Ionic strength dependence of formation constants, protonation, and complexation of aspartic acid with dioxovanadium (V)

The stability constants of complexes of dioxovanadium (V) ion and L-asparrtic acid were determined potentiometrically at various ionic strengths of I = 0.1, 0.3, 0.5, and 0.7 mol. dm⁻³ at 25°C. A sodium chloride solution was used to maintain the ionic strength. The parameters based on these formation constants were calculated and the dependence of protonation and the stability constants on ionic strength are described by a Debye-Huckel type equation.     

Ionic Strength Dependence of Formation Constants and Complexation of Glutamine with Dioxovanadium(V)

The dependence of L-glutamine protonation and its complexation with dioxovanadium(V) on ionic strength (I) is reported in sodium perchlorate solution as a background salt. The measurements have been performed at 25 ± 0.1°C and various ionic strengths in the range 0.1 to 1.0 mol/l, using a combination of potentiometric and spectrophotometric techniques. The overall analysis of the present and the previous data dealing with the determination of stability constants at different ionic strengths allowed us to obtain a general equation, by which a formation constant determined at a fixed ionic strength can be calculated, with a good approximation, at another ionic strength, if 0.1 I 1.0 mol/l (NaClO₄).     

Mechanism of the acid catalysed hydrolysis of the chromatopenta-amminecobalt(III) ion

The kinetics of the acid hydrolysis of chromatopenta-amminecobalt(III) ion has been studied using a stopped-flow method over the acidity range 0.01≤[H⁺]<-1.0 mol dm⁻³ and 20.0°C<-ϕ<-30.0°C at ionic strengths 0.5 and 1.0 mol dm⁻³ (LiNO₃). These studies reveal that the complex is first protonated and subsequently hydrolysed to the aquapentaammine cobalt(III) ion. The rate constants for the hydrolysis of the mono and diprotonated species at 25°C are 0.83±0.01 s⁻¹ and (1.60±0.02)×10⁴ mol⁻¹ dm⁻³ s⁻¹, respectively. TMC 2664     

Determination of the stability constants of the Mo(VI) complex with iminodiacetic acid in different sodium perchlorate aqueous solutions

The stability of molybdenum(VI) complex formed by iminodiacetic acid(IDA) has been studied at 25°C, pH = 6.0, and different ionic strengths ranging from (0.3 to 1.0) mol dm⁻³ of sodium perchlorate. A combination of potentiometric and spectrophotometric techniques have been used based on the continuous variations method. According to our investigations, the metal-to-ligand ratio is 1: 1. The Solver, Microsoft Excel 2000 powerful optimization package, has been used to perform non-linear least-squares curve fitting. In order to obtain better consistency between the experimental and calculated results, two empirical parameters have been introduced in a Debye-Huckel-type equation. This equation enables us to calculate the values of stability constants in the desired range of ionic strength. This article was submitted by the authors in English     

Ionic strength dependence of stability constants,complexation of W(VI) with iminodiacetic acid

The equilibria between tungsten(VI) and iminodiacetic acid (IDA) have been studied in aqueous solution. The stoichiometry and stability constants of the complexes formed are determined from a combination of potentiometric and Uv spectroscopic measurements. All measurements are carried out at 25°C, pH 7.5 and different ionic strengths ranging from (0.1 to 1.0) mol dm⁻³ (NaClO₄). According to these results, tungsten(VI) forms a mononuclear complex with IDA of the type (WO₃L²⁻). By introducing two empirical parameters C and D in the complex-formation reaction between tungsten(VI) and IDA, the dependence of the dissociation and stability constants on ionic strength is described by a modified Debye-Huckel-type equation. Finally, a pattern for the ionic strength dependence is obtained.     

Determination and comparison of stability constants of tungsten(VI) and molybdenum(VI) with nitrilotriacetic acid and glutamic acid at different ionic strengths

The formation constants of species formed in the systems H⁺?+?W(VI)?+?nitrilotriacetic acid (NTA) and H⁺?+?NTA have been determined in aqueous solution for pH?=?4–9 at 25°C and different ionic strengths ranging from 0.1 to 1.0?mol?dm^?3 NaClO₄, using potentiometric and spectrophotometric techniques. It was shown that tungsten(VI) forms a mononuclear 1?:?1 complex with NTA of the type WO₃L^3? at pH?=?7.5. The composition of the complex was determined by the continuous variations method. The complexation of molybdenum(VI) with glutamic acid was investigated in aqueous solution ranging in pH from 4 to 9, using polarimetric, potentiometric and spectrophotometric techniques. The composition of the complex was determined by the continuous variations method. It was shown that molybdenum(VI) forms a mononuclear 1?:?1 complex with glutamic acid of the type MoO₃L^2? at pH?=?6.0. The dissociation constants of glutamic acid and the stability constants of the complex were determined at 25°C and at ionic strengths ranging from 0.1 to 1.0?mol?dm^?3 sodium perchlorate. In both complex formation reactions the dependence of the dissociation and stability constants on ionic strength is described by a Debye-Huckel type equation. Finally, a comparison has been made between the patterns of ionic strength dependence for the two complexes and the results have been compared with data previously reported.     

Thermodynamic Studies on the Complexation of Cobalt(II) with Dopamine in a Cosolvent System

Equilibrium constants for formation of a cobalt(II) complex with the bidentate ligand dopamine have been studied with spectrophotometric methods in water + ethanol cosolvent systems at 15, 25, and 35 (±0.1) °C and an ionic strength of 0.2 mol⋅dm⁻³. The ionic strength was maintained using sodium chloride and a phosphate buffer. The stability constants of the complex and the resulting Gibbs energy changes are obtained. The results are discussed in terms of the effect of solvent on protonation and complexation.     

pH-metric studies on formation constants of the complexes of substituted pyrazoles with some lanthanide metal ions and the influence of ionic strengths on complex equilibria in a 70% dioxane-water mixture

The pK a values of N-heterocyclic compounds (substituted pyrazoles) in a 70% (v/v) dioxane-water mixture have been determined using pH-metric measurements. The stability constants of the complexes of Dy(III), Nd(III), Sm(III), and Tb(III) with 3-(2-hydroxyphenyl)-5-methylpyrazole, l-phenyl-3-(2-hydimyphenyl)-5-methylpyrazole 3-(2-hydroxy-4-methylphenyl)-5-methylpyrazole, and l-phenyl-3-(2-hydroxy-4-methylphenyl)-5-methylpyrazole have been determined by the pH-metric method at ( 300 ± 0.1) K. The effect of ionic strengths on the complexes of Sm³⁺ and Pr³⁺ ions with pyrazole has been investigated in the internal from 0.02 to 0.1 mol dm⁻³ (sodium perchlorate) in the pH range 2–3.     

A study of solvent effects on complex formation of tungsten(VI) with ethylenediaminediacetic acid in aqueous solutions of propanol

By using spectrophotometric and potentiometric techniques, the formation constants of the species formed in the systems H⁺+W(VI) + ethylenediaminediacetic acid and H⁺ + ethylenediaminediacetic acid were determined in aqueous solutions of propanol at 25°C and a constant ionic strength of 0.1 mol dm⁻³ sodium perchlorate. The composition of the complex was determined by the continuous variation method. It was shown that tungsten(VI) formed a mononuclear 1: 1 complex with ethylenediaminediacetic acid of the type WO₃L³⁻ at −log[H⁺] = 5.8. The formation constants in various media were analyzed in terms of the Kamlet-Taft parameters. Solvents were parameterized by dipolarity/polarizability scales π*, hydrogen-bond donor (HBD) strength α, and hydrogen-bond acceptor strength β. Linear dependences (LSERs) on these solvent parameters were used to correlate and predict a wide variety of solvent effects and provide an analysis of them. Linear relationships were observed when log K_S values were plotted versus π*. Finally, the results are discussed in terms of the effect of solvents on complex formation. The article is published in the original.     

Kinetics and the Mechanism of Iron(II) Reduction of cis-α-halogeno(cetylamine) (triethylenetetramine)cobalt(III) Complex Ion in Aqueous Acid Medium

The kinetics and mechanism of iron(II) reduction of cis- α-chloro/bromo(cetylamine)(triethylenetetramine) cobalt(III) surfactant complex ions were studied spectrophotometrically in an aqueous acid medium by following the disappearance of Co^III using an excess of the reductant under pseudo-first-order conditions: [Fe^II = 0.25 mol dm⁻³, [H⁺ = 0.1 mol dm⁻³, [μ = 1.0 mol dm⁻³ ionic strength in a nitrogen atmosphere at 303, 308 and 313 K. The reaction was found to be second order and showed acid independence in the range [H⁺ = 0.05−0.25 mol dm⁻³. The second order rate constant increased with Co^III concentration and the presence of aggregation of the complex itself altered the reaction rate. The effects of [Fe^II], [H⁺] and [ μ] on the rate were determined. Activation and thermodynamic parameters were computed. It is suggested that the reaction of Fe²⁺(aq) with Co^III complex proceeds by an inner-sphere mechanism.     

Complexation of Tungsten(VI) with Methyliminodiacetic Acid at Different Ionic Strengths

The results of this research give ionic strength dependence patterns for the complexation of tungsten(VI) with methyliminodiacetic acid at T?=?298?K. The formation data reported in this work were obtained at different ionic strengths (0.1?<?I/mol·dm^?3?<?1.0) of sodium perchlorate on the basis of Job??s continuous variation method, which show that a 1:1 complex forms at pH?=?7.50. UV experimental data were collected for the calculation of the stability constants according to the extended Debye?CHückel theory, the specific ion interaction theory and the parabolic model. Finally, these three models have been compared.     

Formation of Diazepam–Lanthanides(III) Complexes in the 50–50 Volume % Ethanol–Water Solvent System and Study of the Effect of Temperature on the Complex Formation Constants

Diazepam (7-chloro-1,3-dihydro-1-methyl-5-phenyl-2H-1,4-benzodiazepin-2-one) is an important derivative of the 1,4-benzodiazepine compound commercially distributed as Valium. The complex formation constants of diazepam with some light lanthanide(III) metal ions have been studied by potentiometric measurements. All titrations were performed in 50–50% (volume/volume) ethanol–water solvent mixtures at constant ionic strength (0.10 mol⋅dm⁻³). The ionic strength was maintained by using sodium perchlorate. The complex formation constants were determined at 25.00, 35.00 and 45.00 °C. With increasing temperature, a decrease was observed in the protonation constant (pK) of diazepam.     

Interaction of Molybdenum(VI) with Methyliminodiacetic Acid at Different Ionic Strengths by Using Parabolic,Extended Debye-Hückel and Specific Ion Interaction Models

The main aim of this research is to study the complexation of molybdenum(VI) with methyliminodiacetic acid in NaClO₄ aqueous solutions at pH = 6.00 and ionic strengths (0.1<I/mol⋅dm⁻³<1.0) at 25 °C by using potentiometric and UV spectrophotometric measurements in order to obtain thermodynamic stability constants at I=0 mol⋅dm⁻³. A comparison with previous literature data was made for the stability constants, though few data were available. The stability constants data have been analyzed and interpreted by using extended Debye-Hückel theory, specific ion interaction theory and parabolic model. Finally it might be concluded that parabolic model applies better for this complexation reaction.     

Comparison of the application of Debye-Huckel and specific ion interaction theories for the complexation of tungsten(VI) with ethylenediaminediacetic acid

Equilibrium of the reaction of tungsten(VI) with ethylenediaminediacetic acid (EDDA) has been investigated in aqueous solution of pH 7.5 and 25°C. All measurements have been carried out at different ionic strengths ranging from (0.1 to 1.0) mol dm⁻³ (NaClO₄). According to our results the metal to ligand ratio is 1: 1. Stability constants and stoichiometry of the complex have been determined from a combination of potentiometric and UV spectroscopic measurements. In this semi-empirical model, two parameters have been introduced in a Debye-Huckel type equation based on the Gauss—Newton nonlinear least-squares method and minimizing the sum of the squares of the errors. Comparison of the ionic strength effect on these complex formation reactions has been made using a Debye-Huckel type equation and Bronsted—Guggenheim—Scatchard specific ion interaction theory (SIT). Published in Russian in Zhurnal Neorganicheskoi Khimii, 2009, Vol. 54, No. 5, pp. 864–868. The article is published in the original     

Study on the Salting-out Effect using Silica Species by FAB-MS

The salting-out effect has been characterized on the basis of the relative peak intensity of silica species, observed by FAB-MS (fast atom-bombardment mass spectrometry) in solutions of sodium chloride, sodium nitrate, sodium sulfate, calcium chloride, lithium chloride and magnesium chloride. A critical change in the peak intensity ratios of the linear and cyclic tetramers of silica against the sodium ion (Na⁺) concentrations was observed at Na⁺ concentration between 0.1 and 1 mol⋅dm⁻³. The degrees of the changes of these peak intensity ratios increased in the order NaNO₃ < Na₂SO₄ < NaCl. In CaCl₂ solutions, these peak intensity ratios changed significantly at Ca²⁺ concentrations between 0.05 and 0.5 mol⋅dm⁻³. The salting-out effect observed is the total change in the concentration of silica brought about by complex factors, such as the changing solubility of silicate complexes, the increases in the concentrations of different kinds of soluble silicate complexes induced by changes in the hydrophobicity and hydrophilicity of the solution, and the contribution of hydrolysis.     

Ionic strength dependence of formation constants. Part II: potentiometric study of the copper(II)-malonate-glycinate system in the range 0.01≤I≤1.0

Summary The ternary copper(II)-malonate-glycinate system has been investigated by potentiometric measurements using a glass electrode, at 37° and at different ionic strengths (0.01I1.0 mol dm^–3), with KNO₃ as background salt. Complex formation between K⁺ and malonate has also been taken into account, and the parameters for the dependence on ionic strength have been obtained for each formation constant. A general equation, valid for all the complexes formed in this system, for the dependence, log K=f(I), is also proposed. The stabilization parameters of the ternary complex are also analyzed as a function of the ionic strength.     

Speciation of phytate ion in aqueous solution. Cadmium(II) interactions in aqueous NaCl at different ionic strengths

Interactions between myo-inositol 1,2,3,4,5,6-hexakis(dihydrogen phosphate) (phytic acid) and cadmium(II) were studied by using potentiometry (at 25 °C with the ISE-H⁺ glass electrode) in different metal to ligand (Phy) ratios (1:1≤Cd²⁺:Phy≤4:1) in NaCl_aq at different ionic strengths (0.1≤I/mol L⁻¹≤1). Nine Cd_iH_jPhy^{(12−2i−j)−} species are formed with i=1 and 2 and 4≤j≤7; and trinuclear Cd₃H₄Phy²⁻. Dependence of complex formation constants on ionic strength was modeled by using Specific ion Interaction Theory (SIT) equations. Phytate and cadmium speciation are also dependent on the metal to ligand ratio. Stability of Cd_iH_jPhy^{(12−2i−j)−} species was modeled as a function of both the ligand protonation step (j) and the number of metal cations bound to phytate (i), and relationships found were used for the prediction of species other than those experimentally determined (mainly di- and tri-protonated complexes), allowing the possibility of modeling Phy and Cd(II) behavior in natural waters and biological fluids. A critical evaluation of phytate sequestering ability toward cadmium(II) has been made under several experimental conditions, and the determination of an empirical parameter has been proposed for an objective “quantification” of this ability. A thorough analysis of literature data on phytate–cadmium(II) complexes has been performed. Previous contributions to this series: [1–8]     

Complexes of pyrimidine DNA bases with thallium(I)

The stability constants of complexes of a thallium(I) ion with cytosine and thymine were determined in aqueous solution at 25°C and 0.1 mol dm⁻³ ionic media, using a combination of potentiometric and spectrophotometric techniques. Sodium perchlorate was used to maintain the ionic strength. The composition of the formed complexes was determined and it was shown that thallium(I) forms two mononuclear 1:1 species with cytosine of the type TIHL⁺ and TIL, and a mononuclear 1:1 complex species with thymine in the form TIHL, in the pH range of study (1–11), where L represents the fully dissociated ligand. The cumulative stability constants, β _xyz, of the complexes, [(thallium)_x(H)_y(ligand)_z], were calculated by a nonlinear fitting method and their distributions were presented as a function of-log[H⁺]. This text was submitted by the authors in English.     

Second Dissociation Constant of H<Subscript>2</Subscript>Te and the Absorption Spectra of HTe<Superscript>–</Superscript>, Te<Superscript>2–</Superscript> and Te<Subscript>2</Subscript><Superscript>2–</Superscript> in Aqueous Solution

We have measured the second acid dissociation constant, K _2a , at several ionic strengths for hydrogen telluride (H₂Te) using the Charge Transfer to Solvent (CTTS) uv spectra of its anions HTe⁻ and Te²⁻. Since it is produced in our solutions, we have also determined the spectra of Te₂ ²⁻ both in the uv and in the visible regions. At 25 ^∘C, K _2a = (1.28 ± 0.02) × 10⁻¹² by extrapolation to zero ionic strength. Its value at an ionic strength equal to 0.5 mol.dm^-3 was estimated to be (8.7 ± 0.2) × 10⁻¹². The solution thermodynamics of these species are also discussed and comparisons are made to related acids.     

Mechanistic investigation of oxidation of a diketone by bromamine-B in acid medium

Oxidation of acetylacetone (AA) by bromamine-B (BAB) in HC1 medium (0.1 to 0.6 mol dm⁻³) at constant ionic strength has been investigated at 40°C. The rate is first order in [BAB]₀ and fractional order each in [AA]₀ and [H⁺]. The reaction is also catalysed by chloride ion. Michaelis-Menten type of kinetics is observed. Decrease in dielectric constant of medium increases the rate. A solvent isotope effect κ′H₂O/κ′D₂O = 0.96 has been noted. Activation parameters for the rate limiting step have been computed. The mechanism involves the enol form of the diketone.