卷 91, 编号 1 (2017)

A thermochemical study of the processes of L-proline dissolution in aqueous solutions of acetonitrile, 1,4-dioxane, acetone, dimethyl sulfoxide, nitromethane and tetrahydrofuran at Т = 298.15 K in the range of organic solvent concentrations x₂ = 0–0.25 mole fractions is performed. Standard values of the enthalpies of solution and transfer of L-proline from water to mixed solvent, and the enthalpy coefficients of pairwise interactions between L-proline and molecules of organic solvents, are calculated. The effect the composition of a water–organic mixture and the structure of organic solvents have on the enthalpy characteristics of L-proline dissolution and transfer is examined. The effect the energy properties of intermolecular interactions between components of a mixed solvent has on the intermolecular interactions between L-proline and molecules of cosolvent is estimated. The correlation between the enthalpy characteristics of L-proline dissolution and electron-donor properties of organic cosolvent in aqueous solutions is determined.

The kinetics of complex formation between zinc and 5,10,15,20-tetraphenylporphyrin and 5,10,15,20-tetra(4-hydroxyphenyl)porphyrin in acetonitrile is studied in the temperature range from 298 to 318 K. The fluorescent properties of these compounds are examined, the emission in the red region of the spectrum is measured, and the fluorescence quantum yields are determined. It is found that although the electronic absorption spectra of the studied compounds are almost identical, hydroxyl substituents are observed to have a considerable effect on the chelating ability of ligands. The rate constant of the formation of ZnT(4-OH-Ph)P is thus approximately three times higher than that of ZnTPhP, with the energy consumption being lower (about 20 kJ mol^–1). The calculated fluorescence quantum yields of H₂TPhP, H₂T(4-OH-Ph) P, ZnTPhP, and ZnT(4-OH-Ph)P in acetonitrile are half those in toluene, while the ratio between the quantum yields of ligands and their metal complexes is a constant equal to approximately 3 and does not depend on which solvent is used.

The pH of the formation of hydroxo complexes and hydrates in an aqueous solution of terbium Tb(III) is determined using combined means of potentiometric and conductometric titration. The stability constants of the hydroxo complexes, the products of hydroxide solubility, and the Gibbs energy of terbium hydroxo complex formation are calculated.

ΔG, ΔH, and ΔS of the second dissociation step of aminomethanesulfonic acid and its N-methyl, N-hydroxyethyl, N-(tert-butyl), N-benzyl derivatives in aqueous solutions (at the isoelectric point where the ionic strength is 4.75 × 10^–4 М) are determined on basis of pH measurements at 293–313 K. It is found that an increase of the electron-acceptor properties of the substituents at nitrogen atom reduces the effect temperature has on the thermodynamic functions of dissociation. Enthalpy–enthropy compensation at an isothermodynamic temperature of 303 K is recorded.

The heat effects of the interaction between a solution of α-aminobutyric acid and solutions of HNO₃ and KОН are measured by means of calorimetry in different ranges of рН at 298.15 K and values of ionic strength of 0.25, 0.5, and 0.75 (KNO₃). The heat effects of the stepwise dissociation of the amino acid are determined. Standard thermodynamic characteristics (Δ_rH⁰, Δ_rG⁰, and Δ_rS⁰) of the reactions of acid–base interaction in aqueous solutions of α-aminobutyric acid are calculated. The connection between the thermodynamic characteristics of the dissociation of the amino acid and the structure of this compound is considered.

The evaporation of MgAl₂O₄ spinel is studied via high-temperature Knudsen effusion mass spectrometry in the temperature range of 1850–2250 K. In the gas phase, molecular components typical of the simple oxides in the spinel and traces of gaseous complex oxide MgAlO are identified above the samples. The resulting values of the partial vapor pressures of the molecular components contained in the gas phase over the spinel are compared with those corresponding to simple oxides for the first time.

Ce_0.46Zr_0.54O₂ solid solution prepared using a cellulose template was employed as a carrier for vanadium catalysts of the oxidative dehydrogenation of propane. The properties of VO_х/Ce_0.46Zr_0.54O₂ catalyst (5 wt % vanadium) are compared with the properties of the neat support. The carrier and catalyst are studied by means of BET, SEM, DTA, XRD, and Raman spectroscopy. It is shown that the CeVO₄ phase responsible for the ODH process is formed upon interaction between vanadate ions and cerium ions on the surface of the solid solution. The catalytic properties of the catalyst and the support are studied in the propane oxidation reaction at temperatures of 450 and 500°C with pulse feeding of the reagent. It is found that the complete oxidation of propane occurs on the support with formation of CO₂ and H₂O. Three products (propene, CO₂, and H₂O) form in the presence of the vanadium catalyst. It is suggested that there are two types of catalytic centers on the catalyst’s surface. It is concluded that the centers responsible for the complete oxidation of propane are concentrated mainly on the carrier, while the centers responsible for propane ODH are on the CeVO₄.

The properties of a nickel catalyst obtained by treatment of nickel–aluminum alloy with sodium hydroxide in the presence of H₂O₂ and additionally stabilized with increased pressure were studied. Additional stabilization decreased the catalyst activity by 25%, but gave a more distinct picture for an XRD analysis of the active catalyst surface and decreased the time of deactivation of the dehydrated catalyst with air oxygen. The catalyst stabilization was explained by the displacement of water, decrease in the pore size, and surface inhomogeneity.

Kinetic parameters are estimated using two criteria in addition to the traditional criterion that considers the consistency between experimental and modeled conversion data: thermodynamic consistency and the consistency with entropy production (i.e., the absolute rate of the change in entropy due to exchange with the environment is consistent with the rate of entropy production in the steady state). A special procedure is developed and executed on a computer to achieve the thermodynamic consistency of a set of kinetic parameters with respect to both the standard entropy of a reaction and the standard enthalpy of a reaction. A problem of multi-criterion optimization, reduced to a single-criterion problem by summing weighted values of the three criteria listed above, is solved. Using the reaction of NO reduction with CO on a platinum catalyst as an example, it is shown that the set of parameters proposed by D.B. Mantri and P. Aghalayam gives much worse agreement with experimental values than the set obtained on the basis of three criteria: the sum of the squares of deviations for conversion, the thermodynamic consistency, and the consistency with entropy production.

Nanosized zinc oxide (nano-ZnO) was prepared by a microwave irradiation method using zinc nitrate and triethanolamine as starting materials and distilled water as a solvent. The as-prepared powder was characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The photocatalytic degradation of cetyltrimethylammonium bromide (CTAB) using the prepared material under UV irradiation was studied.The effects of ZnO dosage and initial pH on the photodegradation of CTAB were investigated. As the ZnO load increased, the CTAB degradation first increased and then decreased. The optimum ZnO dosage was 3 g L^–1. Photodegradation of CTAB is more efficient in slightly alkaline media (pH 9).

Conformers of the biologically active compounds CH₃P(O)(OR)(SCH₂CH₂NR₂^′), where (I) R = i-C₄H₉, R′ = C₂H₅ and (II) R = C₂H₅, R′ = i-C₃H₇, are calculated within the AM1 level of theory. The elongated and twisted forms with maximum and minimum distances between a nitrogen atom and those of a phosphorus tetrahedron, respectively, and bearing a syn and anti oriented alkoxy group relative to a phosphoryl oxygen, are studied. It is found that the differences between the energy, electronic, and geometric parameters of these forms are apparent in differences between their properties, e.g., the ability to participate in complexation and protonation, reactions that to some extent simulate the interaction between a substance and a biological object.

Reduced ion mobility and scattering cross sections are calculated from experimentally obtained spectra of the ion mobility of linear aliphatic alcohols with carbon atom numbers from 2 to 9. A linear increase in the scattering cross sections as the molecular weight grows is found. According to the results from experiments and quantum chemical calculations, alcohol cluster ions do not form a compact structure. Neither are dipole moments compensated for during dimerization, in contrast to the aldehydes and ketones described earlier. It was concluded from ab initio calculations that charge delocalization in monomeric and dimeric ions of alcohols increases the dipole moment many times over.

The ranges of concentrations of silver and gold nanoparticles in which the rate constants of the test for the photodynamic therapy (PDT) reaction of oxidation of tryptophan in an aqueous medium in the presence of photosensitizer remain virtually the same (without nanoparticles) are found. This testifies to the feasibility of causing additional photothermal damage on tumor cells by transforming the absorbed energy of electromagnetic radiation in the area of the plasmon resonances of the administered nanoparticles into heat energy in the PDT of tumors. Metal nanoparticles are obtained by photochemical and chemical methods, and by laser ablation. Tetraphenylporphyrin solubilized with Pluronic F127 (to attain its solubility in aqueous systems), the optical absorption band of which is close to the plasmon absorption bands of nanoparticles, is used as a photosensitizer.

XRD phase analysis and thermal analysis are used to confirm the formation of a continuous series of solid solutions in which one cation is substituted for another in the systems Co(II) hydrogen maleate–Ni(II) hydrogen maleate; Fe(II) hydrogen maleate–Co(II) hydrogen maleate; and Fe(II) hydrogen maleate–Ni(II) hydrogen maleate. The unit cell volume of these solid solutions is shown to depend linearly on their composition. The linear character of changes in the initial temperatures of dehydration and thermal decomposition is established. Using the example of the first of these systems, it is shown that when heated, bimetallic nanoparticles embedded in the polymeric matrix of composites obtained via the thermal decomposition of solid solutions of hydrogen maleates undergo a second-order phase transition, resulting in decomposition of the solid solutions of metals at the Curie temperature.

In the present work, the multi-walled carbon nanotubes (MWCNTs) were modified by the treatment with concentrated nitric and sulfuric acid mixture (3: 1 vol/vol). The obtained material was characterized by X-ray diffraction (XRD). The effect of two surfactants, methylcellulose (MC) and cetyltrimethylammonium bromide (CTAB) on dispersing of MWCNTs in aqueous solution was monitored by UV–Vis spectroscopy and transmission electron microscopy (TEM). Also, the dispersing effect of the surfactants was simulated by three-dimensional Monte Carlo method. The results showed that the oxidative treatment leads to purification of the neat MWCNTs, and directly improved their dispersing. The mixture containing both MC and CTAB surfactants has better dispersing effect than individual surfactants. The optimum concentration ratio of MC, CTAB, and MWCNTs was 2: 3: 1. In the simulation model, MWCNTs were dispersed randomly. The simulation results may be helpful for the further research on mechanical and electrical properties of composites reinforced with MWCNTs.

A procedure for calculating the surface tension of droplets consisting of two components in the vapor phase is considered. The calculations are performed using the lattice gas model in the quasi-chemical approximation with allowance for the correlation effects of the nearest interacting molecules. A layered model of the structure of a vapor–liquid interface is used. Ways of calculating the surface tension of droplets with different radii are considered. They are based on different thermodynamic definitions of reference surfaces. Typical dependences of the surface tension of metastable and equilibrium droplets on the droplets’ radii are analyzed for four types of phase diagram. It is found that if the energy of interaction between the components of one type exceeds by 150% the energies of interaction between components of another type and between particles of different types, and if the component with the highest energy of interaction predominates in a droplet, this results in a nonmonotonic profile of the component with the lowest energy of interaction in the region of transition. Mixture components are distributed in the region of transition such that the component with the highest energy of interaction is concentrated on the liquid side and the other component is concentrated on the vapor side. The surface tension of equilibrium droplets is less than that of metastable droplets.

The effect the ionic strength of an aqueous ethanol mobile phase containing buffer salt has the on retention and thermodynamics of adsorption of optical isomers of some α-phenylcarboxylic acids on chiral adsorbent Nautilus-E with grafted antibiotic eremomycin is investigated. It is shown that ion exchange processes participate in the adsorption of enantiomers of α-phenylcarboxylic acids. It is established that electrostatic interactions contribute to the retention of enantiomers of α-phenylcarboxylic acids and affect selectivity only slightly. The dependences of retention characteristics, selectivity, and thermodynamic parameters on the concentration of the buffer salt in the eluent are determined. A statistical analysis of enthalpy–entropy compensation is performed, and the compensation effect is shown to be true. It is found that the points corresponding to the investigated adsorbates are distributed over the compensation dependence according to the spatial structural characteristics of molecules.

Five equations for kinetic curves which connect the number of theoretical plates N and time of analysis t₀ for five different versions of optimization, depending on the parameters being varied (e.g., mobile phase flow rate, pressure drop, sorbent grain size), are obtained by means of mathematical modeling. It is found that a method based on the optimization of a sorbent grain size at fixed pressure is most suitable for the optimization of rapid separations. It is noted that the advantages of the method are limited by an area of relatively low efficiency, and the advantage of optimization is transferred to a method based on the optimization of both the sorbent grain size and the drop in pressure across a column in the area of high efficiency.

A technique is developed for obtaining a titania–graphite oxide composite with a high surface area in which the TiO₂ particles are covered by graphite oxide. It is established that the experimental value of the composite specific surface area passes through a maximum at about 200°С, depending on the temperature of preliminary annealing in an inert atmosphere.

Vibration-averaged V-structures for liquid ethylene glycol (EG) and monoethanolamine (MEA) are found in the temperature range of the solvents’ liquid phase by means of molecular dynamics. The obtained V-structures’ characteristics are compared to X-ray diffraction data on the crystalline phases of these compounds. Good agreement between theoretical and experimental data is observed. The V-structures are compared to that of water.