Showing papers on "Stability constants of complexes published in 1970"

ADSORPTION STRENGTH OF ZINC FOR SOIL HUMUS : III. Relationship Between Stability Constants of Zinc-humic and-fulvic Acid Complexes, and the Degree of Humification

Abstract: Durable soil humus has, as one of its functions, chelation power for di- and trivalent metal ions. One of the authors 0, 2) has reported that the percentage of chelated zinc, which has greater adsorption strength than that of the exchangeable zinc, to the total zinc adsorbed increased with the progress of humification when zinc was added to humic soils, and that the adsorption strength of zinc is closely related to nature of soil humus. Randhawa and Broadbent (3, 4) reported stability constants of zinc-humic acid complexes calculated to be 4.42 at pH 3. 6, 6. 18 at pH 5. 6, and 6. 80 at pH 7.0 by the ion-exchange equilibrium method. Schnitzer and Skinner (5, 7) determined the stability constants of different metal-fulvic acid complexes originating from a podzolic soil by the same method and showes the order of their stability. But in these investigations, only one kind of sample soil has been used, and the relation between the stability constant and nature of soil humus has not been shown. Nair a...

Potassium-Adenosine Triphosphate Complex: Formation Constant Measured with Ion-Selective Electrodes

Abstract: Valinomycin and glass electrodes were used to measure activity of potassium ions in equilibrium with adenosine triphosphate. The thermodynamic formation constant of the complex is approximately 25 times greater than indirect measurements predict.

Thermodynamic considerations in co-ordination. Part VII. Solubility of the histidine–H+ system and stability constants, free energies, enthalpies, and entropies of protonation of histidine and tryptophan and of formation of their manganese(II), iron(II), cobalt(II), nickel(II), copper(II), and zinc(II) complexes

Abstract: Acidic or basic perchlorate solutions of histidine precipitate histidine hydroperchlorate (histidine HCIO4,H2O), solubility product –log Ks= 17·65 in 3M-perchlorate at 25·0°. Tryptophan has higher pK values than histidine in this medium. Near pH 7·4 (the pH of blood) the formation constants indicate that the complexes of MnII, FeII, CoII, and NiII with histidine are tridentate and that those with tryptophan are bidentate. The zinc–histidine complex is less stable than that of cobalt, whereas for all other amino-acids the reverse is true. Calorimetry shows that the main driving force behind metal ion–amino-acid complex formation is an enthalpy effect, the bond strengths obeying the Irving–Williams order. It is suggested that the zinc ion is tetrahedral, the carboxy-group not being chelated.

Studies on the Sulfur-containing Chelating Agents. XXIV. Acid Dissociation and Chelate Formation of Penicillamine

Abstract: This study was initiated to study on the relationship between the chelate formation and the detoxication activity of penicillamine against heavy metal poisoning. The equilibrium of acid dissociation and the mode of the coordination of metal chelates were investigated by means of potentiometric titration, ultraviolet-visible spectra and proton magnetic resonance spectra. The equilibrium constants among various chemical species of penicillamine in aqueous solution were determined and the results were comparable with those in cysteine. The mode of coordination between penicillamine and metal ions was deduced through the comparison of the formation constants and the absorption spectra of the metal chelates of penicillamine with those of the related compounds. In the chelates produced from penicillamine with Co2+, Zn2+ and Ni2+, the coordination occurs through sulfur and nitrogen atoms while the carboxyl group remains off in coordination, and in the chelates produced from penicillamine with Hg2+, Cd2+ and Pb2+, sulfur, nitrogen and also oxygen atoms contribute to the coordination. The investigation by proton magnetic resonance spectroscopy in an aqueous solution gave more reliable information for the coordination of carboxyl group in penicillamine toward Hg2+, Cd2+ and Pb2+.

Free-energy relationships in coordination chemistry. I. Linear relationships among equilibrium constants

Abstract: After a review of previous semi-empirical free-energy relationships applying to the formation of metal complexes, the following equations are derived within a framework of logical assumptionsThese compare stability constants of complexes formed by a metal ion M and a ligand L with those formed by a reference metal Ms and a reference ligand Lo. The derivation of these equations reveals an inherent relationship between the constants B and C, which is formulated through an "exactness" test. The application of these relationships to stoichiometric equilibrium constants is discussed.In the testing of the foregoing equations with data for various ligand families reacting with numerous metal ions, two principal modes of behavior were noted. In one, there was a mutual dependence of B on the particular metal ions compared and of C on the particular ligands compared. In the other, all values of B and C were found to equal unity irrespective of metal ion or ligand compared. The cause of this distinction is not yet u...

Charge transfer complexes between halogens and pyridines. Part 4.—Effect of the acid strength of the acceptors

Abstract: Charge transfer equilibria between bromine, iodine, iodine chloride and iodine bromide as acceptors and various meta and para-substituted pyridines as donors have been studied spectrophotometrically in carbon tetrachloride at 30°C. Formation constants of the complexes have been correlated with Hammett's substituent constants, ionization constants of the donors and acid strength of the acceptors. Correlations with intermolecular and/or interhalogen spectral parameters are also discussed.

Chromium(III) Complexes with Iminodiacetic Acid or l-Aspartic Acid

Abstract: The formation constants of chromium (III) complexes with iminodiacetic acid (IDA) and l-aspartic acid (Asp) as the terdentate ligands were determined by the pH method in the ionic strength, μ=0.1 and at 25°C: their values were logk1=10.9 and logk2=10.5 for IDA and logk1=10.1 and logk2=9.5 for Asp, respectively. That the overall formation constants of chromium(III)-IDA complexes obtained were slightly larger than those of the corresponding -Asp complexes was explained by the stronger chelate effect in the former complexes than in the latter ones. The solid chromium (III) complexes with IDA and Asp were also prepared. Based on chemical analyses and the conductivity measurement or the behavior toward the ion exchangers, the chemical formulas of these complexes are possibly K[Cr(ida)2]·3H2O and K[Cr(OH)2asp] respectively. X-Ray powder diffraction patterns indicated that the former crystalline complex has tetragonal unit lattice, the axial parameter being a=14.57 and c=12.38 A, whereas the latter is amorphous ...

Thermodynamic considerations in co-ordination. Part VIII. A calorimetric and potentiometric study of complex formation between some lanthanide(III) ions and histidine

Abstract: The changes in free energy, enthalpy and entropy for the formation of tripositive lanthanum, praeseodymium, neodymium, samarium, gadolinium, dysprosium, erbium, and ytterbium complexes with histidine (histH) have been determined at 25·0° and l= 300 mol l–1(with sodium perchlorate) The formation constants, and thus the free-energy changes, were measured potentiometrically and the enthalpy changes were measured by calorimetry The entropy changes were calculated from the relationship ΔGn°=ΔHn°–TΔSn° The calorimeter described for the measurement of enthalpies has a built-in electrode pair so that potentiometry and heat measurements may be made simultaneously The experimental results for all the lanthanide complexes are interpreted in terms of the three complexes: [Ln(hist)]2+, [Ln(hist)2]+, and [Ln(histH)]3+

Application of the Continuous Variation Method to the Conductometric Determination of Formation Constants–Hexamminecobalt(III) Chloride - Sodium Sulfate and Tris(ethylenediamine) cobalt(III) Chloride - Sodium Sulfate Systems

Abstract: The conductance behavior of mixtures was investigated with the following systems in aqueous solutions of various ionic strengths at 25°C; NaCl - KCl, NaCl - NaClO4, NaCl - Na2SO4, [CO-(NH3)6] Cl3 - Na2SO4 and [CO(en)3]Cl3 - Na2SO4. Appreciable deviations of the measured conductivities from additivity were observed in the last two systems involving the cobalt(III) complexes. The deviation was attributed to the ion-pair formation of the complex cations with sulfate ions; the ion-pair formation constants at various ionic strengths were determined by means of computer analysis of the deviation without relying on the Onsager conductance equation. The thermodynamic ion-pair formation constants at 25°C were as follows: logK=3.53 for [CO(NH3)3+·SO42− and logK=3.60 for [CO(NH3]3+·SO42−. The analysis of conductance behavior of mixtures was proved to be a useful method of studying ion-pair formation particularly at relatively high ionic strengths.

L'action de l'ammoniac sur l'hydroxyde de cadmium et la stabilité des complexes en milieu aqueux

Abstract: The solubility of precipitated Cd(OH)2 was determined at 25°C in 1 M NaClO4, as a function of pH and of the ammonia content of the solutions. Formation constants were obtained for the following hydroxo, ammine and hydroxo-ammine complexes: CdOH+, Cd(OH)2, Cd(OH), CdNH, Cd(NH3), Cd(NH3), Cd(NH3) and Cd(OH)2NH3. The solubility product of the hydroxide was also calculated. The presence of polynuclear species was investigated by titrimetric determinations of the hydrogen ion concentration at constant metal concentration.

Studies on the Sulfur-containing Chelating Agents. XXVI. Formation of Mixed Ligand Chelates Containing Penicillamine and Sulfhydryl Compounds

Abstract: Formation of new mixed ligand chelates consisting of penicillamine, bivalent metals, such as mercury, lead and cadmium, and some of the secondary ligands, such as mercaptoacetic acid, N-acetylpenicillamine, glutathione, 2-mercaptoethylamine, α-mercaptopropionyl glycine and penicillamine methyl ester, in the ratio of 1 : 1 : 1 were recognized potentiometrically, but there was no indication for the existence of the similar mixed ligand chelate in the cases of ethylmercaptan, glycine and histidine. The mixed ligand chelate is formed in two steps ; the simple penicillamine metal chelate is formed in the first step, and the secondary ligand becomes to coordinate to 1 : 1 penicillamine chelate to yield the 1 : 1 : 1 mixed ligand chelate in the second step. The order of the relative formation constants of mixed ligand chelates was Cd2+>Hg2+>Pb2+. The formation constants of mixed ligand chelates are linearly correlated to the dissociation constants of sulfhydryl group in secondary ligands. Moreover, among these mixed ligand chelates, the decrease of binding affinity of the carboxyl group in penicillamine tends to increase the formation of the mixed ligand chelate.

Formation Constants of Chromium(II) Complexes with (O,O)-, (O,N)- and (N,N)-Type Ligands and Comparison with Those of the Other First Transition Metal Complexes

Abstract: The formation constants of the bivalent chromium complexes with various chelating ligands were determined by the pH titration method at the ionic strength μ=0.1 and at 25°C. The values of the formation constants for (O,O)-type complexes were logk1=3.85±0.05 and logk2=2.96±0.05 for oxalate ion, logk1=3.92±0.05 and logk2=3.21±0.05 for malonate ion, and logk1=9.89±0.05 for sulfosalicylate ion: for (O,N)-type complexes we obtained logk1=7.72±0.05 and logk2=7.54±0.05 for glycine, logk1=9.05±0.05 for 8-hydroxyquinoline, and logk1=7.53±0.05 for β-alanine. Based on these values together with the corresponding values of the (N,N)-type complexes, the effect of the coordinating atoms and of the number of members in a chelate ring upon the stabilities was discussed. These values were compared with those for the other transition metal complexes.