Vol 91, No 12 (2017)

Enthalpies of dissolution of crystalline LiCl and enthalpies of dilution of LiCl solutions in N-methylacetamide (NMA) with electrolyte concentrations no greater than 0.32m are measured on an isoperibolic calorimeter at 308.15, 318.15, and 328.5 K. Standard enthalpies of the dissolution of LiCl in NMA are calculated at different temperatures. The thermodynamic properties of the solution and its components are calculated and analyzed in the investigated range of concentrations and temperatures.

The heat capacity of TmPO₄ in temperature ranges of 9.11–346.05 and 304.6–1344.6 K is measured via adiabatic and differential scanning calorimetry, respectively. The measurement data are used to calculate the temperature dependences of the heat capacity, entropy, change in enthalpy, and reduced Gibbs energy of TmPO₄ in the range of 10–1344 K. The Gibbs energy of formation of thulium orthophosphate from elements Δ_fG⁰(298.15 K) is determined.

The possibility of dissolving frozen crystallization centers in amorphous alloys of the Fe–B system is considered by means of thermodynamic calculations. This can in turn improve the thermal stability of an amorphous alloy. The effect isothermal annealing has on the thermal stability of multicomponent amorphous alloys based on iron is investigated via the highly sensitive dilatometric technique, measurements of microsolidity, and electron microscopic investigations. The annealing temperature is determined empirically on the basis of the theses of the thermodynamic theory of the high temperature stability of multicomponent amorphous alloys, according to which there exists a range of temperatures that is characterized by a negative difference between the chemical potentials of phases in a heterogeneous amorphous matrix–frozen crystallization centers system. The thermodynamic condition of the possible dissolution of frozen crystallization centers is thus met. It is shown that introducing regimes of thermal processing allows us to expand the ranges of the thermal stability of iron-based amorphous alloys by 20–40 K through purifying an amorphous matrix of frozen crystallization centers. This conclusion is proved via electron microscopic investigations.

The kinetics of oxidative degradation of phenol and chlorophenols upon acoustic cavitation in the megahertz range (1.7 MHz) is studied experimentally in model systems, and the involvement of in situ generated reactive oxygen species (ROSs) is demonstrated. The phenols subjected to high frequency ultrasound (HFUS) are ranked in terms of their rate of conversion: 2,4,6-trichlorophenol > 2,4-dichlorophenol ~ 2-chlorophenol > 4-chlorophenol ~ phenol. Oxidative degradation upon HFUS irradiation is most efficient at low concentrations of pollutants, due to the low steady-state concentrations of the in situ generated ROSs. A dramatic increase is observed in the efficiency of oxidation in several sonochemical oxidative systems (HFUS in combination with other chemical oxidative factors). The system with added Fe²⁺ (a sono-Fenton system) derives its efficiency from hydrogen peroxide generated in situ as a result of the recombination of OH radicals. The S₂O₈^2-/Fe²⁺/HFUS system has a synergetic effect on substrate oxidation that is attributed to a radical chain mechanism. In terms of the oxidation rates, degrees of conversion, and specific energy efficiencies of 4-chlorophenol oxidation based on the amount of oxidized substance per unit of expended energy the considered sonochemical oxidative systems form the series HFUS < S₂O₈^2-/HFUS < S₂O₈^2-/Fe²⁺/HFUS.

New quinoid redox polymers were obtained by chemical modification of commercial weakly basic anion exchangers with quinone and its derivatives. The redox properties of quinone and quinoid redoxites with respect to phosphine were studied in alcohol solutions of copper complexes.

A model that considers the contributions from hydration, ion association, and electrostatic interactions to the nonideality of 2‒1 electrolyte solutions is substantiated. The parameters of the model’s equations are the mean ion hydration number, the spread of the distribution of hydrated ion stoichiometric coefficients in the standard state, and the number of association. The model is successfully used to describe literature experimental data on the concentration dependence of osmotic coefficients of aqueous CaCl₂ solutions at temperatures ranging from 0 to 100°C. The modeling of the above systems shows that as the temperature rises, the hydration number falls slightly, the distribution of the hydration number broadens, and the ion paring of the salt rises by the first degree.

Heat effects arising from interactions between triglycine solutions and Cu(NO₃)₂ solutions are studied at 298.15 K and ionic strengths of 0.2 to 1.0 (KNO₃) via isothermal calorimetry. Using experimental data, enthalpies of formation are calculated for species CuH₋₁L, CuH₋₂L⁻, and CuH₋₃L²⁻, along with Δ_rH°, Δ_rG°, and Δ_rS° of the complexation process. A relationship is revealed between the structures of deprotonated single-ligand triglycine complexes of Cu(II) and the thermodynamic parameters of their formation.

The ion-exchange sorption of silver(I) chloride complexes from 1–4 M aqueous solutions of HCl on a series of Purolite anionites with various functional groups was studied. The ion-exchange equilibria in the systems were found to be anomalous according to Raman spectroscopy, which does not significantly affect the sorption properties of the ionites.

Solubilities of L-cystine, L-tyrosine, and L-leucine in aqueous NaCl media at 298.15 K have been studied. Indispensable and related solvent parameters such as molar mass, molar volume, etc., were also determined. The results are used to evaluate the standard transfer Gibbs free energy, cavity forming enthalpy of transfer, cavity forming transfer Gibbs free energy and dipole-dipole interaction effects during the course of solvation. Various weak interactions involving solute–solvent or solvent–solvent molecules were characterized in order to find their role on the solvation of these amino acids.

The kinetics of the reaction between the two-electron reduced form of cobalamin (super-reduced cobalamin, cob(I)alamin, or Cbl(I)) and sodium selenite in an alkaline medium is studied spectrophotometrically. It is shown that the selenite rapidly oxidizes Cbl(I) to cob(II)alamin (Cbl(II)). It is established that the active form of the oxidant is the protonated selenite anion (HSeO₃^-), which receives six electrons during the reaction and transforms into HSe^–. The reactions of cob(I)alamin oxidation by selenite and sulfite are compared.

The interaction between cyclodextrins (β- and γ-CD) and ferrocenyl azoles (i.e., pyrazole ferrocenes (I, III–V) and benzimidazole ferrocenes (VI, VII)), along with 1-ferrocenylethanol (II), each in the form of (R)- and (S)-enantiomers, in forming inclusion complexes is studied for the first time using detailed quantum chemical calculations. Compounds are calculated in terms of the density functional theory (DFT), using the Becke–Lee–Yang–Parr (B3LYP) approach in the 6-31G* basis sets. For the considered CD complexes with enantiomers of I–VII, structures in which a guest partially enters a host cavity from the side of the heterocyclic substituent (pyrazole or benzimidazole) are found to be energetically advantageous. It is shown that for successful resolution of (R,S)-enantiomers on chiral phases containing cyclodextrins, we must consider the interaction between outer hydroxyl groups on the CD cone’s surface, in addition to the correspondence of geometric dimensions. The calculated data correlate well with the data from the chromatographic separation of guest enantiomers on cyclodextrin sorbents.

First-principles calculations are performed to investigate the crystal and electronic structures of BiOF crystal and its oxygen vacancy BiO_7/8F. By analyzing the energy band structures, the total density of states and the partial densities of states, it is found that the band gaps for the perfect BiOF and BiO_7/8F are 3.12 and 2.65 eV, respectively, which are smaller than the experiment value of 3.64 eV. There is a new electronic state within the forbidden band in the BiO_7/8F, which could serve as a capture center for excited electrons, consequently improves the effective separation of electron-hole pairs, and makes the optical absorption band edge red shift. The calculated results demonstrate that the BiOF crystal and its oxygen vacancy BiO_7/8F could be the potential application as photocatalytic semiconductor materials.

New stationary phases for HPLC are obtained via layer-by-layer deposition of polyelectrolytes and studied: (1) silica gel modified layer-by-layer with 6,10-ionene and dextran sulfate (Sorbent 1); (2) silica gel twice subjected to the above modification (Sorbent 2); and (3) silica gel modified with 6,10-ionene, gold nanoparticles, and dextran sulfate (Sorbent 3). The effect the content of the organic solvent in the mobile phase and the concentration and pH of the buffer solution have on the chromatographic behavior of several pharmacologically active nitrogen-containing compounds is studied. The sorbents are stable during the process and allow the effective separation of beta-blockers, calcium channel blockers, alpha-agonists, and antihistamines. A mixture of caffeine, nadolol, tetrahydrozoline, pindolol, orphenadrine, doxylamine, carbinoxamine, and chlorphenamine is separated in 6.5 min on the silica gel modified with 6,10-ionene, gold nanoparticles, and dextran sulfate.

One dimensional WO₃ nanowires with high aspect ratio of >200 were synthesized by hydrothermal method. The effects of reaction temperature and time on phase and morphologies were studied and discussed. In this research, a suitable hydrothermal condition is at 200°C for 48 h. XRD, SEM, and TEM results show that the product is hexagonal WO₃ phase with diameter of 25 nm and several ten micrometers long with growth in the c direction. The electrochemical properties were tested for rechargeable lithium batteries. The WO₃ NWs electrode exhibits a stability trend over the 30 cycle testing. Some long-term activation process is attributed to the WO₃ NWs electrode during charge/discharge reaction.

The behavior of two thin silicon films on a surface of perfect graphite is studied by means of molecular dynamics. One film is a five-layer section of Si(001) crystal, while the other is a double layer of silicene. The structure of Si films of graphite is studied by plotting Voronoi polyhedra with the exclusion of small geometric elements, and by calculating the function of radial distribution. The Si(001) film on graphite has greater sustainability than the double layer of silicene. Both the Si(001) film with diamond-like structure and the silicene film are transformed slightly in horizontal directions; in the latter case, mainly the bottom layer is distorted. Increasing the vertical displacements of atoms in the silicene resulted in strong cohesion of its layers and greater roughness. However, the positioning of the double layer of silicene on graphite is more energetically favorable than that of the Si(001) film on the graphite substrate.

Gas chromatography is used to study the sorption characteristics and retention of a series of mono-, di-, and triethylene glycol ethers on nonpolar phase DB-1 in the temperature range of 70–180°C. Temperature dependences of the retention indices of the compounds are obtained and their linear character in the investigated range of temperatures is demonstrated. The enthalpies of sorption of the investigated compounds are calculated and analyzed, based on the temperature dependences of the retention factors.

Ellipsometry and electrochemical measurements are used to study the adsorption of some substituted 1,2,4-triazoles on copper and their effect on dissolution of copper in aqueous buffer solutions at pH 7.4. It is found that the adsorption of triazole compounds on copper is polymolecular at potential Е = 0.0 V, in relation to a normal hydrogen electrode. The first layer is described by the Temkin equation with free adsorption energy (−ΔG_a⁰) = 55.2–76.3 kJ/mol and an energy heterogeneity factor that varies from 0.91 to 2.5. The maximum value of −ΔG_a⁰ is found for an acid and a hydrogen sulfide corrosion inhibitor that is a mixture of triazole derivatives. The same inhibitor is the one least sensitive to the energy heterogeneity of the surface of a copper electrode, due to its high chemical reactivity and ability to be adsorbed on different active sites. This inhibitor is likely chemisorbed on copper and forms an ultrathin coating in an aqueous solution that is vastly superior to similar coatings produced by the familiar corrosion inhibitors of triazole group compounds in protecting against atmospheric corrosion.

The content of hydrogen peroxide is determined in NaCl-containing (0.001–0.1 M) aqueous solutions of adenosine-5'-diphosphate (ADP) and adenosine (Ado) irradiated with near-UV light at 77 K. The obtained data are compared to estimates of the integral intensity (Int) of the EPR signals from the irradiated solutions prior to their thawing and the contents of different components in these spectra (including peroxyl free radicals), calculated by analyzing these spectra from their modeling. It is found that at a low content of photosensitizers (2 × 10⁻⁴ M), the relationship between [H₂O₂] and Int differs for ADP and Ado (a positive linear correlation in the case of ADP and a decreasing nonlinear dependence for Ado). It is assumed that these differences are due to the combination of two main factors: (1) the difference between the self-association constants (K_sa) of ADP and Ado and (2) the effect of the freezing process, during which added NaCl exerts a disaggregating action of the formation of ADP and Ado associates. The relation between [H₂O₂] and the EPR signal characteristics differs for high (1 × 10⁻³ M) and low (2 × 10⁻⁴ M) concentrations of photosensitizers, suggesting there are two paths of hydrogen peroxide formation in the investigated systems. According to the first path, H₂O₂ is formed during thawing as a result of interaction between peroxyl radicals O₂^-· and HO₂^· that accumulate during irradiation. According to the second path, the formation of H₂O₂ is direct (without releasing peroxyl radicals into the medium). This probably occurs inside aggregates of adenine derivatives, which form upon freezing the solution. In both cases, adding CaCl₂ to test solutions of Ado and ADP ([CaCl₂] = 0.1–0.2 × [NaCl]) results in a substantial drop in the yield of H₂O₂.

The interaction of arsenic trioxide with human insulin was investigated by circular dichroism (CD), cyclic voltammetry and electrophoresis techniques. The interfacial behavior of insulin in presence of As₂O₃ onto the Ag electrode surface was studied at 310 K in phosphate buffer solution (PBS). According to Far-UV CD spectroscopy results, As₂O₃ caused to decrease in structural compactness and variety of alpha helix into beta structures. Near-UV CD indicated that As₂O₃ dissociates disulfide linkage in insulin structure. The kinetic parameters, including charge-transfer coefficient and apparent heterogeneous electron transfer rate constant were also determined. The thermodynamic parameters of insulin denaturation in presence of arsenic trioxide were calculated and reported. The obtained results indicated strong adsorption of insulin in presence of arsenic trioxide onto the Ag surface via chemisorptions.

Geometric estimates of the characteristic sizes of simple single crystals with tetragonal, cubic, and octahedral shapes of the surface are obtained. The Wolf theorem with independent contributions from each face to the surface tension can be applied to these if the edge size is at least ~53 lattice constants. Energy estimates of the individuality of free energy contributions from each face are consistent with this estimate. The resulting minimum edge sizes also agree with an independent estimate obtained earlier using the contributions from fluctuations in the near-surface region of the phase.