Optical, tsvetometric, and acid-base characteristics of methyl orange

The optical and tsvetometric characteristics of 4-dimethylaminoazobenzen-4′-sulphoacid (methyl orange, MO) in water solutions at pH 2–9 are studied. The equations of calibration plots of the dependence of colorimetric functions on concentration are obtained and calculated as molar coefficients of colorimetric functions. The method determines The constants of MO dissociation at an ionic force of 0.01–0.2 are determined by spectrophotometry; they are given to an ionic force of 0 and are compared to the literature data. The advantages of tsvetometry over spectrophotometry are shown in determining the MO concentration.     

Acid-base,spectrophotometric, and colorimetric properties of 1,2-dihydroxyantraquinonone-3-sulfoacid (Alizarin Red S)

Acid-base, spectrophotometric, and colorimetric properties of 1,2-dihydroxyantraquinonone-3-sulfoacid (Alizarin Red S, ARS) have been studied in aqueous solutions at pH 3–13. Equations of calibration curves have been obtained for the dependences of absorbance and colorimetric functions (CF) on the ARS concentration. Molar absorption coefficients and CF have been determined. Dissociation constants of ARS have been determined using a spectrophotometric technique in its computational and graphical versions at an ionic strength from 0.1 to 0.5.     

Metal chelates of phosphonate-containing ligands-IV (Stability of some 1,6-hexamethylenediamine-N,N,N',N'-tetra(methylenephosphonic) acid metal chelates)

The stability constants of the complexes formed between the anion of 1,6-hexamethylenediamine-N,N,N',N'-tetra(methylenephosphonic) acid and some transition and non-transition metal ions have been measured potentiometrically at a temperature of 25 degrees and an ionic strength of 0.1M (KNO(3)). The acid dissociation constants of the ligand and stability constants of the protonated complexes are also reported. Comparisons are made with the acid dissociation constants of the analogous compounds EDTA, ENTMP and HDTA, and possible structural formulae are given.     

Determination of cationic mobilities and pKa values of 22 amino acids by capillary zone electrophoresis

The effective mobilities of the cationic forms of common amino acids--mostly proteinogenic--were determined by capillary zone electrophoresis in acidic background electrolytes at pH between 2.0 and 3.2. The underivatized amino acids were detected by the double contactless conductivity detector. Experimentally measured effective mobilities were fitted with the suitable regression functions in dependence on pH of the background electrolyte. The parameters of the given regression function corresponded to the values of the actual mobilities and the mixed dissociation constants (combining activities and concentrations) of the compound related to the actual ionic strength. McInnes approximation and Onsager theory were used to obtain thermodynamic dissociation constants (pK(a)) and limiting (absolute) ionic mobilities.     

The step dissociation constants of ethylenediamine-N,N′-diacetic-N,N′-dipropionic and ethylenediamine-N,N,N′,N′-tetrapropionic acids

The step dissociation constants of ethylenediamine-N,N′-diacetic-N,N′-dipropionic and ethylenediamine-N,N,N′,N′-tetrapropionic acids at 298.15 K and ionic strengths of 0.1, 0.5, and 1.0 (KNO₃) were determined potentiometrically. The results were extrapolated to zero ionic strength by the equation with one individual parameter. The thermodynamic constants of dissociation were calculated. The results are compared with the corresponding data on related compounds.     

Acid Dissociation Constants and Rare Earth Stability Constants for DTPA

Diethylenetriamine-N,N,N′,N″,N″-pentaacetic acid (DTPA) is an octadentate aminopolycarboxylate complexing agent whose f-element complexes find important practical applications in nuclear medicine and in advanced nuclear fuel reprocessing. This investigation focuses primarily on the latter application, specifically on characterization of lanthanide–DTPA complexes of relevance to the Trivalent Actinide–Lanthanide Separations by Phosphorus reagent Extraction and Aqueous Komplexants (TALSPEAK) process. To function acceptably, the TALSPEAK process requires the presence of moderate concentrations (0.5–2.0 mol·L^?1) of a (Na⁺/H⁺) lactate (or citrate) buffer. Competition between DTPA, lactate, and the extractant bis(2-ethylhexyl)phosphoric acid (HDEHP) for the lanthanides and trivalent actinides governs the course of the extraction process. To facilitate modeling and to support process improvements, the acid dissociation constants and stability constants for rare earth complexes with DTPA have been determined in 2.0 mol·L^?1 ionic strength (NaClO₄) media. The acid dissociation constants for DTPA and the stability constant for [Eu(DTPA)]^2? also were determined in sodium trifluoromethanesulfonate at 2.0 mol·L^?1 ionic strength to evaluate the potential impact of changing the nature of the electrolyte. The thermodynamic data are compared with earlier reports of similar data at lower ionic strength and used to complete calculations exploring the relative stability of lanthanide–DTPA and lactate complexes under TALSPEAK extraction conditions. Lanthanide–DTPA stability trends are discussed in comparison with literature data on a variety of other metal ions.     

Enthalpies of Dissolution of Crystalline Naproxen Sodium in Water and Potassium Hydroxide Aqueous Solutions at 298 K

The enthalpies of dissolution of crystalline naproxen sodium in water and aqueous solutions of KOH at 298.15 K are measured by direct calorimetric means in a wide range of concentrations. The acid–base properties of naproxen sodium at ionic strength I ~ 0 and I = 0.1 (KNO₃) and a temperature of 298.15 K are studied by spectrophotometric means. The concentration and thermodynamic dissociation constants are determined. The standard enthalpies of the formation of naproxen sodium and the products of its dissociation in aqueous solution are calculated.     

Studies on 1,2-Bis(O-Aminophenoxy)Ethane-N,N,N′,N′;-Tetraacetic Acid Chelates of the Tripositive Lanthanide Ions

The acid dissociation constants of 1,2-bis(cis-aminophenoxy)ethane-N,N,N′,N′;-tetraacetic acid (H₄BAPAT or H₄Z), and the stability constants of its chelates with tripositive rare-earth metal ions have been determined by the potentiometric titration and mercury indicator electrode methods at 15°, 25′ and 35°C and an ionic strength of 0.1 (KNO₃). The existence of a monohydrogen chelate species, LnHZ, and the normal chelate, LnZ^?, is illustrated. Enthalpy and entropy changes characterizing the formation of the normal chelates and the dissociation of the last two protons of chelating acid have been calculated at 25°C. These functions have been compared with corresponding values for related chelating agents.     

Spectrophotometric studies on 5,7-dibromo-8-aminoquinoline chelates of some bivalent transition metals

The acid dissociation constant of 5,7-dibromo-8-amino-quinoline and the stability constant of 1:1 chelates of some bivalent transition metals were determined spectrophotometrically in 50% v v dioxan-water medium at an ionic strength of 0.50 at 25.0 +/- 0.1 degrees and compared with those of 8-aminoquinoline. The dissociation constant was found to be 7.54 x 10(-2) and the stability constants (log K(1)) were 2.3 (copper), 1.8 (nickel), 1.8 (zinc), 2.2 (cobalt) and 1.6 (cadmium), respectively. The dissociation constants are greater and the stability constants smaller than the corresponding values for 8-aminoquinoline and 8-quinolinol.     

Determination of the thermodynamic parameters and stability constants of UO2(2+), Th4+, and Ce3+ complexes with some azo-benzene-N-malonic acid derivatives

Proton-ligand dissociation and metal-ligand formation constants of azobenzene-N-malonic acid (I), p-Cl-azobenzene-N-malonic acid (II), p-Br-azobenzene-N-malonic acid (III) and p-COOH- azobenzene-N-malonic acid (IV) with UO2(2+), Th4+ and Ce3+ were evaluated potentiometrically using Bjerrum's method at 25, 35 and 45 +/- 0.5 degrees C and ionic strength 0.1 M in 40% v/v ethanol-water medium. The order of stability constants was found to be Ce3+ > Th4+ > UO2(2+). The effect of temperature on the dissociation and stability constants of the formed complexes was studied and the corresponding thermodynamic functions were derived and discussed. The ratio of metal-ligand was determined conductometrically. The structure of the ligands under investigation as well as their metal complexes has been elucidated by elemental analysis, IR and 1HNMR spectroscopy.     

The influence of water-acetone solvents on the acid-base properties of glycylglycine

The protonation and dissociation constants of glycylglycine in variable-composition water-acetone solvents were determined potentiometrically at the ionic strength of solutions 0.1 M (NaClO₄) and 298 K. Reagent solvation contributions to shifts of acid-base equilibria are analyzed.     

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.     

邻苯二酚-3,6-二甲撑亚氨基二乙酸的酸离解平衡及其与碱土金属、锰(II)、镉(II)、锌(II)、钴(II)、镍(II)、铜(II)、铁(II)、钍(IV)及铀酰离子配合物稳定性的研究

本文报道用PH滴定法测得KNO3水溶液中邻苯二酚-3,6-二甲撑亚氨基二乙酸(CBMIDA, H6L)的六级酸解离常数及CBMIDA的镁(II)、钙(II)、锶(II)、钡(II)、镍(II)、锌(II)、钴(II)、镉(II)、锰(II)、铜(II)、铁(II)、钍(IV)和铀酰离子的配合物稳定常数及配合物的质子化常数. 讨论了CBMIDA的逐级酸离解的动态平衡机理以及金属离子与CBMIDA形成的各种配合物的配位形式.     

Stabilité des carboxylates de terres,III. Maléates,méthylsuccinates et malates

The stability constants of maleates, methylsuccinates and malates of rare earths have been determined at 25.0 °C and at ionic strength 0,100 (NaClO₄) by a potentiometric method. Each ligand forms 1 : 1 and 1 : 2 complexes in aqueous solution, the malates being the most stable. The first and the second dissociation constants of the ligand acids were also measured. The 1 : 2 maleates of La, Pr, Nd, Sm, and Eu have been isolated.     

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.     

The dissociation of ethylenedithiodiacetic acid in aqueous solution

The dissociation of ethylenedithiodiacetic acid (H₂Edtda) was studied by potentiometric titration at 298.15 K and ionic strength values of 0.5, 1.0, and 1.5 against the background of sodium and lithium nitrates. The concentration and thermodynamic dissociation constants were determined.     

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.     

Dissociation constants of some o,o'-substituted azo dyes

The dissociation constants, pK(a) (H(2)L(-)) and pK(a)(HL(2-)), were determined spectrophotometrically in aqueous media at ionic strength 0.2 for six o,o'-substituted azo dyes, namely C.I. 13900, C.I. 15685, C.I. 18744, C.I. 18760, C.I. 18821 and Calmagite.     

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.     

Formation of Glycinate Complexes of Iron(II) at Different Ionic Strengths of Solution

Complexation of iron(II) in aqueous glycine (α-aminoacetic acid) solutions is studied in the pH range 1.0–8.0 at 298.16 K at various ionic strengths (NaClO₄). The stability constants of the resulting complexes go down as the ionic strength of the solution increases. The stability constants of the complexes are determined using the experimental “electromotive force of the system versus pH” curves by iterative fitting of the theoretical oxidation function to the experimental one with the Excel program. The correlation between the stability constants of complexes and ionic strength of the solution is also calculated using the Debye–Hückel equation and SigmaPlot 10.0 software. Statistical analysis of the calculated data is performed with P value of 0.95.