Solution studies on chelates of nickel, zinc and cadmium with 2-thiopicolinanilide

The protonation constants of 2-thiopicolinanilide (TPA) and the stability constants of its complexes with Ni, Zn and Cd have been determined potentiometrically in 50% w/w ethanol-water medium, at 25 degrees and 0.100M ionic strength (LiClO(4)). Co-ordination centres in TPA are suggested.     

Ionic strength dependence of formation constants-V Protonation constants of some nitrogen-containing ligands at different temperatures and ionic strengths

The protonation constants of 2,2'-bipyridyl, 1,10-phenanthroline, 1,3-diaminopropane, l-histidine and histamine have been determined potentiometrically, in the temperature range 10-40 degrees and at ionic strengths ranging from 0.04 to 1 (potassium chloride). The dependence of the protonation constants on ionic strength is described by a simple general equation. The enthalpy changes for the protonation of the ligands have been calculated from the temperature dependence of the protonation constants.     

Thermodynamic studies on protonation constant of adenosine and guanosine at different temperatures and ionic strengths

Stepwise protonation constants of two purine nucleosides (adenosine and guanosine) were determined at different temperatures (293.15 to 308.15) and various ionic strengths (0.101 to 3.503 mol · kg⁻¹ NaClO₄) using a combination of potentiometric and spectrophotometric method. The thermodynamic parameters (i.e. enthalpy change, ΔH, and entropy change, ΔS) of the protonations were calculated at different temperatures using van’t Hoff and virial equations. The dependence of the protonation constant on ionic strength is modeled by a Debye–Hückel type equation and discussed. Finally, the protonation constants of the nucleosides and the enthalpy change of protonations were determined at zero ionic strength.     

The thermodynamic model of inorganic arsenic species in aqueous solutions Potentiometric study of the hydrolitic equilibrium of arsenic acid

Protonation constants of arsenic acid were determined at different ionic strengths in NaClO(4) (0.1, 0.5, 1.0, 3.0 mol dm(-3)), NaCl (0.5 and 1.0 mol dm(-3)) and KCl (0.5, 1.0 and 3.0 mol dm(-3)) ionic media by means of a potentiometric study. The distribution of arsenate species was defined depending on two important variables in natural environments: pH and composition. All the experimentation was performed at 25 degrees C. The differences found in the protonation constants for different medium compositions, were explained by the different behaviour of the interaction parameters of the species considered in the different media and ionic strengths. These parameters were reported for all hydrolitic As(V) species and were calculated using the Modified Bromley's Methodology (MBM). The corresponding thermodynamic stepwise formation constants were also determined (log degrees K(1)=11.58+/-0.01, log degrees K(2)=7.06+/-0.01, log degrees K(3)=2.25+/-0.01). All the results obtained showed not only the importance of the ionic strength but also of the composition of the ionic medium on the distribution of the acid-base species of As(V) as a function of pH in natural waters.     

Unexpected dependence of the protonation constant of 2,2'-bipyridyl on ionic strength

The protonation constants of 2,2'-bipyridyl and ammonia have been determined by pH titration at 25 degrees , at ionic strengths of 0.1, 0.2, 0.5, 1.0, 1.5 and 2.0M obtained by using LiNO(3), NaNO(3), KNO(3), LiClO(4) and NaClO(4) as background electrolytes. The protonation constants generally change by about 0.3-0.4 log units for both ligands in nitrate media. A similar change in the protonation constant of ammonia was observed in perchlorate media. There is, however, a change of about 0.8-0.9 log units in the protonation constant of bipyridyl in the perchlorate media. This phenomenon is interpreted by postulating ion-pair formation between perchlorate and the protonated form of bipyridyl, HBp(+) + ClO(4)(-) rlharr2; HBp(+).ClO(4)(-) with formation constants of 0.54 in 2M lithium nitrate and 0.45 in 2M sodium nitrate.     

Protonation equilibria and solubility of l-cystine

l-Cystine is the natural least soluble of the naturally occurring amino acids. Its solubility is a function of the hydrogen ion concentration depending on its protonation. This paper presents an investigation on properties of l-cystine in a constant ionic medium of NaCl at different concentrations (3.00,2.00,1.00,0.500,0.150 mol dm(-3)) and at 25 degrees C. In such experimental conditions, solubility and its changes as a function of hydrogen ion concentration were determined. Protonation of cystine was studied in acid and basic solution, by measuring the electromotive force of galvanic cell involving a glass electrode. Four protonation constants for l-cystine were determined in all the selected concentrations of ionic medium. The different values obtained for the constants in ionic medium of different concentration could be explained both with the variation of activity coefficients or with the complex formation between l-cystine and sodium ions. Variations of solubility for different concentration of NaCl were observed as well.     

Protonation constants of 1-hydroxyethylidene-1,1-diphosphonic acid, diethylenetriamino-N,N,N',N',N'-penta-acetic trans-1,2-diaminocyclohexane-N,N,N',N'-tetra-acetic acid

The stepwise stability constants for the protonation of hydroxyethylidenediphosphonic acid (HEDP), diethylenetriaminopenta-acetic acid (DTPA) and diaminocyclohexanetetra-acetic acid (DCTA) have been determined potentiometrically with a hydrogen electrode at an ionic strength of 1 (KCl) and at 10-35 degrees . The data were treated by a least-squares method for estimation of DeltaH and DeltaS values.     

Spectrophotometric and potentiometric determination of the protonation constants of dithiocarbazates and studies on some of their metallic chelates

The protonation constants of 2-methyldithiocarbazate, 3,3-dimethyldithiocarbazate and 3-methyl-3-phenyldithiocarbazate, have been determined potentiometrically (I = 1.00M) and spectrophotometrically (I = 0.01M) at 25 degrees in aqueous solution. The analytical properties of the reagents have been studied, and also the compositions of some of their insoluble metallic chelates.     

Salt effects on the protonation and on alkali and alkaline earth metal complex formation of 1,2,3-propanetricarboxylate in aqueous solution

The protonation of 1,2,3-propanetricarboxylate (tricarballylate, tca) was studied in LiCl, NaCl, KCl, MgCl(2), CaCl(2) and tetraethylammonium iodide (Et(4)NI) aqueous solutions, at 25 degrees C, in the ionic strength range 0 < I < 1M, using the pH-metric technique. The differences between protonation constants determined in Et(4)NI and those determined in the other background salts were interpreted in terms of complex formations. Least squares calculations are consistent with the formation of MLH(j) (j = 0,1.2), M(2)LH(i) (i = 0,1,2), M(2)L species, when M = Mg(2+), Ca(2+). Potentiometric measurements performed in mixed NaClKCl, NaClCaCl(2) and MgCl(2)CaCl(2) solutions showed the formation of mixed metal complexes NaKL, NaKHL, NaCaL and CaMgL. The dependence on ionic strength of protonation and complex formation constants was evaluated using a simple Debye-Hückel type equation.     

Potentiometric study of the protonation equilibrium of Tris(Hydroxymethyl) aminomethane in aqueous sodium perchlorate solutions at 25 degrees C: construction of a thermodynamic model

The protonation equilibrium of the Tris(Hydroxymethyl)aminomethane (TRIS) has been studied using an automated potentiometric system. The temperature was kept constant at 25 degrees C and the ionic strength was 0.1, 0.5, 1.0, 2.0 and 3.0 mol dm(-3) in NaClO(4). The experimental constants, obtained at different ionic strengths, were correlated by means of the modified Bromley methodology (MBM) and the thermodynamic protonation constant found to be log (0)beta = 8.07 +/- 0.01 . Those values together with some others for NaCl medium were used to construct a thermodynamic model on both molal and molar scales for the protonation equilibrium of TRIS.     

Protonation and complex formation constants of 3-amino-1,2,4-triazole in NaCl and CaCl(2) media at different temperatures and ionic strengths

The protonation of 3-amino-1,2,4-triazole was studied potentiometrically (glass electrode) in sodium chloride and calcium chloride solutions, 0.13 I 0.92M, at 10, 25, 37 and 45 degrees . The effect of the background electrolyte on the protonation constants is explained by a complex formation model. The species CaL(+), CaHL(2+) and H(2)LCl (HL = 3-amino-1,2,4-triazole) are proposed. Stability constants, together with their dependence on temperature (DeltaH degrees ) and on ionic strength, are reported for the protonated and complex species.     

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.     

Protonation of polyamines in NaCl aqueous solution and binding of Cl by polyammonium cations

Equilibrium constants relative to the binding of Cl⁻ by nine open chain polyammonium cations (di, tri and tetra) were determined by potentiometric measurements (H⁺-glass electrode), at T=25°C. To this end the protonation constants of these amines were measured in NaCl aqueous solutions, in the ionic strength range 0.1<I≤1 mol dm⁻³. The different amines (some of which are N-alkyl substituted) were chosen in order to consider several factors affecting the values of protonation constants, the chloride complex formation constants and the dependence on ionic strength of apparent protonation constants. As concerns these last two points, it was found that fully N-alkyl substituted amines behave in a very similar way, with respect to partially or non-substituted ones. Simple linear relationships are reported involving chloride formation constants, parameters for the dependence on ionic strength of protonation constants and charges in polyammonium cations. The complexes formed by two linear polyamines with NO₃⁻ have also been studied for comparison. Literature data are examined.     

Stability order of the lanthanide chelates of two disubstituted 3-hydroxy-4H-pyran-4-ones in aqueous solution

The stability constants of the 1:1 chelates formed by tervalent lanthanides with 2-bromo-3-hydroxy-6-(hydroxymethyl)-4H-pyran-4-one and 3-hydroxy-6-(hydroxymethyl)-2-iodo-4H-pyran-4-one were determined by spectrophotometric titration in aqueous potassium chloride solution at 25 degrees . The determinations were done at two different ionic strengths near 0.1 and the value at I = 0.1 was interpolated. The log beta(101) values of both complex series exhibit the same trend; the stability increases gradually with decrease in the ionic radius and shows a break at Gd and Lu.     

Penicillamine disulfide (PNS) and alkaline cations

D-penicillamine disulfide (PNS) shows protolytic properties and is able to form complexes with cations, because it has two aminic groups and two carboxylic groups. The four protonation constants of its deprotonated species were determined by means of electromotive force (e.m.f.) measurements of a galvanic cell involving a glass electrode at 25 degrees C and in a constant ionic medium constituted by N(CH3)4Cl 3.00 or 1.00 mol dm-3. At 25 degrees C and in 3.00 mol dm-3 N(CH3)4Cl as ionic medium, equilibria taking place between PNS and lithium, sodium and potassium ions were investigated. Experimental data, again obtained from e.m.f. measurements, were explained by assuming the formation of species of the type MH2PNS ed M2H2PNS, where M indicates a cation. Stability constants for each proposed species were calculated. A comparison with cystine is discussed.     

Thermodynamics study of the dimerization equilibria of rhodamine B and 6G in different ionic strengths by photometric titration and chemometrics method

The dimerization constants of rhodamine B and 6G have been determined by studying the dependence of their absorption spectra on the temperature in the range 20-80 degrees C at different total concentrations of rhodamine B (5.89 x 10(-6) to 2.36 x 10(-4)M) and rhodamine 6G (2.34 x 10(-5) to 5.89 x 10(-4)M) and in different concentrations of LiCl, NaCl and KCl salts as supporting electrolytes. The monomer-dimer equilibrium of rhodamine B and 6G have been determined by chemometrics refinement of the absorption spectra obtained by thermometric titrations performed at different ionic strengths. The quantitative analysis of the data of undefined mixtures, was carried out by simultaneous resolution of the overlapping spectral bands in the whole set of absorption spectra. The dimerization constants are varied by changing the ionic strength and the degree of dimerization are decreased by increasing of the ionic strength of the medium. The enthalpy and entropy of the dimerization reactions were determined from the dependence of the equilibrium constants on the temperature (van't Hoff equation). From the thermodynamic results the TDeltaS degrees -DeltaH degrees plot was sketched. It shows a fairly good positive correlation which indicates the enthalpy-entropy compensation in the dimerization reactions (compensation effect).     

Double-double effect and the coordination number

The thermodynamics of protonation of the lanthanide(III) chelates of trans-1,2-diaminocyclohexanetetraacetic acid (LnDCTA⁻) was studied by potentiometric titration at the ionic strength of 1 (KCl). The protonation constants determined change monotonically and the double-double effect in the log K against Z variation is manifested in all four segments of the lanthanide series. The variations of the protonation enthalpy and entropy with Z are estimated to be also monotonical. The direction of the double-double effect observed indicates that the coordination number in the protonated chelates is higher by 1 in the entire series than in non-protonated chelates i. e. the protonation is accompanied by the coordination of the additional water molecule. The coordination number 10 is expected for the HLnDCTA chelates at least at the beginning of the series. Presumably the present conclusions are valid also for the LnEDTA⁻ system. Presented in part at the XIX ICCC, Prague (September 1978).     

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.     

The influence of the ionic medium on the behaviour of sodium glycocholate and cholate aqueous solutions

In the framework of research on the sodium bile salts, solutions of sodium cholate and glycocholate had been studied only at three ionic medium concentrations. In this paper, experiments in two other concentrations of ionic medium are carried out both to verify the behaviour dependence on the ionic medium and to apply the results of this paper to a future investigation on solutions containing contemporary sodium cholate and glycocholate. To this aim, solubility, protonation constants, lead (II) salts solubility products at 25 degrees C and in 0.300 and 0.750 mol dm(-3) N(CH3)4Cl were determined. The formed species in solutions containing lead (II) together with the selected bile salts and the behaviour of the sodium salts in micellar and premicellar solutions were investigated, too. The obtained results were compared with those obtained at the other ionic medium concentrations.     

Ionic strength dependence of formation constant-XVI. Protonation of some nitrophenols and dihydroxybenzoic acids in aqueous (tetraethylammonium iodide) solution at 25 degrees

The protonation of 2- and 3-nitrophenol (NO(2) Ph) and 2,X and 3,Y dihydroxybenzoic acids (DBA, X = 4,5,6; Y = 4,5) has been studied potentiometrically in aqueous tetraethylammonium iodide solutions, at T = 25 degrees in the ionic strength range 0.05:5 相似文献