Vol 92, No 8 (2018)

The partial pressure values of vapor species over spinel solid solutions and the boundary of the solid spinel solutions in the MgAl₂O₄ (solid solution) + Al₂O₃ region are determined on the basis of the data obtained by Knudsen effusion mass spectrometric method in the temperature range 2000–2200 K. The obtained thermodynamic information is compared to the information available in the literature. The values of oxide activities, Gibbs energies, enthalpies and entropies of formation of solid solutions show a slightly negative deviations from ideality.

The catalytic properties of cadmium sulfide nanoparticles in the photochemical decomposition of hydrogen peroxide are studied. It is shown that in aqueous H₂O₂ solutions of any concentration, cadmium sulfide accelerates the reaction and does not change its order. The quantum yield of the reaction is 1 and does not depend on the concentration of hydrogen peroxide. The scattering of light by particles and an increase in their concentration reduces the quantum yield.

The spontaneous decay of the CH₃CO₃ radical, which plays an important role in the oxidation reactions of organic compounds (particularly acetaldehyde), is simulated using computer programs for calculating molecular mechanics; Gaussians; the capabilities of the ChemBio 12.0 software package; and the fundamental concepts of quantum mechanics. Simulations allow us to calculate the probabilities of a radical’s activation, the formation of the transition state, and its decay due to energy absorbed from excited molecules of formaldehyde, an intermediate product of the acetaldehyde oxidation. It is shown that the activation stage is a limiting stage of the CH₃CO₃ radical’s decay.

The dissolution of compounds based on 1-imino-2-phenyl-1H-inden-3-amine with fragments of 3,5-diamino-1,2,4- and 2,5-diamino-1,3,4-thiadiazoles in DMF and ethanol is investigated by means of isothermal saturation with spectrophotometric concentration monitoring in the temperature range of 298–318 K. Characteristics of the dissolution of the products of condensation with compositions 1 : 2, 2 : 1, and 2 : 2 in individual solvents are presented. Thermodynamic parameters of the dissolution of the synthesized compounds are calculated.

The efficiency and kinetics of extracting phenol from aqueous solutions using nonionic surfactants at the cloud point temperature are studied via NMR. The nonionic surfactants are neonoles AF9-8, AF9-9, AF9-10, and AF9-12; ethoxylated fatty alcohols C₁₂E₄ and C₁₂E₅; pluronics PE6200 and RE6400; and syntanol Brij 35. The efficiency of extraction using neonols and ethoxylated fatty alcohols lies in the range of 40–60%, and reaches 80% when using pluronics PL6200 and PE6400. The obtained data could be of interest to researchers in the field of phase equilibria.

A quantum chemical study of the structure of different molecular configurations of 18-crown-6 ether (18C6) in the free state, as well as in methanol, ethanol, dimethylsulfoxide, dimethylformamide, and acetonitrile media is performed using the GAUSSIAN 03 software package in the B3LYP version of the electron density functional theory using the cc-pVTZ basis set. The structure of molecules in the solvated state is studied by means of a self-consistent reaction field in the polarizable continuum model (PCM). Based on the calculation results, it is concluded that the configuration of the macrocycle of the C_i symmetry is in all cases the one most stable. The geometrical parameters and the charges on the atoms in the free and solvated states are calculated for this configuration of 18C6. To provide details of the intermolecular interactions between the solvent and solute molecules in the studied solvents, enthalpies of solvation ∆_solvH⁰(18C6) are calculated via quantum-chemical simulations using the PCM model. It is established that the solvation energy of 18C6 in alcohols is mostly determined by the universal interactions between the crown-ether and solvent molecules, and the contributions from the universal and specific interactions to the solvation enthalpy of the macrocycle are virtually equal in aprotic solvents.

The mechanism proposed in the literature and explaining the population of ion-pair states I₂ (D \(0_{{\text{u}}}^{ + }\)) and I₂ (β 1_g) when a mixture of I₂ vapor and a rare gas is irradiated with the first harmonic of a YAG laser (λ_f = 1064 nm) and the emission of a dye laser tuned to the region of the I₂ (B ← X) transition, is discussed. Alternative mechanisms involving nonlinear optical effects that can occur when iodine vapor is exposed to laser radiation are considered.

The sites of reactions in 5-hydroxy-6-methyluracil (HMU) and its dimeric and tetrameric associates are studied theoretically in terms of the electrostatic potential (ESP). The ESP approach allows us to construct the most stable combinations of HMU associates and to study HMU self-assembly without simulating all possible associates. A self-assembly scheme is proposed for HMU. N1–H···O1 bonds initially form between the molecules. If the first recognition center (RC) is occupied, N3–H···O2 bonds form with the participation of the third RC. The resulting ribbons with alternating contacts 1–1 and 3–3 are cross-linked through the electrostatic attraction of hydroxyl groups and the forces of dispersion between methyl groups.

The role of succinate ions in the structure of crystals containing 262 crystallographically nonequivalent succinate ions and atoms of f-elements A (А = U(VI), La(III), or lanthanides) is analyzed using the TOPOS-InterMol program complex. It is estimated that С₄Н₄О\(_{4}^{{2 - }}\) anions can display 10 topologically different types of coordination to the atoms of metals A, acting as three- or four-dentate ligands and forming from three to eight О–А bonds. It is estimated that of the two theoretically possible types of metallacycles, succinate ions usually form tetratomic cycles. Alternative heptatomic cycles are formed by only 4 out of 262 succinate ions. It is shown the type of a di-anion’s coordination affects that of its preferable coordination (trans φ³ or gauche φ¹) in a crystal’s structure. It is estimated that a change in the type of coordination or conformation of succinate ions can determine the polymorphism of succinate-containing polymers.

We first report the hybrids of TiO₂ and graphene (Gr) used as the support of Pd nanoparticles, showing high performance electrocatalysts for formic acid oxidation. The hybrids are prepared with the solvothermal method, and tetrabutyl titanate and graphene-oxide (GO) are used as the precursors. The initial mass ratios of Ti:GO in the precursors are 0.07, 0.15, 0.26, 0.60, respectively. Compared to Pd/graphene, the as-obtained Pd/TiO₂–Gr electrocatalysts exhibit higher catalytic activity and stability. Among them, the Pd/TiO₂–Gr (Ti : GO = 0.26, initial mass ratio) exhibit the highest activity. Its current density is about 3.1 times of Pd/graphene, and the agglomeration of Pd metal that can be seen in Pd/graphene has been inhibited in the as prepared Pd/TiO₂–Gr. Thus the electrocatalytic performance of Pd for formic acid oxidation is greatly improved by the binary TiO₂–graphene support.

LiFePO₄ nanoparticles have been synthesized by a rapid microwave-solvothermal process at 200°C within 10 min. In spite of the low synthesis temperature, the as-synthesized powders with thinner thickness along [010] direction are highly crystalline. Sample exhibited excellent rate capability and showed good cyclic performance. The short reaction times of just 10 min show the basis for an efficient and time-saving synthesis of nanosized LiFePO₄.

The effect the composition of a water–acetonitrile eluent has on the sorption of benzimidazoles by octadecyl silica gel is studied using the Snyder–Soczewinski model. Three-parameter equations associating retention factors and certain physicochemical characteristic of the molecules of benzimidazoles are obtained via linear regression analysis. Standard changes in the enthalpy of the transfer of benzimidazoles from the water–acetonitrile phase to the layer of octadecyl silica gel and entropic components of the process are calculated from the temperature dependences of the retention factors. The enthalpy–entropy dependences of sorption are discussed.

The thermodynamic parameters of sorption of a test mixture of hydrocarbons on a new type of PEG-like stationary phases are determined from the temperature dependence of sorbate retention in the temperature range of 35–110°C. The determined entropy and enthalpy of sorption are close for all the studied stationary phases, despite the different ratios of ethylene glycol and acrylate moieties in the polymer’s phase structure. At the same time, the studied phases exhibit greatly different separation abilities, due apparently to the kinetic properties of the phases, as is indicated by differences in the efficiency of the columns with these phases and in the diffusion coefficients of sorbates on these phases.

Polymeric polyelectrolyte hydrogel composites based on a copolymer of acrylic acid and acrylamide are synthesized. The composites are filled with bentonite (1 to 5 wt %). The kinetics of the collapse of hydrogel composites in aqueous solutions of salts of alkali and alkaline-earth metals at a constant temperature of 25°C are studied. Gravimetry is used to study the kinetics of the swelling and collapse of a gel of the cross-linked copolymer of acrylic acid and acrylamide, and its composites with bentonite in aqueous solutions of salts of mono- and divalent metals. It is found that the presence of bentonite prevents the collapse of composites based on acrylic hydrogels in aqueous solutions of electrolytes, due to the steric and electrostatic interactions between filler particles. By comparing these two kinetic models, it is shown that Peleg’s kinetic model best describes the experimental data on the collapse of the polymer hydrogel composite in aqueous solutions of metal salts. It is established that the kinetic constant of hydrogel collapse does not depend on the radius of metal ions at equal concentrations of the studied salts in a solution.

Monolith chromatographic columns are prepared for HPLC with sorbents based on 1-vinylimidazole and 4-vinylpyridine. A comparative estimation of column selectivity is performed using a model of the linear solvation energy relationship (LSER). Column polarity is shown to vary over a wide range by changing the content of 1-vinylimidazole and 4-vinylpyridine in the initial polymerization mixture. Examples are given of separation on the prepared columns.

Mono- and diethylene oxide derivatives of tetra(p-hydroxyphenyl)porphyrin (THPP) with different conformation states are synthesized. These compounds exhibit high photosensitization activity in the generation of singlet oxygen in organic and aqueous (in the solubilized state) phases. It is shown that introducing ethylene oxide moieties into the hydroxyphenyl substituents of THPP increases its solubility in chloroform. In addition, the activity of singlet oxygen ¹Δ_g generation in the reaction of anthracene photooxidation by THPP tetra derivatives in chloroform, where the ethylene oxide fragments are introduced into two phenyl rings and hexadecyl fragments are introduced into another two, is higher than the activity of mono- and di-modified THPP molecules with enthylene oxide molecules at one hydroxyphenyl cycle. The activity of tetra-substituted porphyrin in chloroform, however, is comparable to that of nonsubstituted tetraphenylporphyrin, considered to be one of the most active photosensitizers. The produced ethylene oxide derivatives of THPP are solubilized with pluronic F-127 (triblock copolymer of ethylene- and propylene-oxides)—one of the least toxic and effective polymeric detergents—forming water-soluble forms of the respective porphyrins. It is established that the pluronic solubilization capability (the lowest molar concentration of pluronic required for the complete transfer of porphyrin of a particular molar concentration dissolved in organic phase to the water-soluble form) is higher for asymmetrical mono- and di-derivatives of the THPP than for symmetric tetra-substituted THPP. It is shown that the activity of the solubilized water-soluble form of mono- and tetra-derivatives in tryptophan photoxidation is higher than that of unsubstituted THPP and is comparable to the activity of tetraphenylporphyrin.

Recently, metal-free organic dyes have been successfully incorporated in dye-sensitized water oxidation photoanode utilizing red light. In order to understand the interfacial structures and the related electronic/optical properties of the dye-sensitized water oxidation photoanode at nanoscale level, a metal free porphyrin dye/TiO₂ interface that has been applied in a water splitting system experimentally is modelled via first principles. The DFT calculations predict vertical adsorption of the organic dye onto the TiO₂ substrate via its carboxylic acid anchor. The calculated UV–Vis absorption spectra of the porphyrin organic dye/TiO₂ system demonstrate peak absorption wavelengths at ca. 500, 580, and 620 nm, consistent with the experiments. Detailed electronic structure analysis including band structure, density of states and orbital distributions suggests effective dye sensitization and interfacial electron transfer in the organic dye/TiO₂ system in the water oxidation photoanode, which is essential for water splitting efficiency.

A luminescent technique is proposed for determining concentrations of hydrogen peroxide without the use of chemical reagents. It is shown that intense luminescence of solutions is observed in the range of 320‒460 nm. A smooth change in the luminescent properties of solutions at hydrogen peroxide concentrations of (0.0017‒133) × 10⁻³ mol/L is found.

The heat capacity and bulk properties of barium and cadmium iodide solutions in dimethylformamide (DMF) at 298.15 K are measured via calorimetry and densimetry. Standard partial molar heat capacities \(\bar {C}_{{p,2}}^{^\circ }\) and volumes \(\bar {V}_{2}^{^\circ }\) ВаI₂ and CdI₂ in DMF are calculated. The standard values of heat capacity \(\bar {C}_{{p,i}}^{^\circ }\) and volume \(\bar {V}_{i}^{^\circ }\) of barium and cadmium in DMF at 298.15 K were determined.