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Arsenite
In chemistry, an arsenite is a chemical compound containing an arsenic oxyanion where arsenic has oxidation state +3. Note that in fields that commonly deal with groundwater chemistry, arsenite is used generically to identify soluble AsIII anions. IUPAC have recommended that arsenite compounds are to be named as arsenate(III), for example ortho-arsenite is called trioxidoarsenate(III). Ortho-arsenite contrasts to the corresponding anions of the lighter members of group 15, phosphite which has the structure and nitrite, which is bent. A number of different arsenite anions are known: * ortho-arsenite, an ion of arsenous acid, with a pyramidal shape * meta-arsenite, a polymeric chain anion. * pyro-arsenite, * a polyarsenite, * a polyarsenite, *, a polymeric anion In all of these the geometry around the AsIII centers are approximately trigonal, the lone pair on the arsenic atom is stereochemically active. Well known examples of arsenites include sodium meta-arsenite which contai ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Arsenic
Arsenic is a chemical element with the symbol As and atomic number 33. Arsenic occurs in many minerals, usually in combination with sulfur and metals, but also as a pure elemental crystal. Arsenic is a metalloid. It has various allotropes, but only the gray form, which has a metallic appearance, is important to industry. The primary use of arsenic is in alloys of lead (for example, in car batteries and ammunition). Arsenic is a common n-type dopant in semiconductor electronic devices. It is also a component of the III-V compound semiconductor gallium arsenide. Arsenic and its compounds, especially the trioxide, are used in the production of pesticides, treated wood products, herbicides, and insecticides. These applications are declining with the increasing recognition of the toxicity of arsenic and its compounds. A few species of bacteria are able to use arsenic compounds as respiratory metabolites. Trace quantities of arsenic are an essential dietary element in rats, ham ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sodium Arsenite
Sodium arsenite usually refers to the inorganic compound with the formula NaAsO2. Also called sodium ''meta''-arsenite, it is the sodium salt of arsenous acid. Sodium ''ortho''-arsenite is Na3AsO3.Greenwood, N. N.; & Earnshaw, A. (1997). Chemistry of the Elements (2nd Edn.), Oxford:Butterworth-Heinemann. . The compounds are colourless solids. Synthesis and structure A mixture of sodium ''meta''-arsenite and sodium ''ortho''-arsenite is produced by treating arsenic trioxide with sodium carbonate or sodium hydroxide. Sodium arsenite is amorphous, typically being obtained as a powder or as a glassy mass. The compound consists of the polymer sO2associated with sodium cations, Na+. The polymer backbone has the connectivity -O-As(O−)-. Health effects Sodium arsenite can be inhaled or absorbed through the skin. Along with its known carcinogenic and teratogenic effects, contact with the substance can yield symptoms such as skin irritation, burns, itching, thickened skin, rash, lo ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Arsenous Acid
Arsenous acid (or arsenious acid) is the inorganic compound with the formula H3AsO3. It is known to occur in aqueous solutions, but it has not been isolated as a pure material, although this fact does not detract from the significance of As(OH)3. Properties As(OH)3 is a pyramidal molecule consisting of three hydroxyl groups bonded to arsenic. The 1H NMR spectrum of arsenous acid solutions consists of a single signal consistent with the molecule's high symmetry. In contrast, the nominally related phosphorous acid H3PO3 adopts the structure HPO(OH)2. The structural analogue of arsenous acid (P(OH)3) is a very minor equilibrium component of such solutions. The differing behaviors of the As and P compounds reflect a trend whereby high oxidation states are more stable for lighter members of main group elements than their heavier congeners. One tautomer of arsenous acid is HAsO(OH)2, which is called arsonic acid. It has not been isolated or well-characterized. Synthesis The preparat ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Photosynthesis
Photosynthesis is a process used by plants and other organisms to convert light energy into chemical energy that, through cellular respiration, can later be released to fuel the organism's activities. Some of this chemical energy is stored in carbohydrate molecules, such as sugars and starches, which are synthesized from carbon dioxide and water – hence the name ''photosynthesis'', from the Greek ''phōs'' (), "light", and ''synthesis'' (), "putting together". Most plants, algae, and cyanobacteria perform photosynthesis; such organisms are called photoautotrophs. Photosynthesis is largely responsible for producing and maintaining the oxygen content of the Earth's atmosphere, and supplies most of the energy necessary for life on Earth. Although photosynthesis is performed differently by different species, the process always begins when energy from light is absorbed by proteins called reaction centers that contain green chlorophyll (and other colored) pigments/chromoph ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Arsenic Trioxide
Arsenic trioxide, sold under the brand name Trisenox among others, is an inorganic compound and medication. As an industrial chemical, whose major uses include in the manufacture of wood preservatives, pesticides, and glass. As a medication, it is used to treat a type of cancer known as acute promyelocytic leukemia. For this use it is given by injection into a vein. Common side effects include vomiting, diarrhea, swelling, shortness of breath, and headaches. Severe side effects may include APL differentiation syndrome and heart problems. Use during pregnancy or breastfeeding may harm the baby. Arsenic trioxide has the formula . Its mechanism in treating cancer is not entirely clear. Arsenic trioxide was approved for medical use in the United States in 2000. It is on the World Health Organization's List of Essential Medicines. Approximately 50,000 tonnes are produced a year. Due to its toxicity, a number of countries have regulations around its manufacture and sale. Uses M ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Reinerite
Reinerite is a rare arsenite (arsenate(III)) mineral with chemical formula Zn3(AsO3)2. It crystallizes in the orthorhombic crystal system. Physical properties Reinerite is most commonly found as a sky blue colored mineral, however, it may also be a light yellowish green color. Reinerite has a relative hardness of 5 to 5.5 on the Mohs Scale which is equivalent to that of a knife blade and or shard of glass. It has a density of 4.27 g/cm3, and it exhibits a nonmetallic luster that may be described as glassy or vitreous.Lutgens, Frederick, and Edward Tarbuck. Essentials of Geology. 10th. Upper Saddle River, New Jersey: Pearson Prentice Hall, 2009. 42. Print. Environment Reinerite develops in dolomite-hosted locations. It is known especially from Namibia, Africa, within the mines of Tsumeb. At the Tsumeb location, Reinerite develops within the polymetallic lead-zinc-copper deposit, below the surface, in the second oxidation zone. It occurs in association with chalcocite, bornite, ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Arsenate
The arsenate ion is . An arsenate (compound) is any compound that contains this ion. Arsenates are salts or esters of arsenic acid. The arsenic atom in arsenate has a valency of 5 and is also known as pentavalent arsenic or As(V). Arsenate resembles phosphate in many respects, since arsenic and phosphorus occur in the same group (column) of the periodic table. Arsenates are moderate oxidizers, with an electrode potential of +0.56 V for reduction to arsenites. Occurrence Arsenates occur naturally in a variety of minerals. Those minerals may contain hydrated or anhydrous arsenates. Unlike phosphates, arsenates are not lost from a mineral during weathering. Examples of arsenate-containing minerals include adamite, alarsite, annabergite, erythrite and legrandite. Where two arsenate ions are required to balance the charge in a formula, it is called diarsenate for example trizinc diarsenate, Zn3(AsO4)2. Ions The word arsenate is derived from arsenic acid, H3AsO4. This mode ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Arsenic Contamination Of Groundwater
Arsenic contamination of groundwater is a form of groundwater pollution which is often due to naturally occurring high concentrations of arsenic in deeper levels of groundwater. It is a high-profile problem due to the use of deep tube wells for water supply in the Ganges Delta, causing serious arsenic poisoning to large numbers of people. A 2007 study found that over 137 million people in more than 70 countries are probably affected by arsenic poisoning of drinking water. The problem became serious health concern after mass poisoning of water in Bangladesh. Arsenic contamination of ground water is found in many countries throughout the world, including the US. The World Health Organization recommends limiting arsenic concentrations in water to 10 μg/L, although this is often an unattainable goal for many problem areas due to the difficult nature of removing arsenic from water sources. Approximately 20 major incidents of groundwater arsenic contamination have been reported. Of ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Fowler's Solution
Fowler's solution is a solution containing 1% potassium arsenite (KAsO2), and was once prescribed as a remedy or a tonic. Thomas Fowler (1736–1801) of Stafford, England, proposed the solution in 1786 as a substitute for a patent medicine, "tasteless ague drop". From 1865, Fowler's solution was a leukemia treatment. From 1905, inorganic arsenicals like Fowler's solution saw diminished use as attention turned to organic arsenicals, starting with Atoxyl. As arsenical compounds are notably toxic and carcinogenic—with side effects such as cirrhosis of the liver, idiopathic portal hypertension, urinary bladder cancer, and skin cancers—Fowler's solution fell from use. (In 2001, however, the U.S. Food and Drug Administration (FDA) approved a drug of arsenic trioxide to treat acute promyelocytic leukaemia Acute promyelocytic leukemia (APML, APL) is a subtype of acute myeloid leukemia (AML), a cancer of the white blood cells. In APL, there is an abnormal accumulation of imma ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Arsenios Autoreianos
Arsenios Autoreianos (Latinized as Arsenius Autorianus) ( el, Ἀρσένιος Ἀυτωρειανός), ( 30 September 1273), Ecumenical Patriarch of Constantinople, lived about the middle of the 13th century. Born in Constantinople c. 1200, Arsenios received his education in Nicaea at a monastery of which he later became the abbot, though not in orders. Subsequently, he gave himself up to a life of solitary asceticism in a Bithynian monastery, and is said to have remained some time in a monastery on Mount Athos. Overview From this seclusion he was called by the Byzantine Emperor Theodore II Lascaris to the position of patriarch at Nicaea in 1255. Upon the emperor's death Arsenios may have shared guardianship of his son John IV Lascaris with George Muzalon: while the later historians Nikephoros Gregoras and Makarios Melissenos say the Patriarch was so named, the contemporary historians Pachymeres and Acropolites name only Mouzalon. Nevertheless, a few days after Theodore's de ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Enzyme
Enzymes () are proteins that act as biological catalysts by accelerating chemical reactions. The molecules upon which enzymes may act are called substrates, and the enzyme converts the substrates into different molecules known as products. Almost all metabolic processes in the cell need enzyme catalysis in order to occur at rates fast enough to sustain life. Metabolic pathways depend upon enzymes to catalyze individual steps. The study of enzymes is called ''enzymology'' and the field of pseudoenzyme analysis recognizes that during evolution, some enzymes have lost the ability to carry out biological catalysis, which is often reflected in their amino acid sequences and unusual 'pseudocatalytic' properties. Enzymes are known to catalyze more than 5,000 biochemical reaction types. Other biocatalysts are catalytic RNA molecules, called ribozymes. Enzymes' specificity comes from their unique three-dimensional structures. Like all catalysts, enzymes increase the reaction ra ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Redox
Redox (reduction–oxidation, , ) is a type of chemical reaction in which the oxidation states of substrate (chemistry), substrate change. Oxidation is the loss of Electron, electrons or an increase in the oxidation state, while reduction is the gain of electrons or a decrease in the oxidation state. There are two classes of redox reactions: * ''Electron-transfer'' – Only one (usually) electron flows from the reducing agent to the oxidant. This type of redox reaction is often discussed in terms of redox couples and electrode potentials. * ''Atom transfer'' – An atom transfers from one substrate to another. For example, in the rusting of iron, the oxidation state of iron atoms increases as the iron converts to an oxide, and simultaneously the oxidation state of oxygen decreases as it accepts electrons released by the iron. Although oxidation reactions are commonly associated with the formation of oxides, other chemical species can serve the same function. In hydrogen ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
