Manganese

Manganese is a chemical element with atomic number 25 located in group 7 of the periodic table of elements and symbolized as Mn. It is found as a free element in nature, often in combination with iron and in many minerals. As a free element, manganese is an industrial metal alloy metal with important uses, especially in stainless steels.

Manganese phosphating is used as a treatment to prevent rust and corrosion of steel. Depending on their oxidation state, manganese ions have different colors and are used industrially as pigments. Alkali and alkaline earth metal permanganates are powerful oxidizers. Manganese dioxide is used as the cathode.

Manganese ions function as cofactors for a number of enzymes in higher organisms, where they are essential in the detoxification of superoxide free radicals. The element is a trace mineral essential to all known living things. In larger amounts, and apparently with much greater activity upon inhalation, manganese can cause a poisoning syndrome in mammals, with sometimes irreversible neurological damage.

Main features

Pure manganese sample.

Manganese is a grayish-white transition metal, similar to iron. It is a hard and very brittle metal, refractory and easily oxidized. The metal manganese can be ferromagnetic, but only after undergoing special treatment.

Its most common oxidation states are 2+, 3+, 4+, 6+ and +7, although compounds with all oxidation numbers from 1+ to 7+ have been found; Compounds in which manganese has the 7+ oxidation state are very strong oxidizing agents. Within biological systems, the Mn²⁺ cation frequently competes with the Mg²⁺ cation. It is used above all alloyed with iron in steel and other alloys.

Applications

• The engines flap is reduced by the use of a manganese compound that is added to leadless gasoline. This increases the fuel octane.
• The manganese is used in standard disposable batteries.
• The manganese is essential to produce steel and iron. The manganese is an essential component for the manufacture of low-cost stainless steel.
• The manganese is polished with aluminum to produce a alloy that is more corrosion resistant. Most aluminum cans for beverages contain between 0.8 % and 1.5 % of manganese.
• In chemistry, manganese oxide is used to oxidize bencyclic alcohol.
• Iron contamination can make the glass dye green. Since ancient times a manganese compound is added to the glass to counter this effect.
• Dioxygen and dichlorus are processed using manganese dioxide. This same compound is also a brown pigment that can be used to make paints.
• Glass and ceramic can be colored by various manganese compounds.
• In some parts of the world, manganese is used to make coins.

History

Manganese dioxide, MnO₂, pyrolusite, have been found in rock paintings (giving a black color). Manganese compounds have also been used throughout history, for example by the Egyptians and Romans, to discolor glass or give it color. It has also been used to obtain the purplish-brown color in ceramic glazes. Manganese has also been found in the iron mines used by the Spartans, and it is thought that perhaps the special hardness of their steels is due to this.

In the 17th century, the German chemist Glauber first produced permanganate, a widely used laboratory reagent. In 1774, the Swedish chemist Scheele discovered the production of chlorine by reacting pyrolusite with hydrochloric acid. This method was used for many years, to use chlorine as a fabric bleach and disinfectant, until the introduction of electrolytic methods. Scheele also assumed that an unknown element was found in pyrolusite, but it was isolated by Johan Gottlieb Gahn by reduction of carbon dioxide (1774), a few years after the experiments carried out in Vienna by Ignatius Gottfried Kaim (1770), described in his work "De metalleis dubiis" and which, despite its limited diffusion, confirm him as the first scientist to isolate manganese.

In the early 19th century manganese began to be tested in steel alloys. In 1816 it was found that it hardened steel, without making it more brittle.

Biological paper

Manganese is a trace element, that is, an essential chemical element for all forms of life.

In humans it is required for the proper functioning of the immune system, regulation of blood sugar and cellular energy, reproduction, digestion, bone growth, blood coagulation and hemostasis, and defense against reactive oxygen species.

Manganese has been shown to have both a structural and an enzymatic role. It is present in more than thirty enzymes, highlighting manganese superoxide dismutase (Mn-SOD), which catalyzes the dismutation of superoxides, O₂^-; Mn-catalase, which catalyzes the dismutation of hydrogen peroxide, H₂O₂; as well as in concavalin A (from the lectin family), where manganese has a structural role.

The human body manages to absorb manganese in the small intestine, finishing most of it in the liver, from where it is distributed to different parts of the body. About 10 mg of manganese is stored mainly in the liver and kidneys. In the human brain, manganese is bound to manganese metalloproteins, the most relevant being glutamine synthetase in astrocytes.

Manganese is also important in oxygenic photosynthesis in plants. The oxygenic complex is part of photosystem II contained in the chloroplast membranes; it is responsible for the final photo-oxidation of water during the light phase of photosynthesis and has a metalloenzyme with four manganese atoms. For this reason, most fertilizers contain manganese.

Abundance and obtaining

It is the twelfth most abundant element in the earth's crust and is widely distributed.

It is found in hundreds of minerals, although only a dozen are of industrial interest. Highlights: pyrolusite (MnO₂), psilomelan (MnO₂ H₂O), manganite (MnO(OH)), braunite (3Mn ₂O₃MnSiO₃), rhodonite (MnSiO₃), rhodochrosite (MnCO₃), hübnerite (MnWO₄), etc. In the seabed it has also been found in manganese nodules, where the manganese content ranges from 15 to 30%, and where it would be possible to extract it.

The countries with the largest manganese mineral deposits are South Africa, Ukraine, Bolivia and China.

The metal is obtained by reducing the oxides with aluminum, and ferromanganese is also obtained by reducing the oxides of iron and manganese with carbon.

World production in 2019, in millions of tons per year

1.	South Africa	5,80
2.	Australia	3.18
3.	GabonGabon	2.51
4.	BrazilBrazil	1.74
5.	GhanaGhana	1.55
6.	ChinaChina	1.33
7.	India	0.80
8.	Ukraine Ukraine	0.50
9.	Ivory CoastIvory Coast	0.48
10.	BurmaBurma	0.43

Source: USGS.

Compounds

Bone oxide.

Potassium permanganate, KMnO₄, is a very common laboratory reagent due to its oxidizing properties.

Manganese dioxide, MnO₂ is used as a depolarizer in dry cells. It can also be used to decolorize glass that has a green color due to the presence of traces of iron. This oxide is also used to color amethyst glass, and is responsible for the color of amethyst (a variety of quartz). In addition, it is used in the production of chlorine and oxygen. Some Aluminum coins contain Manganese as an alloy.

Precautions

Manganese is an essential element, requiring a contribution of between 1 to 5 mg per day, an amount that is obtained through food.^{[citation required]} Prolonged exposure to manganese compounds, inhaled or oral, can cause adverse effects on the nervous and respiratory systems. Potassium permanganate, KMnO₄, is corrosive.^{[citation required]}

Toxicity

Exhibition

Inhalation of manganese dust is harmful to health and can be the cause of several clinical conditions. The most common cases of poisoning are related to the workplace; among others, the manufacture of steel, ceramics, glass, paint, linoleum, phosphorus, dry batteries and fireworks. The maximum amount allowed in the industry is 5 mg per m³ of air.

Distribution in the organism

Once exposure to manganese has been high, the distribution of the xenobiotic and its levels are heterogeneous with maximum accumulation in the globus pallidus (one of the three nuclei that form the basal ganglia).

Three transporters have been found that are capable of mediating Mn efflux: ferroportin, SLC30A10, and the solute carrier P-type ATPase via Ca-ATPase1 (SPCA1). There is clear evidence supporting the ability of ferroportin and SPCA1 to mediate Mn efflux and detoxification in cell culture although their role in Mn detoxification at the whole organism level remains to be elucidated. On the other hand SLC30A10 seems to play a fundamental role in the maintenance of cellular Mn levels and protection against Mn toxicity throughout the organism.

Mechanism of action

Manganese poisoning can produce pathophysiological processes at the nervous system level, more specifically by blocking the synthesis of neurotransmitters. Manganese inhibits the enzyme tyrosine-hydroxylase, which is the catecholamine-synthesizing enzyme, and also inhibits dopamine-beta-hydroxylase, the enzyme in charge of dopamine synthesis.

In humans and in rats with chronic iron deficiency, Mn has been shown to accumulate in the basal ganglia due to competition between the two metals (Fe and Mn) for shared transporters.

At the lung level, it can produce welder's fever, which is produced by the release of pyrogens by pulmonary macrophages when they are injured by the particles of the metallic compound.

At the cardiovascular level, it blocks the entry of calcium, leading to bradycardia and hypotension.

Physiopathological changes

Acute poisoning is known as manganism, which begins to manifest with sleep disturbances, excitement and euphoria. The affected person feels irresistible desires to dance or march without rest, with fits of unmotivated laughter and logorrhea. Brain lesions in the basal ganglia predominate, with a picture similar to Parkinson's, an expressionless face and salivation. Encephalopathy with neuronal degeneration occurs in various nuclei of the brain and cerebellum (Purkinje cells). It is associated with mental disorders such as emotional instability and hallucinations. The administration of L-DOPA improves the symptoms. It is also related to Amyotrophic Lateral Sclerosis (ALS) due to degeneration of motor neurons. In 73% of cases it leads to sexual impotence. The painting is irreversible.

The diagnosis is confirmed with the detection of manganese in the blood, cases of up to 80 μg per 100 ml have been detected. In early stages, the progression of the disease can be halted by administering calcium adatamil. Treatment also includes daily injections of calcium gluconate (10 ml at 10%), administration of high doses of vitamins B₁ and B₁₂ and atropine or scopolamine. in doses of 1 mg, in order to relieve tremors.

Manganese-induced parkinsonism can occur in patients with impaired liver function who cannot properly eliminate manganese in the bile, as well as in individuals receiving total parenteral nutrition without high exposure. It should be noted that patients undergoing microdialysis due to chronic renal failure can develop it without having been exposed to exogenous particles of this metal.

In addition, recent genetic studies have shown that homozygous mutations in SLC30A10 lead to familial Mn-induced parkinsonism.

Welder's fever is characterized by a short latency period, after which symptoms reminiscent of the flu appear: cough, dyspnea, fever, joint pain, nausea, vomiting, mental confusion, etc., and profuse sweating, all of which persist for 24 hours.

Slag from steelmaking produces a highly irritating dust that inhaled causes Thomas slag pneumonia. This picture of acute pneumonitis generally does not respond well to antibiotics, although it does respond well to chelating substances such as calcium adatamil or versene.

On the other hand, manganese is also hepatotoxic, being related to Canalicular cholestasis.

It can also cause teratogenesis, which if it occurs during organogenesis (weeks 3-8) the consequences can be fatal, since this period is of maximum susceptibility since the embryonic cells have lost their totipotential character.

Biomarkers

Manganese (Mn), after absorption, is stored in intracellular compartments of tissues and therefore the concentration of Mn in the blood does not always accurately reflect the concentration of Mn in the target tissue, particularly in the brain. There are differences between the concentrations of Mn in the target tissues and the concentration in the blood, so this is a poor biomarker.

Mn exposure alters iron homeostasis, so the Mn / Fe ratio (MIR) in plasma or erythrocytes reflects not only steady-state concentrations of Mn or Fe in the individuals analyzed, but also a biological response to Mn exposure (altered Fe homeostasis). Human studies support the potential value of using MIR to distinguish individuals with Mn exposure. Furthermore, magnetic resonance imaging (MRI), in combination with non-invasive assessment of γ-aminobutyric acid (GABA) by magnetic resonance spectroscopy (MRS), provide convincing evidence of Mn exposure, even without clinical symptoms of Mn poisoning. Mn. For subjects exposed to Mn over a long period of time at low doses or subjects exposed in the past but not the present, neither blood nor MRI provide convincing information of Mn exposure or poisoning. However the plasma or the Mn/Fe ratio give a more sensitive measurement.

Considering the large accumulation of Mn in bone, the development of an X-ray fluorescence spectroscopy or a method based on neutron spectroscopy may represent another novel non-invasive tool to assess Mn exposure and its toxicity.