scholarly journals Nuclear magnetic resonance and potentiometric studies of the complexation of methylmercury(II) by dithiols

1985 ◽  
Vol 63 (9) ◽  
pp. 2430-2436 ◽  
Author(s):  
Alan P. Arnold ◽  
Allan J. Canty ◽  
R. Stephen Reid ◽  
Dallas L. Rabenstein
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Equilibrium Constants ◽  
Formation Constants ◽  
Resonance Spectroscopy ◽  
Nmr Study ◽  
Wide Ph Range ◽  
Anionic Species ◽  
Ph Range ◽  
Nuclear Magnetic

Complexation of methylmercury, CH3Hg(II), by 2,3-dimercaptosuccinic acid (DMSA), 2,3-dimercaptopropanesulfonate (DMPS, Unithiol), dithioerythritol (DTE), and 2,3-dimercaptopropanol (British AntiLewisite, BAL) has been studied by 1H nuclear magnetic resonance spectroscopy and by potentiometric titration. In the nmr study, the equilibrium constants for displacement of mercaptoacetate from its CH3Hg(II) complex by the dithiols were determined over a wide pH range, from mercaptoacetate chemical shift data. Similar competition reactions between the dithiols and mercaptoethanol were used in the potentiometric study. Using previously determined CH3Hg(II) formation constants for the competing ligands, equilibrium constants for the formation of mono- and bis-CH3Hg(II) complexes with the dithiols have been determined. The formation constants for the mono-CH3Hg(II) complexes with the vicinal dithiols BAL and DMPS are significantly higher than expected by consideration of the basicity of the sulfhydryl donors, in comparison with those for DMSA, non-vicinal DTE, and monothiols. We interpret this to indicate chelation of CH3Hg(II) by BAL and DMPS but not by DMSA. The conditional formation constants at physiological pH are discussed with reference to the effectiveness of BAL, DMPS, and DMSA as antidotes for methylmercury poisoning. In particular, the constants obtained indicate that, for dithiol antidotes at concentrations greater than that of methylmercury (II), methylmercury(II) complexes formed at physiological pH are of 1:1 stoichiometry. For BAL, a substantial proportion of the complex will be in the neutral form, in contrast to DMPS and DMSA which form anionic species only.

Nuclear magnetic resonance studies of the solution chemistry of metal complexes. XV. Trimethyllead complexes of inorganic ligands

1978 ◽  
Vol 56 (24) ◽  
pp. 3104-3108 ◽  
Author(s):  
Emiko K. Millar ◽  
Christopher A. Evans ◽  
Dallas L. Rabenstein
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Biological Fluids ◽  
Formation Constants ◽  
Solution Chemistry ◽  
Resonance Spectroscopy ◽  
Ligand Type ◽  
Conjugate Bases ◽  
Inorganic Ligands ◽  
Nuclear Magnetic

The formation constants of the trimethyllead(IV) complexes of SO32−, SeO32−, S2O32−, SCN−, HPO42−, CO32−, Cl−, Br−, and I− have been determined in aqueous solution by 1H nuclear magnetic resonance spectroscopy. The formation constants are in general fairly small and the extent to which complexes form is strongly dependent on pH. At high pH (CH3)3PbOH forms while at low pH protonation of those ligands which are the conjugate bases of weak acids competes with complex formation. There is no indication of high selectivity in the binding of trimethyllead(IV) by a particular ligand type, and calculations indicate that trimethyllead(IV) is likely to be distributed among a variety of ligands in biological fluids, including chloride which forms uncharged and presumably lipid soluble (CH3)3PbCl.

Skeletal muscle metabolism and work capacity: a 31P-NMR study of Andean natives and lowlanders

1991 ◽  
Vol 70 (5) ◽  
pp. 1963-1976 ◽  
Author(s):  
G. O. Matheson ◽  
P. S. Allen ◽  
D. C. Ellinger ◽  
C. C. Hanstock ◽  
D. Gheorghiu ◽  
...  
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Muscle Metabolism ◽  
Work Capacity ◽  
Calf Muscle ◽  
Whole Body ◽  
Resonance Spectroscopy ◽  
Muscle Work ◽  
Nmr Study ◽  
Nuclear Magnetic

Two metabolic features of altitude-adapted humans are the maximal O2 consumption (VO2max) paradox (higher work rates following acclimatization without increases in VO2max) and the lactate paradox (progressive reductions in muscle and blood lactate with exercise at increasing altitude). To assess underlying mechanisms, we studied six Andean Quechua Indians in La Raya, Peru (4,200 m) and at low altitude (less than 700 m) immediately upon arrival in Canada. The experimental strategy compared whole-body performance tests and single (calf) muscle work capacities in the Andeans with those in groups of sedentary, power-trained, and endurance-trained lowlanders. We used 31P nuclear magnetic resonance spectroscopy to monitor noninvasively changes in concentrations of phosphocreatine [( PCr]), [Pi], [ATP], [PCr]/[PCr] + creatine ([Cr]), [Pi]/[PCr] + [Cr], and pH in the gastrocnemius muscle of subjects exercising to fatigue. Our results indicate that the Andeans 1) are phenotypically unique with respect to measures of anaerobic and aerobic work capacity, 2) despite significantly lower anaerobic capacities, are capable of calf muscle work rates equal to those of highly trained power- and endurance-trained athletes, and 3) compared with endurance-trained athletes with significantly higher VO2max values and power-trained athletes with similar VO2max values, display, respectively, similar and reduced perturbation of all parameters related to the phosphorylation potential and to measurements of [Pi], [PCr], [ATP], and muscle pH derivable from nuclear magnetic resonance. Because the lactate paradox may be explained on the basis of tighter ATP demand-supplying coupling, we postulate that a similar mechanism may explain 1) the high calf muscle work capacities in the Andeans relative to measures of whole-body work capacity, 2) the VO2max paradox, and 3) anecdotal reports of exceptional work capacities in indigenous altitude natives.

KETO–ENOL TAUTOMERISM IN β-DICARBONYLS STUDIED BY NUCLEAR MAGNETIC RESONANCE SPECTROSCOPY: II. SOLVENT EFFECTS ON PROTON CHEMICAL SHIFTS AND ON EQUILIBRIUM CONSTANTS

1965 ◽  
Vol 43 (5) ◽  
pp. 1516-1526 ◽  
Author(s):  
Max T. Rogers ◽  
Jane L. Burdett
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Magnetic Resonance Spectroscopy ◽  
Nuclear Magnetic Resonance Spectroscopy ◽  
Chemical Shifts ◽  
Equilibrium Constants ◽  
Tautomeric Equilibrium ◽  
Resonance Spectroscopy ◽  
Proton Chemical Shifts ◽  
Nuclear Magnetic

The effect of various solvents on the proton chemical shifts of a number of acyclic β-di-ketones and β-ketoesters has been observed by nuclear magnetic resonance spectroscopy. These shifts are discussed in terms of the dissociation of intramolecular and intermolecular hydrogen bonds on dilution. A complex of benzene with the enol tautomer of the β-dicarbonyl molecule is proposed. The effect of solvents on the position of the tautomeric equilibrium is discussed.

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

1981 ◽  
Vol 59 (10) ◽  
pp. 1505-1514 ◽  
Author(s):  
R. Stephen Reid ◽  
Dallas L. Rabenstein
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Formation Constants ◽  
Solution Chemistry ◽  
The Other ◽  
Mercaptoacetic Acid ◽  
Resonance Spectroscopy ◽  
Mercaptosuccinic Acid ◽  
Wide Range ◽  
Nuclear Magnetic

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 Brønsted basicity of the deprotonated sulfhydryl group increases according to the relation log Kf = 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.

Complexes of vanadium(V) with α-hydroxycarboxylic acids studied by 1H, 13C, and 51V nuclear magnetic resonance spectroscopy

1987 ◽  
Vol 65 (10) ◽  
pp. 2434-2440 ◽  
Author(s):  
M. Madalena Caldeira ◽  
M. Luísa Ramos ◽  
Nuno C. Oliveira ◽  
Victor M. S. Gil
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Magnetic Resonance Spectroscopy ◽  
Relative Stability ◽  
Nuclear Magnetic Resonance Study ◽  
Resonance Spectroscopy ◽  
Magnetic Resonance Study ◽  
Hydroxycarboxylic Acids ◽  
Ph Range ◽  
Nuclear Magnetic

A proton, carbon-13, and vanadium-51 nuclear magnetic resonance study is reported on the number, stoichiometry, geometry, and relative stability of the complexes that form when vanadate(V) solutions are mixed with each one of the following organic α-hydroxyacids in the pH range ~2.5 – ~7: glycolic, lactic, chloro-3- and phenyl-3-lactic, mandelic, glyceric, and malic acids. The predominant complexes have 1:1 composition (almost certainly in a polymeric structure) in contrast with the 1:2 (metal:ligand) stoichiometry of the corresponding Mo(VI) and W(VI) complexes.

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