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.

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.

NUCLEAR MAGNETIC RESONANCE SPECTRA OF GLYCOL-CLEAVAGE OXIDATION PRODUCTS OF METHYL ALDOPENTOPYRANOSIDES

1966 ◽  
Vol 44 (15) ◽  
pp. 1757-1764 ◽  
Author(s):  
A. S. Perlin
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Deuterium Oxide ◽  
Periodate Oxidation ◽  
Chair Conformation ◽  
The Other ◽  
Oxidation Products ◽  
Hydroxyl Group ◽  
Resonance Spectroscopy ◽  
Nuclear Magnetic

The products obtained by the periodate oxidation of methyl α- and β-D-xylopyranosides have been examined by nuclear magnetic resonance spectroscopy. In deuterium oxide each product exists mainly in two forms, one of which is a hydrated dialdehyde and the other a hemialdal (1,4-dioxane derivative). In dimethyl sulfoxide the dialdehyde cyclizes slowly to yield the hemialdal which, at equilibrium, is found to be by far the most stable of the many isomeric forms possible. The spectrum of this hemialdal in both solvents provides an example of a degenerate ABX type of pattern. The spectra of the products prepared from 5-deuterated xylosides show that the 1-methoxyl group of each hemialdal is axial and the 4-hydroxyl group equatorial, and that the one derived from the β-anomer possesses an inverted chair conformation relative to that of the other hemialdal and of the glycoside itself. The 2-hydroxyl group of each hemialdal appears to be axially oriented. The data support the long-standing view that glycol scission of anomeric aldopentopyranosides leads to products that are mirror images.It has been found also that each product yields a mixture of several p-nitrobenzoates.

A nuclear magnetic resonance study of hydrogen bonding of δ-valerolactam

1969 ◽  
Vol 47 (19) ◽  
pp. 3655-3660 ◽  
Author(s):  
J. M. Purcell ◽  
H. Susi ◽  
J. R. Cavanaugh
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Hydrogen Bond ◽  
Hydrogen Bonding ◽  
Magnetic Resonance ◽  
Chemical Shifts ◽  
Bond Formation ◽  
Resonance Spectroscopy ◽  
Hydrogen Bond Formation ◽  
Wide Range ◽  
Nuclear Magnetic

The association of amide groups of δ-valerolactam through hydrogen bonding has been investigated by means of high resolution nuclear magnetic resonance spectroscopy in CCl4 and CDCl3 solutions. Chemical shifts of the NH proton signal were measured over a wide range of temperatures and concentrations. Thermodynamic properties associated with the [Formula: see text] hydrogen bond formation were evaluated from a least squares analysis by a direct search procedure with a digital computer. The obtained enthalpy values for hydrogen bond formation are in general agreement with results obtained by other methods.

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.

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