Vol 97, No 9 (2023)

A comparison is made of CrOx–ZrO2–SiO2 catalysts (9 wt % chromium oxide based on Cr2O3); (Cr + Zr)/Si molar ratio of 0.8) synthesized using different orders of introducing components: (i) the simultaneous precipitation of all components, (ii) the deposition of CrOx on ZrO2–SiO2 via impregnation, and (iii) the co-precipitation of CrOx and ZrO2 on SiO2. The SiO2 precursors are TEOS in methods (i) and (ii), and SiO2 produced by calcination of rice husk in (iii). The catalysts are tested in the nonoxidative dehydrogenation of propane in a flow system with a fixed catalyst bed at 500–600°С. The co-precipitation of CrOx and ZrO2 ensures high efficiency of the catalysts. At 500 and 550°C, the most efficient catalyst is CrZr/SiO2 synthesized by depositing CrOx and ZrO2 on SiO2; at 600°C, the best on-stream behavior is exhibited by CrZrSi catalyst synthesized via the simultaneous precipitation of all components. SEM/EDX, XRD, H2-TPR, and Raman spectroscopy are used to show that in the catalysts synthesized via the co-precipitation of CrOx and ZrO2, these components (which form active sites) are uniformly distributed, have close contact, and are adequately dispersed, while Cr6+ is readily reduced to Cr3+ by the hydrogen contained in the reaction medium.

The thermal effects of acidic and basic dissociation of glycyl-D-phenylalanine dipeptide at a temperature of 298.15 K and ionic strengths of solution of 0.5, 0.75, and 1.0 M against the background of different supporting electrolytes were calculated from the results of direct calorimetric measurements performed on a calorimeter with an isothermal shell and automatic recording of the temperature–time curve. The influence of the nature of supporting electrolytes NaCl, NaClO4, NaNO3, KNO3, and LiNO3 on the thermal effects of stepwise dissociation of the dipeptide is considered. The standard thermal effects of ionization of glycyl‑D‑phenylalanine in two steps were found by extrapolation to zero ionic strength. The standard changes in thermodynamic functions (enthalpy, entropy, and Gibbs energy) in the acidic and basic dissociation of g-lycyl-D-phenylalanine dipeptide were calculated.

The formation and decay of molecular negative ions (MNIs) formed during resonant scattering of electrons by triclocarban molecules were studied by dissoiative electron attachment (DEA) spectroscopy. The most intense channel observed in the mass spectrum are MNIs formed at the thermal energy of trapped electrons with a lifetime relative to electron autodetachment of ~2800 μs. The experimental results were interpreted using CAM-B3LYP/6-311+G(d,p) calculations, which made it possible to reveal a number of important features of the geometry of molecular and fragment negative ions. Namely, the most stable geometry of MNIs is such that one of the chlorine atoms is coordinated with two hydrogen atoms of the structural element of urea. The charge on the chlorine atom is ~–0.7e–, which allows us to interpret this state as the result of the “roaming” of the chlorine atom in the MNI. According to calculations, the adiabatic electron affinity (EAa) of the triclocarban molecule is 1.66 eV. Evaluation of EAa in a simple Arrhenius approximation gives 1.2–1.4 eV. An analysis of the potential of the appearance of fragment ions with a C6H3Cl2NH2 structure made it possible to discover the noncovalent structure of these pseudo-MNIs, in which the chlorine atom is coordinated with two hydrogen atoms of the amino group.

The 13C NMR chemical shifts of fullerene C60 exo-derivatives were calculated using quantum chemical hybrid functionals combined with Pople, Dunning correlation-consistent, and def2-TZVP split valence basis sets taking into account the solvent effect (polarizable continuum model). A relationship between theoretical and experimental 13C NMR chemical shifts (CSs) is assessed quantitatively to select a functional/basis set combination. It is found that the CAM-B3LYP/6-31G and M06L/6-31G combinations have the best convergence with experimental data in modeling the 13С NMR CSs of sp3 fullerene carbon atoms in С60 derivatives, whereas X3LYP/6-31G and CAM-B3LYP/6-31G(d) in modeling the 13С NMR CSs of their sp2 fullerene carbon atoms.

The interaction of tetra-4-(2-methoxyphenoxy)phthalocyanine and tetra-4-(3-methoxyphenoxy)phthalocyanine with pyridine, 2-methylpyridine, morpholine, piperidine, n-butylamine, tert-butylamine, diethylamine, and triethylamine in benzene has been studied. The acid–base reaction involving n-butylamine and piperidine is an unusually slow process, leading to the formation of kinetically stable proton transfer complexes. The structure of these complexes is proposed. The change in the reactivity of tetraphenoxy-substituted phthalocyanines depending on the proton-acceptor ability and spatial structure of the nitrogen-containing base is considered. Pyridine, 2-methylpyridine, and morpholine do not form proton transfer complexes because of their weak basicity. A similar picture is observed in the case of tert-butylamine, diethylamine, and triethylamine, which have a more sterically screened nitrogen atom than that in n-butylamine and, as a result, do not react with tetraphenoxy-substituted phthalocyanines.

The first results of the hydrogenation of S6-symmetric trifluoromethylfullerene C60(CF3)12 in two types of reactions were reported: (1) high-temperature radical hydrogenation with 9,10-dihydroanthracene and (2) nucleophilic hydrogenation with sodium tetraborohydride under mild conditions. The high-temperature radical hydrogenation of S6-C60(CF3)12 is accompanied by partial elimination of CF3 groups and leads to the formation of a complex mixture of products of a composition C60(CF3)8–12H18–22. During the hydrogenation of NaBH4 under mild conditions, selective formation of the hydride C60(CF3)12H12 was recorded by mass spectroscopy. A kinetic analysis of the sequential nucleophilic hydrogenation of S6-C60(CF3)12 was performed, using quantum-chemical modeling at the level of density functional theory, under the assumption of linear correlation between the activation energy and the enthalpy of elementary steps of the same type. The isomeric composition was predicted for the series of anionic intermediates C60(CF3)12H−2n−12−1− and their protonation products C60(CF3)12H2n, where n = 1–6. The hydrogenation of S6-C60(CF3)12 should lead to the formation of the thermodynamically and kinetically most stable product ortho-S6-C60(CF3)12H12, in which all hydrogen atoms are located in neighboring positions near the CF3 groups, forming together with them a near-equatorial belt of 24 addends while retaining the triphenylene fragments at two opposite poles. The average bond dissociation energy BDE(C–H) in ortho-S6-C60(CF3)12H12 is 298 kJ mol–1, which is approximately 20 kJ mol–1 higher than the BDE(C–H) of known fullerene hydrides C60H18 and C60H36 (PBE0/def2-SVP).

Enzymatic catalysis is characterized by multistage chemical reactions from enzyme-substrate complexes to products. In a number of cases, in the course of experimental studies, it is possible to characterize the structures and properties of intermediates of complex chemical reactions in proteins. The use of modern computer simulation methods makes it possible to significantly supplement the knowledge of the mechanisms of enzymatic catalysis reactions and provide detailed data on reaction intermediates, including structures with atomic resolution. The materials accumulated to date make it possible to create a unique dat-abase called ENIAD (ENzyme-In-Action-Databank). The article describes the principles of building the ENIAD database, as well as a multiplatform web interface for accessing data (https://lcc.chem.msu.ru/eniad/).

The results of quantitative analysis of widely used surface samples are shown. Corrosion damage to copper and steel surfaces can be analyzed quantitatively using cobalt chloride as the internal standard. The study also demonstrates the feasibility of comparative quantitative analysis of blue ink using methylene blue homologues as standards. When conducting quantitative analysis on surfaces with inhomogeneous morphology, it has been observed that direct analysis is not possible because of uneven ionization of the sample. It has been found that when analyzing such surfaces, it is necessary to exclude points with a low signal-to-noise ratio from consideration. The work highlights the extensive possibilities of utilizing quantitative analysis in mass spectrometric visualization of the surface. The work is aimed at demonstrating the capabilities of the laser desorption mass spectrometric method for analyzing the surfaces of various materials, which will make this method universal for searching for a wide range of contaminants on the surface of materials of various nature.

The adsorption of methylene blue and eosin Y on opal-cristobalite rocks has been studied. The amount of methylene blue and eosin Y adsorbed on opal-cristobalite rocks is determined by the amorphous silica and clay minerals contained in the rocks. The possibility of using the results of IR spectroscopy for accurate determination of the amorphous silica content in opal-cristobalite rocks is shown. For opal-cristobalite rocks, a higher value of the point of zero charge is associated with lower silicon and aluminum contents in them and higher total content of alkali and alkaline earth metals.

The electrochemical properties and electrocatalytic activity of 1,3-dimethyl-2-phenyl-1H-benzo[d]imidazolium-3 iodide (I), a representative of a new class of organic metal-free electrocatalysts, in the reaction of formation of molecular hydrogen, in the presence of acids of various strengths (methanesulfonic acid (CH3SO3H), perchloric acid (HClO4), and trifluoroacetic acid (CF3COOH)) have been studied. It is shown that the efficiency of the electrocatalytic process strongly depends on pKa of the acids used. Using gas chromatography and preparative electrolysis at half-wave potentials, it was shown that molecular hydrogen formed with high Faraday yields in all cases. The behavior of the catalytic wave on the cyclic voltammogram (CV), at various ratios of acid and catalyst concentrations in the presence of all acids is typical for the process proceeding according to a homogeneous mechanism. The mechanism of the process was studied by the density functional method (DFT), and its main intermediates were identified. The protonation of electrochemically generated radicals at the C-2 carbon atom of compound I, with the formation of a C-protonated radical cation, was shown to be the key stage of the electrocatalytic hydrogen evolution reaction (HER).