What is chromium ?

Chromium

Chromium is a chemical element which has the symbol Cr and atomic number 24. It is a steely-gray, lustrous, hard metal that takes a high polish and has a high melting point. It is also odourless, tasteless, and malleable. The name of the element is derived from the Greek word “chr?ma”, meaning color, because many of its compounds are intensely colored. It was discovered by Louis Nicolas Vauquelin in the mineral crocoite (lead chromate) in 1797. Crocoite was used as a pigment, and after the discovery that the mineral chromite also contains chromium this latter mineral was used to produce pigments as well.

Chromium was regarded with great interest because of its high corrosion resistance and hardness. A major development was the discovery that steel could be made highly resistant to corrosion and discoloration by adding chromium and nickel to form stainless steel. This application and electroplating are currently the highest-volume uses of the metal. Chromium and ferrochromium are produced from the single commercially viable ore, chromite, by silicothermic or aluminothermic reaction or by roasting and leaching processes. Although trivalent chromium (Cr(III)) is required in trace amounts for sugar and lipid metabolism in humans and its deficiency may cause a disease called chromium deficiency, hexavalent chromium (Cr(VI)) is a toxin and a carcinogen, so that abandoned chromium production sites need environmental cleanup.

Occurrence

Chromium is the 21st most abundant element in Earth’s crust with an average concentration of 100 ppm. Chromium compounds are found in the environment, due to erosion of chromium containing rocks and can be distributed by volcanic eruptions. The concentrations range in soil is between 1 and 3000 mg/kg in sea water 5 to 800 µg/liter and in rivers and lakes 26 µg/liter to 5.2 mg/liter. The relation between Cr(III) and Cr(VI) is strongly depending on pH and oxidative properties of the location, but in most cases the Cr(III) is the dominating species, although in some areas the ground water can contain up to 39 µg of total chromium of which 30 µg is present as Cr(VI).

Chromium is mined as chromite (FeCr₂O₄) ore. About two-fifths of the chromite ores and concentrates in the world are produced in South Africa, while Kazakhstan, India, Russia, and Turkey are also substantial producers. Untapped chromite deposits are plentiful, but geographically concentrated in Kazakhstan and southern Africa.

Though native chromium deposits are rare, some native chromium metal has been discovered.

Se also selenium

Antioxidant is ?

Antioxidant

An antioxidant is a molecule capable of slowing or preventing the oxidation of other molecules. Oxidation is a chemical reaction that transfers electrons from a substance to an oxidizing agent. Oxidation reactions can produce free radicals, which start chain reactions that damage cells. Antioxidants terminate these chain reactions by removing free radical intermediates, and inhibit other oxidation reactions by being oxidized themselves. As a result, antioxidants are often reducing agents such as thiols or polyphenols.

Although oxidation reactions are crucial for life, they can also be damaging; hence, plants and animals maintain complex systems of multiple types of antioxidants, such as glutathione, vitamin C, and vitamin E as well as enzymes such as catalase, superoxide dismutase and various peroxidases. Low levels of antioxidants, or inhibition of the antioxidant enzymes, causes oxidative stress and may damage or kill cells.

As oxidative stress might be an important part of many human diseases, the use of antioxidants in pharmacology is intensively studied, particularly as treatments for stroke and neurodegenerative diseases. However, it is unknown whether oxidative stress is the cause or the consequence of disease. Antioxidants are also widely used as ingredients in dietary supplements in the hope of maintaining health and preventing diseases such as cancer and coronary heart disease. Although initial studies suggested that antioxidant supplements might promote health, later large clinical trials did not detect any benefit and suggested instead that excess supplementation may be harmful. In addition to these uses of natural antioxidants in medicine, these compounds have many industrial uses, such as preservatives in food and cosmetics and preventing the degradation of rubber and gasoline

Disease prevention

Antioxidants can cancel out the cell-damaging effects of free radicals. Furthermore, people who eat fruits and vegetables, which are good sources of antioxidants, have a lower risk of heart disease and some neurological diseases, and there is evidence that some types of vegetables, and fruits in general, probably protect against a number of cancers. These observations suggested that antioxidants might help prevent these conditions. There is some evidence that antioxidants might help prevent diseases such as macular degeneration, suppressed immunity due to poor nutrition, and neurodegeneration. However, despite the clear role of oxidative stress in cardiovascular disease, controlled studies using antioxidant vitamins have observed no reduction in either the risk of developing heart disease, or the rate of progression of existing disease. This suggests that other substances in fruit and vegetables (possibly flavonoids), or a complex mix of substances, may contribute to the better cardiovascular health of those who consume more fruit and vegetables.

It is thought that oxidation of low density lipoprotein in the blood contributes to heart disease, and initial observational studies found that people taking Vitamin E supplements had a lower risk of developing heart disease. Consequently, at least seven large clinical trials were conducted to test the effects of antioxidant supplement with Vitamin E, in doses ranging from 50 to 600 mg per day. However, none of these trials found a statistically significant effect of Vitamin E on overall number of deaths or on deaths due to heart disease. Further studies have also been negative. It is not clear if the doses used in these trials or in most dietary supplements are capable of producing any significant decrease in oxidative stress.

Many nutraceutical and health food companies now sell formulations of antioxidants as dietary supplements and these are widely used in industrialized countries. These supplements may include specific antioxidant chemicals, like resveratrol (from grape seeds or knotweed roots), combinations of antioxidants, like the “ACES” products that contain beta carotene (provitamin A), vitamin C, vitamin E and Selenium, or herbs that contain antioxidants – such as green tea and jiaogulan Although some levels of antioxidant vitamins and minerals in the diet are required for good health, there is considerable doubt as to whether antioxidant supplementation is beneficial, and if so, which antioxidant(s) are beneficial and in what amounts.

It has been suggested that moderate levels of oxidative stress may increase life expectancy in the worm Caenorhabditis elegans, by inducing a protective response to increased levels of reactive oxygen species. However, the suggestion that increased life expectancy comes from increased oxidative stress conflicts with results seen in the yeast Saccharomyces cerevisiae, and the situation in mammals is even less clear. However, antioxidant supplements do not appear to increase life expectancy.

What is Selenium ?

Selenium

Selenium is a chemical element of atomic number 34, represented by the chemical symbol Se, an atomic mass of 78.96. It is a non-metal, chemicals with sulfur and tellurium, and rarely occurs in the element of character. It is toxic in large quantities, but the traces of which are for the cellular function in most, if not all, animals, the center of the activity of enzymes Glutathione peroxidase and thiorédoxines reductase (which indirectly reduce “oxidation of the molecules of certain animals and some plants) and three deiodinase enzymes known (converter, thyroid hormone to another). Selenium requirements in plants differ by species, with some plants apparently requiring none.

Isolated selenium in different forms, the stable, which is a grayish-purple semi-dense (semiconductor), forming a trigonal polymer chain. A better management of electricity, the light in the darkness, and is used in photocells. Selenium is also present in many forms of non-drivers, such as a glass of black allotrope, and various forms of crystalline red eight built cyclic molecules, like its lighter chemical cousin sulfur.

Selenium is available in commercial quantities of sulphide minerals as pyrite, partial substitution of sulfur in the mineral matrix. Minerals, hydrogen or selinioucho séléniate compounds are also known, but all are rare.

Selenium is naturally in a number of inorganic forms, including selenide, selenate and selenite. In soil, selenium appears to soluble as selenate (as sulphate), which are leached into rivers very easily by runoff.

Selenium is a biological, and hydrogen to organic dimethyl selinioucho, selenomethionine, selenocysteine and methylselenocysteine. In these compounds, selenium plays a role similar to that of sulfur.

Selenium is usually hydrogen in many selenide sulfur minerals like copper, silver or lead. It is a by-product of processing of these ores, from the anode mud of copper refineries and the mud from the lead chambers of sulfuric acid plants. The sludge can be treated with a range of resources for free selenium.

Natural sources of selenium include certain selenium-rich soils, and selenium that has been bioconcentrated by certain toxic plants such as locoweed. The anthropogenic sources of selenium include the burning of coal and mining industry and smelting of sulfide ores.

Applications :

Chemistry :
Selenium is a catalysts for many chemical reactions and is widely used in various industrial units and laboratory equipment, especially Organoselenium chemistry. It is also that in determining the structure of proteins and nucleic acids using X-ray crystallography (to include one or more items with MAD and SAD phasing.)

Manufacture and use of materials :
The largest use of selenium in the world for the manufacture of glass and ceramics, for the red color in glass, enamels and varnishes, and remove the color of the glass from the green color from iron impurities.
Selenium is bismuth brass replace toxic lead. It is also used to improve the abrasion resistance of vulcanized rubber.

Electronics :
Due to the properties and photovoltaic senior picture, the selenium is in the copier, photocells, light meters and solar cells. It was the rectifier. These applications are often used by properties with silicon, or to be 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.

Press Amorphous selenium to convert the X-ray images on the structure and functions of the semiconductor in xeroradiography, flat panel x-ray cameras.

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.

For medical purposes :
Selenium disulphide SeS₂ or Selenium (IV) sulfide, containing the active ingredient in some shampoos. The effect of the active ingredient to kill scalp fungus Malassezia which causes shedding of dry skin fragments.. The substance is also in the body lotion for the treatment of Tinea Versicolor by infection with another type of fungus Malassezia.

Nutrition :
Selenium is widely distributed in vitamins and other supplements in small amounts (usually 50 to 200 micrograms per day for adult humans). Some are equipped with feed and selenium.