Moscow University Chemistry Bulletin最新文献

The activation energies for the diffusion of oxygen ions in yttria-stabilized zirconia (YSZ) (one of the promising solid electrolytes for fuel cell technologies), as estimated in molecular dynamics (MD) studies using the Buckingham classical potential, are found to be significantly lower than the experimental values. A possible reason for this discrepancy is the improper calibration of the potential, whose parameters were previously tuned using simple model systems. In this study, three sets of potential parameters are developed based on the calibration of interatomic potentials using periodic DFT calculations in an extended system. The results of MD simulations using these developed parameter sets significantly better reproduce the experimental values of activation energy when varying the dopant content in the solid electrolyte.

The evolution of the electronic characteristics of chemical bonds formed and broken along the path of the bimolecular nucleophilic substitution reaction at a tetrahedral central atom, which is the Tt=C, Si, and Ge atom, is analyzed. For this purpose, the reaction paths of the step-by-step replacement of the chlorine atom with the phenyl fragment are modeled, and the energy characteristics of the equilibrium initial, transition, and final states are obtained within the framework of the DFT. For different reaction centers, which are atoms of the carbon group (Tt), changes in electron density distributions and shifts in the positions of the extremes of the total static and electrostatic potential for the forming C–Tt and breaking Tt–Cl bonds along the reaction path are compared. Quantitative criteria are refined that determine the region of existence of a typical noncovalent tetrel bond Tt…Cl, allowing it to be distinguished from a covalent one. Establishment of the properties of the transition state stabilizing tetrel bond may be useful for monitoring the efficient synthesis of covalent organic framework precursors.

The nanoascorbate of chitosan of Bombyx mori is synthesized from low-molecular-weight chitosan (LMWC) using the suspension method. Its physicochemical and antimicrobial properties against Fusarium oxysporum, which causes diseases of mulberry trees, are studied. The resulting chitosan nanoascorbate based on LMWC has a higher inhibition zone compared to any other variants against the mulberry Fusarium oxysporum culture. It is found that when wheat seeds are treated with nanoascorbate chitosan at a component ratio of LMWC : AC = 4 : 1, the incidence of smut fungus decreases by 6.6 and 2.4% compared to the control and standards, respectively. The influence of a ratio of chitosan and ascorbic acid components on the formation of chitosan nanoascorbate is found. The structural properties of Bombyx mori nanoascorbate chitosan are studied with IR spectroscopy.

A technique for the indirect determination of the hydrogen index of aqueous solutions of small volumes (ranging from microliters to hundreds of microliters) by digital colorimetry with the use of consumer optical raster imaging devices is proposed. Determining the pH does not require constant color scales or information about the concentration of the acid-base indicator in the solution. A prototype of a handheld pH analyzer, based on a smartphone, is developed for out-of-laboratory applications. The accuracy of the pH determination results is confirmed by the potentiometry and spectrophotometry techniques.

A new technique is proposed for obtaining thin films of a cross-copolymer of poly-N-isopropylacrylamide and acrylamide on glass and silicon surfaces. The technique is based on polymerization of individual monomers followed by the crosslinking of polymer chains during spin-coating onto a substrate. The effect of temperature on the hydrophobicity of the obtained films is studied. Reversible changes in the contact angle are demonstrated when the substrate temperature is varied above and below 35°C.

Matrix solid-phase dispersion using a humate-based magnetic sorbent is proposed as an efficient method for the concentration of bisphenol A from fish muscular and hepatic tissue samples followed by the chromatography-mass spectrometry determination of an analyte prederivatized with acetic anhydride. Under the optimum concentration conditions (the stirring time is 10 min and the sorbent weight is 0.05 g), the recovery of bisphenol A upon single sorption reaches 85%. The percentage desorption exceeds 99% (the eluate is methanol, the time is 3 min, and the volume is 1 mL). The maximum enrichment factor is 718. The limit of the detection of bisphenol A is 0.15 μg/kg (on a dry basis) for muscular tissue and 0.25 μg/kg for liver.

Hybrid nanoforms based on silver and the antibacterial drug dioxidine (2,3-bis-(hydroxymethyl)quinoxaline 1,4-di-N-oxide) are prepared by the method of joint cocondensation of metal and ligand vapors on a liquid nitrogen-cooled surface. The samples obtained are characterized by FTIR-, UV-Vis, and XPS-spectroscopy, as well as ТЕМ, SEM, and powder X-ray phase analysis (ХРА). It is shown that cryomodified nanoforms preferably consist of the anhydrous triclinic (T-phase) crystal phase of dioxidine. The dimensions of dioxidine particles ranged from 50 to 300 nm and the average size of doping silver nanoparticles is 15 ± 3 nm. The broadening of the diffraction patterns belonging to silver shows the transition of metallic silver to the nanoscale state. The FTIR results indicate hybrid nanoforms stabilized by the donor-acceptor interactions of surface silver atoms with the hydroxyl groups and with the donor N-atoms of quinoxaline cycles of dioxidine molecules.

N-Acetylaspartylglutamate (NAAG) is the most common dipeptide in brain cells, which is synthesized using the enzyme N-acetylaspartylglutamate synthase. In this study, we utilize bioinformatics methods to predict the protein structure based on the primary sequence of the coding gene, classical molecular dynamics to obtain a stable protein complex with N-acetylaspartate and glutamate ligands within the trajectory, and machine learning methods to analyze, describe, and select potential reactive and nonreactive conformations of the model system describing the enzyme–substrate complex. Molecular dynamics trajectories are obtained for a set of selected conformations within the framework of the method of combined quantum and classical molecular mechanics, and the active site of the protein–ligand complex and potential reaction mechanism are characterized.

The configurations of small copper clusters (Cu₂, Cu₃, Cu₁₃) and their complexes including a complex containing a copper atom with dioxidine (Dx) are calculated by density functional theory modeling with B3LYP5 parametrization. The trends of the changes in the geometry configuration and metal cluster–dioxidine ligand interaction energy depending on the size of the metal cluster are assessed. The dissociation energy of the complexes increases with the metal cluster size but the maximum value (55.1 kcal/mol) is implemented for a Cu₃–Dx complex. There is coordination of the metal atom to one or two oxygen atoms of the dioxidine molecule for all the complexes.

The technological scheme of cesium extraction from spent fuel before hydrometallurgical reprocessing is developing in order to reduce the heat dissipation and specific activity of spent fuel. The scheme includes the joint high temperature treatment of spent fuel and molybdenum trioxide, flushing the product with an alkali solution to remove cesium, and then dissolving the fuel in nitric acid. Implementation of this technology will allow reducing the cooling time of the spent fuel and reduce the radiation impact on personnel, equipment, and technological environment. This article presents the results of the experimental substantiation of the choice of temperature of the high-temperature treatment, comparative analysis of the efficiency of flushing solutions of different compositions, and determining the duration of the cesium fractionation process. The research was conducted in laboratory conditions with the use of spent fuel imitators and radionuclide markers.