- A Long-Path Fourier Transform Infrared Study of the Kinetics and Mechanism for the HO-Radical Initiated Oxidation of Dimethylmercury
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Gaseous and aerosol products formed in the HO-radical initiated reaction of CH3HgCH3 were studied by the long-path FT IR method in the photolysis of CH3HgCH3-C2H5ONO-NO mixtures typically at 10, 10, and 20 ppm each in 700 torr of air at ca. 300 K.The results were consistent with the predominant occurence of the displacement reaction of HO + CH3HgCH3 -> CH3HgOH + CH3 as the primary process.The relative rate constant for the HO-radical reactions of CH3HgCH3 and C2H4 was determined to be k(C3H4)/k(CH3HgCH3) = 0.43 +/- 0.03(?).This value combined with the literature value of k(C2H4) = (8.48 +/- 0.39) X 10-12 cm3 molecule-1 s-1.
- Niki, H.,Maker, P. D.,Savage, C. M.,Breitenbach, L. P.
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- METHYLMERCURY(III) COMPLEXES WITH TRYPTOPHAN AND ITS N-ACETYL DERIVATIVE
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CH3HgOH reacts with tryptophan in aqueous ethanol to form a 2:1 neutral complex in which CH3Hg groups are bound to the terminal amino group and to the deprotonated indole nitrogen.When this complex is dissolved in water, 1H and 13C nuclear magnetic resonance show that the indole CH3Hg group hydrolyzes, leading to an amino-bound 1:1 species.Under the same conditions, N-acetyltryptophan forms a neutral 1:1 compound where the metal is bound to a carboxylate oxygen, and a neutral 2:1 complex in which an extra CH3Hg group is fixed to the deprotonated indole ring.It is shown by 1H and 13C nuclear magnetic resonance that the 1:1 species is stable in DMSO-d6, but that the 2:1 compound is readily hydrolyzed to the 1:1 compound by traces of water.The solid-state infrared and Raman spectra are discussed.In the crystal structure of the 2:1 tryptophan complex, the ligand adopts a conformation favoring a short intramolecular ? interaction between Hg and the indole ring.No such ? interaction is found in the crystal structure of the 1:1 carboxylate-bonded complex with acetyltryptophan.
- Corbeil, Marie-Claude,Beauchamp, Andre L.
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p. 2458 - 2464
(2007/10/02)
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- A Raman spectroscopic study of the complexation of the methylmercury(II) cation by amino acids
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A systematic Raman spectroscopic investigation of the complexation of CH3Hg(1+) by the standard amino acids is reported.It is shown that the vibrational bands due to the ligand-Hg and Hg-CH3 stretching modes and to the symmetric -CH3 bending mode of the -HgCH3 unit are well suited to characterize the extent of complexation and the sites of attachment of the cation.Coordination, which occurs mostly on sulfur and nitrogen atoms by substitution of a proton on the thiol group of cysteine or on amino groups in general, is best identified by the frequency of the ligand-Hg stretching vibration in the 250-550 cm-1 region of the spectrum.
- Alex, Serge,Savoie, Rodrigue
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p. 491 - 496
(2007/10/02)
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- Methylmercury(II) sulfhydryl interactions. Potentiometric determination of the formation constants for complexation of methylmercury(II) by sulfhydryl containing amino acids and related molecules, including glutathione
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Formation constants for the interaction of methylmercury(II) with 2-mercaptoethanol, mercaptoacetic acid, O-methylmercaptoacetate, 2-mercaptosuccinic acid, L-cysteine, D,L-penicillamine, N-acetyl-D,L-penicillamine, glutathione, thiocholine, and 4-mercapto-N-methylpiperidine have been determined by potentiometric titration.For the equilibrium MeHg+ + RSn- 1-n, log β occurs in the range 14.60(1)-17.14(1), with the lowest value obtained for the cationic complex of thiocholine, MeHgSCH2CH2N+Me3.Acid dissociation constants for the ligands are reported.Formation constants for the addition of both one and two equivalents of MeHg(II) to L-cysteine have been determined, giving log K ca. 4.1 for the reaction MeHgSCH2CH(N+H3)(CO2H) + MeHg+ (MeHg)2S+CH2CH(N+H3)(CO2H) occurring at low pH, and log K 8.8 for the reaction MeHgSCH2CH(NH2)CO2- + MeHg+ MeHgSCH2CH(N+H2HgMe)CO2- occurring at higher pH.
- Arnold, Alan P.,Canty, Allan J.
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p. 1428 - 1434
(2007/10/02)
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- Nuclear magnetic resonance studies of the solution chemistry of metal complexes. XVII. Formation constants for the complexation of methylmercury by sulfhydryl-containing amino acids and related molecules
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Complexation of methylmercury, CH3Hg(II), by mercaptoacetic acid, mercaptoethanol, mercaptosuccinic acid, cysteine, penicillamine, homocysteine, and N-acetylpenicillamine has been studied by 1H nuclear magnetic resonance spectroscopy.The equilibrium constant for displacement of mercaptoacetic acid from its CH3Hg(II) complex by each of the other thiols was measured over a wide range of pH.From the displacement constants and a literature value for the formation constant of the mercaptoethanol complex of CH3Hg(II), formation constants were calculated for thiol complexes with the other ligands, including microscopic formation constants for cysteine and penicillamine complexes in which the amino groups are protonated and deprotonated.Detailed information on the acid-base chemistry of the free amino and carboxylic acid groups in the complexes is also reported.The formation constants increase as the Bronsted basicity of the deprotonated sulfhydryl group increases according to the relation logKf = pK + 6.86 .The conditional formation constants of the CH3Hg(II) complexes are strongly pH dependent due to competitive reactions involving hydrogen and hydroxide ions at low and high pH.The results at physiological pH are discussed with reference to the effectiveness of mercaptosuccinic acid, N-acetylpenicillamine, and penicillamine as antidotes for methylmercury poisoning.
- Reid, R. Stephen,Rabenstein, Dallas L.
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p. 1505 - 1514
(2007/10/02)
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