Nuclear magnetic resonance studies of the solution chemistry of metal complexes. XIV. The aqueous chemistry of trimethyllead(IV) and its carboxylic acid complexes

1977 ◽  
Vol 55 (18) ◽  
pp. 3255-3260 ◽  
Author(s):  
T. L. Sayer ◽  
S. Backs ◽  
C. A. Evans ◽  
E. K. Millar ◽  
D. L. Rabenstein
Keyword(s):  
Carboxylic Acid ◽  
Magnetic Resonance ◽  
Proton Magnetic Resonance ◽  
Ph Dependence ◽  
Equilibrium Constants ◽  
Formation Constants ◽  
Solution Chemistry ◽  
Resonance Spectroscopy ◽  
Coupling Constant ◽  
Proton Coupling

The aqueous solution chemistry of the trimethyllead(IV) species and the trimethyllead(IV) complexes of six carboxylic acids of pKa values ranging from 2.75 to 4.95 has been investigated by proton magnetic resonance spectroscopy. Equilibrium constants for the reaction of (CH3)3Pb+ with hydroxide ion to form (CH3)3PbOH and ((CH3)3Pb)2OH+, and the formation constants of the carboxylic acid complexes were determined from the pH dependence of the chemical shift of the methyl protons of trimethyllead. The formation constants of the complexes increase as the pKa of the ligand increases. The lead-207-proton coupling constant was found to be insensitive to complexation.

Nuclear Magnetic Resonance Studies of the Solution Chemistry of Metal Complexes. II. Protonation of the Peptide Linkages of Bis(glycylglycinato)cobaltate(III)

1971 ◽  
Vol 49 (23) ◽  
pp. 3767-3771 ◽  
Author(s):  
Dallas L. Rabenstein
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Proton Magnetic Resonance ◽  
Proton Magnetic Resonance Spectroscopy ◽  
Equilibrium Constants ◽  
Solution Chemistry ◽  
Resonance Spectroscopy ◽  
Ph Titration ◽  
Magnetic Resonance Studies ◽  
Protonation Equilibria

Protonation of bis(glycylglycinato)cobaltate(III) in acidic aqueous solutions has been investigated by proton magnetic resonance spectroscopy. Chemical shift measurements indicate that the site of protonation is the peptide oxygen rather than the Co(III)-coordinated, deprotonated peptide nitrogen as previously proposed, and that the two peptide linkages are protonated in a stepwise fashion rather than simultaneously. Equilibrium constants for the stepwise protonation equilibria have been derived from the n.m.r. data. The equilibrium constant for the first protonation step has also been determined by pH titration.

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.

Metal – Aminopolycarboxylic Acid Complexes. II. Studies of Triethylenetetraaminehexaacetic Acid and its Lead(II) Complexes in Aqueous Solution by Proton Magnetic Resonance Spectroscopy

1971 ◽  
Vol 49 (12) ◽  
pp. 2086-2095 ◽  
Author(s):  
P. Letkeman ◽  
J. B. Westmore
Keyword(s):  
Magnetic Resonance ◽  
Proton Magnetic Resonance ◽  
Proton Magnetic Resonance Spectroscopy ◽  
Equilibrium Constants ◽  
The Other ◽  
Resonance Spectroscopy ◽  
Carboxylate Groups ◽  
Triethylenetetraaminehexaacetic Acid ◽  
Nitrogen Bonds ◽  
Aminopolycarboxylic Acid

Nuclear magnetic resonance (n.m.r.) spectroscopy was used to determine the preferred protonation sites in TTHA. For its 1:1 complex with Pb(II) the following equilibrium constants for protonation were obtained (triethylenetetraaminehexaacetic acid ≡ H6A)[Formula: see text]The non-protonated complex is considered to have four coplanar (or nearly coplanar) metal–nitrogen bonds with the center carboxylate groups coordinated above and below this plane, and with the terminal carboxylate groups playing only a small part in the coordinate bonding. The first and second protonations of the complex occur preferentially at the terminal and center nitrogen atoms, respectively, on the same side of the complex, accompanied by breaking of the respective metal–nitrogen bonds. This causes partial unwrapping of the complex from one side. Rapid interconversion between configurations in which unwrapping and rewrapping occurs first from one side of the molecule and then from the other leads to simplified n.m.r. spectra.

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.

Determination of the molecular conformation of uridine in aqueous solution by proton magnetic resonance spectroscopy. Comparison with β-pseudouridine

1970 ◽  
Vol 48 (18) ◽  
pp. 2866-2870 ◽  
Author(s):  
Barry J. Blackburn ◽  
Arthur A. Grey ◽  
Ian C. P. Smith ◽  
Frank E. Hruska
Keyword(s):  
Magnetic Resonance ◽  
Proton Magnetic Resonance ◽  
Molecular Conformation ◽  
Chemical Shifts ◽  
Proton Magnetic Resonance Spectrum ◽  
Coupling Constants ◽  
Complete Analysis ◽  
Resonance Spectroscopy ◽  
Proton Coupling ◽  
Anti Conformation

A complete analysis of the 220 MHz proton magnetic resonance spectrum of aqueous uridine is reported. From the data a model for the molecular conformation is presented and compared with that of β-pseudouridine. It is concluded that in both compounds the ribose rings are in rapid equilibrium between classical puckered structures. The temperature-independence of the ribose proton coupling constants and chemical shifts suggests that all the conformers involved in this equilibrium have very similar energies. Both compounds exhibit a preference for the gauche–gauche rotamer about the exocyclic 4′—5′ bond; this conclusion is shown to be independent of the parameters in the Karplus equation or the energy minima chosen for the rotamers. The anti conformation of the uracil base is shown to exist in both compounds. It is proposed that the special structural significance of β-pseudouridine in transfer RNA must be due to the potential hydrogen bond that may be formed by the nitrogen atom at position one in uracil.

TRIDENTATE COMPLEXES OF PERIODATE AND SOME FURANOSE DERIVATIVES

1965 ◽  
Vol 43 (7) ◽  
pp. 2071-2077 ◽  
Author(s):  
A. S. Perlin ◽  
E. Von Rudloff
Keyword(s):  
Magnetic Resonance ◽  
Proton Magnetic Resonance ◽  
Proton Magnetic Resonance Spectroscopy ◽  
General Concept ◽  
Resonance Spectroscopy ◽  
Proton Proton ◽  
Preferential Formation ◽  
Proton Coupling ◽  
The Stability ◽  
Transient Intermediate

1,2-O-Isopropylidene-α-D-glucofuranose (I) is highly resistant to glycol scission by periodate in alkaline solution. This atypical effect is caused by preferential formation of a stable periodate complex. Proton magnetic resonance spectroscopy shows that the 3-, 5-, and 6-protons of I (and the 3- and 5-protons of I-6,6′-d2) become strongly deshielded during this process, which, together with accompanying changes in proton–proton coupling, establishes that the complex (II) has a 3,5,6-tridentate structure. Variations in the stability of II with pH suggest that it can exist either as a monoanion or dianion. A complex analogous to II is formed by ethyl α-D-thioglucofuranoside, whereas methyl β-D-galactofuranoside forms a complex that probably has the 2,5,6-structure. The characteristics of these tridentate complexing reactions support the general concept that a five-membered cyclic complex is a transient intermediate of α-glycol oxidation by periodate.

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. XIII. The Lability of the Metal–Nitrogen Bonds in the Cadmium, Zinc, and Mercury Complexes of Selected Polyaminocarboxylic Acids

1975 ◽  
Vol 53 (6) ◽  
pp. 787-791 ◽  
Author(s):  
Dallas L. Rabenstein ◽  
George Blakney ◽  
Bryan J. Fuhr
Keyword(s):  
Magnetic Resonance ◽  
Structural Changes ◽  
Solution Chemistry ◽  
Coupling Constants ◽  
Resonance Spectroscopy ◽  
Proton Coupling ◽  
Mercury Complexes ◽  
Relative Kinetic ◽  
Nitrogen Bonds ◽  
Stability Results

The lability of the metal–nitrogen bonds in the Cd(II), Zn(II), and Hg(II) complexes of (HO2CCH2)2N(CH2)nN(CH2CO2H)2 (n = 2, 3, 4) has been investigated by proton magnetic resonance spectroscopy. The acetate methylenic protons of each of the complexes give rise to AB multiplet patterns, indicating the metal–nitrogen bonds to be inert on the n.m.r. time scale. From the temperature dependence of the multiplet patterns, the relative lability of the metal–nitrogen bonds in each series of complexes has been established. In the Cd(II) and Zn(II) complexes, the metal–nitrogen bonds become more labile as the size of the internal chelate ring increases whereas it becomes more inert in the Hg(II) complexes. Also, the mercury–proton coupling constants increase as n is increased from two to four, which is interpreted as evidence that the increased kinetic stability results from structural changes to a more linear N—Hg—N arrangement. The metal–nitrogen bonds in the Cd(II) complexes having n = 3 and 4 is more labile than in the corresponding Zn(II) complexes. The thermodynamic stability patterns of the complexes are discussed in terms of their relative kinetic stabilities.

Proton magnetic resonance and Raman spectroscopic studies of methylmercury (II) complexes of inorganic anions

1976 ◽  
Vol 54 (16) ◽  
pp. 2517-2525 ◽  
Author(s):  
Dallas L. Rabenstein ◽  
M. Coreen Tourangeau ◽  
Christopher A. Evans
Keyword(s):  
Magnetic Resonance ◽  
Chemical Shift ◽  
Proton Magnetic Resonance ◽  
Formation Constants ◽  
Spin Coupling ◽  
Donor Atom ◽  
Coupling Constant ◽  
Spin Coupling Constant ◽  
Raman Spectral Data ◽  
Spin Spin Coupling

Complexation of methylmercury(II) by sulfate, selenate, carbonate, sulfite, selenite, thiocyanate, selenocyanate, sulfide, and selenide in aqueous solution has been studied by proton magnetic resonance and Raman spectroscopy. Formation constants were determined for the SO42−, SeO42−, CO32−, SO32−, SeO32−, SeO3H−, SCN−, and SeCN− complexes from the pH dependence of the chemical shift and the 199Hg−1H spin–spin coupling constant of the methyl group of CH3Hg(II) in solutions containing both CH3Hg(II) and ligand. The chemical shift and the 199Hg–1H spin–spin coupling constant of the CH3Hg(II) in each of the complexes were also obtained from the same measurements. Proton magnetic resonance parameters were measured for several complexes with sulfide and selenide. The ligand donor atom in each of the complexes was identified using the formation constants, the 199Hg–1H spin–spin coupling constant of the complexed methylmercury and the Raman spectral data. It is of particular interest that, in the selenite complex, the methylmercury is bonded to an oxygen atom whereas sulfur is the donor atom in the sulfite complex.

Nuclear Magnetic Resonance Studies of the Solution Chemistry of Metal Complexes. III. Acetylglycine Complexes of Cadmium, Zinc, and Lead

1972 ◽  
Vol 50 (7) ◽  
pp. 1036-1043 ◽  
Author(s):  
Dallas L. Rabenstein
Keyword(s):  
Exchange Rate ◽  
Magnetic Resonance ◽  
Metal Ion ◽  
Formation Constants ◽  
Solution Chemistry ◽  
Resonance Spectroscopy ◽  
Metal Ion Binding ◽  
The Exchange Rate ◽  
Ion Binding Sites ◽  
Cadmium Zinc

The aqueous solution chemistry of the cadmium, zinc, and lead complexes of acetylglycine has been investigated by proton magnetic resonance spectroscopy. These systems were investigated as models for the interaction of cadmium, zinc, and lead with the C-terminal end of peptides and proteins. The acid ionization constant of acetylglycine (pKa = 3.44) and the formation constants of the cadmium (log Kf1 = 1.23), zinc (log Kf1 = 0.86), and lead (log Kf1 = 1.38, log Kf2 = 1.20) complexes at 25 °C were determined from chemical shift measurements (Kf1 = [ML+]/[M2+][L−]; Kf2 = [ML2]/[ML+][L−]). The rates of exchange of the peptide proton of acetylglycine in the free and complexed forms with solvent protons were measured from exchange-broadened n.m.r. spectra. The exchange rate of the peptide proton increases when the acetylglycine is complexed by these metals; in the case of the cadmium–acetylglycine complex the exchange rate is 53 times faster. The potential metal ion binding sites at the C-terminal end of peptides are discussed, and the possibility of chelation through an oxygen atom of the carboxylate group and an atom of the peptide linkage is considered.

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