selenocysteine, all of which have high bioavailability and are toxic in large doses. The selenide ion is Se2-. A selenide is a chemical compound in which selenium serves as a anion with oxidation number of -2, much as sulfur does in a sulfide. ... In pharmacology, bioavailability is used to describe the fraction of an administered dose of unchanged drug that reaches the systemic circulation, one of the principal pharmacokinetic properties of drugs. ... The selenate ion is SeO42-. Selenates are analogous to sulfates and have similar chemistry. ... Selenous acid, H2SeO3, is an oxygen acid of selenium. ... Hydrogen selenide is H2Se, the simplest hydride of selenium. ... Selenomethionine: chemical structure Selenomethionine is an amino acid containing selenium. ... Skeletal formula of L-selenocysteine Space-filling model of L-selenocysteine Selenocysteine is an amino acid that is present in several enzymes (for example glutathione peroxidases, tetraiodothyronine 5 deiodinases, thioredoxin reductases, formate dehydrogenases, glycine reductases and some hydrogenases). ... In pharmacology, bioavailability is used to describe the fraction of an administered dose of unchanged drug that reaches the systemic circulation, one of the principal pharmacokinetic properties of drugs. ...


Selenium poisoning of water systems may result whenever new agricultural runoff courses through normally-dry undeveloped lands. This process leaches natural soluble selenium compounds (such as selenates) into the water, which may then be concentrated in new "wetlands" as it evaporates. High selenium levels produced in this fashion have been found to have caused certain congenital disorders in wetland birds.[7]


Deficiency

Selenium deficiency is relatively rare in healthy well-nourished individuals. It can occur in patients with severely compromised intestinal function, or those undergoing total parenteral nutrition. Alternatively, people dependent on food grown from selenium-deficient soil are also at risk. In the USA, the Dietary Reference Intake for adults is 55 micrograms per day. In anatomy, the intestine is the segment of the alimentary canal extending from the stomach to the anus and, in humans and other mammals, consists of two segments, the small intestine and the large intestine (or colon). ... Total parenteral nutrition (TPN), is the practice of feeding a person intravenously, circumventing the gut. ... Dietary Reference Intake is a set of guidelines set up in 1997 to give more detailed guidance than the RDA system which preceded it. ...


Selenium deficiency can lead to Keshan disease, which is potentially fatal. Selenium deficiency also contributes (along with iodine deficiency) to Kashin-Beck disease.[8] The primary symptom of Keshan disease is myocardial necrosis, leading to weakening of the heart. Kashin-Beck disease results in atrophy, degeneration and necrosis of cartilage tissue.[9] Keshan disease also makes the body more susceptible to illness caused by other nutritional, biochemical, or infectious diseases. These diseases are most common in certain parts of China where the soil is extremely deficient in selenium. Studies in Jiangsu Province of China have indicated a reduction in the prevalence of these diseases by taking selenium supplements. Keshan disease is a congestive cardiomyopathy caused by dietary deficiency in the mineral selenium. ... Myocardium is the muscular tissue of the heart. ... Necrosis (in Greek Νεκρός = Death) is the name given to accidental death of cells and living tissue. ... Atrophy is the partial or complete wasting away of a part of the body. ... Necrosis (in Greek Νεκρός = Death) is the name given to accidental death of cells and living tissue. ... Cartilage is a type of dense connective tissue. ... Jiangsu (Simplified Chinese: 江苏; Traditional Chinese: 江蘇; pinyin: Jiāngsū; Wade-Giles: Chiang-su; Postal System Pinyin: Kiangsu) is a province of the Peoples Republic of China, located along the east coast of the country. ...


Selenium is also necessary for the conversion of the thyroid hormone thyroxine (T4) into its more active counterpart, triiodothyronine, and as such a deficiency can cause symptoms of hypothyroidism, including extreme fatigue, mental slowing, goitre, cretinism and recurrent miscarriage.[5] Thyroxine, or 3:5,3:5 tetra­iodothyronine (often abbreviated as T4) is the major hormone secreted by the follicular cells of the thyroid gland. ... The thyroid hormones, thyroxine (T4) and triiodothyronine (T3), are tyrosine-based hormones produced by the thyroid gland. ... This article or section does not cite its references or sources. ... A goitre (or goiter) (Latin struma), also called a bronchocele, is a swelling in the neck (just below Adams apple or larynx) due to an enlarged thyroid gland. ... Cretinism (most likely from the Latin Christiānum, Christian) is a condition of severely stunted physical and mental growth due to untreated congenital deficiency of thyroid hormones (hypothyroidism). ... Habitual abortion or recurrent pregnancy loss (RPL) is the occurrence of repeated pregnancies that end in miscarriage of the fetus, usually before 20 weeks of gestation. ...


Controversial Health Effects

Cancer

Several studies have suggested a link between cancer and selenium deficiency.[10][11][12][13][14][15][16] A study conducted on the effect of selenium supplementation on the recurrence of skin cancers did not demonstrate a reduced rate of recurrence of skin cancers, but did show a significantly reduced occurrence of total cancers.[17] Dietary selenium prevents chemically induced carcinogenesis in many rodent studies.[18] In these studies, organic seleno-compounds are more potent and less toxic than selenium salts (e.g., selenocyanates, selenomethionine, selenium-rich Brazil nuts, or selenium-enriched garlic or broccoli). Selenium may help prevent cancer by acting as an antioxidant or by enhancing immune activity. Not all studies agree on the cancer-fighting effects of selenium. One study of naturally occurring levels of selenium in over 60,000 participants did not show a significant correlation between those levels and cancer.[19] The SU.VI.MAX study[20] concluded that low-dose supplementation (with 120 mg of ascorbic acid, 30 mg of vitamin E, 6 mg of beta carotene, 100 µg of selenium, and 20 mg of zinc) resulted in a 31% reduction in the incidence of cancer and a 37% reduction in all cause mortality in males, but did not get a significant result for females.[21] The SELECT study[22] is currently investigating the effect of selenium and vitamin E supplementation on incidence of prostate cancer. However, selenium has been proven to help chemotherapy treatment by enhancing the efficacy of the treatment, reducing the toxicity of chemotherapeutic drugs, and preventing the body's resistance to the drugs.[23] One of the studies[24] showed that in just 72 hours, the efficacy of treatment using chemotherapeutic drugs, such as Taxol and Adriamycin, with selenium yeast is significantly higher than the treatment using the drugs alone. The finding was shown in various cancer cells (breast, lung, small intestine, colon, liver). Space-filling model of the antioxidant metabolite glutathione. ... Tocopherol, or Vitamin E, is a fat-soluble vitamin in eight forms that is an important antioxidant. ... Prostate cancer is a disease in which cancer develops in the prostate, a gland in the male reproductive system. ... Cancer is a class of diseases or disorders characterized by uncontrolled division of cells and the ability of these to spread, either by direct growth into adjacent tissue through invasion, or by implantation into distant sites by metastasis (where cancer cells are transported through the bloodstream or lymphatic system). ...


HIV/AIDS

Some research has indicated a geographical link between regions of selenium deficient soils and peak incidences of HIV/AIDS infection. For example, much of sub-Saharan Africa is low in selenium. However, Senegal is not, and also has a significantly lower level of AIDS infection than the rest of the continent. AIDS appears to involve a slow and progressive decline in levels of selenium in the body. Whether this decline in selenium levels is a direct result of the replication of HIV[25] or related more generally to the overall malabsorption of nutrients by AIDS patients remains debated. Species Human immunodeficiency virus 1 Human immunodeficiency virus 2 Human immunodeficiency virus (HIV) is a retrovirus that causes acquired immunodeficiency syndrome (AIDS, a condition in humans in which the immune system begins to fail, leading to life-threatening opportunistic infections). ... Acquired Immune Deficiency Syndrome or acquired immunodeficiency syndrome (AIDS or Aids) is a collection of symptoms and infections resulting from the specific damage to the immune system caused by the human immunodeficiency virus (HIV). ... A political map showing national divisions in relation to deonte Shepard Club Of America Free burgers for new members the ecological break (Sub-Saharan Africa in green) A geographical map of Africa, showing the ecological break that defines the sub-Saharan area Sub-Saharan Africa is the term used to...


Low selenium levels in AIDS patients have been directly correlated with decreased immune cell count and increased disease progression and risk of death.[26] Selenium normally acts as an antioxidant, so low levels of it may increase oxidative stress on the immune system leading to more rapid decline of the immune system. Others have argued that HIV encodes for the human selenoenzyme glutathione peroxidase, which depletes the victim's selenium levels. Depleted selenium levels in turn lead to a decline in CD4 helper T-cells, further weakening the immune system.[27] Space-filling model of the antioxidant metabolite glutathione. ... Glutathione peroxidase (PDB 1GP1, EC 1. ... A helper (or TH) T cell is a T cell (a type of white blood cell) which has on its surface antigen receptors that can bind to fragments of antigens displayed by the Class II MHC molecules found on professional antigen-presenting cells (APCs). ...


Regardless of the cause of depleted selenium levels in AIDS patients, studies have shown that selenium deficiency does strongly correlate with the progression of the disease and the risk of death.[28][29][30] Selenium supplementation may help mitigate the symptoms of AIDS and reduce the risk of mortality. It should be emphasized that the evidence to date does not suggest that selenium can reduce the risk of infection or the rate of spread of AIDS, but rather treat the symptoms of those who are already infected.


Production and allotropic forms

Selenium is a common byproduct of copper refining, or the production of sulfuric acid.[31][32][33] Isolation of selenium is often complicated by the presence of other compounds and elements. Commonly, production begins by oxidation with sodium carbonate to produce sodium selenite. The sodium selenite is then acidified with sulfuric acid producing selenous acid. The selenous acid is finally bubbled with sulfur dioxide producing elemental red amorphous selenium.


Selenium produced in chemical reactions invariably appears as the amorphous red form-- an insoluble brick red powder. When this form is rapidly melted, it forms the black, vitreous form which is usually sold industrially as beads. The most thermodynamically stable and dense form of selenium is the electrically conductive gray (trigonal) form, which is composed of long helical chains of selenium atoms. The conductivity of this form is notably light sensitive. Selenium also exists in three different deep red crystalline monoclinic forms, which are composed of Se8 molecules, similar to many allotropes of sulfur.[34]


Non-biological applications

Chemistry


Selenium is a catalyst in many chemical reactions and is widely used in various industrial and laboratory syntheses. It is also widely used in structure determination of proteins and nucleic acids by X-ray crystallography (incorporation of one or more Se atoms helps with MAD phasing.)


Manufacturing and materials use


The largest use of selenium world-wide is in glass and ceramic manufacturing, where it is used to give a red color to glasses, enamels and glazes as well as to remove color from glass by counteracting the green tint imparted by ferrous impurities. Glass can be made transparent and flat, or into other shapes and colors as shown in this sphere from the Verrerie of Brehat in Brittany. ... Fixed Partial Denture, or Bridge The word ceramic is derived from the Greek word κεραμικός (keramikos). ... In a discussion of art technology, enamel (or vitreous enamel, or porcelain enamel in American English) is the colorful result of fusion of powdered glass to a substrate through the process of firing, usually between 750 and 850 degrees Celsius. ... Composite body, painted, and glazed bottle. ...


Selenium is used with bismuth in brasses to replace more toxic lead. It is also used to improve the abrasion resistance in vulcanized rubbers. General Name, Symbol, Number bismuth, Bi, 83 Chemical series poor metals Group, Period, Block 15, 6, p Appearance lustrous reddish white Atomic mass 208. ... For other uses, see Brass (disambiguation). ... For Pb as an abbreviation, see PB. General Name, Symbol, Number lead, Pb, 82 Chemical series Post-transition metals or poor metals Group, Period, Block 14, 6, p Appearance bluish gray Standard atomic weight 207. ... Vulcanization refers to a specific curing process of rubber involving high heat and the addition of sulfur. ... This does not cite any references or sources. ...


Electronics


Because of its photovoltaic and photoconductive properties, selenium is used in photocopying, photocells, light meters and solar cells. It was once widely used in rectifiers. These uses have mostly been replaced by silicon-based devices, or are in the process of being replaced. The most notable exception is in power DC surge protection, where the superior energy capabilities of selenium suppressors make them more desirable than metal oxide varistors. Photovoltaic tree in Styria, Austria Photovoltaics, or PV for short, is a solar power technology that uses solar cells or solar photovoltaic arrays to convert light from the sun directly into electricity. ... Photoconductivity is an optical and electrical phenomenon in which a material becomes more conductive due to the absorption of electro-magnetic radiation such as visible light, ultraviolet light, or gamma radiation. ... This article or section does not cite any references or sources. ... A photoresistor is an electronic component whose resistance decreases with increasing incident light intensity. ... A light meter is a device used to measure the amount of light. ... A solar cell, made from a monocrystalline silicon wafer A solar cell or photovoltaic cell is a device that converts light energy into electrical energy. ... AC, half-wave and full wave rectified signals A rectifier is an electrical device, comprising one or more semiconductive devices (such as diodes) or vacuum tubes arranged for converting alternating current to direct current. ... Surge and noise protector Most hV6 A surge protector is an appliance designed to protect electrical devices from power surges and voltage spikes. ... A varistor is a type of resistor with a significantly non-ohmic current-voltage characteristic. ...


Sheets of amorphous selenium convert x-ray images to patterns of charge in xeroradiography and in solid-state flat panel x-ray cameras. In the NATO phonetic alphabet, X-ray represents the letter X. An X-ray picture (radiograph) taken by Röntgen An X-ray is a form of electromagnetic radiation with a wavelength approximately in the range of 5 pm to 10 nanometers (corresponding to frequencies in the range 30 PHz...


Photography


Selenium is used in the toning of photographic prints, and it is sold as a toner by numerous photographic manufacturers including Kodak and Fotospeed. Its use intensifies and extends the tonal range of black and white photographic images as well as improving the permanence of prints. Toning is any chemical process used to modify the color of monochrome photographic prints. ... Eastman Kodak Company (NYSE: EK) is a large multinational public company producing photographic equipment. ...


Biological applications

Nutrition


Selenium is used widely in vitamin preparations and other dietary supplements, in small doses (typically 50 to 200 micrograms per day for adult humans). Some livestock feeds are fortified with selenium as well. Retinol (Vitamin A) For the record label, see Vitamin Records A vitamin is an organic compound required in tiny amounts for essential metabolic reactions in a living organism. ... A dietary supplement is intended to supply nutrients, (vitamins, minerals, fatty acids or amino acids) that are missing or not consumed in sufficient quantity in a persons diet. ... Fodder growing from barley In agriculture, fodder or animal feed is any foodstuff that is used specifically to feed domesticated livestock, including cattle, goats, sheep, horses, chickens and pigs. ...


In popular culture

See selenium's entries at fictional applications of real materials.

In various fictional settings, real materials may be portrayed as having different or additional properties, particularly when interacting with the unique elements of the setting itself. ...

Compounds

See also Selenium compounds and organoselenium chemistry. Mercury selenide (HgSe) is a chemical compound of mercury and selenium. ... Hydrogen selenide is H2Se, the simplest hydride of selenium. ... R-phrases , , S-phrases , , , , U.S. Permissible Exposure Limit 5 ppm IDLH (NIOSH) 100 ppm Flash point non-flammable RTECS number WS4550000 Supplementary data page Structure and properties n, εr, etc. ... Selenic acid, H2SeO4, is an oxygen acid of selenium. ... Selenous acid, H2SeO3, is an oxygen acid of selenium. ... Selenium sulfide is an antifungal agent often used in shampoos for the treatment of dandruff and seborrheic dermatitis. ... Sodium selenite, Na2SeO3, is a selenium compound. ... Zinc selenide (ZnSe), is a light yellow binary solid compound. ... Organoselenium compounds are chemical compounds containing carbon to selenium bonds. ...


References

  1. ^ http://minerals.usgs.gov/minerals/pubs/commodity/selenium/830398.pdf
  2. ^ Barclay, Margaret N. I.; Allan MacPherson, James Dixon (1995). "Selenium content of a range of UK food". Journal of food composition and analysis 8: 307-318. 0889-1575. 
  3. ^ A list of selenium rich foods can be found on The Office of Dietary Supplements Selenium Fact Sheet.
  4. ^ http://ods.od.nih.gov/factsheets/selenium.asp#h7
  5. ^ a b http://www.atsdr.cdc.gov/toxprofiles/tp92-c3.pdf
  6. ^ http://www.tc.gc.ca/canutec/erg_gmu/search/guide.asp?Guide=117&Lang=EN
  7. ^ http://www.webpages.uidaho.edu/~childers/3_31_05%20selenium.pdf
  8. ^ http://www.atsdr.cdc.gov/toxprofiles/tp92-c3.pdf
  9. ^ http://content.nejm.org/cgi/content/short/339/16/1112
  10. ^ http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=%209290116&dopt=Abstract
  11. ^ http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=8993799&dopt=Abstract
  12. ^ http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=%209829869&dopt=Abstract
  13. ^ http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=9279064&dopt=Abstract
  14. ^ http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=3923345&dopt=Abstract
  15. ^ http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=10335455&dopt=Abstract
  16. ^ http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=2136228&dopt=Abstract
  17. ^ http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=8971064&dopt=Abstract
  18. ^ Chemoprevention Database
  19. ^ http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=7707436&dopt=Abstract
  20. ^ http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=9503043&dopt=Abstract
  21. ^ http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=15557412&dopt=Citation
  22. ^ http://www.crab.org/select/
  23. ^ http://nutrition-health.info/index.php/Selenium_and_Chemotherapeutic_Drugs
  24. ^ http://nutrition-health.info/index.php/Selenium_Cancer_1
  25. ^ http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=10608913&dopt=Abstract
  26. ^ http://ods.od.nih.gov/factsheets/selenium.asp#h6
  27. ^ http://www.hdfoster.com/index.html#Publications
  28. ^ http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=9342257&dopt=Abstract
  29. ^ http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=10225235&dopt=Abstract
  30. ^ http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=9481135&dopt=Abstract
  31. ^ http://www.atsdr.cdc.gov/toxprofiles/tp92-c5.pdf
  32. ^ http://periodic.lanl.gov/elements/34.html
  33. ^ http://www.webelements.com/webelements/elements/text/Se/key.html
  34. ^ http://www.chemistryexplained.com/A-Ar/Allotropes.html

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  Results from FactBites:
 
Selenium - Wikipedia, the free encyclopedia (1394 words)
Selenium also occurs in organic compounds such as dimethyl selenide, selenomethionine and selenocysteine, all of which have high bioavailability and are toxic in large doses.
Selenium poisoning as a result of agricultural runoff was also found to have caused birth defects in birds.
Regardless of the cause of depleted selenium levels in AIDS patients, studies have shown that selenium deficiency does strongly corelate with the progression of the disease and the risk of death[25][26][27].
Selenium - definition of Selenium in Encyclopedia (694 words)
Selenium is an essential micronutrient in all known forms of life; it is a component of the unusual amino acid selenocysteine.
Selenium is used to improve the abrasion resistance in vulcanized rubbers.
Selenium occurs as selenide in many sulfide ores, such as those of copper, silver, or lead.
  More results at FactBites »

 
 

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