Divalent ions mercury

A summary of the thermodynamic properties of elemental mercury and its compounds has appeared. Although Hg is considered a class b or soft metal ion see Class A Class B Behavior and Hard Soft Acids and Bases), its coordination behavior suggests that it functions as a harder acid than the divalent ion. Advanced texts have discussed the chemistry of the element and its compounds. ... 

We end this chapter with a brief discussion of two sample preparation methods. The first is to determine mercury (Hg) and the second method determines cyanide (CN ). Both parameters are important with respect to the evaluation of a sample as a hazardous waste. The presence of either Hg or cyanide renders a sample hazardous due to the acute toxicity of both species. Mercury exists either in elemental form, as the dimer ion Hg2 in which the oxidation state of the element is +1, or as the divalent ion Hg. The elemental form is the familiar liquid silver metal obtained by roasting cinnabar, HgS (106). The cyanide ion is a moderately strong base derived from the weak acid hydrocyanic acid, HCN. HCN is a gas at room tem-... 

Cation liquid ion-exchanger sensors are much more varied in type (99). Some examples are dialkyl- and di(alkylphenyl) phosphates for calcium and divalent ions (as discussed above) tetraphenylborates for onium ions and for drug type cations either by directly or by potentiometric titration lead diethyldithiocarbamate in trichloroethane for lead(II) (100) and mercury(II) PAN chelate in trichloromethane for mercury (101). 

According to the results of Clarkson et al. (1980) the divalent cation should be seen as the effective form of metallic mercury, especially because metallic mercury cannot form a chemical bond. Metallic mercury is non-polar and soluble in lipids. Particularly in vapour form it dissolves readily in membrane lipids so that it penetrates the alveolar membranes quickly and efficiently when inhaled, and is diffused into the blood. There it is partially absorbed by the erythrocytes and oxidised to the divalent ion which reacts with SH groups. Inspite of the efficient diffusion into the erythrocyte, sufficient quantities of the metallic mercury dissolved in the blood can be transported to the brain, where they are also reduced to the mercury ion (Magos, 1967 Magos et al., 1973). As far as the toxicity of mercury is concerned, its oxidation produces different effects in the... 

Several other rather novel methods for the separation of the lanthanides are discussed in the above text. Eu, Yb, and Sm can be reduced by amalgams of the alkali or alkaline earth metals to either the metal or the divalent ions which can be precipitated as sparingly soluble sulfates, RSO4. Electrolytic reduction at a mercury cathode can be used to separate the above three elements. A number of... 

Brine Purification. In mercury cells, traces of heavy metals in the brine give rise to dangerous operating conditions (see p. 32), as does the presence of magnesium and to a lesser extent calcium (521. In membrane cells, divalent ions such as Ca or Mg are harmful to the membrane. The circulating brine must be rigorously purified to avoid any buildup of these substances to undesirable levels [7]. Calcium is usually precipitated as the carbonate with sodium carbonate magnesium and iron, as hydroxides with sodium hydroxide and sulfate, as barium sulfate. 

The mercurous ion Hg2 has a single intermetallic bond joining the Hg(I) metal centers. Irradiation into the <7 —> (7 orbital of this ion leads to the formation of the Hg" ion. When the photolysis of Hg2 is carried out in the presence of ethyl alcohol, reduction of the Hg" ion to elemental mercury occurs. If the divalent ion Hg is also present in the reaction, a rapid electron transfer reaction occurs between Hg and Hg " to give... 

More importantly, the mobile species are likely to be associated and the nature of these species and degree of association will depend on the anion, cation and salt concentration. The majority of studies on divalent cation polymer electrolytes have involved divalent ions as the salt. These series of salts have an associated problem in that results may not be directly comparable because there is considerable variation in the character of the anion-cation bond. For example, the chlorides of zinc, cadmium and mercury show a sharp transition from ionic to covalent character. Likewise, the tendency oF for example, zinc halides to form complexes, decreases on going from the chloride to the iodide. Mercury halides are too covalent to allow free Hg + ion to form in solution. Thus, HgCl dissociates only slightly to give FlgCL and CL. 

In mammals, as in yeast, several different metallothionein isoforms are known, each with a particular tissue distribution (Vasak and Hasler, 2000). Their synthesis is regulated at the level of transcription not only by copper (as well as the other divalent metal ions cadmium, mercury and zinc) but also by hormones, notably steroid hormones, that affect cellular differentiation. Intracellular copper accumulates in metallothionein in copper overload diseases, such as Wilson s disease, forming two distinct molecular forms one with 12 Cu(I) equivalents bound, in which all 20 thiolate ligands of the protein participate in metal binding the other with eight Cu(I)/ metallothionein a molecules, with between 12-14 cysteines involved in Cu(I) coordination (Pountney et ah, 1994). Although the role of specific metallothionein isoforms in zinc homeostasis and apoptosis is established, its primary function in copper metabolism remains enigmatic (Vasak and Hasler, 2000). 

The double-layer effect in the electrode kinetics of the amalgam formation reactions was discussed [67]. The dependences on the potential of two reduction (EE) mechanisms of divalent cations at mercury electrode, and ion transfer-adsorption (lA) were compared. It was suggested that a study of temperature dependence of the course of these reactions would be helpful to differentiate these two mechanisms. 

The apparent anomaly between mercury and the lighter elements of transition group 2. in that mercury regularly forms both univalent and divalent compounds, while zinc and cadmium do so very rarely, is partly under mm id from the observation that mercury III salts ionize even in the gaseous late to Hg.. rather than Hg Evidence for this double ion is provided by its Hainan spectral line, by the lineal CI-Hg-Hg-CI units in crystals or mercury It chloride, and by the cml of incrciirytll nitrate concentration cells The anomaly is fuitlicr removed by the obsetv.ttioii that cadmium also forms a (much less stable) diatomic ton Cdj T eg., ill Cd.-lAICL) . 

Fuhninic acid, C=N H C=N-OH, is a divalent carbon derivative hke carbon monoxide it is formally an oxime of carbon monoxide. Free fuhninic acid is unstable, but the explosive mercury salt, which is used as a detonator, is obtained by treatment of elemental mercury with a mixture of ethanol and lutric acid. The fulminate ion, C=N-0, like carbon monoxide and cyanide ion, functions as a strong-field... 

A high affinity of polyvalent metal phosphates for divalent cations is not an unusual fact [1]. There are dozens of known exchangers with much higher capacities than that found for the 1. Nevertheless, this layered compound is an extremely interesting ion-exchanger. He shows a uniquely high affinity for the mercury(II) ion, while all other known titanium phosphate or titanium arsenate sorbents do not exhibit any preference for the Hg cation. 

Metal ions in aqueous solution generally hydrolyze to form a series of mononuclear ind polynuclear hydroxy complexes. Iron(III) for example forms [FeOH] ", [Fe(OH)2], Fe(OH)3(aq), [Fe(OH)4] , [Fe2(OH)2] and probably other polynuclear species. The formation af a monohydroxy complex (equation 1) can be used as a guide to the degree of electron withdrawal by the cation. Typical pJCa values for various cations are listed in Table 2. (The pJCa values of and HjO are -1.7 and 15.7 respectively.) The tetrahedrally coordinated [Be(H20)4] ion is more acidic than expected when compared with octahedrally coordinated aqua ions of divalent metals. Each hydrogen must carry a somewhat greater portion of the positive charge than it would in an octahedral complex, and this makes removal of a proton easier. Similar considerations apply to square planar Pd (aq). Mercury(II) and tin(II) are also more acidic than would be expected. The high acidity of mercury(II) is due to the unusual stability of linear H2O—Hg—OH, while Sn (aq) has between two and three coordinated water molecules in the inner coordination sphere. ... 

After exposure to mercury vapor, mercury is distributed throughout the body in different chemical and physical states. Metallic mercury dissolves in the blood upon inhalation, and some remains unchanged (Magos 1967). Metallic mercury in the blood is oxidized to its divalent form in the red blood cells (Halbach and Clarkson 1978). The divalent cation exists as a diffusible or nondiffusible form. The nondiffusible form is mercuric ions that bind to protein and are held in high-molecular weight complexes, existing in equilibrium with the diffusible form. 

Metallic and Inorganic Mercury. Data on the distribution of ingested elemental mercury were not located, and data on the ingestion of inorganic mercury are limited. The metallic mercury that is absorbed from an oral exposure is expected to resemble many aspects of the distribution of mercuric salts because metallic mercury is oxidized to mercuric ion in biological fluids, and the resulting distribution reflects that of the mercuric ion. Unlike elemental mercury, however, the amount of divalent mercury that crosses the blood-brain and placental barriers is much lower because of its lower lipid solubility (Clarkson 1989). 

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