Russian Journal of Physical Chemistry A

The enthalpies of interaction of Tyr-Pro hydrochloride solution with HCl at 298.15 K and ionic strength values of 0.25 M, 0.5 M and 0.75 M (background electrolyte KCl) were measured by calorimetric method. The step dissociation constants of Tyr-Pro were determined by the potentiometric method at a temperature of 298.15 K and a solution ionic strength value of 0.2 M (background electrolyte KCl). The following values of pK1 = 2.87 ± 0.05, pK2 = 7.51 ± 0.05 and pK3 = 9.79 ± 0.05 were obtained. The enthalpies of stepwise dissociation of the dipeptide were calculated using the universal HEAT program. Standard thermodynamic characteristics (Δ rH°, Δ rG°, Δ rS°) of acid-base interaction reactions in aqueous solutions of Tyr-Pro were calculated. The influence of the background electrolyte concentration on the enthalpies of peptide dissociation is considered.

Possible reaction pathways of aminolysis of succinic anhydride by benzocaine — concerted and two-step — have been investigated by the density functional theory method (level ωB97M—V/ma-def2-QZVPP//r2SCAN-3c). For each mechanism three variants are considered: without catalysis, self-catalysis by the reagent molecule (benzocaine) and autocatalysis by the product (succinamide). Thermodynamic and activation parameters of all elementary stages in the gas phase are calculated. It is shown that different mechanisms are involved in the course of the reaction: at early stages, both concerted and two-stage pathways of self-catalysis can be realized with equal probability; as the product is formed, the preferred route of reaction becomes stage autocatalysis with the limiting first stage.

Crystallochemical analysis of all known compounds of f-metals containing glutarate ions C5H6O42– has been carried out. It was found that 154 crystallographically non-equivalent glutarate ions exhibit 11 topologically different types of coordination to f-metal atoms in crystal structures. It has been found out that for aliphatic dicarboxylate ions [O2C—(CH2)n—CO2]2– at n > 1 the types of coordination that lead to the formation of four-membered metallocycles are characteristic. Using glutarate ions as an example, a new method of quantitative evaluation of the conformation of chains consisting of five carbon atoms connected by single C—C bonds has been tested for the first time. It is shown that in the characterized structures 154 glutarate ions realize four different conformations, each of which corresponds to a certain «double» symbol: φ3/φ3, φ1/φ3, φ(1)/φ(1), or φ(1)/φ2.

The results of investigation of the influence of the method of preparation on the properties of Co/Mo/MgO catalysts and carbon nanotubes (CNTs) synthesized on them by chemical vapor deposition are presented. The catalysts were prepared by modified precipitation method and glycine-nitrate method. The structure and properties of CNTs were studied by low-temperature nitrogen adsorption, scanning and transmission electron microscopy, and Raman spectroscopy. The effect of the addition of synthesized CNTs on the conductivity of NMC811 (LiNi0.8Mn0.1Co0.1O2) based cathode material was investigated.

The application of energy-efficient and environmentally safe technology of gas hydrate crystallization for purification of natural gas from hydrogen sulfide (H2S) and carbon dioxide (CO2) is considered. Thermodynamic modeling of the influence of H2S and CO2 concentrations from 1.00 to 20.00 mol. % on gas hydrate dissociation pressures and filling of gas hydrate cavities with the gas mixture CH4 — C2H6 — C3H8 — n-C4H10 — CO2 — H2S — N2 in the temperature range of 273.15—283.15 K has been carried out. It is obtained that increasing the concentration of H2S leads to a significant decrease in the dissociation pressures of gas hydrates. The filling of small gas hydrate cavities with H2S molecules reaches 0.91. Increasing the concentration of CO2 leads to a slight increase in the dissociation pressures of gas hydrates. It is found that CO2 is poorly concentrated in the gas hydrate phase of the considered gas mixture. To extract CO2 it is necessary to apply multiple gas hydrate crystallization or to use natural gas deposits with low concentrations of C3H8.

The results of studying the sorption of lanthanum(III) and erbium(III) ions from model solutions on ASC silica gel modified with monoethanolamine are presented. The influence of solution composition (pH and salt background) on sorption equilibria was investigated. The sorption rate constants of La(III) and Er(III) ions for pseudo-first and pseudo-second order equations at 296, 303 and 313 K were calculated. The adsorption isotherms of the selected ions were treated in the coordinates of the Langmuir, Freundlich, Dubinin-Radushkevich and Temkin equations. Using the sorption equilibrium constants of the Langmuir model, the thermodynamic parameters of sorption were calculated for different temperatures. According to the obtained values of thermal effects of the process, the sorption of lanthanum(III) and erbium(III) ions on the studied sorbent is mainly due to physical forces. With increasing temperature, the equilibrium for both ions shifts towards desorption. The kinetics of sorption of La(III) and Er(III) ions in their combined presence has been studied.

On the example of two polymorphic transformations in crystals of organic compounds (glycine and carbamazepine) and dehydration of carbamazepine dihydrate the influence of the material of the drum of a vibrating ball mill (steel or various polymers) on the result of mechanical impact on the sample is shown, as well as the possibility to use for studying this influence the method of manufacturing polymer liners in steel drums by 3D printing available in laboratory conditions.

The structure of integral curves obtained by processing chronopotentiograms (CPG) of an aluminum anode polarized by a weak (at the level of one to several μA/cm2) current in chloride-containing medium is self-similar. This universal property allows us to find their fitting function and calculate the reduced (compressed dependence; the initial number of points is 1000, described by the number of AFC-14 modes). The initial curve is invariant with respect to its transformed counterpart after five-fold compression. For two different types of data, obtained with open circuit and with metal polarization by microcurrent, a common fitting platform related to its parameters can be obtained. There are various methods of detrending: i. e., obtaining a trend from the original trendless noise. The simplest method of obtaining a trend that does not give computational errors is obtained from a numerical integration formula using the trapezoidal method. It is this trend, obtained from the original trendless sequence without additional data processing errors, that it makes sense to define as a clear trend. The approximation parameters can be used to compare various random processes, including those caused by reactions on the metal surface with changes in its microrelief during redox processes.

The photocatalytic activity of iron-containing silicon nitride-based metal-ceramic composites in the process of oxidative degradation of the pharmaceutical pollutant diclofenac (DCF) has been investigated. The composites were obtained by nitriding ferrosilicon without additives and ferrosilicon with shungite (modifier for SiC production) in combustion mode. It is noted that the use of urea allows to additionally modify the ceramic matrix of composites with semiconducting phases (Fe2O3, C3N4) capable of absorption in the region of near-UV and visible light. The phase composition has been established, morphological features and optical properties of the composites have been studied. The acid-base properties of the surface have been evaluated. Adsorption and catalytic activity of composites in the absence and with H2O2 addition under UV irradiation (Fenton photochemical process), under ozonation conditions under UV and visible light irradiation were studied. The highest degree of DCF degradation was found when heterogeneous photocatalysis and Fenton process were combined (84%) and under photocatalytic ozonation conditions (88%). The kinetics of photocatalytic degradation of DCF was investigated using a pseudo-first-order model. The degradation products of DCF were determined GC—MS.

The interaction of copper(II) ions with natural lipids (soybean lecithin with different phospholipid composition) in aqueous medium has been studied. Using methods of thin-layer chromatography, dynamic light scattering and mathematical processing of UV-spectra by Gauss method, it was revealed that in aqueous medium lecithin forms rather large liposomes with a diameter of about 900 nm, the size of which decreases in the presence of copper(II) ions regardless of their concentration. It was found that copper(II) ions both initiate lipid peroxidation processes and form complexes with polar «heads» of phospholipids. It is shown that these processes depend on the composition of lecithin lipids and their ability to oxidation.