卷 63, 编号 2 (2018)

For the last 100 years, crystallography has passed a complex and interesting way: from descriptive mineralogy; through chemistry, chemical analysis, and new crystal growth technologies; to physics (X-ray diffraction analysis, physical materials science) and then to biology and protein crystallography. Actually, the starting point in the development of modern crystallography is the discovery of X-ray diffraction. Specifically X rays revealed the complex, three-dimensional, and periodic structure of all materials surrounding us.

X-ray natural circular dichroism (XNCD) and its structural nature have been investigated in a langasite (La₃Ga₅SiO₁₄) crystal at an incident radiation energy close to the Ga K-absorption edge and the La L_2,3-absorption edges. An XNCD signal was observed mainly beyond the absorption edge, which confirmed the existence of delocalized mixed p–d electronic states in Ga and d–f and d–p electronic states in La. Calculations with application of the multiple scattering method have made it possible to separate the contributions from three crystallographically nonequivalent Ga sites to the absorption spectrum and the XNCD signal and explain adequately the largest contribution of the Ga atom occupying the 1a site to the XNCD signal.

Crystals of ferroelectric‒ferroelastic gadolinium molybdate Gd₂(MoO₄)₃, calcium molybdate CaMoO₄, and double sodium‒gadolinium molybdates of stoichiometric (Na_1/2Gd_1/2MoO₄) and cationdeficient (Na_2/7Gd_4/7MoO₄) compositions, which are used to design solid-state lasers, phosphors, and white LEDs, have been simulated by the interatomic potential method. Their structural, mechanical, and thermodynamic properties are calculated using a unified system of interatomic potentials and effective ion charges, which demonstrated transferability and made it possible not only to describe the existing experimental data but also to predict some important physical and thermodynamic properties of molybdate crystals. The influence of the deviation from stoichiometry and partial ordering of cations on sites in nonstoichiometric crystals on the properties and local structure of sodium‒gadolinium molybdates is discussed.

An accurate structure analysis of a Ba₃TaGa₃Si₂O₁₄ single crystal from langasite family was performed using four X-ray diffraction data sets collected on a diffractometer equipped with a CCD area detector (sp. gr. P321, Z = 1, sinθ/λ ≤ 1.35 Å^–1; at 295 K a = 8.516(1) Å, c = 5.1910(6) Å, R/wR = 0.58/0.56%, Δρ_min/Δρ_max =–0.73/0.42 e/ų, 4414 independent reflections; at 106 K a = 8.5109(9) Å, c = 5.1861(9) Å, R/wR = 0.75/0.86%, Δρ_min/Δρ_max =–0.81/1.06 e/ų, 4382 reflections). The distinguishing feature of the Ba₃TaGa₃Si₂O₁₄ structure is a strong disorder of the Ga atom at the 3f site. Structural transformations in the series of Сa₃TaGa₃Si₂O₁₄–Sr₃TaGa₃Si₂O₁₄–Ba₃TaGa₃Si₂O₁₄–Ba₃TaFe₃Si₂O₁₄ crystals were analyzed.

Triphenylbismuth bis[3-(2-furyl)acrylate] Ph₃Bi[O₂CCH=CH(C₄H₃O)]₂ and triphenylbismuth di-meta-nitrocinnamate Ph₃Bi(O₂CCH=CH–C₆H₄NO₂-m)₂ were synthesized and studied by X-ray diffraction. The crystal structures (sp. gr. P1, Z = 2; sp. gr. P2₁, Z = 2, respectively) contain one and two tetrahydrofuran solvent molecules, respectively, per bismuth complex. The bismuth atom has a trigonal-bipyramidal coordination geometry. Additional weak Bi···O interactions (2.748–2.835 Å) cause large angle distortions in the equatorial plane of the trigonal bipyramid.

The L232H mutant of the enhanced green fluorescent protein (EGFP) was expressed and crystallized. An X-ray diffraction data set was collected from the crystals to 1.53 Å resolution. An analysis of the three-dimensional structure revealed a stacking interaction between the amino-acid residues Н78 and Н232, which contributes to the fastening of the C-terminal region of the protein in the vicinity of the chromophore and influences chromophore maturation of hybrid fluorescent proteins produced by fusion of the target proteins with the C-terminus of EGFP. This hypothesis was experimentally confirmed by investigating chromophore maturation of the hybrid proteins fused to the N- and C-termini of EGFP and EGFP-L232H.

The small-angle X-ray scattering in calomel (univalent mercury chloride Hg₂Cl₂) single crystals at low temperatures has been investigated. Data on the size of superstructural ferroelectric domains have been obtained for the first time. Lang measurements with anomalous X-ray transmission have made it possible to trace the temperature dynamics of crystal lattice of the high-temperature D_4h phase of Hg₂Cl₂ from 300 K to the Curie temperature (186 K) and the formation of ferroelastic domains in the temperature range of 186–100 K. The lowering of paraphase symmetry in the closest vicinity of the phase transition temperature is indicative of tricritical point transition.

The rotation of the plane of polarization of light transmitted in the directions parallel (ρ_||) and perpendicular (ρ_⊥) to the optical axis has been calculated for langasite family crystals. It is shown that the ρ_|| and ρ_⊥ values are, respectively, negative and positive for all the right-handed crystals under study. An analysis of the interatomic potential constructed based on X-ray diffraction data has suggested that this anisotropy of optical activity is structurally based of electron density regions shaped as helices. The atomic helix with an axis parallel to the optical axis is right-handed and three-start, whereas in the direction perpendicular to the optical axis there are three left-handed two-start helices, which intersect in the origin of the unit-cell coordinate system.

A concentration series of fluorite crystals Ca_1–xSr_xF₂ (0 ≤ x ≤ 1) has been grown by directional crystallization according to the Bridgman technique. Experimental (weakly quadratic) concentration dependences of the lattice parameter a(x) and density ρ(x) are obtained for the Ca_{1 – x}Sr_xF₂ (0 ≤ x ≤ 1) solid solution. A calibration density curve ρ(x), which is suitable for non-destructive testing of the composition of optical elements made of Ca_{1 – x}Sr_xF₂ crystals with an error of Δх = ± 0.001, was constructed.

The electro-optic response in planar-aligned chiral nematic liquid crystals in an electric field oriented perpendicular to the helical structure axis is studied as a function of the magnitude and sign of the dielectric anisotropy of liquid crystal in order to understand the mechanism of this electro-optic effect. The main contribution to the electro-optic response is shown to be due to the interaction of the electric field with the dielectric anisotropy. The flexoelectric effect also contributes to the electro-optic response, but its magnitude is much smaller.

An X-ray study of the interaction of Langmuir monolayers with nanoparticles under the conditions when nanoparticles arrive at the monolayer from the side of the air medium has been performed for the first time. Measurements by the X-ray standing-wave method and two-dimensional diffraction have made it possible to investigate the transport of nanoaerosol particles through a lipid monolayer and observe the structural changes occurring in it. Nanoaerosol particles were formed by electrohydrodynamic sputtering of desalted solutions of ferritin. It was shown that nanoaerosol particles pass through the monolayer without disrupting the two-dimensional packing of lipid molecules. The ferritin molecules penetrating the aqueous subphase after sputtering are found to be adsorbed under the monolayer.

The change in the free-electron density in ultrathin (5 nm) superconducting NbN films in the initial state and after irradiation by O⁺ ions to doses of (0.1–0.9) × 10¹⁷ cm^–2 has been studied by electron energy-loss spectroscopy (EELS). The analysis has been performed on cross section samples prepared by the focused ion beam method, using plasmon oscillations with energies up to 50 eV. The radiation-induced replacement of nitrogen atoms with oxygen atoms in niobium nitride is found to change the electrical properties of the material, which leads to a decrease in the free-electron density with an increase in the irradiation dose.

The role of native and radiation-induced defects in the state switching kinetics for one-dimensional systems (nanowires, molecular single-chain magnets, biological macromolecules, and many others) has been studied. An analytical approach to the description of the influence of randomly located defects on the dynamics of new-phase domains is developed using an analogy with stochastic processes in queueing theory. This method makes it possible to calculate threshold phenomena and the dependence of switching fields on material parameters.

The conditions for preparing hydroxyapatite/anatase Ca₁₀(PO₄)₆(OH₎₂/TiO₂ nanocomposites with a core–shell structure by sol‒gel processing have been optimized. The photocatalytic activity of these nanocomposites is close to that of the commercial photocatalysts based on titanium dioxide (precursor Ti(OBut)₄ concentration 40 vol %, hydroxyapatite/TiO₂ sol ratio 1: 2, annealing temperature 500°C). The photocatalytic activity of hydroxyapatite/TiO₂ composites with different anatase contents has been estimated for the first time from the singlet oxygen yield. It is shown that the degree of modification of apatite particle surface affects significantly the structural characteristics of the hydroxyapatite/TiO₂ composite. An increase in the relative anatase content reduces the sizes of apatite crystallites and increases their specific surface.

Single-phase ceramic samples from the region of morphotropic phase boundary in the (1–x)(Na_0.5Bi_0.5)TiO_3–xBaTiO₃ and (1–y)[(Na_0.5Bi_0.5)TiO_3–xBaTiO₃]–yBi(Mg_0.5Ti_0.5)O₃ systems, modified by low-melting LiF and 0.6NaCl–0.4LiF additives, have been prepared by solid-state synthesis. The effect of additives on the phase formation, structural parameters, and dielectric and ferroelectric properties of the ceramics has been studied. A decrease in the ceramic sintering temperature is found. A slight increase in the unit-cell volume upon modification of the ceramics under study by lithium fluoride and 0.6NaCl–0.4LiF additive is revealed. First-order ferroelectric phase transitions near 700–800 K have been observed. The prospects for improving the piezoelectric properties of modified ceramic samples are proved.

A biogenic fabrication of selenium nanoparticles has been considered, with characterization of these nanoparticles. Anoxygenic phototrophic bacteria reduce sodium selenite to produce amorphous selenium nanospheres that are more homogeneous in size than biogenic selenium nanoparticles reported in the literature and those obtained by chemical route. These biogenic selenium nanoparticles can be used to investigate the selenium metabolism in microorganisms.

A mathematical model of the hydrodynamic processes occurring during crystal growth from solutions is considered. Specific features of solution flows in crystallizers of different designs are discussed.

A technique of temperature-controlled biocrystal nucleation, at which the growth onset of one crystal suppresses the development of other nuclei, is proposed. This is obtained by decreasing gradually the temperature at the point of expected growth at a rate sufficiently low to equalize the protein concentration (under conditions where material is captured by growing crystal) via diffusive and convective processes. An individual growth of lysozyme single crystals in a capillary is demonstrated.

A complex study of a spearhead dated back to IV mill. BC from burial mound no. 1 near Novosvobodnaya village (collection of the State Historical Museum) and, in particular, the material of spearhead superficial crust has been performed. The elemental and phase composition of the metal of spearhead and the superficial crust on its surface have been determined by scanning electron microscopy, jointly with energydispersive X-ray microanalysis and X-ray phase analysis. A comparative analysis of the results of studying the spearhead superficial crust and similar crusts on other artifacts from the mounds near Novosvobodnaya village suggest natural origin of the crust on copper‒arsenic artifacts.