Thermodynamic Model for BiPO4(cr) and Bi(OH)3(am) Solubility in the Aqueous Na+–H+–\mathrm{H}_{2}\mathrm{PO}_{4}^{-}–\mathrm{HPO}_{4}^{2-}–\mathrm{PO}_{4}^{3-}–OH−–Cl−–H2O System

Prior to this study no data for the solubility product of BiPO₄(cr) or the complexation constants of Bi with phosphate were available. The solubility of BiPO₄(cr) was studied at 23±2?°C from both the over- and under-saturation directions as functions of a wide range in time (6–309 days), pH values (0–15), and phosphate concentrations (reaching as high as 1.0 mol?kg^?1). HCl or NaOH were used to obtain a range in pH values. Steady state concentrations and equilibrium were reached in <6 days. The data were interpreted using the SIT model. These extensive data provided a solubility product value for BiPO₄(cr) and an upper limit value for the formation of BiPO₄(aq). Because the aqueous system in this study involved relatively high concentrations of chloride, reliable values for the complexation constants of Bi with chloride were required to accurately interpret the solubility data. Therefore as a part of this investigation, existing Bi–Cl data were critically reviewed and used to obtain values of equilibrium constants for various Bi–Cl complexes at zero ionic strength along with the values for various SIT ion interaction parameters. Predictions based on these thermodynamic quantities agreed closely with our experimental data, the chloride concentrations of which ranged as high as 0.7 mol?kg^?1. The study showed that BiPO₄(cr) is stable at pH values <9.0. At pH values >9.0, Bi(OH)₃(am) is the solubility controlling phase. Reliable values for the Bi(OH)₃(am) solubility reactions involving Bi(OH)₃(aq) and $\mathrm{Bi}(\mathrm{OH})_{4}^{-}$ and the formation constants of these aqueous species are also reported.     

REACTION BETWEEN [PdCl4]2- AND 5,5-DIMETHYL-2-THIOXOIMIDAZOLIDIN-4-ONE

Abstract

The reaction between 5,5-dimethyl-2-thioxoimidazolidin-4-one (H2L) and [PdCl₄]^2- has been studied in aqueous solution by potentiometric and spectrophotometric measurements. In the presence of the palladium salt, H₂L is completely monodeprotonated (HL^?); from spectrophotometric measurements, only two complexes having 1:1 and 1:2 Pd/ligand mol ratios have been identified. Potentiometric titrations, carried out on solutions with 1:1, 1:2, 1:3 and 1:4 metal/ligand mol ratios, show that these complexes must be formulated as Pd(HL)₂ and [Pd₂(HL)₂(μ-H₂O)(μ-OH)]⁺. Ionization constants of the pure ligand and formation constants of the complexes give pH distribution curves of the various species and the spectra of the two complexes. From MeOH, S-coordinated Pd(H₂L)_nCl₂ (n = 2–4) complexes have been separated in the solid state; from water, two complexes of formula Pd(H₂L)(HL)Cl and Pd(HL)Cl have been obtained with HL^? N,S-coordinated to the metal.     

Aqueous Long-Term Solubility of Titania Nanoparticles and Titanium(IV) Hydrolysis in a Sodium Chloride System Studied by Adsorptive Stripping Voltammetry

The solubility of industrially produced titanium dioxide nanoparticles has been studied in aqueous sodium chloride media in the pH range 1 to 13 at 25 °C by using adsorptive stripping voltammetry (AdSV). Kinetic dissolution curves have been obtained as well as long-term solubilities that provide an approximation of the equilibrium solubilities. The titania nanoparticles used in the dissolution experiments have been characterized by nitrogen sorption measurements, XRD and colloid titration. The equilibrium solubilities and titanium(IV) speciation and their dependences on pH have been modelled by assuming the formation of the mononuclear titanium hydroxo complexes [Ti(OH) _n ]⁽⁴⁻ⁿ⁾⁺ (n=2 to 5) to be the only titanium species present. The solubility product of titanium dioxide and equilibrium constants for titanium(IV) hydrolysis, calculated from the AdSV solubility data, are presented.     

Stability of crown-ether complexes with alkali-metal ions in ionic liquid-water mixed solvents

Stability constants of sodium and cesium ion complexes with 18-crown-6 (18C6) and dibenzo-18-crown-6 (DB18C6) in N-butyl-4-methyl-pyridinium tetrafluoroborate [BMP][BF₄] aqueous solutions were measured using the ²³Na and ¹³³Cs NMR technique at 23 °C. To the best of our knowledge, the estimated values of stability constants reported in this study are the first such values given for ionic liquid solutions. The cationic exchange between the free and complexed species is rapid, and only formation of the 1:1 complexes [M(18C6)]⁺ and [M(DB18C6)]⁺ (M = Na⁺, Cs⁺) were observed. The complex formation constants demonstrated a strong dependence on the [BMP][BF₄] concentration. For [M(18C6)]⁺, in solutions with a 0.33–0.70 mole fraction of water in [BMP][BF₄], lg K values are found to be more than one unit higher than the lg K values measured in pure aqueous solutions, although no information concerning the influence of [BMP][BF₄] on the complex formation selectivity could be observed. DB18C6 complexes revealed significantly lower stability under the same conditions. An extrapolation to zero water content gave the lg K = 2.42 for [Cs(18C6)]⁺ in [BMP][BF₄]. It was discovered that when added to water, [BMP][BF₄] increases the solubility of crown ethers and decreases the solubility of alkali metal nitrates. Complex formation with crown ethers enhances the solubility of alkali metal salts in [BMP][BF₄].     

Synthesis of Two N,N′-bis(N,N-dialkylamide) Derivatives of Diethylenetriaminepentaacetic Acid and the Stabilities of Their Complexes with Gd3+, Ca2+, Cu2+, and Zn2+

Two bis(N,N-dialkylamide) derivatives of DTPA [(carboxymethyl)iminobis (ethylenenitrilo) tetraacetic acid], DTPA-BDMA = the bis(N,N-dimethylamide) and DTPA-BDEA = the bis(N,N-diethylamide) were synthesized. Their protonation constants were determined by potentiometric titration in 0.10 M Me₄NNO₃ and by NMR pH titration at 25.0 ± 0.1 °C. Stability and selectivity constants were measured to evaluate the possibility of using the corresponding gadolinium(III) complexes for magnetic resonance imaging contrast agents. The stability constants of gadolinium(III), copper(II), zinc(II), and calcium(II) complexes with DTPA-BDMA and DTPA-BDEA were investigated quantitatively by potentiometry. The stability constant for gadolinium(III) complexes is larger than those for Ca(II), Zn(II), and Cu(II) complexes. The selectivity constants and modified selectivity constants of the amides for Gd³⁺ over endogenously available metal ions were calculated. Effectiveness of these two ligands in binding divalent and trivalent metal ions in biological media is assessed by comparing pM values at physiological pH 7.4. Spin-lattice relaxivity values R₁ for Gd(III) complexes were also determined. The observed relaxivity values were found to decrease with increasing pH in the acid range below pH 4 and relaxivity values became invariant with respect to pH changes over the range of 4–10. ¹⁷O NMR shifts showed that the [Dy(DTPA-BDMA)] and [Dy(DTPA-BDEA)] complexes had one inner-sphere water molecule. Water proton spin-lattice relaxation rates for the [Gd(DTPA-BDMA)] and [Gd(DTPA-BDEA)] complexes were also consistent with one inner-sphere gadolinium(III) coordination position.     

The solution chemistry of ethylmethylglyoxime : Part I. The proton complex

The solubility of ethylmethylglyoxime (EMG) was studied as a function of pH. The solubility K_sl in 0.1 M aqueous solution is 0.0132 ±0.0006 M. The distribution constants K_Dl of EMG between various organic solvents and 0.1 M aqueous solution were found to be —0.47 for chloroform, —0.51 for benzene, —1.10 for carbon tetrachloride and —1.83 for hexane. The acid dissociation constants were determined from potentiometric titrations; the values pK_a1=10.51 and pK_a2=12.02 were obtaining by fitting the experimental data to normalized curves. The UV spectra of 5·10^-5M EMG solutions of varying pH were measured between 210 and 290 nm. It is shown that H₂A has an absorption maximum at 226 nm and HA^-and A^2- have absorption maxima at nearly the same wavelengths, i.e. 258 and 266 nm, respectively. The spectra of HA^- and A^2- have approximately the same form. The data are compared with those of dimethylglyoxime (DMG). The distribution constants (org/aq) are 4–5 times higher for EMG. The acid dissociation constants are about the same for EMG and DMG, but EMG is more soluble in water than DMG (13.2 and 5.0 mmoles/l, respectively). The UV spectra of EMG and DMG are very similar.     

Cadmium(II) binding by soil-derived fulvic acid measured by anodic stripping voltammetry

Titrations of aqueous solutions of soil fulvic acid (30, 45, and 60 mg l^-1) with cadmium ion solutions at pH 6 and 7 reveal unusual shapes in the stripping current (i_s) vs. total cadmium ion (C_cd²⁺) curves. The expected inflections occur in the titration curves at 8–16 μM. at pH 6 and 12–26 μM at pH 7. In addition, there is an initial rapid increase in i_s at very low C_cd²⁺. The initial rapid increase in current is attributed to labile cadmium—fulvic acid complexes that contribute to i_s by rapid dissociation. Subsequent addition of cadmium ion results in moderately labile complexes and i_s becomes partially kinetically controlled. The stripping current was corrected for kinetic current contributions from dissociation of complexes, and total ligand concentrations, conditional stability constants, and upper slopes were calculated from data well past the titration end-point. The use of upper slopes after kinetic current corrections as in situ calibration curves, allowed calculations of equilibrium cadmium concentrations. The data show that both kinetic current corrections and in situ calibration curves are necessary to avoid substantial errors in calculations of equilibrium cadmium concentrations from anodic stripping voltammetric experiments.     

Neodymium(III) complexing with ampicillin,amoxicillin, and cephalexin

The interaction of Nd³⁺ ions with ampicillin, amoxicillin, and cephalexin anions (L) in aqueous solution at 20°C and ionic strength of 0.1 (KNO₃) was studied by pH titration. The NdL and Nd(OH)L complexes are formed in weak alkaline solution. The distribution curves of neodymium(III) complex species depending on pH were constructed. The formation constants of the complexes were determined.     

The stability and solubility of cadmium(II)-8-oxyquinoline complexes in water and micellar solutions of sodium dodecyl sulfate

The formation of cadmium 8-oxyquinoline (HOx) complexes in water and a 0.01 M aqueous solution of sodium dodecyl sulfate (293 K, 0.01) was studied by pH-metric titration. Mathematical simulation of the most probable equilibria gave complex formation constants logβ₁ = 6.17 ± 0.32 (CdOx⁺) and logβ₂ = 14.60 ± 0.14 (CdOx₂) in aqueous solution and apparent stability constants logβ₁ = 8.64 (CdOx⁺) and logβ₂ = 17.59 (CdOx₂) in a solution of dodecyl sulfate. The solubility of cadmium dioxyquinolate in water at pH from 3 to 6 and a micellar sodium dodecyl sulfate medium was determined by the method of saturated solutions. The solubility product pL _p = 21.3 ± 0.9 (H₂O, 293 K) was calculated by modeling the solution of CdOx₂ with taking into account all acid-base interactions and complex formation reactions.     

Interaction between 1,2-dimethyl-3-hydroxypyrid-4-one and europium(III)

The interaction of the clinically used 1,2-dimethyl-3-hydroxypyrid-4-one with trivalent europium Eu(III), was investigated by using potentiometric and spectroscopic methods. The stability constants of the EuL_n ⁽³⁻ⁿ⁾⁺ complexes determined by spectroscopic and potentiometric measurements were found to be log β₁₁ = 6.5±0.3 and log β₁₂ = 12.0±0.5. However, at pH ≥ 5, hydrolysis of the Eu-L complexes starts, resulting in the formation of needle-type, yellow crystals. The low solubility of the Eu-L complexes in the neutral pH range is disadvantageous with respect to the use of deferiprone as chelating agent for decorporation of trivalent f-elements.     

Complexation in the copper(ii)—L-histidine—D-ornithine system as studied by ESR spectroscopy

Equilibria in the copper (ii)—L-histidine—D-ornithine system were investigated by ESR spectroscopy in an aqueous solution in the pH range 2—11. Analysis of the spectrum lineshape at different pH and ligand to metal ratios showed that the mixed-ligand complexes Cu(OrnH)(HisH₂)⁴⁺, Cu(OrnH₂)(HisH)³⁺, and Cu(Orn)(His) occur in the system along with the binary complexes. The stability constants, g-factors, HFC constants, and relaxation parameters of the complexes were determined, and the structures of the complexes were suggested.     

Synthesis of Two Derivatives of 3,6,9‐tri(carboxymethyl)‐3,6,9‐triazaundecanedioic Acid and the Stabilities of Their Complexes with Ca2+, Cu2+, Zn2+, Dy3+ and Gd3+

Two N‐2‐hydroxy‐1‐phenylethyl and N‐2‐hydroxy‐2‐phenylethyl derivatives of DTPA (3,6,9‐tri(carboxymethyl)‐3,6,9‐triazaundecanedioic acid), DTPA‐H1P = 3,9‐di(carboxymethyl)‐6‐2‐hydroxy‐1‐phenylethyl‐3,6,9‐triazaundecanedioic acid, and DTPA‐H2P = 3,9‐di(carboxymethyl)‐6‐2‐hydroxy‐2‐phenylethyl‐3,6,9‐triazaundecanedioic acid were synthesized. Their protonation constants were determined by Potentiometric titration in 0.10 M Me₄NNO₃ and by NMR pH titration at 25.0 ± 0.1°C. The formations of lanthanide(III), copper(II), zinc(II) and calcium(II) complexes were investigated quantitatively by potentiometry. The stability constant for Gd(III) complex is larger than those for Ca(II), Zn(II) and Cu(II) complexes with these two ligands. The selectivity constants and modified selectivity constants of the DTPA‐H1P and DTPA‐H2P for Gd(III) over endogenously available metal ions were calculated. Comparing pM values at physiological pH 7.4 assesses effectiveness of these two ligands in binding divalent and trivalent metal ions in biological media. The observed water proton relaxivity values of [Gd(DTPA‐H1P)]^? and [Gd(DTPA‐H2P)]^? became constant with respect to pH changes over the range of 4‐10. ¹⁷O NMR shifts showed that the [Dy(DTPA‐H1P)]^? and [Dy(DTPA‐H2P)]^? complexes at pH 6.30 had 1.91 and 2.28 inner‐sphere water molecules, respectively. Water proton spin‐lattice relaxation rates of [Gd(DTPA‐H1P)]^? and [Gd(DTPA‐H2P)]^? complexes were also consistent with the inner‐sphere Gd(III) coordination.     

Électrochimie dans l'oxydipropionitrile: Comportement électrochimique du solvant. Stabilité des complexes argent(I) halogénures. Solvatation des anions

Electrochemical possibilities of oxydipropionitrile have been shown. The system Ag(s)/Ag⁺ has been used to make a reference electrode in this medium. The electroactivity range which depends on the electrolyte and the kind of electrode used has been specified. At a platinum electrode, in LiClO₄ medium, the electroactivity range is very large. At a mercury electrode, water does not interfere but at a platinum electrode it is oxidizable; the electroactivity range depends on its concentration. The second part treats the complexes with silver ion and halides. Stability constants of complexes and solubility products have been obtained from potentiometric titration curves. The determination of the transfer parameters for ionic species is based on the Strehlow assumption that the potential of the ferrocene/ferricinium couple is constant in all solvents. The results show that the silver ion is more strongly solvated in oxydipropionitrile than in water; on the other hand halide ions are little solvated in this solvent.     

O and N NMR studies of the Co(II), Cu(II) and Mn(II) complexes of -proline in aqueous solution

The ¹⁷O and ¹⁴N paramagnetic transverse relaxation time and chemical shift of proline as well as of water, in aqueous solutions of Co(II), Cu(II) and Mn(II) were measured as a function of pH, temperature, and metal ion concentration. The relaxation results were fitted to a theoretical equation linking the Swift-Connick equation to the stability constants of the major complexes in equilibrium. Stability constants for the major complexes of the three ions in this work were determined, along with thermodynamic parameters for some of the complexes. Two complexes of Co(II) were detected directly by ¹⁷O NMR at basic pH, and were assigned to CoPrO₂ and CoPro₃⁻. The hyperfine coupling constant for these two complexes, A/h, was determined directly from the isotropic shift and was found to be −0.63 and −0.31 MHz, respectively. CoPrO₂ could be detected in the pH range 6–12, for Co(II) concentrations greater than 0.04 M, and its chemical shift was around 700 ppm downfield from free proline, at 300 K. CoPro₃⁻ was detected only at pH 11, in the temperature range 275–284 K, with a chemical shift of 390 ppm downfield from free proline.     

Complexation,solubilities and thermodynamic functions for cerium(III) fluoride-water system

The solubility, solubility product and the thermodynamic functions for the CeF₃–H₂O system have been measured using the radiometric, conductometric and potentiometric techniques. The radiometric values for the solubility and solubility product, the lowest and more acceptable for reasons cited in previous papers, are 3.14·10^–5 M and 2.17·10^–17 respectively. The enthalpy change measured by the conductometric method is almost twice as that obtained by potentiometric method due to abnormal conductances registered at higher temperatures. The average values for H^o and G^o and S^o at 298 K are 53.0±17.4, 91.7±4.0 and –129.7±58.2 KJ·mol^–1 respectively. The positive values for H^o and G^o and the negative value for S^o are indicative of the low solubility of this salt in water. The stability constants for the mono- and difluoride complexes of Ce(III) have been determined potentiometrically using unsaturated solution mixtures of Ce(III) and F^–. These values for CeF⁺ and CeF ₂ ⁺ are 997±98 and (1.03±0.44)·10⁵, respectively. Studies on pH dependence of the solubility shows that the solubility reaches a minimum value at a pH of about 3.2.     

Metal complexes of some asymmetric diaminodiamide ligands—II. Stabilities of complexes of nickel(II) in aqueous solution

Equilibria between a series of asymmetric diaminodiamides and Ni(II) in aqueous solution have been studied by potentiometric and spectrophotometric methods. The ligands were S,R,S- and S,S,S-N,N′-dialanylpropylenediamine (DAPN), S,S-N,N′-dialanylethylenediamine (DAEN), R-N,N′-diglycylpropylenediamine (DGPN), and N,N′-diglycylethylenediamine (DGEN). At lower values of pH the complexes NiL²⁺ and in some cases NiL²⁺₂ were formed. Spectral data indicated that both of these were octahedral. At higher pH the two amide protons were lost and square planar complexes were formed. The diastereomeric DAPN ligands showed stereoselectivity in the equilibrium constants for deprotonation and formation of the square planar complexes. Comparison of optical rotatory dispersion curves and absorption spectra for the various complexes permits partial assignment of structures.     

Calculation of chemical equilibria in CaCl<Subscript>2</Subscript>-heparin-sodium adenosinetriphosphate and MgCl<Subscript>2</Subscript>-heparin-sodium adenosinetriphosphate systems in physiological salines

Chemical equilibria in aqueous solutions of disodium adenosinetriphosphate (Na₂H₂ATP), high-molecular-weight heparin (H₄Hep) and Na₂H₂ATP and in MCl₂-H₄Hep-Na₂H₂ATP-H₂O-NaCl (M = Ca²⁺ or Mg²⁺) solutions in the 0.15 M NaCl background were studied using computer simulation and pH titration at 2.3 ≤ pH ≤ 10.5. Formation constants were determined for two protonated ATP species, three protonated complex species of heparin with ATP of equimolar stoichiometry, and mixed-ligand calcium and magnesium complexes with heparin and adenosinetriphosphate. The formation constants for mixed-ligand calcium(II) complexes with heparin are more than two times those of homoligand calcium complexes with heparin. As a result, the Ca²⁺ ion concentration at 6.8 ≤ pH ≤ 7.4 (the pH range of blood plasma stability) decreases from 40 to 100 wt % depending on the ratio of the initial concentrations of CaCl₂, H₄Hep, and Na₂H₂ATP.     

Equilibrium Studies of Dibutyltin(IV)–Zwitterionic Buffer Complexation

Equilibrium studies in aqueous solution are reported for dibutyltin(IV) (DBT) complexes of the zwitterionic buffers “Good’s buffers” Mes and Mops. Stoichiometric and formation constants of the complexes formed were determined at different temperatures and ionic strength 0.1 mol·L^?1 NaNO₃. The results show that the best fit of the titration curves were obtained when the complexes ML, MLH_?1, MLH_?2 and MLH_?3 were considered beside the hydrolysis product of the dibutyltin(IV) cation. The thermodynamic parameters ΔH ^o, ΔS ^o and ΔG ^o calculated from the temperature dependence of the formation constant of the dibutyltin(IV) complexes with 2-(N-morpholino)ethanesulfonic acid (Mes) and 3-(N-mor-pholino)-propanesulfonic acid (Mops) were investigated. The effect of dioxane as a solvent on the formation constants of DBT–Mes and DBT–Mops complexes decrease linearly with the increase of dioxane proportion in the medium. The concentration distribution of the various complexes species was evaluated as a function of pH.     

Heteropolynuclear cobalt(II) and nickel(II) ethylenediaminetetraacetates in aqueous solutions of aminoethanoic acid

Complexation in the Co(II)?Ni(II)?aminoethanoic acid (HGly)?EDTA (H₄Edta) system was studied at different molar ratios of components by absorption spectrophotometry. The mathematical modeling of A = f(pH) curves was used to establish that bi-, tri-, and tetranuclear heteroligand complexes like [(CoGly)Edta(NiGly)]^2?, [(CoGly₂)Edta(NiGly₂)]^4?, [(CoGly₂)Edta(NiGly₂)₂]^4?, [(CoGly₂)₂Edta(NiGly₂)]^4?, and [(CoGly₂)₂Edta(NiGly₂)₂]^4?, whose accumulation fraction attained 80?100% at optimal pH values, were formed depending on the ratio of reagents and the acidity of a medium. The formation equilibrium and total stability constants of these complexes were calculated, and a hypothesis about their structure was made.     

Ethylenediamine and Hydroxyethylenediamine Complexes of Zinc(II): A Potentiometric Study of Composition and Stability

The equilibrium potential of saturated zinc amalgam is studied as a function of concentration of free ethylenediamine molecules, [en], in the region [en] 0.001–1 M in solutions of pH 9.5, 10.5, and 11.5. At the concentration of zinc(II) ions 2 × 10^–3 M and [en] = 1 M only simple trisethylenediamine complexes of zinc(II) form in all the solutions. At smaller [en] and pH 9.5 and 10.5, complexes Zn(en)₂ ²⁺ and Zn(en)₂OH⁺ are also present; these are complemented at pH 11.5 by Zn(en)₂(OH)₂ at [en] 0.005–0.1 M. Stability constants for these complexes are calculated.