Chelation refers to the case when more than one atom bonds to a central metal ion at one time to form a ring structure. Chelation of metals by ligands available by the biopolymers leads to the formation of stable structures. The following figure shows the structure of a metal ion chelated with ethylenediamine tetracarboxylic acid (EDTA), a hexa-donating compound with two nitrogen and four oxygen donor atoms .
In general, since a chelating agent may bond to a metal ion in more than one place simultaneously, chelated compounds are more stable than complexes involving mono-dentate ligands.
The ammonia molecule has a trigonal pyramidal shape with a bond angle of 107.8°, as predicted by the valence shell electron pair repulsion theory (VSEPR theory).
Ammonia is found in trace quantities in the atmosphere, being produced from the putrefaction (decay process) of nitrogenous animal and vegetable matter. This high-pressure reactor was built in 1921 by BASF in Ludwigshafen and was re-erected on the premises of the University of Karlsruhe in Germany.
The form of sal-ammoniac (nushadir), ammonia was important to the Muslim alchemists as early as the 8th century, first mentioned by the Persian chemist Jabir ibn Hayyan,[12] and to the European alchemists since the 13th century, being mentioned by Albertus Magnus.[13] It was also used by dyers in the Middle Ages in the form of fermented urine to alter the colour of vegetable dyes. The Haber-Bosch process to produce ammonia from the nitrogen in the air was developed by Fritz Haber and Carl Bosch in 1909 and patented in 1910. Prior to the advent of cheap natural gas, hydrogen as a precursor to ammonia production was produced via the electrolysis of water or using the chloralkali process. The carbon dioxide is then removed either by absorption in aqueous ethanolamine solutions or by adsorption in pressure swing adsorbers (PSA) using proprietary solid adsorption media. To produce the desired end-product ammonia, the hydrogen is then reacted with nitrogen (derived from process air) using a magnetite catalyst under high pressure to form anhydrous liquid ammonia.
Hydrogen required for ammonia synthesis could also be produced economically using other sources like coal or coke gasification, less economically from the electrolysis of water into oxygen + hydrogen and other alternatives which are presently impractical for large scale. In certain organisms, ammonia is produced from atmospheric nitrogen by enzymes called nitrogenases. Ammonia is also a metabolic product of amino acid deamination catalyzed by enzymes such as glutamate dehydrogenase 1. The ammonia molecule readily undergoes nitrogen inversion at room temperature; a useful analogy is an umbrella turning itself inside out in a strong wind. Ammonia may be conveniently deodorized by reacting it with either sodium bicarbonate or acetic acid. The salts produced by the action of ammonia on acids are known as the ammonium salts and all contain the ammonium ion (NH4+). By creating a solution with a pH much higher than a neutral water solution, proteins (enzymes) will denaturate, leading to cell damage, death of the cell, and eventually death of the organism. The combustion of ammonia in air is very difficult in the absence of a catalyst (such as platinum gauze), as the temperature of the flame is usually lower than the ignition temperature of the ammonia-air mixture. Amides can be prepared by the reaction of ammonia with a number of carboxylic acid derivatives.
The hydrogen in ammonia is capable of replacement by metals, thus magnesium burns in the gas with the formation of magnesium nitride Mg3N2, and when the gas is passed over heated sodium or potassium, sodamide, NaNH2, and potassamide, KNH2, are formed. Ammine complexes of chromium(III) were known in the late 19th century, and formed the basis of Alfred Werner's revolutionary theory on the structure of coordination compounds. An ammine ligand bound to a metal ion is markedly more acidic than a free ammonia molecule, although deprotonation in aqueous solution is still rare. Approximately 83% (as of 2004) of ammonia is used as fertilizers either as its salts or as solutions. Nitric acid is used for the production of fertilizers, explosives, and many organonitrogen compounds.
Solutions of ammonia ranging from 16% to 25% are used in the fermentation industry as a source of nitrogen for microorganisms and to adjust pH during fermentation. Because of its favourable vaporization properties, ammonia is an attractive refrigerant.[6] It was commonly used prior to the popularisation of chlorofluorocarbons (Freons).
Ammonia is used to scrub SO2 from the burning of fossil fuels, and the resulting product is converted to ammonium sulfate for use as fertilizer. Ammonia was used during World War II to power buses in Belgium, and in engine and solar energy applications prior to 1900. To meet these demands, significant capital would be required to increase present production levels. Ammonia engines or ammonia motors, using ammonia as a working fluid, have been proposed and occasionally used.[43] The principle is similar to that used in a fireless locomotive, but with ammonia as the working fluid, instead of steam or compressed air. Selasyon (celasyon, veya k?skaclama terimleri de kullan?l?r) iki veya cok disli bir kimyasal ligand?n iyonik bir substrata baglanmas? veya komplekslenmesidir.
Selasyon Selasyon (celasyon, veya k?skaclama terimleri de kullan?l?r) iki veya cok disli bir kimyasal ligand?n iyonik bir substrata baglanmas? veya komplekslenmesidir. Toprak Toprak hava ve su gibi, canl?lar?n yasamas? icin vazgecilmez unsurlardan bir digeri de toprakt?r. Potasyum Potasyum ilk olarak 1807 y?l?nda Humphrey Davy taraf?ndan potasyum hidroksitten elektroliz yolu ile izole edilmistir. Kromatografi Hareketli bir faz ile sabit bir faz?n temas etmesi ile maddelerin yer degistirme h?zlar?n?n farkl?last?r?larak ayr?lmas?n? saglayan teknige kromatografi denir.
Titanyum Nitrit Titayum nitrit (TiN) kaplamalar, yuksek sertlikleri, dusuk as?nma oranlar? ve gorunuslerinden dolay? y?llard?r, as?nma onleme ve dekoratif amac ile yayg?n olarak kullan?lmaktad?r. As propriedades toxicas do chumbo e de seus compostos, apesar de conhecidas ha muito tempo, continuam causando problemas para a saude das pessoas e danos ao meio ambiente. A diminuicao do uso de gasolina contendo chumbo, implementada ha mais de duas decadas, reduziu significativamente a concentracao deste metal no meio ambiente. O objetivo deste artigo e o de chamar a atencao as possiveis fontes de intoxicacao ainda existentes, aos mecanismos de acao toxica do chumbo e, principalmente, aos agentes utilizados para tratar as intoxicacoes que ele causa. Atualmente, o chumbo ainda e um poluente presente nas nuvens de poeira que se formam nas demolicoes de predios e residencias pintados ha muitos anos. Embora em menor escala, e importante destacar tambem a possibilidade de contato com o metal pela reutilizacao indevida das caixas de baterias para estoque de agua ou na fabricacao clandestina de destilados alcoolicos pela utilizacao de serpentinas soldadas com chumbo.
A absorcao de chumbo, de um modo geral, ocorre atraves do estomago, do intestino e do sistema respiratorio. As diferentes formas de absorcao do chumbo estao intimamente relacionadas com o tipo de orgao ou tecido aos quais ele pode se ligar no corpo humano.
Os problemas neurologicos sao mais comuns em criancas, e os problemas gastrointestinais ocorrem com maior frequencia em adultos. In general, since a chelating agent may bond to a metal ion in more than one place simultaneously, chelates are more stable than complexes involving unidentate ligands. The central nitrogen atom has five outer electrons with an additional electron from each hydrogen atom. Ammonia and ammonium salts are also found in small quantities in rainwater, whereas ammonium chloride (sal-ammoniac), and ammonium sulfate are found in volcanic districts; crystals of ammonium bicarbonate have been found in Patagonian guano. In the 15th century, Basilius Valentinus showed that ammonia could be obtained by the action of alkalis on sal-ammoniac. It was first used on an industrial scale by the Germans during World War I,[6] following the allied blockade that cut off the supply of nitrates from Chile.
The Vemork 60 MW hydroelectric plant in Norway, constructed in 1911, was used purely for plants using the Birkeland-Eyde process.

The process used in producing the hydrogen begins with removal of sulfur compounds from the natural gas (because sulfur deactivates the catalysts used in subsequent steps). At one time, most of Europe's ammonia was produced from the Hydro plant at Vemork, via the electrolysis route. Dilute aqueous ammonia can be applied on the skin to lessen the effects of acidic animal venoms, such as from insects and jellyfish.
It is a protic substance and is capable of formation of amides (which contain the NH2? ion). Dinitrogen is the thermodynamic product of combustion: all nitrogen oxides are unstable with respect to nitrogen and oxygen, which is the principle behind the catalytic converter. Amines can be formed by the reaction of ammonia with alkyl halides, although the resulting –NH2 group is also nucleophilic and secondary and tertiary amines are often formed as by-products.
Acyl chlorides are the most reactive, but the ammonia must be present in at least a twofold excess to neutralise the hydrogen chloride formed. Where necessary in substitutive nomenclature, IUPAC recommendations prefer the name azane to ammonia: hence chloramine would be named chloroazane in substitutive nomenclature, not chloroammonia.
This crystalline solid is only stable under high pressure, and decomposes back into trivalent ammonia and hydrogen gas at normal conditions. It is a pure ?-donor, in the middle of the spectrochemical series, and shows intermediate hard-soft behaviour. Werner noted that only two isomers (fac- and mer-) of the complex [CrCl3(NH3)3] could be formed, and concluded that the ligands must be arranged around the metal ion at the vertices of an octahedron. One example is the Calomel reaction, where the resulting amidomercury(II) compound is highly insoluble. When applied to soil, it helps provide increased yields of crops such as corn, wheat and soybeans. Because ammonia results in a relatively streak-free shine, one of its most common uses is to clean glass, porcelain and stainless steel. Anhydrous ammonia is widely used in industrial refrigeration applications and hockey rinks because of its high energy efficiency and low cost. In a normal engine, in which the water vapour is not condensed, the calorific value of ammonia will be about 21% less than this figure. Although the second most produced chemical, the scale of ammonia production is a small fraction of world petroleum usage. Ammonia engines were used experimentally in the 19th century by Goldsworthy Gurney in the UK and in streetcars in New Orleans in the USA. Bu ligandlar, ki genelde organik bilesiklerdir, selator veya selat ajan? olarak adland?r?l?r (diger kullan?lan terimler: selant, celator, celant, k?skaclay?c?, iyon tutucu).
Eklembacakl?lar taraf?ndan d?s iskeletin kurulmas?nda kullan?lan ve Mantarlar?n hucre ceperini olusturan karbonhidrata kitin denir. Hoje nao sao mais utilizados encanamentos de chumbo e tacas ou garrafas de bebidas fabricadas com este metal, como foi na Roma antiga. Particularmente no Brasil, o chumbo adicionado a gasolina como agente antidetonante foi totalmente substituido pelo etanol, que tambem atua como antidetonante, impedindo ou retardando a detonacao nos motores a explosao.
Esses agentes sao moleculas ou anions especiais chamados de quelantes e atuam como antagonistas no sentido de reduzir os efeitos danosos da intoxicacao. As paredes de casas antigas contem elevada quantidade de chumbo, uma vez que um dos pigmentos utilizados nas tintas era o oxido de chumbo, PbO. Alem do chumbo, outros metais pesados como o mercurio e o cadmio sao altamente nocivos ao organismo humano. Na hipotese de se ingerir acidentalmente ions de chumbo, por exemplo, em aguas contaminadas, este pode ser absorvido pelo sistema gastrointestinal. A encefalopatia, doenca neurologica decorrente do acumulo de chumbo no cerebro, e a mais seria das enfermidades causadas por este metal. These ligands possess a single donor atom and are able to occupy only one site in a coordination sphere.
Ammonia contributes significantly to the nutritional needs of terrestrial organisms by serving as a precursor to food and fertilizers.
This gives a total of eight electrons, or four electron pairs which are arranged tetrahedrally. The kidneys secrete NH3 to neutralize excess acid.[8] Ammonium salts also are found distributed through all fertile soil and in seawater.
Although it is unlikely that biomimetic methods will be developed that are competitive with the Haber process, intense effort has been directed toward understanding the mechanism of biological nitrogen fixation. In humans, it is quickly converted to urea, which is much less toxic, particularly less basic. The remaining water, also containing excess ammonia, will evaporate completely, leaving a clean surface. An excess of ammonia helps minimise multiple substitution, and neutralises the hydrogen halide formed. For historical reasons, ammonia is named ammine in the nomenclature of coordination compounds. The Kalina cycle, which is of growing importance to geothermal power plants, depends on the wide boiling range of the ammonia-water mixture. Although not as powerful as other fuels, it left no soot in the reusable rocket engine and its density approximately matches the density of the oxidizer, liquid oxygen, which simplified the aircraft's design. Uroloji KlinigiInfertilite yani k?s?rl?k herhangi bir korunma olmadan, yani eslerin istemelerine ragmen 1 y?l icerisinde cocuk sahibi olamamalar?d?r. Gunumuzde alternatif enerji kaynaklar? ile cal?san otomobillerin uretilmesi konusunda cal?smalar h?z kazanm?st?r. Apesar de todos os cuidados, ainda sao observados casos de intoxicacoes agudas e cronicas por chumbo, cada vez mais dificeis de serem diagnosticadas. Os antagonistas formam ligacoes quimicas fortes e estaveis com o chumbo acumulado no organismo eliminando-o atraves da urina. Quando as casas antigas sao demolidas, este oxido de chumbo pode ser inalado pelos trabalhadores em elevada quantidade, causando disturbios respiratorios. Posteriormente, ao ser em parte expelido pela urina, o metal e redistribuido no organismo, fixando-se nos ossos e nos dentes na forma de fosfato de chumbo. Alguns de seus sintomas iniciais, como vertigens, dores de cabeca, insonia e irritabilidade, dificultam o diagnostico.
Some ligands have two or more donor atoms that can simultaneously coordinate to a metal ion, thereby occupying two or more coordination sites.
Ammonia, either directly or indirectly, is also a building block for the synthesis of many pharmaceuticals.
Three of these electron pairs are used as bond pairs, which leaves one lone pair of electrons.
The scientific interest in this problem is motivated by the unusual structure of the active site of the enzyme, which consists of an Fe7MoS9 ensemble.
Methylamine is prepared commercially by the reaction of ammonia with chloromethane, and the reaction of ammonia with 2-bromopropanoic acid has been used to prepare racemic alanine in 70% yield. Ammonium salts of carboxylic acids can be dehydrated to amides so long as there are no thermally sensitive groups present: temperatures of 150–200 °C are required. Some notable ammine complexes include tetraamminediaquacopper(II) ([Cu(NH3)4(H2O)2]2+), a dark blue complex formed by adding ammonia to solution of copper(II) salts.

This key material is generated via the Ostwald process by oxidation of ammonia with air over a platinum catalyst at 700–850 °C, ~9 atm. Ammonia is used less frequently in commercial applications, such as in grocery store freezer cases and refrigerated displays due to its toxicity.
It is however significantly less efficient than batteries.[citation needed] The 60 MW Rjukan dam in Telemark, Norway produced ammonia via electrolysis of water for many years from 1913 producing fertilizer for much of Europe. No Brasil, este tipo de intoxicacao nao tem uma classificacao adequada quanto a sua ocorrencia, principalmente pela falta de um numero maior de registros estatisticos sobre o assunto.
A exposicao prolongada pode acarretar problemas mais serios aos trabalhadores, com destaque aqueles de origem neurologica.
Nos cabelos, o chumbo esta ligado aos aminoacidos, principalmente os aminoacidos sulfurados presentes nos fios. Na medida em que a exposicao persiste, o paciente apresenta sintomas semelhantes aos de tumores cerebrais, o que tambem dificulta o diagnostico. Most reptiles, birds, as well as insects and snails solely excrete uric acid as nitrogenous waste.
Ammonia does not burn readily or sustain combustion, except under narrow fuel-to-air mixtures of 15–25% air.
Ethanolamine is prepared by a ring-opening reaction with ethylene oxide: the reaction is sometimes allowed to go further to produce diethanolamine and triethanolamine. If produced from coal, the CO2 can be readily sequestered [39][40] (the combustion products are nitrogen and water). Atualmente, o oxido de chumbo nao e mais utilizado na fabricacao de tintas de parede como ocorreu no passado. Convulsoes e delirios sao os sintomas subsequentes e a pessoa pode atingir o estado de coma. Because they appear to grasp the metal between two or more donor atoms, polydentate ligands are also known as chelating agents (from the Greek word chele, "claw"). The nitrogen atom in the molecule has a lone electron pair, which makes ammonia a base, a proton acceptor. One such ligand is ethylenediamine: This ligand, which is abbreviated en, has two nitrogen atoms (shown in color) that have unshared pairs of electrons. At high temperature and in the presence of a suitable catalyst, ammonia is decomposed into its constituent elements.
Os compostos organicos contendo chumbo sao lipossoluveis (soluveis em gorduras), sendo que uma pequena quantidade do metal pode se acumular no cerebro.
These donor atoms are sufficiently far apart that the ligand can wrap around a metal ion with the two nitrogen atoms simultaneously complexing to the metal in adjacent positions. The molecule's polarity and, especially, its ability to form hydrogen bonds, makes ammonia highly miscible with water.
Ignition occurs when chlorine is passed into ammonia, forming nitrogen and hydrogen chloride; if chlorine is present in excess, then the highly explosive nitrogen trichloride (NCl3) is also formed.
Se o doente intoxicado sobreviver a fase aguda do envenenamento por chumbo, a cura e a recuperacao podem ser totais.
The [Co(en)3]3+ ion, which contains three ethylenediamine ligands in the octahedral coordination sphere of cobalt(III), is shown in Figure 24.4. Notice that the ethylenediamine has been written in a shorthand notation as two nitrogen atoms connected by a line.
Ethylenediamine is a bidentate ligand ("two-toothed" ligand), one that can occupy two coordination sites.
It can wrap around a metal ion using all six of these donor atoms, as shown in Figure 24.6. The generally larger formation constants for polydentate ligands as compared with the corresponding monodentate ligands is known as the chelate effect. Chelating agents are often used to prevent one or more of the customary reactions of a metal ion without actually removing it from solution. For example, a metal ion that interferes with a chemical analysis can often be complexed and its interference thereby removed. Chelating agents are used in medicine to remove metal ions such as Hg2+, Pb2+, and Cd2+, which are detrimental to health. Many enzymes, the body's catalysts, require metal ions to function. Although our bodies require only small quantities of metals, deficiencies can lead to serious illness. Different porphyrins contain different metals and have different substituent groups attached to the carbon atoms at the ligand's periphery. This molecule forms a tetradentate ligand with the loss of the two protons bound to nitrogen atoms. Myoglobin is an example of a globular protein, one that folds into a compact, roughly spherical shape (Figure 24.9(b)).
Myoglobin is found in the cells of skeletal muscle, particularly in seals, whales, and porpoises.
The heme unit is bound to the protein through a nitrogen-containing ligand, represented by the blue N on the left. The iron is coordinated to the four nitrogen atoms of the porphyrin and also to a nitrogen atom from the protein.
The sixth position around the iron is occupied either by O2 (in oxyhemoglobin, the bright red form) or by water (in deoxyhemoglobin, the purplish red form).
The iron is bound to four nitrogen atoms of the porphyrin, to a nitrogen from the surrounding protein, and to an O2 molecule. A metal complex is also at the heart of photosynthesis, the major means for conversion of solar energy into forms that can be used by living organisms. This system of alternating, or conjugated, double bonds gives rise to the strong absorptions of chlorophyll in the visible region of the spectrum.
Figure 24.12 shows the absorption spectrum of chlorophyll as compared with the distribution of solar energy at Earth's surface.
This stored energy is then used to drive the reaction in Equation 24.6 to the right, a direction in which it is highly endothermic.
Once the structures of complexes were more fully understood, it became possible to name them in a more systematic manner.
Let's consider two examples: These examples give you a sense of how coordination compounds are named. Here are the rules that govern naming of this class of substances: In naming salts, the name of the cation is given before the name of the anion. Prefixes that give the number of ligands are not considered part of the ligand name in determining alphabetical order. Thus, in the [Co(NH3)5Cl]2+ ion we name the ammonia ligands first, then the chloride, then the metal: pentaamminechlorocobalt(III).
Note, however, that in writing the formula, the metal is listed first. The names of the anionic ligands end in the letter o, whereas neutral ones ordinarily bear the name of the molecules.
If the ligand itself contains a prefix of this kind (for example, ethylenediamine), alternate prefixes are used (bis-, tris-, tetrakis-, pentakis-, hexakis-) and the ligand name is placed in parentheses.
The oxidation state of the nickel is zero: Because the complex is an anion, the metal is indicated as nickelate(0).

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