Vol 90, No 4 (2016)

A new algorithm is suggested for constructing models of noncrystalline substances from a known pair correlation function (PCF). The algorithm allows the models to be reconstructed for any temperature, including the vicinity of absolute zero. The algorithm compares the coordination numbers of the target and model PCFs for all distances of the PCF histogram. The coordination number comparison algorithm includes calculating, in each iteration, a correction to the pair force function and ensures the convergence of the process to the sought force function at which the PCF of the molecular dynamic (or static) model practically coincides with the target PCF. The algorithm makes it possible to attain a very small standard deviation of the model PCF from the target PCF (~0.01) at which the plots of the two functions are visually indistinguishable. Reconstructed force functions usually differ from the functions used in the construction of target models. This indicates nonuniqueness of the solution of the inverse problem of modeling.

The thermochemical properties of melts of the binary Bi—Yb system were studied by the calorimetry method over the concentration ranges 0 < x_Yb < 0.43 at 1000–1270 K and 0.8 < x_Yb < 1 at 1100–1140 K. It was shown that significant negative heat effects of mixing are characteristic features for these melts. A range 0 < x_Yb < 0.19 of the Bi—Yb phase diagram was investigated by the DTA method. Using the regular associated solution (RAS) model, the activities of components, Gibbs energies and the entropies of mixing in the alloys, and the phase diagram of this system were calculated. They agree with the data from literature.

Temperature dependences of the heat capacity of new zincate-manganites of LaM₂^IIZnMnO₆ (M^II = Mg, Ca, Sr, Ba) composition are studied via experimental calorimetry in the interval of 298.15–673 K. It is found that all compounds have λ-shape effects on the curve of dependence C_p° ~ ƒ(T) with respect to phase transitions of the second kind. Equations for the temperature dependence of the heat capacity are derived with allowance for phase transition temperatures, and thermodynamic functions H°(T) − H°(298.15), S°(T) and Φ^xx(T) are calculated on the basis of experimental data on C_p°(T) and the calculated S°(298.15) value.

Heterogeneous interaction between peroxy radicals and acetaldehyde in a capillary reactor treated with boric acid was studied. The possibility of a reaction occurring between adsorbed peroxy radicals and acetaldehyde was confirmed. Based on a comparison of these data and those obtained for other surfaces along with the ignition and slow oxidation of aldehydes in reactors with identical surfaces, it was concluded that the oxidation of aldehydes includes not only a homogeneous component but a heterogeneous component as well.

The kinetics of n-decanol oxyethylation in the temperature range of 60–150°C at a pressure of 1.4MPa is investigated under conditions of base catalysis and an excess of alcohol in the initial step of the reaction (initial concentration of ethylene oxide in the reaction mixture, approximately 1 mol/L; that of the catalyst, 10⁻¹ to 10⁻³ mol/L). The experimental results are satisfactorily described by a kinetic equation that allows for the association of alcohol molecules and is first order with respect to the concentration of alcohol associates. Based on kinetic studies and thermogravimetry, it is concluded that the structural rearrangement of liquid decanol occurs at a temperature of around 87.5°C.

The mechanochemical synthesis of aluminum oxides and hydroxides is studied by means of X-ray diffraction, volumetry, and thermogravimetry. Kinetic aspects of metallic aluminum powder oxidation depending on time and the method of mechanical activation are investigated. The basic kinetic patterns of the process of the mechanical activation of metallic aluminum powder in an aqueous medium are established.

We proposed here a new process coupling dielectric barrier discharge (DBD) plasma with magnetic photocatalytic material nanoparticles for improving yield in DBD degradation of methyl orange (MO). TiO₂ doped Fe₃O₄ (TiO₂/Fe₃O₄) was prepared by the sol-gel method and used as a new type of magnetic photocatalyst in DBD system. It was found that the introduction of TiO₂/Fe₃O₄ in DBD system could effectively make use of the energy generated in DBD process and improve hydroxyl radical contributed by the main surface Fenton reaction, photocatalytic reaction and catalytic decomposition of dissolved ozone. Most part of MO (88%) was degraded during 30 min at peak voltage of 13 kV and TiO₂/Fe₃O₄ load of 100 mg/L, with a rate constant of 0.0731 min⁻¹ and a degradation yield of 7.23 g/(kW h). The coupled system showed higher degradation efficiency for MO removal.

The kinematic viscosites of chemically heterogeneous Cu—Pb melts were studied in to determine the temperature and concentration limits of the domains of their existence. Experiments are performed by heating and cooling samples in the temperature interval of 1050–1200°C. A quasi-chemical approximation of the irregular solution theory is used to consider the heterogeneous distribution of Cu and Pb atoms, and the short-range order parameter and characteristic enthalpy of mixing are estimated.

Based on the plasma-like theory of electrolyte solutions, areas of concentration with minimum activity coefficients are found, and the predominance of association phenomena leading to the formation of ionic associates or molecular solvates is explained. Alternative nonempirical models for estimating the activity coefficients of electrolytes are developed that produce values close to or coinciding with the available literature data in the 0 to 16 mol/L range of concentrations.

The mathematics and software of the homodesmic approach to calculating enthalpies of formation Δ_fH° of organic compounds are described. The program generates a set of independent homodesmic reactions for a studied compound, increasing the reliability of theoretical determinations of the standard enthalpy of formation. The basic steps of program construction, using the algorithm to determine the basis of homodesmic reactions for organic compounds, and calculations for the enthalpies of formation for a random test set comprising 53 CHNO-containing organic compounds of different classes are described. It is shown that the homodesmic approach provides highly reliable theoretical values of Δ_fH° virtually regardless of the quantumchemical approach that is used. The average absolute error of MAD calculations for Δ_fH° of a test set is 2.2 kJ/mol for the simple B3LYP/6-31G(d) approach and 2.1 kJ/mol for the moderately complicated M06-2X/cc-pVTZ approach, while using the complicated method of G3 calculations reduces the MAD value to 1.7 kJ/mol.

Structures and energy characteristics of clusters composed of monoethanolamine molecules are analyzed using the results of quantum chemical calculations carried out at the density functional level (DFT-B3LYP/6-31G(d,p)) and in the second order of the Møller—Plesset perturbation theory (MP2/6-31G(d, p)). Similar structural motives of hydrogen-bond networks are found in clusters that correspond to the gas-phase aggregation of initially independent molecules and the detachment of thermally distorted crystal lattice fragments. The energies of different hydrogen bonds are compared, and structural motives atypical of crystalline monoethanolamine are found. The studied clusters are shown to be prototypes of the inherent structural fragments of liquid monoethanolamine.

The nucleation of CdS particles on the surface of polystyrene supports from aqueous ammonia—thiourea solutions was studied. The increment in the mass of nanoparticles on the support with time was determined. The degree of binding of Cd(II) ions into sulfide on the surface (support area 14 cm², solution volume 3.7 cm³) after 3 h at 50°C was 2.2% of their total amount. The results agreed well with those of model calculations for spherical (for small times) and ellipsoid particles at a constant surface concentration. The nanoparticles that formed in solution were not involved in the formation of surface films on polystyrene supports. The photoluminescent properties of the obtained films were studied.

The physicochemical characteristics of solutions intended for preparing composites that contain a water-soluble polymer, polyvinylpyrrolidone (PVP), and nanocluster polyoxometalates (POMs) based on molybdenum with Keplerate (Mo₁₃₂ and Mo₇₂Fe₃₀) and toroidal structure (Mo₁₃₈) are studied. Concentration dependences of the kinematic viscosity of solutions upon changes in the absolute and relative contents of the polymer component are obtained along with the frequency dependences of the dielectric loss tangents of such solutions that correlate with them. The data allow us to confirm the composition of POM—polymers associates that form, and to estimate the relaxation parameters of ions in solutions.

Mastery over the microscopic shape and size of a nanoparticle enables accurate control of its properties for some strict application. The mechanism of shape-controlled synthesis was discussed by investigating the formation of silver nanospheres prepared by chemical reduction method using Ag(NH₃)₂⁺ as metal source, ascorbic acid as reducing agent and polyvinylpyrrolidone (K-30) as dispersant. The effects of temperature, PVP/AgNO₃ mass ratio, pH value and the interaction between PVP and silver on the shape and particle size were studied by XRD and SEM. The results show that the morphology of silver particles could transform from branched to spherical and the particle size gradually decrease with the increase of PVP/AgNO₃ mass ratio. The particles size can also be significantly influenced by pH value and temperature. The key point for preparing high dispersity spherical silver powder is that the growth rate of each plane of the particle must be uniform and synchronous. Silver powders with spherical particles with mean size of 0.2 μm were synthesized under the optimum conditions (PVP/AgNO₃ mass ratio 0.6, pH 7, reaction temperature of 40°C).

The kinetics of variation in the electronic work function (EWF) of single-crystal silicon Si(100) exposed to liquid water is studied. It is shown that immersing porous film track-etched membranes (TEMs) with pore sizes of 3.0–0.1 μm in water containing Si(100) considerably reduces the EWF of single-crystal silicon. It is found that a similar effect is observed when TEMs in the form of caps are held over the surface of water containing Si(100) at a distances of around 1.5–2.0 cm. It is speculated that the occurrence of a developed surface of TEMs in an open system changes the supramolecular structure of the water and leads to the formation of associates (H₂O)_n with increased dipole moments (compared to molecular moments), enhancing the Schottky effect during sorption on Si(100) surfaces.

A stable aqueous colloid solution of zinc sulfide (ZnS) nanoparticles was obtained by chemical condensation using ethylenediaminetetraacetic acid disodium salt. The mechanism of prolonged aggregative stability of solution at pH 7–8 with ~7-nm nanoparticles was determined as a result of the zeta potential measurements by dynamic light scattering. The blue and red shifts of the fundamental absorption edge of zinc sulfide semiconductor nanoparticles associated with the small size of nanoparticles and the defective state of their surface were found by optical spectrophotometry.

The effect condensed media based on water-soluble polymers (WSPs) have on the luminescence of Eu³⁺ and Tb³⁺ complexes with derivatives of benzoic acid and β-diketones is investigated. The effect of WSPs is found to depend on the ratio between the triplet energy levels of polymers and ligands. The most intense luminescence is observed in WSP films. The possibility of a proportional increase in the intensity of Ln³⁺ luminescence in WSP solutions over a wider range of concentrations than in an aqueous solution, and of a considerable increase in Ln³⁺ luminescence in WSP solutions and films in the presence of d- and f-element quenchers, is established.

Electrochemical behavior of the Ni^II complex of sodium 1,4-dihydroxy-9,10-anthraquinone-2-sulfonate Na₂[Ni^II(LHSO₃)₂Cl₂] · 2H₂O was studied by cyclic voltammetry in non-aqueous and aqueous buffer. The aim of the present work was to understand the behavior of the semiquinone radical anion formed after reduction of the free quinone centre of a ligand for which the other quinone centre binds a metal ion (Ni^II), not having a stable low oxidation state. In dimethylformamide solution an additional reduction peak appeared at a much more negative potential due to adsorption. The complex Na₂[Ni^II(LHSO₃)₂Cl₂] · 2H₂O undergoes diffusion controlled one-electron reduction unlike the two-electron reduction observed for most hydroxy-9,10-anthraquinones inspite of having two quinone centres in the complex (one on each ligand). In aqueous media a kinetic effect was observed during electron transfer at the electrode surface. The values of the electron transfer rate constants during the reduction of the complex at the electrode were evaluated and found to be dependent on the scan rate. Electrochemical behavior of the chosen hydroxy-9,10-anthraquinone (NaLH₂SO₃) was significantly modified in the complex with quinone. This result is important for biochemical studies, since NaLH₂SO₃ resembles the core moiety of anthracycline antitumor drugs. Several studies have reported that in case of anthracyclines complexation can help to reduce the formation of semiquinone moieties, leading to a lesser generation of superoxide responsible for drug’s cardiotoxicity. The electrochemical behavior of the title complex actually justifies such claims and tries to explain why a reduction in semiquinone formation helps to decrease the formation of superoxide.

The temperature dependence of the phase composition of KNO₃—NaNO₂ mixtures in the 0 to 1 molar fraction range of concentrations of KNO₃ is investigated. A phase diagram of the KNO₃—NaNO₂ binary system in the range of concentrations from 0 to 1 molar fractions of KNO₃ is drawn on the basis of DTA results. The composition of the eutectic mixture and its melting temperature is determined experimentally.