Crystallography Reports最新文献

Using the program code written in GAP language (with the same name in the computer algebra system), with the parallel computation dispatcher on Python script, the necessary and sufficient number of chemical bonds, which can connect the structural units occupying a single characteristic Wyckoff position in a 2D or 3D crystal, was calculated. The number obtained characterizes the number of structure-forming bonds that should be distinguished in the crystal structure when discussing X-ray diffraction data.

ATPase EttA is the most common eubacterial protein of the ABC-F family, which facilitates the conformational transition of the ribosome from one state to another during elongation through a nucleotide-dependent interaction sensitive to the ATP/ADP ratio. Proteins of the ABC-F family confer resistance to antibiotics that bind in the peptidyltransferase center and the ribosomal tunnel; however, the details of the mechanism of action of this protein from Staphylococcus aureus are unclear. A comparison of the amino acid sequences of EttA proteins from S. aureus, Mycobacterium tuberculosis, and Escherichia coli indicates the presence of an additional 75 residues at the C-terminus of the protein, the function of which is unknown. The structure of the SaEttA protein was analyzed using small-angle X-ray scattering, which revealed a distinct domain arrangement and additional density at the C-terminus of the protein.

The thermal stability of the phase composition of TiO₂/ZnO composite particles during the post-growth heat treatment has been investigated. TiO₂/ZnO composite particles were synthesized by processing a metallic mixture of titanium and zinc microparticles in a low-temperature arc discharge plasma in argon under ambient conditions. The obtained materials were characterized using electron microscopy, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy. It was found that the synthesized structures contain up to 40% of titanium dioxide polymorphs—anatase and brookite. During heat treatment at 300°C in air, zinc atoms are displaced from the TiO₂ lattice, accompanied by structural rearrangement of the oxide matrix. Annealing at temperatures of 500–700°C leads to coarsening of most of anatase crystallites and partial recrystallization of the rest into the rutile phase. Annealing at 900°C promotes the formation of zinc titanates (Zn₂TiO₄ and Zn₂Ti₃O₈), which act as catalysts for the anatase-to-rutile phase transition. Upon annealing at 950°C, the rutile monophase is stabilized in the synthesized samples. A simple and environmentally friendly method is thus proposed for the large-scale synthesis of TiO₂/ZnO composite particles containing a high fraction (up to 40%) of anatase and brookite, which remain stable up to 700°C and can be effectively applied in photostimulated degradation processes of organic pollutants.

Parameters of tracks of swift heavy ions stopped in the electron energy loss regime in SiC films with a thickness of 10–100 nm have been determined. A model has been used that describes all stages of the track formation, from ionization and heating of the lattice (MC TREKIS-3) to its complete relaxation (classical molecular dynamics). Under irradiation by a 710-MeV Bi ion, surface nanohillocks are formed, the height of which increases with the film thickness L, attaining a constant value of 5.7 nm at L > 30 nm. Nanocavities surrounded by defect clusters remain along the ion trajectory over the entire volume of the films with L < 100 nm. In the 100 nm-thick film, a defect region near the surface is cone-shaped and extends to a depth of 35 nm.

Zinc oxide films doped with different allotropic modifications of carbon, such as carbon nanospheres, graphite, graphene oxide, and multilayer carbon nanotubes, were synthesized using the sol-gel technology. The scanning electron microscopy analysis of the surface morphology of the samples showed that in one of the allotropic modifications, carbon particles act as growth sites for zinc oxide branches, resulting in the hierarchically organized surface of the samples. Optical spectrophotometric measurements showed that in all cases there was a decrease in the band gap of the samples compared to undoped zinc oxide, as well as an increase in the energy of the Urbach tail, indicating an increase in the degree of energy disorder at the band edges. The observed complex non-monotonic dependence of the changes in the optical absorption of aqueous Nile blue A solutions during photocatalytic degradation may indicate the formation of stable intermediates, as confirmed by IR spectroscopy.

The crystal and molecular structure of the complex of  2,7-dinitro-9,10-phenanthrenequinone with 9-methyl-9H-carbazole (4C₁₄H₆N₂O₆⋅C₁₃H₁₁N) was determined by X-ray diffraction analysis. In the crystal of the complex, the donor molecule and two of the four crystallographically independent acceptor molecules form mixed-type stacks {–D–A(_{1}^{{}}{{'}})–A₁–D'–A(_{3}^{{}}{{'}})–A₃–D–A(_{1}^{{}}{{'}})–A₁–D'–}_∞. The other two acceptor molecules form parallel rows {–A₂–A₄–A₂–A₄–}_∞ || {–A(_{4}^{{}}{{'}})–A(_{2}^{{}}{{'}})–A(_{4}^{{}}{{'}})–A(_{2}^{{}}{{'}})}_∞ running along the stacks. The structures and properties of a number of model charge-transfer complexes of 2,7-dinitro-9,10-phenanthrenequinone with 9-methyl-9H-carbazole were investigated by quantum-chemical calculations at the density functional theory level. The energies of complex formation, the average distances between the donor and acceptor planes, and the charge transfer values from the donor to the acceptor were calculated.

All 65 863 records for cubic, hexagonal, trigonal, and tetragonal crystals, presented at the Cambridge Crystallographic Data Centre (CCDC-2023), have been analyzed for the existence of structural second-order phase transitions, occurring without a change in the crystal syngony. Based on the analysis of the data obtained, two indicators of possible susceptibility of a crystal to a second-order phase transition are proposed. The first indicator is the degree of invariance of electron density relative to the group symmetry operators of the high-symmetry phase η_tot for the atomic structure on the whole and η_subl for the atomic sublattices of his structure. The threshold values (η_tot ≥ 0.487(1) and η_subl ≥ 0.982(1)), at which a crystal can be subjected to a second-order phase transition, are found for at least one atomic sublattice. The second indicator is the group–subgroup relationship for the lattice translations of the high- and low-symmetry phases. Among 39 crystals (180 records) with unestablished transition order, four crystals are found, in the structures of which η_tot and η_subl exceed the threshold values, and the translations of the bases of high- and low-symmetry cells follow the group–subgroup relationship.

Potassic-magnesio-hastingsite with the idealized formula KCa₂(Mg₄Fe³⁺)(Si₆Al₂O₂₂)(OH)₂ was found in blocks of biotite-amphibolic gabbro from serpentinite mélange of the Ilmenogorsky metamorphic complex, located within the Ilmensky Natural Reserve. In this study, we report the results of the crystal structure determination of three potassic-magnesio-hastingsite samples from the type locality. These samples exhibit unusual characteristics, including the predominance of K over Na, high iron content, and approximately equal amounts of Fe³⁺ and Fe²⁺ ions. The crystal structures of three samples were refined in the anisotropic approximation of atomic displacement parameters to R of 4.01, 4.18, and 4.7% using 1043, 1116, and 1148 reflections with I > 2σ(I), respectively. The M(2) site is characterized by a diverse composition of heterovalent cations, including Fe³⁺, Al, Mg, Ti, Fe²⁺, and V. In contrast, the M(1) and M(3) sites are predominantly occupied by Mg and Fe²⁺. Among the trivalent C-cations, Fe³⁺ is dominant and primary occupies M(2) site.

The homologous series of 15 RF₃ (R = ⁵⁷La–⁷¹Lu) is based on the atomic number (Z) of the chemical elements ^ZR. It is a T–x quasi-system (QS) “LaF₃–LuF₃” of 14 partial QS-N systems (N ranges from 1 to 14): ⁵⁷LaF₃–⁵⁸CeF₃, ⁵⁸CeF₃–⁵⁹PrF₃, and further to ⁷⁰YbF₃–⁷¹LuF₃ (ΔZ = 1). The members of the crystallochemical categorical triad—isomorphism, polymorphism, and morphotropy—are the “homologous parameters” of the RF₃ series. The series was first proposed as the vertex “structural homology” (SH) of the crystal-chemical tetrahedron. The SH vertex is linked with the vertices isomorphism and polymorphism by five and nine QS-N, respectively. On the edge “SH–true morphotropy,” there are QS-8 (GdF₃–TbF₃) with peritectic and QS-11 (HoF₃–ErF₃) with eutectic phase reactions of absolute true morphotropic transformation.