Selenium,Bromine,Krypton

Selenium is a chemical element with atomic number 34, chemical symbol Se, and an atomic mass of 78.96. It is a nonmetal, whose properties are intermediate between those of adjacent chalcogen elements sulfur andtellurium. It rarely occurs in its elemental state in nature, but instead is obtained as a side-product in the refining of other elements.Sony VAIO VPCF11S1E Battery

Selenium is found in sulfide ores such as pyrite, where it partially replaces the sulfur. Minerals that are selenide or selenate compounds are also known, but are rare. The chief commercial uses for selenium today are in glassmaking and inpigments. Uses in electronics, once important, have been supplanted by silicon semiconductor devices.Sony VAIO VPCF11S1E/B Battery

It is a semiconductorwith the unusual property of conducting electricity better in the light than in the dark, and is used in photocells. Selenium is a trace mineral that is essential to good health but required only in small amounts. Selenium is incorporated into proteins to make selenoproteins, which are important antioxidant enzymes.Sony VAIO VPCF11Z1E Battery

The antioxidant properties of selenoproteins help prevent cellular damage from free radicals. Free radicals are natural by-products of oxygen metabolism that may contribute to the development of chronic diseases such as cancer and heart disease. Other selenoproteins help regulate thyroid function and play a role in the immune system.Sony VAIO VPCF11Z1E/BI Battery

Selenium salts are toxic in large amounts, but trace amounts are necessary for cellular function in many organisms. It is a component of the enzymes glutathione peroxidase and thioredoxin reductase (which indirectly reduce certain oxidized molecules in animals and some plants).Sony VAIO VPCF11ZHJ Battery

It is also found in three deiodinase enzymes, which convert one thyroid hormone to another. Selenium requirements in plants differ by species, with some plants, it seems, requiring none.

Physical

The most stable allotrope of selenium is a dense purplish-gray solid. In terms of structure, it adopts a helical polymeric chain.Sony VAIO VPCF127HGBI Battery

The Se-Se distance is 2.37 Å and the Se-Se-Se angle is 103°. It is a semiconductor with the unusual property of conducting electricity better in the light than in the dark, and is used in photocells. Gray selenium resists oxidation by air and is not attacked by non-oxidizing acids. With strong reducing agents, it forms polyselenides.Sony VAIO VPCF137HG/BI Battery

Red Se and related molecular allotropes

The second major allotrope of Se is red selenium. The solid consists of individual molecules of eight-membered ringmolecules, like its lighter cousin sulfur. The Se-Se distance is 2.34 Å and the Se-Se-Se angle is 106°. Unlike sulfur, however, the red form converts to the gray polymeric allotrope with heat. Other rings with the formula Sen are also known.Sony VAIO VPC-P111KX/B Battery

Elemental 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 red allotrope crystallises in three habits.Sony VAIO VPC-P111KX/D Battery

Selenium does not exhibit the unusual changes in viscosity that sulfur undergoes when gradually heated.

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 half-life of 327,000 years.Sony VAIO VPC-P111KX/G Battery

The final naturally occurring isotope, 82Se, has a very long half-life (~1020 yr, decaying via double beta decay to 82Kr), which, for practical purposes, can be considered to be stable. Twenty-three other unstable isotopes have been characterized.Sony VAIO VPC-P111KX/P Battery

See also Selenium-79 for more information on recent changes in the measured half-life of this long-lived fission product, important for the dose calculations performed in the frame of the geological disposal of long-lived radioactive waste.Sony VAIO VPC-P111KX/W Battery

Occurrence

Native selenium is a rare mineral, which does not usually form good crystals, but, when it does, they are steep rhombohedrons or tiny acicular (hair-like) crystals. Isolation of selenium is often complicated by the presence of other compounds and elements.Sony VAIO VPC-P112KX/B Battery

Selenium occurs naturally in a number of inorganic forms, including selenide-,selenate-, and selenite-containing minerals.

In living systems, selenium is found in the amino acids selenomethionine, selenocysteine, and methylselenocysteine.Sony VAIO VPC-P112KX/D Battery

In these compounds, selenium plays a role analogous to that of sulfur. Another naturally occurring organoselenium compounds is dimethyl selenide.

Certain solids are selenium-rich, and selenium can be bioconcentrated by certain plants. In soils, selenium most often occurs in soluble forms such as selenate (analogous to sulfate), which are leached into rivers very easily by runoff.Sony VAIO VPC-P112KX/G Battery

Anthropogenic sources of selenium include coal burning and the mining and smelting of sulfide ores.

Production

Selenium is most commonly produced from selenide in many sulfide ores, such as those ofcopper, silver, or lead.Sony VAIO VPC-P112KX/P Battery

It is obtained as a byproduct of the processing of these ores, e.g., from the anode mud of copper refineries and the mud from the lead chambers ofsulfuric acid plants. These muds can be processed by a number of means to obtain selenium. Specifically, most elemental selenium comes as a byproduct of refining copperor producing sulfuric acid.Sony VAIO VPC-P112KX/W Battery

Industrial production of selenium often involves the extraction of selenium dioxide from residues obtained during the purification of copper. Common production begins by oxidation with sodium carbonate to produce selenium dioxide. The selenium dioxide is then mixed with water and the solution is acidified to form selenous acid (oxidation step).Sony VAIO VPCP113KX/B Battery

Selenous acid is bubbled with sulfur dioxide (reduction step) to give elemental selenium.

Chalcogen compounds

Selenium forms two stable oxides: selenium dioxide (SeO2) and selenium trioxide (SeO3). Selenium dioxide is formed by the reaction of elemental selenium with oxygen:Sony VAIO VPC-P113KX/B Battery

It is a polymeric solid that forms monomeric SeO2 molecules in the gas phase. It dissolves in water to form selenous acid, H2SeO3. Selenous acid can also be made directly by oxidising elemental selenium with nitric acid:

3 Se + 4 HNO3 ? 3 H2SeO3 + 4 NO

Unlike sulfur, which forms a stable trioxide, selenium trioxide is unstable and decomposes to the dioxide above 185 °C:Sony VAIO VPCP113KX/D Battery

2 SeO3 ? 2 SeO2 + O2 (?H = ?54 kJ/mol)

Salts of selenous acid are called selenites. These include silver selenite (Ag2SeO3) and sodium selenite (Na2SeO3).

Hydrogen sulfide reacts with aqueous selenous acid to produce selenium disulfide:

H2SeO3 + 2 H2S ? SeS2 + 3 H2O

Selenium disulfide consists of 8-membered rings of a nearly statistical distribution of sulfur and selenium atoms.Sony VAIO VPC-P113KX/D Battery

It has an approximate composition of SeS2, with individual rings varying in composition, such as Se4S4 and Se2S6. Selenium disulfide has been use in shampoo as an anti-dandruff agent, an inhibitor in polymer chemistry, a glass dye, and a reducing agent in fireworks.Sony VAIO VPCP113KX/G Battery

Selenium trioxide may be synthesized by dehydrating selenic acid, H2SeO4, which is itself produced by the oxidation of selenium dioxide with hydrogen peroxide:

SeO2 + H2O2 ? H2SeO4

Hot, concentrated selenic acid is capable of dissolving gold, forming gold(III) selenate.Sony VAIO VPC-P113KX/G Battery

Halogen compounds

Iodides of selenium are not well known. The only stable chloride is Se2Cl2; the corresponding bromide is also known. These species are structurally analogous to the corresponding disulfur dichloride. Selenium dichloride is an important reagent in the preparation of selenium compounds (e.g. the preparation of Se7).Sony VAIO VPCP113KX/P Battery

It is prepared by treating selenium with SO2Cl2. Selenium reacts with fluorine to form selenium hexafluoride:

Se8 + 24 F2 ? 8 SeF6

In comparison with its sulfur counterpart (sulfur hexafluoride), SeF6 is more reactive and is toxic pulmonary irritant. Some of the selenium oxyhalides, such asSeOF2 and selenium oxychloride have been used as specialty solvents.Sony VAIO VPC-P113KX/P Battery

Selenides

Analogous to the behavior of other chalcogens, selenium forms a dihydride H2Se. It is a strongly odiferous, toxic, and colourless gas. It is more acidic than H2S. In solution it ionizes to HSe-. The selenide dianion Se2- forms a variety of compounds, including the minerals from which selenium is obtained commercially.Sony VAIO VPCP113KX/W Battery

Illustrative selenides include mercury selenide (HgSe), lead selenide (PbSe), zinc selenide (ZnSe), and copper indium gallium diselenide (Cu(Ga,In)Se2). These materials are semiconductors. With highly electropositive metals, such as aluminium, these selenides are prone to hydrolysis:Sony VAIO VPC-P113KX/W Battery

Al2Se3 + 6 H2O ? 8 Al2O3 + H2Se

Alkali metal selenides react with selenium to form polyselenides, Sex2-, which exist as chains.

Other compounds

Tetraselenium tetranitride, Se4N4, is an explosive orange compound analogous to S4N4. It can be synthesized by the reaction of SeCl4 with[((CH3)3Si)2N]2Se.Sony VAIO VPC-P114KX/B Battery

Selenium reacts with cyanides to yield selenocyanates:

8 KCN + Se8 ? 8 KSeCN

Organoselenium compounds

Selenium, especially in the II oxidation state, forms stable bonds to carbon.Sony VAIO VPC-P114KX/D Battery

Typical compounds include selenols with the formula RSeH (e.g., benzeneselenol), selenides with the formula RSeR (e.g., diphenylselenide), and diselenides, with the formula RSeSeR (e.g., diphenyldiselenide). Selenoxides, with the formula RSe(O)R, and selenyl chlorides, with the formula RSeCl, are useful intermediates in organic chemistry.Sony VAIO VPC-P114KX/G Battery

History and global demand

Selenium (Greek ?????? selene meaning "Moon") was discovered in 1817 by Jöns Jakob Berzelius, who found the element associated with tellurium (named for the Earth). It was discovered as a byproduct of sulfuric acid production.Sony VAIO VPC-P114KX/P Battery

It came to medical notice later because of its toxicity to humans working in industry. It was also recognized as an important veterinary toxin, seen in animals eating high-selenium plants. In 1954, the first hints of specific biological functions of selenium were discovered in microorganisms.Sony VAIO VPC-P114KX/W Battery

Its essentiality for mammalian life was discovered in 1957. In the 1970s, it was shown to be present in two independent sets of enzymes. This was followed by the discovery of selenocysteine in proteins. During the 1980s, it was shown that selenocysteine is encoded by the codon TGA.Sony VAIO VPCP115JC Battery

The recoding mechanism was worked out first in bacteria and then in mammals(see SECIS element).

Health effects and nutrition

Although it is toxic in large doses, selenium is an essential micronutrient for animals.Sony VAIO VPCP115JC/B Battery

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). See more on plant nutrition below.Sony VAIO VPCP115JC/D Battery

Selenium is a component of the unusual amino acids selenocysteine and selenomethionine. In humans, selenium is a trace element nutrient that functions as cofactor for reduction of antioxidant enzymes, such as glutathione peroxidases and certain forms of thioredoxin reductase found in animals and some plantsSony VAIO VPCP115JC/G Battery

(this enzyme occurs in all living organisms, but not all forms of it in plants require selenium).

The glutathione peroxidase family of enzymes (GSH-Px) catalyze certain reactions that remove reactive oxygen species such as hydrogen peroxide and organic hydroperoxides:Sony VAIO VPCP115JC/P Battery

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

Selenium also plays a role in the functioning of the thyroid gland and in every cell that uses thyroid hormone, by participating as a cofactor for the three known thyroid hormone deiodinases, which activate and then deactivate various thyroid hormones and their metabolites.Sony VAIO VPCP115JC/W Battery

It may inhibitHashimotos's disease, in which the body's own thyroid cells are attacked as alien. A reduction of 21% on TPO antibodies was reported with the dietary intake of 0.2 mg of selenium.

Dietary sources of Se

Dietary selenium comes from nuts, cereals, meat, mushrooms, fish, and eggs.Sony VAIO VPCP115KG Battery

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). In descending order of concentration, high levels are also found in kidney, tuna,crab, and lobster.Sony VAIO VPCP116KG Battery

The human body's content of selenium is believed to be in the 13–20 milligram range.

Indicator plants

Certain species of plants are considered indicators of high selenium content of the soil, since they require high levels of selenium to thrive. The main selenium indicator plants are Astragalus species (including some locoweeds), prince's plume (Stanleya sp.), woody asters (Xylorhiza sp.), and false goldenweed (Oonopsissp.)Sony VAIO VPC-P116KX/B Battery

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. This 400 microgram (µg) Tolerable Upper Intake Level is based primarily on a 1986 study of five Chinese patients who exhibited overt signs of selenosis and a follow up study on the same five people in 1992.Sony VAIO VPC-P116KX/D Battery

The 1992 study actually found the maximum safe dietary Se intake to be approximately 800 micrograms per day (15 micrograms per kilogram body weight), but suggested 400 micrograms per day to not only avoid toxicity, but also to avoid creating an imbalance of nutrients in the diet and to account for data from other countries.Sony VAIO VPC-P116KX/G Battery

In China, people who ingested corn grown in extremely selenium-rich stony coal (carbonaceous shale) have suffered from selenium toxicity. This coal was shown to have selenium content as high as 9.1%, the highest concentration in coal ever recorded in literature.Sony VAIO VPC-P116KX/P Battery

Symptoms of selenosis include a garlic odor 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.Sony VAIO VPC-P116KX/W Battery

Elemental selenium and most metallic selenides have relatively low toxicities because of their low bioavailability. By contrast, selenates and selenites are very toxic, having an oxidant mode of action similar to that of arsenic trioxide. The chronic toxic dose of selenite for humans is about 2400 to 3000 micrograms of selenium per day for a long time.Sony VAIO VPCP118JC Battery

Hydrogen selenide is an extremely toxic, corrosive gas. Selenium also occurs in organic compounds, such as dimethyl selenide, selenomethionine, selenocysteine and methylselenocysteine, all of which have high bioavailability and are toxic in large doses.Sony VAIO VPCP118JC/B Battery

On 19 April 2009, twenty-one polo ponies began to die shortly before a match in the United States Polo Open. Three days later, a pharmacy released a statement explaining that the horses had received an incorrect dose of one of the ingredients used in a vitamin/mineral supplement compound, with which the horses had been injected.Sony VAIO VPCP118JC/P Battery

Such nutrient injections are common to promote recovery after a match, but this mixture had been compounded by a compounding pharmacy not familiar with it. Analysis of blood levels of inorganic compounds in the supplement indicated the selenium concentrations were ten to fifteen times higher than normal in the horses'blood samples, and 15 to 20 times higher than normal in their liver samples.Sony VAIO VPCP118JC/W Battery

It was later confirmed that selenium was the ingredient in question. Selenium is active in only tiny amounts, and has a history of causing accidental poisonings in supplements when the dose that is supposed to be in micrograms is given by mistake in milligrams (1000 times as much).Sony VAIO VPC-P118KX/B Battery

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 the water evaporates.Sony VAIO VPC-P118KX/D Battery

High selenium levels produced in this fashion have been found to have caused certain congenital disorders in wetland birds.

Deficiency

Selenium deficiency is rare in healthy, well-nourished individuals. It can occur in patients with severely compromised intestinal function, those undergoing total parenteral nutrition, and in those of advanced age (over 90).Sony VAIO VPC-P118KX/G Battery

Also, people dependent on food grown from selenium-deficient soil are at risk. Although New Zealandhas low levels of selenium in its soil, adverse health effects have not been detected.

Selenium deficiency may only occur when a low selenium status is linked with an additional stress, such as chemical exposure or increased oxidant stress due to vitamin E deficiency.Sony VAIO VPC-P118KX/P Battery

There are interactions between selenium and other nutrients, such as iodine and vitamin E. The interaction is observed in the etiology of many deficiency diseases in animals and pure selenium deficiency is rare. The effect of selenium deficiency on health remains uncertain, particularly in relation to Kashin-Beck disease.Sony VAIO VPC-P118KX/W Battery

Controversial health effects

Several studies have suggested a possible link between cancer and selenium deficiency. One study, known as the NPC, was conducted to test the effect of selenium supplementation on the recurrence of skin cancers on selenium-deficient men.Sony VAIO VPCP119JC Battery

It did not demonstrate a reduced rate of recurrence of skin cancers, but did show a reduced occurrence of total cancers, particularly for lung, colorectal and prostate cancers (Relative Risk 0.63). There was also a significant reduction in total cancer mortality (?50 %), although without a statistically significant change in overall mortality.Sony VAIO VPCP119JC/BI Battery

The preventative effect observed in the NPC was greatest in those with the lowest baseline selenium levels.[49] In 2009, the 5.5 year SELECT study reported selenium and vitamin E supplementation, both alone and together, did not significantly reduce the incidence of prostate cancer in 35,000 men who "generally were replete in selenium at baseline".Sony VAIO VPCP11S1E/B Battery

The SELECT trial reported vitamin E did not reduce prostate cancer as it had in the alpha-tocopherol, beta carotene (ATBC) study, but the ATBC had a large percentage of smokers, while the SELECT trial did not. There was a slight trend toward more prostate cancer in the SELECT trial, but in the vitamin E only arm of the trial, where no selenium was given.Sony VAIO VPC-P11S1E/B Battery

Dietary selenium prevents chemically induced carcinogenesis in many rodent studies. It has been proposed that selenium may help prevent cancer by acting as anantioxidant or by enhancing immune activity. Not all studies agree on the cancer-fighting effects of selenium.Sony VAIO VPCP11S1E/D Battery

One study of naturally occurring levels of selenium in over 60,000 participants did not show a significant correlation between those levels and cancer. The SU.VI.MAX study concluded low-dose supplementation (with 120 mg of ascorbic acid, 30 mg of vitamin E,Sony VAIO VPC-P11S1E/D Battery

6 mg of beta carotene, 100 µg of selenium, and 20 mg of zinc) resulted in a 30% 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.A Cochrane review of studies concluded that there is no convincing evidence that individuals,Sony VAIO VPCP11S1E/G Battery

particularly those who are adequately nourished, will benefit from selenium supplementation with regard to their cancer risk.However, there is evidence selenium can 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.Sony VAIO VPC-P11S1E/G Battery

Studies of cancer cells in vitro showed that chemotherapeutic drugs, such as taxol andAdriamycin, were more toxic to strains of cancer cells when selenium was added.

In March 2009, vitamin E (400 IU) and selenium (200 micrograms) supplements were reported to affect gene expression and can act as a tumor suppressor.Sony VAIO VPCP11S1E/P Battery

Eric Klein, MD from the Glickman Urological and Kidney Institute in Ohio said the new study “lend[s] credence to the previous evidence that selenium and vitamin E might be active as cancer preventatives”. In an attempt to rationalize the differences between epidemiological and in vitro studies and randomized trials like SELECT,Sony VAIO VPCP11S1E/W Battery

Klein said randomized controlled trials “do not always validate what we believe biology indicates and that our model systems are imperfect measures of clinical outcomes in the real world”.

HIV/AIDS

Some research has indicated a geographical link between regions of selenium-deficient soils and peak incidences of HIV/AIDS infection.Sony VAIO VPC-P11S1E/W Battery

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.Sony VAIO VPCP11Z9E/B Battery

Whether this decline in selenium levels is a direct result of the replication of HIV or related more generally to the overall malabsorption of nutrients by AIDS patients remains debated.

Low selenium levels in AIDS patients have been directly correlated with decreased immune cell count and increased disease progression and risk of death.Sony VAIO VPCS111FM/S Battery

Selenium normally acts as an antioxidant, so low levels of it may increase oxidative stress on the immune system, leading to its more rapid decline. Others have argued T-cell-associated genes encode selenoproteins similar to human glutathione peroxidase. Depleted selenium levels in turn lead to a decline in CD4 helper T-cells, further weakening the immune system.Sony VAIO VPCS115EC Battery

Regardless of the cause of depleted selenium levels in AIDS patients, studies have shown selenium deficiency does strongly correlate with the progression of the disease and the risk of death.

Tuberculosis

Some research has suggested selenium supplementation, along with other nutrients, can help prevent the recurrence of tuberculosis.Sony VAIO VPCS115FG Battery

Diabetes

A well-controlled study showed selenium levels are positively correlated with the risk of having type 2 diabetes. Because high serum selenium levels are positively associated with the prevalence of diabetes, and because selenium deficiency is rare, supplementation is not recommended in well-nourished populations, such as the U.S.Sony VAIO VPCS117GG Battery

More recent studies, however, have indicated selenium may help inhibit the development of type 2 diabetes in men, though the mechanism for the possible preventative effect is not known.

Applications

The demand for Se was around 2300 tonnes/y in the years 1989–1991.Sony VAIO VPCS117GGB Battery

Glass production

The largest commercial use of Se, accounting for about 50% of consumption, is for the production of glass. Se compounds confer a red colour to glass. This colour cancels out the green or yellow tints that arise from iron impurities that are typical for most glass.Sony VAIO VPCS118EC Battery

For this purpose various salts of selenite and selenate are added. For other application, the red colour is desirable, in which case mixtures of CdSe and CdS are added.

Rubber industry

Small amounts of organoselenium compounds are used to modify the vulcanization catalysts used in the production of rubber.Sony VAIO VPCS119FJ/B Battery

Uses in the laboratory

Selenium is a catalyst in some chemical reactions but it is not widely used because of issues with toxicity. In X-ray crystallography, incorporation of one or more Se atoms helps with MAD and SAD phasing.

Alloys

Selenium is used with bismuth in brasses to replace more toxic lead.Sony VAIO VPCS119GC Battery

Electronics

The demand for Se by the electronics industry is declining, despite a number of continuing applications. Because of its photovoltaic and photoconductiveproperties, selenium is used in photocopying, photocells, light meters and solar cells.Sony VAIO VPCS11AFJ Battery

Its use as a photoconductor in plain-paper copiers once was a leading application but in the 1980s, the photoconductor application declined (although it was still a large end-use) as more and more copiers switched to the use of organic photoconductors. It was once widely used in selenium rectifiers.Sony VAIO VPCS11AGJ Battery

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 thanmetal oxide varistors.Sony VAIO VPCS11AHJ Battery

Sheets of amorphous selenium convert x-ray images to patterns of charge in xeroradiography and in solid-state, flat-panel x-ray cameras.

Zinc selenide is used in blue and white LEDs.Sony VAIO VPCS11AVJ Battery

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.Sony VAIO VPCS11J7E/B Battery

Early photographic light meters used selenium, but this application is now obsolete.

Biological role

The substance loosely called selenium sulfide (approximate formula SeS2) is the active ingredient in some anti-dandruff shampoos.Sony VAIO VPCS11M1E/W Battery

The selenium compound kills the scalp fungus Malassezia, which causes shedding of dry skin fragments. The ingredient is also used in body lotions to treat Tinea versicolor due to infection by a different species of Malassezia fungus.

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.Sony VAIO VPCS11V9E Battery

Detection in biological fluids

Selenium may be measured in blood, plasma, serum or urine to monitor excessive environmental or occupational exposure, confirm a diagnosis of poisoning in hospitalized victims or to assist in a forensic investigation in a case of fatal overdosage. Sony VAIO VPCS11V9E/B Battery

Some analytical techniques are capable of distinguishing organic from inorganic forms of the element. Both organic and inorganic forms of selenium are largely converted to monosaccharide conjugates (selenosugars) in the body prior to being eliminated in the urine.Sony VAIO VPCS11X9E/B Battery

Cancer patients receiving daily oral doses of selenothionine may achieve very high plasma and urine selenium concentrations.

Evolution in biology

Over three billion years ago, blue-green algae were the most primitive oxygenic photosynthetic organisms and are ancestors of multicellular eukaryotic algae.Sony VAIO VPCS123FGB Battery

Algae that contain the highest amount of antioxidant selenium, iodide, and peroxidase enzymes were the first living cells to produce poisonous oxygen in the atmosphere. It has been suggested that algal cells required a protective antioxidant action, in which selenium and iodides, through peroxidase enzymes, have had this specific role.Sony VAIO VPCS125EC Battery

Selenium, which acts synergistically with iodine, is a primitive mineral antioxidant, greatly present in the sea and prokaryotic cells, where it is an essential component of the family of glutathione peroxidase (GSH-Px) antioxidant enzymes; seaweeds accumulate high quantity of selenium and iodine.Sony VAIO VPCS128EC Battery

In 2008, a study showed that iodide also scavenges reactive oxygen species (ROS) in algae, and that its biological role is that of an inorganic antioxidant, the first to be described in a living system, active also in an in vitro assay with the blood cells of today’s humans."Sony VAIO VPCS129GC Battery

From about three billion years ago, prokaryotic selenoprotein families drive selenocysteine evolution. Selenium is incorporated into several prokaryotic selenoprotein families in bacteria, archaea and eukaryotes as selenocysteine, where selenoprotein peroxiredoxins protect bacterial and eukaryotic cells against oxidative damage.Sony VAIO VPCS12C7E/B Battery

Selenoprotein families of GSH-Px and the deiodinases of eukaryotic cells seem to have a bacterial phylogenetic origin. The selenocysteine-containing form occurs in species as diverse as green algae, diatoms, sea urchin, fish and chicken. Selenium enzymes are involved in utilization of the small reducing molecules glutathione and thioredoxin.Sony VAIO VPCS12L9E/B Battery

One family of selenium-containing molecules (the glutathione peroxidases) destroy peroxide and repair damaged peroxidized cell membranes, using glutathione. Another selenium-containing enzyme in some plants and in animals (thioredoxin reductase) generates reduced thioredoxin,Sony VAIO VPCS12V9E/B Battery

a dithiol that serves as an electron source for peroxidases and also the important reducing enzyme ribonucleotide reductase that makes DNA presursors from RNA precursors.

At about 500 Mya, plants and animals began to transfer from the sea to rivers and land, the environmental deficiency of marine mineral antioxidants (as selenium, iodine, etc.)Sony VAIO VPCW111XX/P Battery

was a challenge to the evolution of terrestrial life.[75] Trace elements involved in GSH-Px and superoxide dismutase enzymes activities, i.e. selenium,vanadium, magnesium, copper, and zinc, may have been lacking in some terrestrial mineral-deficient areas.Sony VAIO VPCW111XX/PC Battery

Marine organisms retained and sometimes expanded their seleno-proteomes, whereas the seleno-proteomes of some terrestrial organisms were reduced or completely lost. These findings suggest that, with the exception ofvertebrates, aquatic life supports selenium utilization, whereas terrestrial habitats lead to reduced use of this trace element.Sony VAIO VPCW111XX/T Battery

Marine fishes and vertebrate thyroid glands have the highest concentration of selenium and iodine. From about 500 Mya, freshwater and terrestrial plants slowly optimized the production of “new” endogenous antioxidants such as ascorbic acid (Vitamin C), polyphenols (including flavonoids), tocopherols, etc.Sony VAIO VPCW111XX/W Battery

A few of these appeared more recently, in the last 50–200 million years, in fruits and flowers of angiosperm plants. In fact, the angiosperms (the dominant type of plant today) and most of their antioxidant pigments evolved during the late Jurassic period.Sony VAIO VPCW111XXP Battery

The deiodinase isoenzymes constitute another family of eukaryotic selenoproteins with identified enzyme function. Deiodinases are able to extract electrons from iodides, and iodides from iodothyronines. They are, thus, involved in thyroid-hormone regulation, participating in the protection of thyrocytes from damage by H2O2produced for thyroid-hormone biosynthesis.Sony VAIO VPCW111XXT Battery

About 200 Mya, new selenoproteins were developed as mammalian GSH-Px enzymes.

Bromine is achemical element with the symbol Br, an atomic number of 35, and an atomic mass of 79.904. It is in the halogen element group.Sony VAIO VPCW111XXW Battery

The element was isolated independently by two chemists, Carl Jacob Löwig and Antoine Jerome Balard, in 1825–1826. Elemental bromine is a fuming red-brown liquid at room temperature, corrosive and toxic, with properties between those ofchlorine and iodine.Sony VAIO VPCW115XG Battery

Free bromine does not occur in nature, but occurs as colorless soluble crystalline mineral halide salts, analogous to table salt.

Bromine is rarer than about three-quarters of elements in the Earth's crust, however the high solubility of bromide ion has caused its accumulation in the oceans,Sony VAIO VPCW115XGP Battery

and commercially the element is easily extracted from brine pools, mostly in the United States, Israel and China. About 556,000 tonnes were produced in 2007, an amount similar to the far more abundant element magnesium.

At high temperatures, organobromine compounds are easily converted to free bromine atoms, a process which acts to terminatefree radical chemical chain reactions.Sony VAIO VPCW115XW/P Battery

This makes such compounds useful fire retardants and this is bromine's primary industrial use, consuming more than half of world production of the element. The same property allows volatile organobromine compounds, under the action of sunlight, to form free bromine atoms in the atmosphere which are highly effective in ozone depletion.Sony VAIO VPCW115XW/T Battery

This unwanted side-effect has caused many common volatile brominated organics like methyl bromide, a pesticide that was formerly a large industrial bromine consumer, to be abandoned. Remaining uses of bromine compounds are in well-drilling fluids, as an intermediate in manufacture of organic chemicals, and in film photography.Sony VAIO VPCW115XW/W Battery

Bromine has no essential function in mammals, though it is preferentially used over chloride by one antiparasitic enzyme in the human immune system. Organobromides are needed and produced enzymatically from bromide by some lower life forms in the sea, particularly algae, and the ash of seaweed was one source of bromine's discovery.Sony VAIO VPCW117XC/P Battery

As a pharmaceutical, simple bromide ion, Br–, has inhibitory effects on the central nervous system, and bromide salts were once a major medical sedative, before being replaced by shorter-acting drugs. They retain niche uses as antiepileptics.

Physical

Elemental bromine exists as a diatomic molecule, Br2.Sony VAIO VPCW117XC/T Battery

It is a dense, mobile, slightly transparent reddish-brown liquid, that evaporates easily at standard temperature and pressures to give an orange vapor (its color resembles nitrogen dioxide) that has a strongly disagreeable odor resembling that of chlorine. It is one of only two elements on the periodic table that are liquids at room temperature (mercury is the other, althoughcaesium, gallium, and rubidium melt just above room temperature).Sony VAIO VPCW117XC/W Battery

At a pressure of 55 GPa bromine converts to a metal. At 75 GPa it converts to a face centered orthorhombic structure. At 100 GPa it converts to a body centered orthorhombic monoatomic form.Sony VAIO VPCW119XJ Battery

Chemical

Being less reactive than chlorine but more reactive than iodine, bromine reacts vigorously with metals, especially in the presence of water, to give bromide salts. It is also reactive toward most organic compounds, especially upon illumination, conditions that favor the dissociation of the diatomic molecule into bromine radicals:Sony VAIO VPCW119XJ/P Battery

Br2 2 Br·

It bonds easily with many elements and has a strong bleaching action.

Bromine is slightly soluble in water, but it is highly soluble in organic solvents such as carbon disulfide, carbon tetrachloride, aliphatic alcohols, and acetic acid.Sony VAIO VPCW119XJ/W Battery

Bromine has two stable isotopes, 79Br (50.69 %) and 81Br (49.31%). At least 23 other radioisotopes are known. Many of the bromine isotopes are fission products. Several of the heavier bromine isotopes from fission are delayed neutron emitters. All of the radioactive bromine isotopes are relatively short lived.Sony VAIO VPCW11AXJ Battery

The longest half-life is the neutron deficient 77Br at 2.376 days. The longest half-life on the neutron rich side is 82Br at 1.471 days. A number of the bromine isotopes exhibit metastable isomers. Stable 79Br exhibits a radioactive isomer, with a half-life of 4.86 seconds. It decays by isomeric transition to the stable ground state.Sony VAIO VPCW11S1E/P Battery

Bromine was discovered independently by two chemists, Carl Jacob Löwig and Antoine Balard, in 1825 and 1826, respectively.

Balard found bromide chemicals in the ash of seaweed from the salt marshes of Montpellier. The seaweed was used to produce iodine, but also contained bromine.Sony VAIO VPCW11S1E/T Battery

Balard distilled the bromine from a solution of seaweed ash saturated with chlorine. The properties of the resulting substance resembled that of an intermediate of chlorine and iodine; with those results he tried to prove that the substance was iodine monochloride (ICl),Sony VAIO VPCW11S1E/W Battery

but after failing to do so he was sure that he had found a new element and named it muride, derived from the Latin word muria for brine.

Löwig isolated bromine from a mineral water spring from his hometown Bad Kreuznach in 1825.Sony VAIO VPCW121AX Battery

Löwig used a solution of the mineral salt saturated with chlorine and extracted the bromine with diethyl ether. After evaporation of the ether a brown liquid remained. With this liquid as a sample for his work he applied for a position in the laboratory of Leopold Gmelin inHeidelberg. The publication of the results was delayed and Balard published his results first.Sony VAIO VPCW126AG Battery

After the French chemists Louis Nicolas Vauquelin, Louis Jacques Thénard, and Joseph-Louis Gay-Lussac approved the experiments of the young pharmacist Balard, the results were presented at a lecture of the Académie des Sciences and published in Annales de Chimie et Physique.Sony VAIO VPCW127JC/P Battery

In his publication Balard states that he changed the name from muride to brômeon the proposal of M. Anglada. (Brôme (bromine) derives from the Greek ?????? (stench). ) Other sources claim that the French chemist and physicist Joseph-Louis Gay-Lussac suggested the name brôme for the characteristic smell of the vapors.Sony VAIO VPCW127JC/T Battery

Bromine was not produced in large quantities until 1860.

The first commercial use, besides some minor medical applications, was the use of bromine for the daguerreotype. In 1840 it was discovered that bromine had some advantages over the previously used iodine vapor to create the light sensitive silver halide layer used for daguerreotypy.Sony VAIO VPCW127JC/W Battery

Potassium bromide and sodium bromide were used as anticonvulsants and sedatives in the late 19th and early 20th centuries, until they were gradually superseded bychloral hydrate and then the barbiturates.

The diatomic element Br2 does not occur naturally. Instead, bromine exists exclusively asbromide salts in diffuse amounts in crustal rock.Sony VAIO VPCW127JC/WZ Battery

Owing to leaching, bromide salts have accumulated in sea water at 65 part per million (ppm), which is less than chloride. Bromine may be economically recovered from bromide-rich brine wells and from the Dead Seawaters (up to 50,000 ppm). It exists in the Earth's crust at an average concentration of 0.4 ppm, making it the 62nd most abundant element.Sony VAIO VPCW12AAJ Battery

The bromine concentration in soils varies normally between 5 and 40 ppm, but some volcanic soils can contain up to 500 ppm. The concentration of bromine in the atmosphere is extremely low, at only a few ppt. A large number of organobromine compounds are found in small amounts in nature.Sony VAIO VPCW12AKJ Battery

China's bromine reserves are located in the Shandong Province and Israel's bromine reserves are contained in the waters of the Dead Sea. The largest bromine reserve in the United States is located in Columbia County and Union County, Arkansas, U.S.Sony VAIO VPCW12AVJ Battery

Production

Bromine production is rather dynamic and has increased sixfold since the 1960s. Approximately 556,000 tonnes (worth around US $2.5 billion) was produced in 2007 worldwide, with the predominant contribution from the United States (226,000 t) and Israel(210,000 t).Sony VAIO VPCW12S1E/P Battery

US production was excluded from the United States Geological Survey after 2007, and from the 380,000 tonnes mined by other countries in 2010, 140,000 t were produced by China, 130,000 t by Israel and 80,000 t by Jordan.

Bromide-rich brines are treated with chlorine gas, flushing through with air. In this treatment, bromide anions are oxidized to bromine by the chlorine gas.Sony VAIO VPCW12S1E/T Battery

2 Br? + Cl2 ? 2 Cl? + Br2

Laboratory methods of production

In the laboratory, because of its commercial availability and long shelf-life, bromine is not typically prepared. Small amounts of bromine can however be generated through the reaction of solid sodium bromide with concentrated sulfuric acid (H2SO4).Sony VAIO VPCW12S1E/W Battery

The first stage is formation of hydrogen bromide (HBr), which is a gas, but under the reaction conditions some of the HBr is oxidized further by the sulfuric acid to form bromine (Br2) and sulfur dioxide (SO2).

NaBr (s) + H2SO4 (aq) ? HBr (aq) + NaHSO4 (aq)

2 HBr (aq) + H2SO4 (aq) ? Br2 (g) + SO2 (g) + 2 H2O (l)Sony VAIO VPCW213AG/L Battery

Non oxidizing acid alternatives, such as the use of dilute hydrobromic acid with sodium hypobromite, are also available, as the hypobromous acid formed from them is unstable in the presence of bromide, being reduced by it according to the reaction:

2 OBr- (aq) + 4 HBr (aq) ? 2Br2 + 2H2O + 2Br- Sony VAIO VPCW213AG/P Battery

The reactions are the reverse of disproportionation reactions of elemental bromine in base, and are called comproportionation. A similar reaction happens with sodium hypochlorite, acid, and chloride, leading to elemental chlorine.Sony VAIO VPCW213AG/T Battery

Reactions involving an oxidizing agent, such as potassium permanganate or manganese dioxide, on bromide ions in the presence of an acid, also give bromine in the reactions analogous to the formation of elemental chlorine and iodine from an acid and oxidant.Sony VAIO VPCW213AG/W Battery

Like iodine, bromine is soluble in chloroform but only slightly soluble in water. In water, the solubility can be increased by the presence of bromide ions. Concentrated solutions of bromine are rarely prepared in the lab because of hazards.Sony VAIO VPCW215AG/L Battery

As is the case with chlorine solutions or iodine solutions, sodium thiosulphate(or any soluble thiosulphate) is an effective reagent for reducing bromine to colorless odorless bromide, thus dealing with stains and odor from the element in unwanted places. For the same reason, thiosulfate ("fixer's hypo") is used in photography to deal with free bromine in silver bromide film emulsions.Sony VAIO VPCW217JC Battery

Organic compounds are brominated by either addition or substitution reactions. Bromine undergoes electrophilic addition to the double-bonds of alkenes, via a cyclic bromonium intermediate. In non-aqueous solvents such as carbon disulfide, this yields the di-bromo product.Sony VAIO VPCW217JC/L Battery

For example, reaction with ethylene will produce 1,2-dibromoethane. Bromine also undergoes electrophilic addition to phenols and anilines. When used as bromine water, a small amount of the corresponding bromohydrin is formed as well as the dibromo compound.Sony VAIO VPCW217JC/P Battery

So reliable is the reactivity of bromine that bromine water is employed as a reagent to test for the presence of alkenes, phenols, and anilines. Like the other halogens, bromine participates in free radical reactions. For example, hydrocarbons are brominated upon treatment with bromine in the presence of light.Sony VAIO VPCW217JC/T Battery

Bromine, sometimes with a catalytic amount of phosphorus, easily brominates carboxylic acids at the ?-position. This method, the Hell-Volhard-Zelinsky reaction, is the basis of the commercial route to bromoacetic acid. N-Bromosuccinimide is commonly used as a substitute for elemental bromine, being easier to handle, and reacting more mildly and thus more selectively.Sony VAIO VPCW217JC/W Battery

Organic bromides are often preferable relative to the less reactive chlorides and more expensive iodide-containing reagents. Thus, Grignard and organolithium compound are most often generated from the corresponding bromides.Sony VAIO VPCW218JC Battery

Certain bromine-related compounds have been evaluated to have an ozone depletion potential or bioaccumulate in living organisms. As a result, many industrial bromine compounds are no longer manufactured, are being restricted, or scheduled for phasing out.Sony VAIO VPCW218JC/L Battery

The Montreal Protocol mentions several organobromine compounds for this phase out.

Inorganic chemistry

Inorganic bromine compounds adopt a variety of oxidation states from ?1 to +7.

Bromine is an oxidizer, and it will oxidize iodide ions to iodine, being itself reduced to bromide:Sony VAIO VPCW218JC/P Battery

Br2 + 2 I? ? 2 Br? + I2

Bromine will also oxidize metals and metalloids to the corresponding bromides. Anhydrous bromine is less reactive toward many metals than hydrated bromine, however. Dry bromine reacts vigorously with aluminium, titanium, mercury as well as alkaline earths and alkali metals.Sony VAIO VPCW218JC/T Battery

Dissolving bromine in alkaline solution gives a mixture of bromide and hypobromite:

Br2 + 2 OH? ? Br? + OBr? + H2O

This hypobromite is responsible for the bleaching abilities of bromide solutions. Warming of these solutions causes the disproportion reaction of the hypobromite to give bromate, a strong oxidising agent very similar to chlorate.Sony VAIO VPCW218JC/W Battery

3 BrO? ? BrO?3 + 2 Br?

In contrast to the route to perchlorates, perbromates are not accessible through electrolysis but only by reacting bromate solutions withfluorine or ozone.

BrO3? + H2O + F2 ? BrO?4 + 2 HF ,BrO3? + O3 ? BrO?4 + O2

Bromine reacts violently and explosively with aluminium metal, forming aluminium bromide:Sony VAIO VPCW219AJ/L Battery

2 Al + 3 Br2 ? 2 AlBr3

Bromine reacts with hydrogen in gaseous form and gives hydrogen bromide:

H2 + Br2 ? 2HBr

Bromine reacts with alkali metal iodides in a displacement reaction. This reaction forms alkali metal bromides and produces elemental iodine:Sony VAIO VPCW219AJ/P Battery

2 NaI + Br2 ? 2 NaBr + I2

2 KI + Br2 ? 2 KBr + I2

Applications

A wide variety of organobromine compounds are used in industry. Some are prepared from bromine and others are prepared from hydrogen bromide, which is obtained by burning hydrogen in bromine.Sony VAIO VPCW219AJ/W Battery

Illustrative of the addition reaction is the preparation of 1,2-dibromoethane, the organobromine compound produced in the largest amounts:

C2H4 + Br2 ? CH2BrCH2Br

Flame retardant

Brominated flame retardants represent a commodity of growing importance, and represent the largest use of bromine.Sony VAIO VPCW21AAJ Battery

When the brominated material burns, the flame retardant produces hydrobromic acid which interferes in the radical chain reaction of theoxidation reaction of the fire. The mechanism is that the highly reactive hydrogen oxygen and hydroxy radicals react with hydrobromic acid and form less reactive bromine radicals (free bromine atoms).Sony VAIO VPCW21AKJ Battery

These also react with radicals in the first to help terminate the reaction.

The bromine-containing compounds can be placed in the polymers either during polymerization if a small amount of brominated monomer is added or the bromine containing compound is added after polymerization.Sony VAIO VPCW21AVJ Battery

Tetrabromobisphenol A can be added to producepolyesters or epoxy resins. Epoxy used in printed circuit boards (PCB) are normally made from flame retardant resins, indicated by the FR in the abbreviation of the products (FR-4 and FR-2. Vinyl bromide can be used in the production of polyethylene,polyvinylchloride or polypropylene.Sony VAIO VPCY115FGS Battery

Decabromodiphenyl ether can be added to the final polymers.

Gasoline additive

Ethylene bromide was an additive in gasolines containing lead anti-engine knocking agents. It scavenges lead by forming volatile lead bromide, which is exhausted from the engine.Sony VAIO VPCY115FX/BI Battery

This application accounted for 77% of the bromine use in 1966 in the US. This application has declined since the 1970s due to environmental regulations (see below).

Pesticide

Poisonous methyl bromide was widely used as pesticide to fumigate soil and to fumagate housing, by the tenting method.Sony VAIO VPCY115FXBI Battery

Ethylene bromide was similarly used. These volatile organobromine compounds are all now regulated as ozone depletion agents. The Montreal Protocol on Substances that Deplete the Ozone scheduled the phase out for the ozone depleting chemical by 2005,Sony VAIO VPCY118EC Battery

and organobromide pesticides are no longer used (in housing fumagation they have been replaced by such compounds as sulfuryl fluoride, which contain neither the chlorine or bromine organics which harm ozone). Prior to the Montreal protocol in 1991 (for example) an estimated 35,000 tonnes of the chemical were used to control nematodes, fungi, weeds and other soil-borne diseases.Sony VAIO VPCY118GX/BI Battery

Medical and veterinary

Use. Bromide compounds, especially potassium bromide, were frequently used as general sedatives in the 19th and early 20th century. Bromides in the form of simple salts are still used as anticonvulsants in both veterinary and human medicine, although the latter use varies from country to country.Sony VAIO VPCY119FJ/S Battery

For example, the U.S. Food and Drug Administration (FDA) does not approve bromide for the treatment of any disease, and it was removed from over-the-counter sedative products like Bromo-Seltzer, in 1975. Thus, bromide levels are not routinely measured by medical laboratories in the U.S.Sony VAIO VPCY11AFJ Battery

However, U.S. veterinary medical diagnostic testing laboratories will measure blood bromide levels on request, as an aid to treatment of epilepsy in dogs.

Toxicity. Long-term use of potassium bromide (or any bromide salt) can lead to bromism.Sony VAIO VPCY11AGJ Battery

This state of central nervous system depression causes the moderate toxicity of bromide in multi-gram doses for humans and other mammals. The very long half-life of bromide ion in the body (~12 days) also contributes to toxicity from bromide build-up in body fluids. Bromide ingestion may also cause a skin eruption resembling acne.Sony VAIO VPCY11AHJ Battery

Other uses

• The bromides of calcium, sodium, and zinc account for a sizable part of the bromine market. These salts form dense solutions in water that are used as drilling fluids sometimes called clear brine fluids.Sony VAIO VPCY11AVJ Battery

• Bromine is also used in the production of brominated vegetable oil, which is used as an emulsifier in many citrus-flavored soft drinks (for example, Mountain Dew). After the introduction in the 1940s the compound was extensively used until the UK and the US limited its use in the mid 1970s and alternative emulsifiers were developed.Sony VAIO VPCY11M1E/S Battery

• Soft drinks containing brominated vegetable oil are still sold in the US (2011).
• Several dyes, agrichemicals, and pharmaceuticals are organobromine compounds. 1-Bromo-3-chloropropane, 1-bromoethylbenzene, and 1-bromoalkanes are prepared by the antimarkovnikov additionof HBr to alkenes. Ethidium bromide, EtBr, is used as a DNA stain in gel electrophoresis.Sony VAIO VPCY11S1E Battery

• High refractive index compounds
• Bromine, like chlorine, is used in maintenance of swimming pools, especially spas (hot tubs), where it is generated in situ from a bromide plus hydrogen peroxide. In spas, the high water temperatures render chlorinated water purification and buffering compounds unstable, and bromine compounds may improve the life of the free-halogen antimicrobial.Sony VAIO VPCY11V9E/S Battery
• Water purification compounds, disinfectants and insecticides, such as tralomethrin (C22H19Br4NO3).

• Potassium bromide is used in some photographic developers to inhibit the formation of fog (undesired reduction of silver).
• Bromine vapor is used as the second step in sensitizing daguerreotype plates to be developed under mercury vapor. Bromine acts as an accelerator to the light sensitivity of the previously iodized plate.Sony VAIO VPCY218EC/BI Battery

• Bromine is also used to reduce mercury pollution from coal-fired power plants. This can be achieved either by treating activated carbon with bromine or by injecting bromine compounds onto the coal prior to combustion.Sony VAIO VPCY218EC/G Battery

• Bromine can also be artificially substituted for the methyl substituent in the nitrogenous base thymine of DNA, creating the base analog 5-bromouracil. When this base is incorporated into DNA its different hydrogen bonding properties may cause mutation at the site of that base pair. The compound 5-bromouracil is thus an artificial mutagen.Sony VAIO VPCY218EC/L Battery

Biological role

Bromine has no known essential role in human or mammalian health, but inorganic bromine and organobromine compounds do occur naturally, and some may be of use to higher organisms in dealing with parasites.Sony VAIO VPCY218EC/P Battery

For example, in the presence of H2O2 formed by the eosinophil, and either chloride or bromide ions, eosinophil peroxidase provides a potent mechanism by which eosinophils kill multicellular parasites (such as, for example, the nematode worms involved in filariasis); and also certain bacteria (such as tuberculosis bacteria).Sony VAIO VPCY21S1E/L Battery

Eosinophil peroxidase is ahaloperoxidase that preferentially uses bromide over chloride for this purpose, generating hypobromite (hypobromous acid).

Marine organisms are the main source of organobromine compounds. Over 1600 compounds were identified by 1999. Sony VAIO VPCY21S1E/P Battery

The most abundant one ismethyl bromide (CH3Br) with an estimated 56,000 tonnes produced by marine algae each year. The essential oil of the Hawaiian algaAsparagopsis taxiformis consists of 80% methyl bromide. Most of such organobromine compounds in the sea are made via the action of a unique algal enzyme, vanadium bromoperoxidase.Sony VAIO VPCY21S1E/SI Battery

Though this enzyme is the most prolific creator of organic bromides by living organisms, other bromoperoxidases exist in nature that do not use vanadium.

A famous example of a bromine-containing organic compound that has been used by humans since ancient times is the fabric dye Tyrian purple.Sony VAIO VPCZ110 Battery

The brominated indole indigo dye is produced by a medium-sized predatory sea snail, the marine gastropod Murex brandaris. The organobromine nature of the compound was not discovered until 1909 (see Paul Friedländer).

Safety

Elemental bromine is toxic and causes burns.Sony VAIO VPCZ110GB/BI Battery

As an oxidizing agent, it is incompatible with most organic and inorganic compounds. Care needs to be taken when transporting bromine; it is commonly carried in steel tanks lined with lead, supported by strong metal frames.

When certain ionic compounds containing bromine are mixed with potassium permanganate (KMnO4) and an acidic substance, they will form a pale brown cloud of bromine gas.Sony VAIO VPCZ112GD/S Battery

6 Br– + 2 MnO4– + 8 H+ ? 3 Br2 + 2 MnO2 + 4 H2O

This gas smells like bleach and is very irritating to the mucous membranes. Upon exposure, one should move to fresh air immediately. If symptoms of bromine poisoning arise, medical attention is needed.Sony VAIO VPCZ112GX/S Battery

Krypton is a chemical element with the symbol Kr andatomic number 36. It is a member of Group 18 and Period 4 elements. A colorless, odorless, tasteless noble gas, krypton occurs in trace amounts in the atmosphere, is isolated by fractionally distilling liquified air, and is often used with other rare gases in fluorescent lamps. Krypton is inert for most practical purposes.Sony VAIO VPCZ114GX/S Battery

Krypton, like the other noble gases, can be used in lighting and photography. Krypton light has a large number of spectral lines, and krypton's high light output in plasmas allows it to play an important role in many high-powered gas lasers (krypton ion and eximer lasers), which pick out one of the many spectral lines to amplify.\Sony VAIO VPCZ115 Battery

There is also a specific krypton fluoride laser. The high power and relative ease of operation of krypton discharge tubes caused (from 1960 to 1983) the official length of a meter to be defined in terms of the orange spectral line of krypton-86.Sony VAIO VPCZ115FC/B Battery

Krypton was discovered in Britain in 1898 by Sir William Ramsay, a Scottish chemist, and Morris Travers, an English chemist, in residue left from evaporating nearly all components of liquid air.Neon was discovered by a similar procedure by the same workers just a few weeks later.Sony VAIO VPCZ115FC/S Battery

William Ramsay was awarded the 1904 Nobel Prize in Chemistry for discovery of a series of noble gases, including krypton.

In 1960, an international agreement defined the meter in terms of wavelength of light emitted by the krypton-86 isotope (wavelength of 605.78 nanometers).Sony VAIO VPCZ116 Battery

This agreement replaced the longstanding standard meter located in Paris, which was a metal bar made of a platinum-iridium alloy (the bar was originally estimated to be one ten-millionth of a quadrant of the earth's polar circumference), and was itself replaced by a definition based on the speed of light — a fundamental physical constant.Sony VAIO VPCZ116GX/S Battery

In October 1983, the Bureau International des Poids et Mesures(International Bureau of Weights and Measures) defined the meter as the distance that light travels in a vacuum during 1/299,792,458 s.

Characteristics

Krypton is characterized by several sharp emission lines (spectral signatures) the strongest being green and yellow.Sony VAIO VPCZ117 Battery

It is one of the products of uranium fission. Solidified krypton is white and crystalline with a face-centered cubic crystal structure, which is a common property of all noble gases (except helium, with a hexagonal close-packed crystal structure).

Naturally occurring krypton is made of six stable isotopes.Sony VAIO VPCZ117FC/B Battery

In addition, about thirty unstable isotopes and isomers are known. 81Kr, the product of atmospheric reactions, is produced with the other naturally occurring isotopes of krypton. Being radioactive, it has a half-life of 230,000 years. Krypton is highly volatile when it is near surface waters but 81Kr has been used for dating old (50,000–800,000 years) groundwater.Sony VAIO VPCZ118 Battery

85Kr is an inert radioactive noble gas with a half-life of 10.76 years. It is produced by the fission of uranium andplutonium, such as in nuclear bomb testing and nuclear reactors. 85Kr is released during the reprocessing of fuel rods from nuclear reactors. Concentrations at the North Pole are 30% higher than at the South Pole due to convective mixing.Sony VAIO VPCZ118GC/B Battery

Chemistry

Like the other noble gases, krypton is chemically unreactive. However, following the first successful synthesis of xenoncompounds in 1962, synthesis of krypton difluoride (KrF2) was reported in 1963. In the same year, KrF4 was reported by Grosse, et al., but was subsequently shown to be a mistaken identification.Sony VAIO VPCZ118GX/S Battery

There are also unverified reports of a barium salt of a krypton oxoacid. ArKr+ and KrH+ polyatomic ions have been investigated and there is evidence for KrXe or KrXe+.

Compounds with krypton bonded to atoms other than fluorine have also been discovered.Sony VAIO VPCZ119 Battery

The reaction of KrF2 with B(OTeF5)3produces an unstable compound, Kr(OTeF5)2, that contains a krypton-oxygen bond. A krypton-nitrogen bond is found in the cation [HC?N–Kr–F]+, produced by the reaction of KrF2 with [HC?NH]+[AsF?6] below ?50 °C.HKrCN and HKrC?CH (krypton hydride-cyanide and hydrokryptoacetylene) were reported to be stable up to 40 K.Sony VAIO VPCZ119FJ/S Battery

Natural occurrence

The Earth has retained all of the noble gases that were present at its formation except for helium. Krypton's concentration in the atmosphere is about 1 ppm. It can be extracted from liquid air by fractional distillation.Sony VAIO VPCZ119GC/X Battery

The amount of krypton in space is uncertain, as the amount is derived from the meteoric activity and that from solar winds. The first measurements suggest an overabundance of krypton in space.

Applications

Krypton's multiple emission lines make ionized krypton gas discharges appear whitish, which in turn makes krypton-based bulbs useful in photography as a brilliant white light source.Sony VAIO VPCZ119L Battery

Krypton is thus used in some types of photographic flashes used in high speedphotography. Krypton gas is also combined with other gases to make luminous signs that glow with a bright greenish-yellow light.

Krypton mixes with argon as the fill gas of energy saving fluorescent lamps. This reduces their power consumption.Sony VAIO VPCZ119R/B Battery

Unfortunately this also reduces their light output and raises their cost. Krypton costs about 100 times as much as argon. Krypton (along with xenon) is also used to fill incandescent lamps to reduce filament evaporation and allow higheroperating temperatures to be used for the filament.Sony VAIO VPCZ119R/S Battery

A brighter light results which contains more blue than conventional lamps.

Krypton's white discharge is often used to good effect in colored gas discharge tubes, which are then simply painted or stained in other ways to allow the desired color (for example, "neon" type advertising signs where the letters appear in differing colors are often entirely krypton-based).Sony VAIO VPCZ11AFJ Battery

Krypton is also capable of much higher light power density than neon in the red spectral line region, and for this reason, red lasers for high-power laser light-shows are often krypton lasers with mirrors which select out the red spectral line for laser amplification and emission,Sony VAIO VPCZ11AGJ Battery

rather than the more familiar helium-neon variety, which could never practically achieve the multi-watt red laser light outputs needed for this application.

Krypton has an important role in production and usage of the krypton fluoride laser.Sony VAIO VPCZ11AVJ Battery

The laser has been important in the nuclear fusion energy research community in confinement experiments. The laser has high beam uniformity, short wavelength, and the ability to modify the spot size to track an imploding pellet.

In experimental particle physics, liquid krypton is used to construct quasi-homogeneous electromagnetic calorimeters.Sony VAIO VPCZ11CGX/X Battery

A notable example is the calorimeter of the NA48 experiment at CERN containing about 27 tonnes of liquid krypton. This usage is rare, since the cheaper liquid argon is typically used. The advantage of krypton over argon is a small Molière radius of 4.7 cm, which allows for excellent spatial resolution and low degree of overlapping.Sony VAIO VPCZ11DGX/SJ Battery

The other parameters relevant for calorimetry application are: radiation length of X0=4.7 cm, density of 2.4 g/cm3.

The sealed spark gap assemblies contained in ignition exciters used in some older jet engines contain a very small amount of Krypton-85 to obtain consistent ionization levels and uniform operation.Sony VAIO VPCZ11FHX/XQ Battery

Krypton-83 has application in magnetic resonance imaging (MRI) for imaging airways. In particular, it may be used to distinguish between hydrophobic and hydrophilic surfaces containing an airway.

Although xenon has potential for use in computed tomography (CT) to assess regional ventilation, its anesthetic properties limit its fraction in the breathing gas to 35%.Sony VAIO VPCZ11V9R/B Battery

The use of a breathing mixture containing 30% xenon and 30% krypton is comparable in effectiveness for CT to a 40% xenon fraction, while avoiding the unwanted effects of a high fraction xenon gas.

Precautions

Krypton is considered to be a non-toxic asphyxiant.Sony VAIO VPCZ11X9E/B Battery

Krypton has a narcotic potency seven times greater than air, so breathing a gas containing 50% krypton and 50% air would cause narcosis similar to breathing air at four times atmospheric pressure. This would be comparable to scuba diving at a depth of 30 m (100 ft) (seenitrogen narcosis) and potentially could affect anyone breathing it.Sony VAIO VPCZ11Z9E/B Battery

Nevertheless, that mixture would contain only 10% oxygen and hypoxia would be a greater concern.Sony VAIO VPCZ125GX/S Battery,Sony VAIO VPCZ127FC Battery,Sony VAIO VPCZ128GC Battery,Sony VAIO VPCZ12M9E/B Battery,Sony VAIO VPCZ13M9E/B Battery,Sony VAIO VPCZ13V9E/X Battery,Sony VAIO VPCZ13Z9E/X Battery,Sony VAIO VPCZZZHJ Battery,Sony VAIO VPZ117 Battery,Sony VAIO VPZ118 Battery