Protolytic properties of <Emphasis Type="Italic">DL</Emphasis>-alanyl-<Emphasis Type="Italic">DL</Emphasis>-methionine and its complexation in aqueous solutions and micellar solutions

Dissociation constants of DL-alanyl-DL-methionine have been determined in water and micellar solutions of surfactants (anionic sodium n-dodecyl sulfate, cationic cetylpyridinium chloride, and nonionic Brij 35). It has been established that CuA⁺ and CuH_–1A complexes are formed in water and micellar solutions of sodium n-dodecyl sulfate, while CuA⁺, CuH_–1A, and Cu_–2A^– complexes are formed in micellar solutions of cetylpyridinium chloride and Brij 35. Stability of the complexes depends on micelle surface charge and degrees of binding of individual chemical forms by a micellar pseudophase.     

The influence of sodium trifluoroacetate on the acidity function of solutions of trifluoroacetic acid in N,N-dimethylformamide

The influence of CF₃COONa on the acidity function (H ₀) and IR spectra of the CF₃COOH-N,N-dimethylformamide (DMF)-CF₃COONa system ([CF₃COOH] ≤ [DMF], [CF₃COONa] = 0–3 M) and H ₀ of solutions of the salt in 100% CF₃COOH ([CF₃COONa] = 0–1.2 M) was studied. The addition of the salt to 100% CF₃COOH insignificantly changed solution acidity; H ₀ passed a minimum at [CF₃COONa] = 0.7 M because of the formation of (CF₃COO…H…OOCCF₃)^? anions and destruction of acid associates in the presence of the salt. Changes in the acidity of solutions of CF₃COOH in DMF caused by the addition of the salt depended on the n = [CF₃COOH]/[DMF] ratio. At n = 1, the salt almost did not influence H ₀. At n < 1, a substantial decrease in the acidity of solutions was observed, because the salt increased the degree of proton transfer in CF₃COO…H…OC(H)N(CH₃)₂ quasi-ion pairs solvated by DMF molecules.     

Gold(I) complexes with methionine residue in aqueous solutions

Equilibria of stepwise substitution AuCl₂^? + iMet^– = AuCl_2–iMet _i ^– + iCl^–, β _i (i = 1, 2), where Met^– is a methionine residue, in aqueous solutions are studied at 25°C and I = 0.2 M (NaCl). The equilibrium constants are determined: logβ₁ = 3.8 and logβ₂ = 5.4.     

Reduction kinetics of glycinate complexes of palladium(II) on a dropping-mercury electrode in acid perchlorate solutions

Polarograms for the reduction of glycinate complexes of palladium(II) (5 × 10^?5 M) are obtained in equilibrium solutions of pH 0.8–3.0 with different protonated-glycine concentrations c _Hgly (supporting electrolyte, 0.5 M NaClO₄). It is established that the irreversible wave of reduction of complexes Pd(gly)₂ corresponds to the diffusion limiting current I _d ⁽²⁾ . A similar wave at pH 1.5 and c _Hgly = 0.005 M, as well as at pH 1.0 and c _Hgly = 0.05–0.5 M is preceded by the diffusion limiting current I _d ⁽¹⁾ . Values of the I _d ⁽²⁾ /I _d ⁽¹⁾ ratio are close to the ratio between equilibrium concentrations of Pd(gly)₂] and [Pdgly⁺], calculated using the step stability constant for Pd(gly)₂. This fact testifies to the reduction of complexes Pdgly⁺ in the vicinity of I _d ⁽¹⁾ and complexes Pd(gly)₂, in the vicinity of I _d ⁽²⁾ . At pH 0.8–1.2 and [H₂gly⁺] = 1 × 10^?4 to 5 × 10^?3 there is observed the diffusion-kinetic limiting current of the first wave I ₁ ⁽¹⁾ , which increases with increasing [H⁺] and decreasing [H₂gly⁺]. The nature of the slow preceding chemical stage that occurs during the reduction of complexes Pdgly⁺ is discussed.     

Structure and location of proton hydrates in Triton N-42 reverse micelles during injection solubilization of HCl solutions

A Fourier IR spectroscopic study has shown that during injection solubilization* of HCl solutions (V _s/V _o = 1.0-3.5 vol.%) at a concentration of 1-4 M by Triton N-42 reverse micelles in n-decane, the number of water molecules bound to protons is equal to 2.7±0.1. Protons form H₇O₃ ⁺ (70%) and H₅O₂ ⁺ (30%) cations in equilibrium, which are localized in the aqueous cores of the micelles.     

Electrical-percolation effects in micellar solutions of alkyltrimethylammonium bromides

Specific conductivity K of aqueous solutions of alkyltrimethylammonium bromides has been studied in a wide range of concentrations c of surfactants containing 10, 12, 14, and 16 carbon atoms in alkyl chains. In general, three break points have been observed in the K(с) dependences. The first point observed upon increasing overall solution concentration corresponds to critical micelle concentration CMC₁. The CMC₁ values of alkyltrimethylammonium bromides decrease with an increase in the alkyl chain length. They are in satisfactory agreement with the published data. It has been supposed that the second break point in the K(с) dependences corresponds to the formation micellar structures as clusters and the appearance of channels with a higher specific conductivity, which is provided by the contribution from the overlap of electrical double layers existing in the vicinities of micelles. Surfactant concentrations corresponding to these break points have been called “critical percolation concentrations” (CPCs). The position of a CPC in the concentration scale strongly depends on alkyl radical length. All K(с) curves exhibit a third break, which corresponds to second critical micelle concentration CMC₂, at which the properties of ionic-surfactant solutions may substantially change because of the appearance of supramicellar structures. The experimental data obtained have been used to evaluate the parameters of the model of electrical percolation for micellar solutions, i.e., effective conductivity \({\tilde K_m}\) and effective micelle radius r ₀.     

Calculating the Ionization Constant of Functional Groups of Carboxyl Ion Exchangers

The potentiometric titration of a weakly basic carboxyl cation exchanger, obtained via alkaline hydrolysis of an acrylonitrile copolymer with divinyl benzene (degree of crosslinking, 12%) in a wide range of variation in a solution of рН (2–12) and NaCl (concentration 0.01, 0.1, 0.5, 1 М), is considered. The maximum ion-exchange capacity of the ion exchanger for Na⁺ is determined (10.10 ± 0.088 mmol/g of the dry mass) and found to be independent of the solution’s ionic strength. It is established that in the investigated range of NaCl concentrations and рН, the acid–base balance is adequately described by Gregor’s equation. The parameters of this equation are calculated as a function of the NaCl concentration: рK_а = 8.13 ± 0.04, n = 1.50 ± 0.02 for 0.01 М; рK_а = 6.56 ± 0.04, n = 2.60 ± 0.07 for 0.1 М; and рK_а = 5.66 ± 0.6, n = 2.62 ± 0.06 for 0.5 and 1 М. It is shown that to describe the acid–base balance correctly within the proposed model we must estimate the adequacy of the experimental and calculated values of the ion exchanger’s capacity at each рН value according to the calculated parameters of Gregor’s equation.     

The Effect of a Background Electrolyte on the Viscosity of Aqueous Dodecyltrimethylammonium Bromide Solutions

Conductometry and viscometry have been employed to study the effect of a background electrolyte (KBr) taken in concentrations of 0.03 and 0.1 M on the critical micelle concentration of dodecyltrimethylammonium bromide (С₁₂ТАB) and the dependence of relative viscosity η/η₀ of С₁₂ТАB micellar solutions on the overall surfactant concentration. It has been found that, as a first approximation, each of these dependences may be represented as the sum of two linear portions. Concentrations c* of С₁₂ТАB micellar solutions, which correspond to the inflections between the two linear portions in the concentration curves of relative viscosity, have been determined. The Einstein equation η/η₀ = 1 + 2.5p (p is the volume fraction of the dispersed phase and 2.5 is a theoretical parameter that takes into account the spherical shape of the particles) has been transformed into a form corresponding to the concentration dependence of the relative viscosity on the overall surfactant concentration to make it applicable to the consideration of low-concentration systems, which are uncomplicated by intermicellar interaction. In particular, the applicability of the above equation for estimating micelle radii has been studied. It has been shown that the (η/η₀–1) = f(c/с₀₁–1) concentration dependences represented in bilogarithmic coordinates (c is the overall С₁₂ТАB concentration and c₀₁ is the critical micelle concentration) are linear in the absence of a significant intermicellar interaction and have slopes equal to unity. This fact may be considered as a criterion for the applicability of the Einstein equation to micellar solutions.     

Small-angle X-ray scattering in sodium dodecyl sulfate solutions and micelle clustering

The small-angle X-ray scattering (SAXS) in micellar sodium dodecyl sulfate solutions has been studied in the range of overall concentrations c from 8 mM (CMC₁) to 300 mM and the absolute values of scattering vector q from 0.07 to 3.0 nm^–1. The total intensity of isotropic scattering has been revealed to increase with solution concentration. At c > 27 mM, the SAXS spectra have been found to exhibit an interference peak, which testifies a correlation in the arrangement of micelles in the bulk solution. This peak corresponds to the magnitude of q close to 1.55 nm^–1. Using the position of this maximum, average distance r₀ between the centers of micelles has been determined, which is equal to 4.1 nm and remains almost unchanged upon an increase in the overall concentration of sodium dodecyl sulfate. The observed regularities have been explained in terms of the DLVO theory taking into account the electrostatic and molecular intermicellar interaction.     

Counterion effects on the isotopic properties of the Cl<Superscript>−</Superscript> and Li<Superscript>+</Superscript> ions in aqueous solutions

The reduced partition function ratios between isotopic forms (β-factors) were calculated by the ab initio RHF/6-311++G**(3df, 3p) and MP2/6-311++G**(3df, 3p) quantum-chemical methods for hydrated chloride ion and ion pair hydrates NaCl·nH₂O and LiOH · nH₂O. The influence of the Na⁺ cation on the β-factor value and the chlorine isotope separation factor in the precipitation of NaCl from concentrated aqueous solutions was found to be substantial. At the same time, the presence of OH^? counterions had no noticeable effect on the β-factor of the hydrated Li⁺ cation.     

Determination of the Water/AOT/Isooctane Reverse Micelles Size Parameters from Their Refractive Index Data

The present paper aims to study the proprieties of water confined in water/AOT/isooctane reverse micelles from their refractive indices at 298.5 K. The refractive indices of the microemulsions were investigated at increasing water concentration and at different micellar volume fractions, Φ _d. The refractive index of micellar water was deduced for a large water to AOT molar ratio, W ₀. The refractive index of interfacial water was also calculated. Then, the molar faction of interfacial water, α, was deduced for different W ₀ values and compared with those measured by NMR as reported in the literature. The results show qualitative agreement. Finally, the average aggregation number, n _agg, the area per surfactant headgroup, σ, as well as the interfacial thickness, d _i, of the reverse micelles were determined for the W ₀ values studied. The values of these structural parameters also show good qualitative agreement with NMR and small angle X-ray scattering data reported in the literature. Thus, the refractive index method can be a cheap and fast alternative for these two methods.     

Investigation of the α-BiO<Subscript><Emphasis Type="Italic">y</Emphasis></Subscript>F<Subscript>3 − 2<Emphasis Type="Italic">y</Emphasis></Subscript>-based tysonite-type solid solutions by X-ray diffraction and impedance spectroscopy

Tysonite solid solutions Bi_{1 ? x} M _x (O, F)_{3 ? d} (M = Na, Sr, or Nd) based on α-BiO _y F_{3 ? 2y} were prepared by solid-state synthesis at 873 K with subsequent quenching to ice-cold water. Aliovalent substitutions in both the cation and anion sublattices (M ⁿ⁺ → Bi³⁺ and O^2? → F^?) made it possible to vary the anion-vacancy density. The solid solutions were characterized by X-ray diffraction and impedance spectroscopy. The homogeneity regions for the tysonite solid solution were determined; triangulation schemes at 873 K were suggested for the systems BiF₃-BiOF-NaBiF₄ and BiF₃-BiOF-SrF₂, and a scheme of the subsolidus phase diagram for the system BiO_0.1F_2.8-NdF₃ was suggested. In the system BiO_0.1F_2.8-NdF₃, the transition temperature from the low-symmetry tysonite phase (phase II, space group P \(\overline 3 \) c1, Z = 6) to the high-symmetry one (phase I, space group P6₃/mmc, Z = 2) decreases with increasing anion-vacancy density. Conductivity measurements were performed in the temperature range 300–523 K and the frequency range from 5 to 1 × 10⁶ Hz. The conductivity of samples in the system BiO_0.1F_2.8-NdF₃ increases with increasing bismuth-ion and anion-vacancy concentrations.     

Potentiometric study of the kinetics and equilibria of formation of chloroglycinate palladium(II) complexes from bis-glycinato palladium(II) complexes

The equilibria and kinetics of the reaction of Pd(gly)₂ complexes with hydrogen ions and chloride ions has been studied by a potentiometric method. The underlying idea of the method is the measurement of solution pH as a function of reaction time t using a glass electrode. The solutions used had the following initial compositions: xM Pd(gly)₂, xM Hgly, and 1 M NaCl with x = 1 × 10^?4, 5 × 10^?4, and 1 × 10^?3; initial pH₀ was from ～3.5 to ～4.4. The experimentally determined pH versus t dependences and the rate equation for a pseudo-second-order reaction were used to determine the equilibrium constant of formation of Pd(gly)(Hgly)Cl complexes from Pd(gly)₂ complexes and the observed rate constant for this reaction, k _obs. The dependence of k _obs on the pH of the acid solutions studied was assigned to a change in the sequence of the reactions of addition of a hydrogen ion and a chloride ion to the complex Pd(gly)₂.     

Simulation of copper(II) cations sorption on goethite from aqueous solutions of complexons

Effect of complexons of polyaminopolycarboxylic acid series (IDA, NTA, EDTA, and DTPA) and polyphosphonic acid series (HEDP, NTP, and EDTP) on Cu(II) cations sorption on goethite (α-FeOOH) from aqueous solutions has been studied. Obtained results have been considered in the context of complexation reactions in bulk solution and on sorbent surface. It has been found that all complexons (except for EDTA), depending on nature, produce on goethite surface (≡FeOH) triple complexes of type A (surface–metal–complexon) of composition ≡FeOCuLH _i ^1+i?n and ≡FeOCuL(OH) _j ^1?j?n or type B (surface–complexon–metal) of composition ≡FeLH _i Cu^3+i-n and ≡FeLCu(OH) _j ^3?j?n . pH-Ranges for complex existence and stability constants for the surface complexes have been determined. Factors affecting the character of complexon effect (immobilization/remobilization) on the sorbed metal have been analyzed.     

Concurrent oxygen reduction and methanol oxidation in sulfuric acid solutions on platinized platinum electrodes

Steady-state polarization curves are compared in solutions of 0.5 M H₂SO₄ + O₂ (saturated), 0.5 M H₂SO₄ + (0.005–0.1) M CH₃OH, and 0.5 M H₂SO₄ + (0.005–0.1) M CH₃OH + O₂ (saturated) on a Pt/Pt electrode. A considerable difference is found between the currents in mixed solutions and those expected based on the principle of additivity of currents in CH₃OH and O₂ individual solutions. The surface coverages with the CH₃OH and O₂ adsorption products are determined in the potential range of 0.2–0.9 V (RHE). Open-circuit potentials are measured in mixed solutions. The obtained results suggest that the direct heterogeneous interaction between methanol and oxygen occurs alongside with faradaic reactions. This is assumed to lead to a decrease in methanol electrooxidation currents at E ≥ 0.8 V and their increase at E ≤ 0.65 V.     

Properties of the gold(I) sulfite complex in acidic chloride solutions

The effects of various factors on the redox stability of the gold(I) sulfite complex Au(SO₃)₂^3- in acidic chloride solutions is studied. Increased concentrations of gold and H⁺, as well as temperature, reduce the time before traces of gold(0) emerge; increased concentrations of sulfite and especially of Cl^– increase this time. The beaker material (quartz, glass, or polypropylene) is found to have no significant effect. Added organic solvents have different effects. It is shown using UV spectroscopy and pH measurements that the average number of SO₃^2- ions bound to one gold(I) ion can be much greater than two even at an excessive amount of sulfite in the acidic region (pH 2–4) due to the equilibrium Au(SO₃)Cl^2– + SO₃^2- = Au(SO₃)₂^3- + Cl^– with the constant logK₂ = 6.4 ± 0.1 at 25°C and I = 1 M (NaCl).     

Solubility of B-Nb<Subscript>2</Subscript>O<Subscript>5</Subscript> and the Hydrolysis of Niobium(V) in Aqueous Solution as a Function of Temperature and Ionic Strength

B-Nb₂O₅ was recrystallized from commercially available oxide, and XRD analyses indicated that it is stable in contact with solutions over the pH range 0 to 9, whereas solid polyniobates such as Na₈Nb₆O₁₉?13H₂O(s) appear to predominate at pH>9. Solubilities of the crystalline B-Nb₂O₅ were determined in five NaClO₄ solutions (0.1≤I _m /mol?kg^?1≤1.0) over a wide pH range at (25.0±0.1)?°C and at 0.1 MPa. A limited number of measurements were also made at I _m =6.0 mol?kg^?1, whereas at I _m =1.0 mol?kg^?1 the full range of pH was also covered at (10, 50 and 70)?°C. The pH of these solutions was fixed using either HClO₄ (pH≤4) or NaOH (pH≥10) and determined by mass balance, whereas the pH on the molality scale was measured in buffer mixtures of acetic acid?+?acetate (4≤pH≤6), Bis-Tris (pH≈7), Tris (pH≈8) and boric acid?+?borate (pH≈9). Treatment of the solubility results indicated the presence of four species, \(\mathrm{Nb(OH)}_{n}^{5-n}\) (where n=4–7), so that the molal solubility quotients were determined according to:

$0\mathrm{.5Nb}_{2}\mathrm{O}_{5}\mathrm{(cr)+0}\mathrm{.5(2}n-5\mathrm{)H}_{2}\mathrm{O(l)}_{\leftarrow}^{\to}\mathrm{Nb(OH)}_{n}^{5-n}+(n-5)\mathrm{H}^{+}\quad (n=4\mbox{--}7)$

and were fitted empirically as a function of ionic strength and temperature, including the appropriate Debye-Hückel term. A Specific Interaction Theory (SIT) approach was also attempted. The former approach yielded the following values of log?₁₀ K _sn (infinite dilution) at 25?°C: ?(7.4±0.2) for n=4; ?(9.1±0.1) for n=5; ?(14.1±0.3) for n=6; and ?(23.9±0.6) for n=7. Given the experimental uncertainties (2σ), it is interesting to note that the effect of ionic strength only exceeded the combined uncertainties significantly in the case of log?₁₀ K _s6 to I _m =1.0 mol?kg^?1, such that these values may be of use by defining their magnitudes in other media. Values of Δ _f G ^o, Δ _f H ^o, S ^o and \(C_{p}^{\mathrm{o}}\) (298.15 K, 0.1 MPa) for each hydrolysis product were calculated and tabulated.

     

Structural state of solvent in electrolyte solutions

Isoentropic compressibilities were determined for aqueous solutions of five electrolytes ranging from dilute to almost saturated solutions at 278.15–308.15 K based on precision measurements of ultrasound velocity. Using correct relations we have found hydration numbers (h) and molar parameters of volume and compressibility of hydrated complexes (V _h , β_h V _h ), water in the hydration shell (V _1h , β 1_h V _1h ), and void containing a stoichiometric mixture of ions (V _2h , β _2h V _2h ). In the temperature range under study, the hydration numbers h and the parameters β_h V _h are independent of temperature; molar compressibilities of hydration sphere (β _1h V1_h) are independent of concentration. Since β_h V _h is independent of temperature at a constant concentration of electrolyte, Y _K,S ^e also becomes independent of temperature. It is shown that the chemical potentials of bound and unbound water are equal and that γ_R = F(h) is an example of a discontinuous function that defines the abrupt change in the solvent at the complete solvation limit in solution.     

To the Properties of Fluorosilicic Acid: Evolution of Views on the State in Aqueous Solutions (Overview)

The views of different authors on equilibria in solutions of fluorosilicic acid are discussed. The model of the aid as an equilibrium system involving hexacoordinated complexes [SiF_6–n(H₂O)_n]^n–2 (n = 0–2) is believed to be the most adequate.     

Extraction of heterometallic complexes of ruthenium and nonprecious metals by phosphorylmethylated calix[4]arenes from nitrate solutions

Synergetic extraction of [RuNO(NO₂)₄OH]^2? by calix[4]arene phosphine oxides (L) in the form of Ru/M heterometallic complexes was studied in the presence of nonprecious metals (M²⁺). The main extraction laws were recognized for [M(NO₃)₂L _n ] and [RuNO(NO₂)₄OH])ML _m ], where M²⁺ = Zn²⁺, Cu²⁺, Co²⁺, or Ni²⁺ and n, m = 1 or 2; extraction constants were determined for these metals. The variation row of the extraction constants with varying metal (Zn²⁺ > Cu²⁺ > Co²⁺ > Ni²⁺) coincides with the Irving-Williams row. Two or three PO groups of extractant L and the OH and NO₂ groups of the ruthenium anion are coordinated to the M²⁺ atom in Ru/M complexes. The conditions for generation of the Ru/Zn complex and its complete extraction were optimized as applied to the extraction of fission ruthenium from nitrated nitric acid and imitation solutions.