Manganese

Manganese is also an essential human dietary element, important in macronutrient metabolism, bone formation, and free radical defense systems.[14] Manganese is part of the iron group of elements, which are thought to be synthesized in large stars shortly before the supernova explosion.[17] Four allotropes (structural forms) of solid manganese are known, labeled α, β, γ and δ, and occurring at successively higher temperatures.Potassium permanganate is a commonly used laboratory reagent because of its oxidizing properties; it is used as a topical medicine (for example, in the treatment of fish diseases).Solid compounds of manganese(III) are characterized by its strong purple-red color and a preference for distorted octahedral coordination resulting from the Jahn-Teller effect.[37] Of greatest commercial interest is "MMT", methylcyclopentadienyl manganese tricarbonyl, which is used as an anti-knock compound added to gasoline (petrol) in some countries.When conducted under an atmosphere of carbon monoxide, reduction of Mn(II) salts gives dimanganese decacarbonyl Mn2(CO)10, an orange and volatile solid.[38] Polyalkyl and polyaryl derivatives of manganese often exist in higher oxidation states, reflecting the electron-releasing properties of alkyl and aryl ligands.Michele Mercati called magnesia nigra manganesa, and finally the metal isolated from it became known as manganese (German: Mangan).Ignatius Gottfried Kaim (1770) and Johann Glauber (17th century) discovered that manganese dioxide could be converted to permanganate, a useful laboratory reagent.In 1837, British academic James Couper noted an association between miners' heavy exposure to manganese and a form of Parkinson's disease.[50] In 1912, United States patents were granted for protecting firearms against rust and corrosion with manganese phosphate electrochemical conversion coatings, and the process has seen widespread use ever since.[57] In South Africa, most identified deposits are located near Hotazel in the Northern Cape Province, (Kalahari manganese fields), with a 2011 estimate of 15 billion tons.[58] Manganese is mainly mined in South Africa, Australia, China, Gabon, Brazil, India, Kazakhstan, Ghana, Ukraine and Malaysia.Coastal sediments normally have lower Mn concentrations, but can increase due to anthropogenic discharges from industries such as mining and steel manufacturing, which enter the ocean from river inputs.Internal cycling such as photo-reduction from UV radiation can also elevate levels by speeding up the dissolution of Mn-oxides and oxidative scavenging, preventing Mn from sinking to deeper waters.The dMn can then travel up to 4,000 km due to the microbial capsules present, preventing exchange with particles, lowing the sinking rates.[72] The Mn(III,IV) oxides exist as brownish-black stains and small nodules on sand, silt, and clay particles.[52][82] Copper alloys of manganese, such as Manganin, are commonly found in metal element shunt resistors used for measuring relatively large amounts of current.[99][100] Manganese is an essential human dietary element and is present as a coenzyme in several biological processes, which include macronutrient metabolism, bone formation, and free radical defense systems.[101] The U.S. Institute of Medicine (IOM) updated Estimated Average Requirements (EARs) and Recommended Dietary Allowances (RDAs) for minerals in 2001.Excessive exposure or intake may lead to a condition known as manganism, a neurodegenerative disorder that causes dopaminergic neuronal death and symptoms similar to Parkinson's disease.According to results from a 2010 study,[110] higher levels of exposure to manganese in drinking water are associated with increased intellectual impairment and reduced intelligence quotients in school-age children.It is hypothesized that long-term exposure due to inhaling the naturally occurring manganese in shower water puts up to 8.7 million Americans at risk.Mn can affect the renewal of immunocytes and their functionality, such as phagocytosis and activation of pro-phenoloxidase, suppressing the organisms' immune systems.[69] Methylcyclopentadienyl manganese tricarbonyl (MMT) is an additive developed to replace lead compounds for gasolines to improve the octane rating.Increased ferroportin protein expression in human embryonic kidney (HEK293) cells is associated with decreased intracellular Mn concentration and attenuated cytotoxicity, characterized by the reversal of Mn-reduced glutamate uptake and diminished lactate dehydrogenase leakage.[50][121] Unlike Parkinson's disease, manganism is not associated with loss of the sense of smell and patients are typically unresponsive to treatment with L-DOPA.[122] Symptoms of late-stage manganism become more severe over time even if the source of exposure is removed and brain manganese levels return to normal.The proposed mechanism for manganese toxicity is that dysregulation leads to oxidative stress, mitochondrial dysfunction, glutamate-mediated excitotoxicity, and aggregation of proteins.