Moscow University Chemistry Bulletin最新文献

The study of ytterbium halide crystals using the compound-tunable embedding potential (CTEP) method is carried out in the framework of the density functional theory. For subsequent calculations the optimization of atomic bases is carried out, and for this purpose stoichiometric molecular systems were studied, using the coupled-cluster methods. The chemical shift of the lines of the X-ray emission spectrum, K_α1 and K_α2, in YbHal₃ relative to YbHal₂ was chosen as a criterion for verifying the computational accuracy of the properties localized on the nucleus of a heavy atom, Yb, since this method is a unique tool for analyzing partial electron densities near a heavy nucleus specifically for compounds of d- and f-elements. In the study, five main versions for the halogen basis set sizes were considered. The stability of the results was obtained using the CCSD and CCSD(T) coupled cluster methods for molecular systems YbF₂, YbF₃, YbCl₂ and YbCl₃.

The multireference configuration interaction method based on single and double excitations (MR–CISD), l-independent core polarization potential (CPP), and diffuse function-saturated cc-pVQZ and aug-cc-pV5Z basis sets for Na and He atoms, respectively, is used to perform nonrelativistic calculations of potential energy curves and permanent dipole moment functions for the ground and excited electronic states of the exciplex Na–He molecule up to the Na(6²S) state. The ab initio results obtained within a wide range of internuclear distances R [1.7, 20.0] (Å) quantitatively confirm the undulating behavior of interatomic potentials, predicted in the framework of the inelastic scattering theory. It is established that at large R the interatomic potentials and dipole moments of highly excited (3, 6, 10)²Σ⁺ states, converging to the Na (n = 4, 5, 6²S) + He(2²S) atomic limits, are modulated by the nodal structure of the radial Rydberg wave function (n > 3) of the s-electron of an Na atom during its scattering on a remote He atom.

Gcn5-related N-acetyltransferases catalyze the transfer of an acetyl group to a primary amino group of a wide class of substrates. Deprotonation of the amino group upon binding to the enzyme is necessary to activate the nucleophilic attack on the substrate. The process of binding of glutamate to N-acetylglutamate synthase is considered using the methods of molecular modeling and quantum chemistry. It is shown that deprotonation of the primary amino group of glutamate occurs upon its incorporation into the active site of the enzyme with the participation of the side chain of the aspartate residue.

The possibility of the elution of hydrophilic organophosphorus substances using a concentration gradient of formic acid in an aqueous mobile phase on a Hypercarb porous graphitized carbon sorbent is studied. The analytes are detected on a monoquadrupole mass spectrometer. The retention of analytes is studied by varying the composition of the mobile phase before injection of the sample solution. It is shown that the effect of the stepwise gradient elution on the retention of analytes is primarily due to the state of the sorbent surface rather than the elution ability of the phases. The displacement “quasi-ion exchange” mechanism of analyte retention seems to be most probable.

Based on the solution of the direct vibrational-rotational problem with the Watson Hamiltonian using Van Vleck perturbation theory, employing the quantum-chemical (CCSD(T)/aug-cc-pVQZ) molecular geometry of molecule ({text{D}}_{2}^{{16}}{text{O}}), sextic force field, and cubic dipole moment surface, absorption spectra and spectroscopic constants of effective rotational Hamiltonians (A-reduction) for the ground state and ν₂ band are predicted. Theoretical sixth-order vibrational (fourth for dipole operators) and third-order rotational perturbative methods are based on a systematic procedure for calculating rotational commutators using the normal ordering of cylindrical angular momentum operators. The obtained reduced spectroscopic constants are refined and augmented by being fitted into sets of experimental energy levels. The new effective Hamiltonians significantly improve the reproduction of the experimental data for J ≤ 30, and the computed intensities accurately reproduce the observed values.

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.