Methyl mercury complexes

An x-ray study of allopurinol (53) indicates that it exists in the 1H form. It is apparent that hydrogen bonding patterns in the crystal lattice may be responsible for the preferred protonation site in the solid state. Intramolecular N(l)-H-N(7) and N(5)-H-0(4) contacts for allopurinol and N(2)-H-0(4) contacts for allopurinol cation are observed. The crystal structure of the methyl mercury complex (56) indicated that N-l and N-5 are respective coordination sites. Similar structures have been proposed for allopurinol copper complexes <87ZN(B)195>. 

Periana et al. [46] reported selective catalytic oxidation of methane by sulfuric acid to produce methyl bisulfate at 180 °C. The reaction is catalyzed by mercuric ions. Sulfur dioxide is the product of sulfuric acid reduction. At methane conversion of 50%, 85% selectivity to methyl bisulfate is observed. The major side product is carbon dioxide. The mercury turnover efficiency is 10 s The ion reacts with methane as an electrophile substituting a proton and producing initially an intermediate methylated mercury complex, CHsHgOSOsH. The complex is formed in appreciable steady-state concentration and was observed directly by C and NMR spectroscopy. Under tbe reaction conditions, methyl mercuric bisulfate decomposes to produce methyl bisulfate, CHsOSOjH, and the reduced mercurous species, Hg2. The catalytic cycle is completed by reoxidation ofHg2 with H2SO4 to regenerate and to form other products, SO2 and HaO. 

In an earlier paper Westoo pointed out that if methylmercury attached itself to a sulphur atom by reaction with a thiol or hydrogen sulphide then the non-volatile HgS compound produced would not be included in the determination. More recently he has developed a modification to this method described below, to render it applicable to a wider range of foodstuffs (egg-yolk and white, meat and liver) by binding interfering thiols in the benzene extract of the sample to mercuric ions added in excess or, by extracting the benzene extract with aqueous cysteine to form the cysteine-methyl mercury complex. 

Since P2S5 attacks both the lactone and the lactam function in the B/C component with equal facility, it was necessary to resort to intermediate conversion of the free lactam to a methyl-mercury complex which allowed specific activation of the lactam oxygen towards attack by the alkylating agent, without affecting the lactone carbonyl. 

With respect to Cr a distinction should be made between Cr(III), which is the common oxidation state in the soils, being rather immobile and so toxic, and Cr(VI), which is very mobile and very toxic. With respect to Hg, the situation is even more complex, due to the occurrence of mercuric mercury (Hg2+), mercurous mercury (Hg2+), elemental mercury (Hg°) and organic mercury species, such as methyl mercury, (CH3)2Hg (see Section 18.5). Furthermore, volatilization of elemental mercury and organic mercury species is common. A description of these... 

C4H 2OSi, Silane, methoxytrimethyl-, 26 44 CH4N, Propane, 2-isocyant-2-methyl-ruthenium complex, 26 275 C][l,4]-dithiin-2-thione, 26 389 CHfc, 1,3-Cyclopentadiene cobalt complex, 26 191-197, 309 chromium, molybdenum, and tungsten complexes, 26 343 iron complex, 26 232-241 mercury-molybdenum-ruthenium complex, 26 333... 

CsHuN, Ethanamine, A-ethyl-A-methyl-tungsten complex, 26 40, 42 C6HF5, Benzene, pentafluoro-gold complexes, 26 86-90 C H4I2, Benzene, 1,2-diido-iridium complex, 26 125 CJT, Phenyl platinum complex, 26 136 C,H,N, Pyridine osmium complex, 26 291 OHtS, Benzenethiol osmium complex, 26 304 QH7P, Phosphine, phenyl-cobalt-iron complex, 26 353 QH 1-Butyne, 3,3-dimethyl-mercury-molybdenum-ruthenium complex, 26 329-335 C6H 4P, Phosphine, triethyl-platinum complex, 26 126 platinum complexes, 26 135-140 CsHisPO, Triethyl phosphite iron complex, 26 61... 

Literally hundreds of complex equilibria like this can be combined to model what happens to metals in aqueous systems. Numerous speciation models exist for this application that include all of the necessary equilibrium constants. Several of these models include surface complexation reactions that take place at the particle-water interface. Unlike the partitioning of hydrophobic organic contaminants into organic carbon, metals actually form ionic and covalent bonds with surface ligands such as sulfhydryl groups on metal sulfides and oxide groups on the hydrous oxides of manganese and iron. Metals also can be biotransformed to more toxic species (e.g., conversion of elemental mercury to methyl-mercury by anaerobic bacteria), less toxic species (oxidation of tributyl tin to elemental tin), or temporarily immobilized (e.g., via microbial reduction of sulfate to sulfide, which then precipitates as an insoluble metal sulfide mineral). 

The classical compartmental and more complex PBPK models require actual pharmacokinetic data to calibrate some parameters such as metabolic rate constants. However, PBPK models are more data-intensive and require greater numbers of chemical-specific and receptor-specific inputs. Although PBPK models have been used extensively in the last 20 years to address cross-species differences and other uncertainties, there are cases in which simpler one- or two-compartment models have been sufficient for risk assessment, for example for methyl mercury (EPA 2001). 

TK interactions between metals and organic compounds are also possible phenan-threne appears to enhance the uptake of cadmium from sediment in the amphipod Hyalella azteca (Gust and Fleeger 2005). In the same species, chlorpyrifos enhances the accumulation of methyl mercury, but methyl mercury reduces acetylcholinesterase inhibition caused by chlorpyrifos, presumably due to the formation of a chlor-pyrifos-MeHg complex (Steevens and Benson 1999). 

Bioavailability and toxicity of metal ions in aqueous systems are often proportional to the concentration of the free metal ion and thus decrease upon complexation. However, there are some metal compounds more dangerous than the metallic element itself (e.g., mercury vs. methyl mercury). 

The ion Ca + does not form stable amine complexes. Except for methyl mercury, CH3Hg+, all the metal ions carry two positive charges. Owing to the strongly chelating... 

The value of the equilibrium constant for the reaction indicates that the favored direction of the reaction is actually from right to left. It is driven to the right by the strong complexation of Hg + with any of a large number of hgands. The third common form of mercury is as organic mercurials such as methyl mercury, CH3Hg+. 

SYNS ARTHO LM LIQUI-SAN LM SEED PROTECTANT METASOL METAZOL 8-(METHYLMERCURIOXY)QUINOLINE METHYLMERCURY (3-HYDROXYQUINOLATE METHYLMERCURY 8-HYDROXYQUINOLINATE Q METHYLMERCURY OXINATE METHYLMERCURY OXYQUINOLINATE ORTHO-LM APPLE SPRAY ORTHO LM CONCENTRATE ORTHO LM SEED PROTECTANT 8-(QUINOLINOLATO)METHYL MERCURY 8-QUINOLINOL, MERCURY COMPLEX... 

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