Structural parameters of the immediate environment of ions in saturated aqueous solutions of lanthanide chlorides,according to X-ray diffraction data

Saturated aqueous solutions of lanthanide chlorides are studied by means of X-ray diffraction. Models of the investigated solutions are used to calculate quantitative characteristics of the immediate environment of ions in solutions using the obtained experimental data. It is established that all of the investigated systems are characterized by similar structures. Cations coordinate six solvent molecules in the first coordination sphere as the Ln³⁺–OH₂ distances become shorter upon transitioning from light to heavy ions. Non-contact ion associates form in all the systems.     

Intermolecular interactions in dioxane-water solutions of substituted coumarins according to ultrasonic data

Density, ultrasonic velocity of pure dioxane (Dx) and ligands, 4,6-dimethyl-7-hydroxycoumarin (L₁), 6-ethyl-7-hydroxy-4-methylcoumarin (L₂), and 3-chloro-7-hydroxy-4-methylcoumarin (L₃) in different percent of Dx-water mixture have been investigated at 303.15 K. Acoustical parameters such as adiabatic compressibility (β), intermolecular free length (L _f ), acoustical impedance (Z), relative association (R _A ), apparent molar compressibility (Φ_β), and apparent molar volume (Φ _V ) have also been evaluated from the experimental data of density and ultrasonic velocity. An excellent correlation between a given parameters is observed at all percent of dioxane-water and the result suggests nature of intermolecular interactions between the components.     

Conformational characteristics of polyethylene glycol macromolecules in aqueous solutions according to refractometry data

The aqueous solutions of polyethylene glycols with molecular masses of 600, 1000, 1500, 3000, 6000, and 20000 were studied by refractometry. The conformational polarizabilities, mean-square distances between the ends of the macromolecular chain, segment lengths, and the number of Kuhn segments in a macromolecule were determined using the Lorentz-Lorentz equation. The polarizability of a hydrated macro-molecule was represented as the sum of polarizabilities of the nonhydrated macromolecule with retained conformation and polarizabilities of the water molecules involved in hydration of macromolecules. The size of macromolecules stabilized starting from a certain concentration. It was concluded that the initial concentration of stabilization shifts toward low concentrations as the molecular mass of polyethylene glycol increases. The dependence of the mean-square distance between the ends of the macromolecular chain on the number of Kuhn segments was expressed as the exponential function with index 0.3.     

The brilliant blue FCF ion-molecular forms in solutions according to the spectrophotometry data

The brilliant blue FCF acid–base properties in aqueous solutions have been studied and its ionization constants have been defined by tristimulus colorimetry and spectrophotometry methods. The scheme of the acid–base dye equilibrium has been proposed and a diagram of the distribution of its ionic-molecular forms has been built. It has been established that the dominant form of the dye was the electroneutral form, which molar absorptivity (ε₆₂₅ = 0.97 × 10⁵) increases with the increase of the dielectric permittivity of the solvent. It has been shown that the replacement of polar solvents by less polar ones is causing a bathochromic shift of the maximum absorption band of the dye, the value of which is correlated with the value of the Hansen parameter. Tautomerization constants have been defined in a number of solvents and associated with the value of the Dimroth-Reichardt parameter.     

Heteromolecular structures in aqueous solutions of dimethylformamide and tetrahydrofuran,according to molecular dynamics data

The complex dielectric permittivity of aqueous solutions of tetrahydrofuran and dimethylformamide in wide ranges of temperature (220–300 K) and pressure (0.1–12 MPa) is studied by means of molecular dynamics. The autocorrelation functions of the dipole moments of molecules are calculated. Dielectric permittivity spectra are obtained. The dielectric relaxation times are determined as functions of the tetrahydrofuran and dimethylformamide concentrations in the indicated binary mixtures. The dielectric relaxation frequency shifts toward low frequencies in the range of tetrahydrofuran and dimethylformamide concentrations x ≤ 0.5 molar fraction, due to the formation of heteromolecular structures with hydrogen bonds. This is confirmed by the negative values of the excess dielectric permittivities of binary solutions at x ～ 0.3–0.4 molar fraction.     

Supramolecular structure of aqueous solutions of glucose according to dynamic light scattering data

The nature and structure of large-scale fluctuations in aqueous glucose solutions were studied by dynamic light scattering. The two-component model of solution was used. The supramolecular structure of the solutions was determined and their phase diagram at low concentrations was schematically constructed. The volume of clusters in solution was calculated.     

Methanol and acetonitrile associates in aqueous and chloroform solutions according to 1H NMR spectroscopic data

Association of methanol and acetonitrile in a nonpolar (CDCl₃) and polar (H₂O and D₂O) solvents was studied by ¹H NMR spectroscopy and quantum chemistry. The results were compared with the data obtained by decomposition of the spectral curves in the range 800–1100 nm by the independent component analysis (ICA) technique. The content of homoassociates consisting of four and two or three molecules in the case of methanol and acetonitrile, respectively, gradually increased with the amount of the organic solvent in solution. The aqueous solutions under study consisted of few associates of compositions 1: 1, 1: 2, and 1: 4.5 for acetonitrile and 1: 1 and 1: 3 for methanol (water: organic solvent). The quantum-chemical calculation of the NMR spectra of the particles existing in solution confirmed our conclusions about the structure of the solutions.     

Structure of liquid ethylenediamine according to data on molecular scattering of light

M. V. Lomonosov Moscow State University. Institute of General and Inorganic Chemistry, Academy of Sciences of the USSR. Translated from Zhurnal Strukturnoi Khimii, Vol. 30, No. 4, pp. 175–177, July–August, 1989.     

Coordination of ions in aqueous solutions of dysprosium chloride according to the X-ray diffraction data

Aqueous solutions of dysprosium chloride in a wide concentration range are studied by X-ray diffraction analysis under standard conditions. The scattered X-ray radiation intensity curves are characterized by prepeaks at low values of the wave vector. Their interpretation and an analysis of changes at different concentrations are performed. The structure of concentrated solutions is formed due to interionic interactions of different types. On the contrary, dilute solutions are characterized by the determining role of the quasi-tetrahedral structure of the solvent. The prepeaks are also observed on the intensity curves of dilute solutions, indicating that these solutions retain the “long-range” ordering.     

The structure of diluted binary solutions of amides according to the heat capacity data

The specific heat capacities of hexamethylphosphoric triamide, diethylpropionamide, their aqueous solutions, and mixtures of hexamethylphosphoric triamide with formamide were measured in the temperature range from 288.15 to 318.15 K. The dependences of the partial molar heat capacity of aqueous solutions of amides on the composition of the mixture have maxima in the region of 0.02–0.04 molar fractions of amide. The maximum on a similar dependence for solutions of hexamethylphosphoric triamide corresponds to the concentration of 0.01 molar fractions. The conclusion on the formation of solvates (hydrates) in the systems studied was made. The heat capacity coefficients of pair and triple interactions were calculated in terms of the McMillan-Mayer theory. A change in the heat capacity characteristics with the temperature change was analyzed. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2479–2483, December, 1998.     

Sizes of ionic surfactant micelles and their clustering according to data on viscosity of micellar solutions

Data available on the viscosity of micellar solutions of surfactants belonging to the homologous series of alkyltrimethylammonium bromides containing 10, 12, 14, and 16 carbon atoms in their alkyl chains, as well as sodium dodecyl sulfate solutions, have been analyzed. It has been shown that the systems under consideration may be adequately described by the Einstein equation. The results obtained have made it possible to identify the concentration ranges in which the intermicellar interaction does not affect significantly the flow of the micellar solutions. Data on the relative viscosity of the studied micellar solutions have been employed to calculate the hydrodynamic radii of micelles formed by the surfactants with different lengths of hydrocarbon radicals in their molecules.     

The solubility of oxygen in sea water and solutions of electrolytes according to the pulse proton NMR data

The possibility of determining the content of dissolved oxygen (O₂) in distilled water, sea water, and aqueous solutions of electrolytes with errors of ～2% without preliminary instrument calibration was demonstrated. The reasons for different relaxation efficiency coefficients reported by various authors were analyzed. The results of the determination of the content of O₂ from the rate of spin-lattice relaxation in sea water and separate solutions of sea water components at 25°C depending on water salinity (S) up to 180‰ inclusive are presented. Noticeable changes in the steepness of the dependence of the content of O₂ on S at 80–90‰ were observed; these changes were related to the attainment of the boundaries of the complete solvation of the main sea water ions. The main reasons for the discrepancies between the oxygen salting out coefficients K _S found by various authors were explained, and the interrelation between the solubility of O₂ and ion hydration characteristics was revealed. The O₂ salting out constants for sea water and solutions of slats contained in sea water obtained from relaxation measurement data are given. The filling of “ice-like formation” voids was shown to be the main mechanism of the solution of O₂ in water and aqueous solutions of electrolytes.     

Adiabatic compressibility and structural features of non-electrolyte aqueous solutions

Structural characteristics of the hydration complexes of non-electrolytes such as the hydration numbers h, molar adiabatic compressibility of hydration complexes β _h V _h , the molar volume of water in the hydration sphere V _1h , the solute molar volume without hydration environments V _2h and others are determined using the data on the ultrasonic velocity, the density and heat capacity of aqueous solutions of urea, urotropine, acetonitrile, and a number of amides of N-acetyl amino acids. A theoretical model of solvation is also applied. A comparison of the environments of hydrated urotropine molecules with those of urea and acetonitrile molecules in an aqueous medium shows a considerable hydrophobic interaction of urotropine with a solvent.     

Adiabatic compressibility of tetraethylammonium tetrafluoroborate solutions in propylene carbonate

The density and ultrasound propagation velocity for Et₄NBF₄ solutions in propylene carbonate were determined in a concentration range of 0.01–0.8 mol/kg at 283.15, 298.15, and 308.15 K. Apparent molar compressibilities and volumes of the studied electrolyte in solvent were calculated. Solvation numbers and molar adiabatic compressibilities of solvate complexes were determined using the isoentropic compression method. These quantities indicated weak solvation of tetraethylammonium tetrafluoroborate in propylene carbonate in the range of concentrations practically used in ionistors.     

Structure of complexes of divalent copper with phenanthroline in aqueous neutral media according to ESR data

The structure of copper complexes with phenanthroline in aqueous solutions has been studied by ESR in the X and Q bands at 300 and 77K. It has been shown that the Cu²⁺ ions are ordered by a cooperative Jahn-Teller exchange interaction when [phen][Cu₂₊] 2.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 22, No. 1, pp. 99–102, January–February, 1986.     

Adiabatic compressibility and solvation of drag reducing polymers in aqueous solutions

Adiabatic compressibilities of aqueous solutions of some drag reducing polymers have been evaluated from ultrasonic velocity and density measurements. The solvation numbers of the repeat units of the polymers have been further evaluated by using Passynsky equation. It is observed that the solvation number increases with the shear stability of drag reducing polymers in turbulent flow.