Vol 69, No 5 (2024)

The paper provides digital processing of 2D X-ray projection images of a Coulomb-type point defect in a Si(111) crystal recorded by a detector against the background of statistical Gaussian noise. A managed filter and a wavelet filter with a 4th-order Daubechies function are used. The efficiency of filtering 2D images is determined by calculating the relative quadratic deviations of the intensities of filtered and reference (noiseless) 2D images averaged over all points. A comparison of the calculated values of the relative deviations of the intensities shows that the considered methods work quite well and both, in principle, can be effectively used in practice for noise processing of X-ray diffraction images used for 3D reconstruction of nanoscale defects of crystal structures.

For the first time, the crystal α-Na_0.35Dy_0.65F_2.30 was studied using X-ray diffraction at 293 K and 85 K and electron diffraction at 293 K. A unified cluster model of the defective structure of nanostructured crystals with a fluorite-type structure, based on the polymorphism of ordered phases KR₃F₁₀ (R = Er, Yb), was expanded with a matrix part model based on the structure of the KYF₄ compound. The unified cluster model was applied to construct the defective structure of α-Na_0.35Dy_0.65F_2.30. It was found that the matrix part of the crystal contains Na⁺ и Dy³⁺ cations in a 1:1 ratio. Some of the anions in the matrix are displaced to the 32f positions (space group Fm3m). The excess Dy³⁺ forms octahedral-cubic clusters with Na⁺ [Na_14–nDy_nF_64+n] with cores in the form of distorted and regular cuboctahedrons {F₁₂}. These are composed of interstitial anions in two 32f positions and one 48i position. The cluster component of the α-Na_0.35Dy_0.65F_2.30 crystal contains octahedral-cubic clusters of f-, f–i- and i-types. Electron diffraction showed that α-Na_0.35Dy_0.65F_2.30 is a nanostructured crystal. Its cluster component is in the form of plate-like inclusions about 5 nm thick with superstructural ordering and individual octahedral-cubic clusters. A model of their structure was proposed. Lowering the temperature to 85 K increases the number of interstitial F_(32f)1 anions in the matrix component of the crystal.

Trimethylenediamine ethylenediaminetetraacetate zincate trihydrate [HN(CH₂CH₂)₃NH]ZnL · 3H₂О and tetramethylethylenediamine ethylenediaminetetraacetate zincate dihydrate [H(CH₃)₂NCH₂CH₂N(CH₃)₂H]ZnL · 2H₂О were synthesized by reacting zinc oxide with ethylenediaminetetraacetic acid (H₄L) and then with its triethylenediamine or tetramethylethylenediamine salts. The resulting compounds precipitate from aqueous or organic solvents in the form of thread-like, cubic and pyramidal crystals, which are characterized by elemental analysis, scanning electron microscopy, IR spectroscopy, thermogravimetry and differential scanning calorimetry.

The results of studying DNA-protein complexes using two independent structural methods – molecular dynamics (MD) and small-angle X-ray scattering (SAXS) – are compared. MD is a computational method that allows visualization of macromolecule behavior in real environmental conditions based on the laws of physics but suffers from numerous simplifications. SAXS is an X-ray method that allows the reconstruction of the three-dimensional structure of an object in solution based on the one-dimensional profile of small-angle scattering, which presents the problem of ambiguity in solving inverse problems. The use of structural characteristics of complexes obtained by the SAXS method for validating 3D structural models obtained in MD experiments has significantly reduced the ambivalence of theoretical predictions and demonstrated the effectiveness of combining MD and SAXS methods for solving structural biology problems.

An explanation of the effects arising at the collision of a stream of metal particles with a size of 10–100 microns, moving at a speed of 1–3 km/s, with a solid target is proposed. It is assumed that at the moment of impact on the target, the particle loses some electrons and for some time, due to the presence of an oxide shell, retains a positive charge. The flow of electrons passing through the target at the moment of impact generates an electromagnetic field pulse. A particle with a charge of about 10^–9 C, having penetrated into a solid target, presses on the channel wall with a force of about 500 MPa and moves in it under the action of forces caused by the polarization of the target substance. The combination of high pressure and displacement leads to a significant reduction in the particle-wall friction force. The proposed hypothesis, if confirmed, can help find ways to protect electronic devices of spacecraft from impacts from streams of fast dust particles.

Crystals of sodium hexafluorosilicate Na₂SiF₆ millimeter size were grown by the hydrothermal method. According to X-ray diffraction analysis, it was revealed that Na₂SiF₆ samples are twinned according to the merohedral law and crystallize in sp. gr. P321 with unit cell parameters equal at 295 K <a> = 8.8582(12), <c> = 5.0396(11) Å, <V> = 342.47(17) ų on average the results of repeated measurements. A multi-temperature diffraction study of Na₂SiF₆ was carried out, based on the results of which the temperature dynamics of the optical properties of crystals was calculated. The structural similarity of Na₂SiF₆ crystals with crystals of the langasite family La₃Ga₅SiO₁₄ was found. This made it possible to explain the optical activity of Na₂SiF₆ by considering electron density spirals similar to langasite, twisted around a triple axis of symmetry passing through the origin of the Na₂SiF₆ cell. The fractures in the temperature dependences of the refractive indices and rotation of the plane of polarization of light are explained by taking into account the anomalous features of interatomic interactions along the triple axis of the crystal cell passing through the Si2(2d) position with coordinates (1/3, 2/3, z). It was found that the main factor influencing the temperature dynamics of optical parameters is the Si2(2d)–F2(6g) distance, which increases abnormally with cooling.

The experience of developing and applying methods for measuring the refractive coefficients of crystals of the highest and middle categories based on multi-angle spectrophotometric reflection methods is presented: by the reflection spectrum from one face at an angle of incidence of light close to normal, and by the reflection method when light falls at Brewster angle. The advantages and limitations of the methods and the requirements for the samples are described. It is shown that the reflection method at an angle of incidence close to normal is applicable for optically isotropic media. The Brewster angle method is applicable for crystals of the highest and middle categories. The measurement accuracy of both methods has been determined. The applicability of these methods is shown for samples of crystals of the highest and middle categories Gd₃Al₂Ga₃O₁₂:Ce and La₃Ga_5.5Ta_0.5O₁₄ respectively.

The photopolymerization of Langmuir-Schaefer films of diacetylene N-arylcarbamate symmetrical molecules containing different numbers of methylene groups in the molecules was studied. The result of diyne films UV irradiation was the effective transition of the films into the stable state of blue phase polydiacetylene. The number of CH₂ groups in the molecules affected the efficiency of the monomers film transition into the polymer and the conjugation length of the polymer chains. Studying the morphology of the films using scanning electron microscopy showed the horizontal position of diyne molecules on the substrates in the state of domains, the sizes of which depended on the number of CH₂ groups in the molecules.

Nanowires of Fe_xCo_yCu_{(100–x–y)} and Fe_xNi_yCu_{(100–x–y)} alloys have been studied. The features of obtaining such structures by the matrix synthesis method have been investigated. Elemental analysis of nanowires grown at sequentially increasing voltages revealed a significant decrease in the amount of copper, as well as a change in the ratio of the main magnetic elements. X-ray phase analysis showed that FeCoCu is a three-component solid solution, while FeNiCu contains three phases of solid solutions: FeCu with copper content up to 80%, FeNi with high iron content, and NiCu in an amorphous or fine-crystalline state with nickel content up to 80%. Mössbauer spectroscopy revealed that the addition of copper can lead to a change in the angle of magnetic moment misalignment in nanowires, which correlates with magnetometry data.

The molecular dynamics of two types of lysozyme octamers was simulated under crystallization conditions in the MARTINI coarse-grained force field. Comparative analysis of the obtained results with the simulation data for the same octamers modelled in the all-atom field Amber99sb-ildn showed that octamer “A” demonstrates greater stability compared to octamer “B” in both force fields. Thus, the results of molecular dynamics simulations of octamers using both force fields are consistent. Despite several differences in the behavior of the protein in different fields, they do not affect the validity of the data obtained using MARTINI. This confirms the applicability of the MARTINI force field for studying crystallization solutions of proteins.

Two mechanisms of the effect of the transition state of building particles (activated complexes according to S. Arrhenius) on the crystal growth rate within the framework of the fluctuation model of dislocation crystal growth are discussed. Transition state clusters adsorbed on the surface of the growing face perform the function of an impurity that lowers the surface energy of the crystal at the time moments between free energy fluctuations. Thus, the transition state of the crystallizing substance by the first mechanism affects the relaxation rate of the secondary adsorption of impurities and shortens the time period of attachment of building particles to the crystal face. Other clusters formed in solution reduce the number of free particles and under conditions of low concentration of the building substance are able to decrease the crystallization rate. Nevertheless, in a natural multicomponent crystallization environment, at low concentrations of building material, significant thermal effect of crystallization and small deviations from equilibrium, the role of the transition state in crystal growth is generally insignificant.