Application of Ion-Exclusion Chromatography to the Study of Equilibria of Anionic Complexes

Abstract

An ion-exclusion chromatographic method for the determination of a stability constant of an anionic metal complex has been devised. The stability constants (1og β₁) of magnesium diphosphate and magnesium triphosphate complexes at 1=0.1 and 15°C were evaluated to be 5.06 and 5.89 in sodium chloride solution.     

The effect of the presence of valinomycin on the interfacial tension of lecithin membrane

The effect of the presence of valinomycin in lecithin membrane on its interfacial tension has been studied. The experiments have been carried out at various forming solution compositions and at various potassium ion concentrations in electrolyte solution. Potassium chloride was used as the electrolyte. A complex was formed between the valinomycin molecule and K+ ion. The following parameters describing the complex were determined: K, the stability constant of the valinomycin-K+ complex and B, partition coefficient. These values are equal to 3.52 x 10(5) m3 mol(-1) and 6.0, respectively.     

The effect of interaction between K(+) ions and gramicidin D on the lecithin membrane interfacial tension

The effect of the presence of gramicidin D in a lecithin membrane on its interfacial tension has been studied. The studies have been carried out at various forming solution compositions and at various potassium ion concentrations in the electrolyte solution. Potassium chloride was used as the electrolyte. The complex was formed between the gramicidin molecule and K(+) ion. The following parameters describing the complex were determined: the surface area occupied by GK(+) complex (A(GK(+))), the interfacial tension of the GK(+) membrane complex (gamma(GK+)), and the stability constant of the gramicidin-K(+) complex (K). These values are 156 A(2), 1.89 mN m(-1) and 0.033 m(3) mol(-1), respectively.     

Suspension Polymerization of Vinyl Chloride with Programmed Temperature: Morphological Characteristics and Thermal Stability of Polyvinyl Chloride)

Polyvinyl chloride) obtained by intermittent polymerization in suspension with temperature programming, has been characterized from the point of view of morphological properties and of thermal stability. The data have been compared with the values of the morphological characteristics and thermal stability for the PVC samples obtained under identical polymerization conditions, but at constant temperature. The polyvinyl chloride) obtained by polymerization with temperature programming has the same properties as the polyvinyl chloride) obtained by simple polymerization at constant temperature, with an identical average molecular weight. However, the former polymer shows improved thermal stability, as well as a decrease in the volumetric properties.     

Spectrophotometric determination of trace amounts of thallium with 7-(4,5-dimethylthiazolyl-2-azo)-8-hydroxyquinoline-5-sulphonic acid

A new reagent, 7-(4,5-dimethylthiazolyl-2-azo)-8-hydroxyquinoline-5-sulphonic acid, has been examined to evaluate its usefulness as a spectrophotometric reagent for thallium(III). A purple-red complex is formed in aqueous solution at pH 4-5 in the presence of cetylpyridinium chloride and the stoichimetric ratio is 1:2 (Tl:reagent). The apparent stability constant is 1.5 x 10(11). The effect of diverse ions has been studied and a method for determining trace amounts of thallium is proposed.     

Effect of anion concentration on the stability of the uranyl-ascorbate complex

The effect of anion concentration and the dependence of uranyl ascorbate on the nature of anion present is systematically studied for nine different anions over the concentration range (0.2–2.0) × 10⁻² M. These anions, commonly encountered in pharmaceutical preparations with ascorbic acid (vitamin C) are nitrate, sulfate, chloride, bromide, fluoride, phosphate, citrate, oxalate, and tartrate. Based on the absorbance data, and on the value of the replacement constant K calculated, the studied anions may be arranged according to their complexing power on uranium as follows: citrate > tartrate > phosphate > oxalate > fluoride > sulfate > nitrate > chloride > bromide.This order is substantiated by the calculated values of the side reaction coefficients α_M of the uranyl ligand complex or the conditional stability constant of uranyl-ascorbate calculated at different ligand concentrations.     

Evaluation of cadmium–metallothionein stability constants based on voltammetric measurements

A voltammetric study on the binding properties of the commercially available rabbit liver metallothionein (MT) Sigma M 7641 for cadmium ions was performed. The capacity of metallothionein to complex cadmium and the stability constants of Cd–T complex (T denotes the apoprotein or thionein molecule) have been determined from the direct titration of the defined MT concentration with the standard CdCl₂ solution in 0.59 M sodium chloride medium at pH 7.9 and 2.0. At pH 7.9 the formation of the Cd–T complex has been followed measuring the specific anodic signal height of the complex. Stability constants of Cd–T have been evaluated from the experimental data using three different procedures. The calculated apparent stability constants K=(7.6±0.2)·10⁸ dm³ mol⁻¹ of Cd–T complex in 0.59 M NaCl at pH 7.9 and 25°C indicate that under the given experimental conditions all the three procedures are equally applicable.     

Determination of 1,3-bis(4-hydroxyiminomethylpyridinium)-propane dichloride (TMB-4) with Pd(II)

The colour reaction of TMB-4 and palladium(II) chloride has been investigated. The optimum reaction conditions, spectral characteristics, stability constant and composition of the yellow water-soluble complex have been established. A new spectrophotometric method is proposed for microdetermination of TMB-4.     

Spectrophotometric Determination of Dissociation Constants of Thiovioluric Acid and the Stability Constant of its Fe(II) Complex

Spectrophotometric studies of Fe(II)-thiovioluric acid system indicates the presence of a 1:2 complex in the pH range 4.0–6.5. The apparent equilibrium constant (K′₁) has been determined by general absorbance-extinction concentration scheme. The first and second dissociation constants of the acid have been studied at an ionic strength of 0.1 M while the third dissociation constant has been determined at I = 1 M. The effects of sudden pH change and buffer compositions on the dissociations have also been investigated. The stability constant of the complex has been calculated from the apparent equilibrium constant at ionic strength of 0.1 M. The stability constant works out to be 15.67 at pH 5.5.     

Stability constants of zinc halide complexes in DMSO—water and DMF—water mixtures

The overall stability constants of zinc bromide and iodide complexes in DMSO—water and those of zinc chloride, bromide and iodide in DMF—water mixtures have been determined potentiometrically at mole ratios about 0.2–1 for the organic solvents at 25°C and in a 0.5 M ammonium perchlorate ionic medium. The complex formation is much stronger in DMF and its mixtures than in DMSO and the log βs are generally higher in solvent mixtures than those expected from the values measured in the pure components.     

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.     

Differential Pulse Polarographic Investigation of Copper (II) - Cephalexin Complex

Abstract

It has been found by dp polarography that cephalexin forms a complex Cu(CEF)₂, at pH = 8.7, ionic strength μ = 0.2 and room temperature. The stoichiometric ratio and stability constant values have been evaluated by Lingane's and De Ford and Hume's methods. The overall stability constants, logβ₂ = 9.44 and 9.13, have been determined with methods applied.     

Substoichiometric extraction of gold(III). Determination of the extraction constant of gold dichloride diethyldithiocarbamate

The extraction constant of gold dichloride diethyldithiocarbamate has been determined (log K = 68.2 ± 0.2) by studying the competition from palladium in the substoichiometric extraction of gold with copper diethyldithiocarbamate in chloroform. Experimental conditions that allowed the equilibrium to be reached for any palladium concentration were chosen so that the influence of the palladium concentration on the extraction kinetics has also been studied. A program for the computation of any stability constant from extraction data for mixtures of three cations has been written.     

Absolute aggregation rate constants in aggregation of kaolinite measured by simultaneous static and dynamic light scattering

The aggregation rate was determined for the < 0.2 microm size fraction of kaolinite (KGa-2) using simultaneous static and dynamic light scattering at pH 9.5. It was found that method suggested by Holthoff et al. [Langmuir 1996, 12, 5541] is suitable for determination of the absolute aggregation rate constant of a clay dispersion without using the particle optical factors. The determined fast aggregation rate constant is k11,fast = (3.7 +/- 0.2) x 10(-18) m3 s(-1). Stability behavior of kaolinite colloids was studied as a function of concentration of sodium chloride by simultaneous static and dynamic scattering. The critical aggregation concentration was found to be 0.085 +/- 0.005 mol dm(-3). When calculating the relationship between the stability ratio and the electrolyte concentration using the DLVO theory, the best fit to the experimental data was achieved with a Hamaker constant of A = (4.7 +/- 0.2) x 10(-20) J.     

Determination of crotonaldehyde in ethanol by differential pulse polarography

The extraction constant of gold bisdiethyldithiocarbamate chloride has been determined (log K' = 81.5± 0.7) by studying the competition from palladium in the extraction of gold with an excess of copper diethyldithiocarbamate in chloroform. Gold bisdiethyldithiocarbamate chloride is an ion pair which can dissociate: a dissociation constant of this compound has been determined by studying the influence of chloride concentration on the extraction of gold with the same reagent. In sulphuric acid medium, the low extraction ratio of gold observed cannot be attributed to extraction of gold bisdiethyldithiocarbamate sulphate as dependence on sulphate concentration has not been obtained. A program for the computation of this type of stability constant from extraction data for mixtures of cations and ligands is given.     

Complex formation of cucurbit[6]uril with amines in the presence of different salts

The complex formation of cucurbit[6]uril with cyclohexylmethylamine hydrochloride and hexylamine hydrochloride has been studied in aqueous solution using potentiometric titrations. The influence of salts like NaCl, KCl, RbCl, CsCl, BaCl₂ and tetramethylammonium chloride and tetraethylammonium perchlorate on the complex formation with amines has been studied at different concentrations of these salts. With increasing salt concentration the stability constants for the complex formation with cyclohexylamine hydrochloride and hexylamine hydrochloride decreases. However, no specific influence is observable. These results show that 2:1 complexes between these salts and cucurbituril are not formed or that their concentration in solution is rather low.     

Investigation of the extraction equilibrium of the vanadium-par complex between aqueous medium and a chloroform solution of a quaternary ammonium chloride

Partition of the VO(2)L(-) complex (formed from vanadium(V) and PAR [4-(2-pyridylazo)-resorcinol]) between water and a chloroform solution of TOMACl (trioctylmethylammonium chloride) has been studied. The V-PAR-TOMACl complex extracted into the chloroform phase was found to be 1:1:1 in composition. The extraction equilibrium constant is log K = 4.0 +/- 0.1.     

Formation of a polynuclear cobalt(ii) complex on a polydentate nanoplatform of carboxylated boltorn H20

A method of synthesis of a polynuclear cobalt(II) complex with carboxylated Boltorn H20, a hyperbranched polyol of second generation, has been suggested. The logarithm of stability constant and the composition of the complex species BH20(OC(O)CH₂CH₂COO)₁₂Co₁₂ in a 50% acetone solution have been calculated from the electronic absorption spectra: log?? = 13.7 ± 0.2 and the composition M : L = 12 : 1. The IR spectroscopy and NMR (¹³C and ¹H) point to the coordination of Co(II) ions not only at the surface of the molecule but also near its core.     

Spectrophotometric study of competitive complexation equilibria involving overlapped spectral responding species: Determination of the stability constant of bismuth-pyrophosphate complex

Spectrophotometric study of competitive complex formation equilibria involving overlapped spectral responding species applying a simple and versatile algorithm was carried out. The algorithm involves multivariable regression for calculation of equilibrium concentrations from multiwavelength data and mass action law for the stability constant calculation. The used regression functions are part of common statistical software. Stability constants and complex stoichiometry of competing equilibria were simultaneously determined. The species concentration profiles at several spectral overlapping and ??-coefficient of competing reaction were obtained. Non-absorbing bismuth ?? pyrophosphate (PPh) system was studied as a competitive reaction of bismuth ?? 4-(2-Pyridylazo) resorcinol (PAR) complex. The formation of Bi-PPh complex with 1:1 stoichiometry was proved in the studied concentration region (C_Bi = 1×10^?5 mol L^?1; C_PPh = 5×10^?6 ? 1×10^?4 mol L^?1). The stability constant of the complex at pH 1 and ?? = 1.0 have been determined: log?? = 4.2±0.2.      

Determination of the association constant of NaSO 4 − with the sodium-selective electrode

The association constant of the NaSO ₄ ^? complex has been determined using a sodium-selective electrode in an aqueous medium of 0.5 M ionic strength at 25°C. The constant calculated was 2.5±0.2, and no evidence was found under the present conditions for the existence of higher complexes.