Vol 63, No 3 (2018)

This work describes the analysis of the crystal structures of chitosan, its main polymorphic modifications, and its characteristic mutual chain packing and hydrogen bond systems in the crystalline regions of conformers. The analysis takes into consideration the crystal structures of chitosan complexes (salts) with organic and inorganic acids and their structural transformations. Notably, the transformation of the hydrated form of chitosan into anhydrous is found to be irreversible and occurs either at high temperatures or through a less stable form of hydrated salts. The interaction with polyanions during the formation of multilayer films can be considered as a way to form the anhydrous crystalline form of chitosan.

The finiteness of atomic volumes and symmetry impose limitations on the positions in crystal space that are allowed for occupation when crystal atomic structures are formed. The results of studying the geometric features of the forbidden regions of crystal space are presented. A new classification of symmetry space groups, based on the symmetry of crystal space forbidden regions, is proposed.

Structural models of the α, β, and γ modifications of Nb₅Si₃ silicides, which are used as a reinforcing phase in composites obtained in situ based on the Nb‒Si system, have been constructed by computer simulation methods. A geometric analysis of unit cells is performed using the H-poisk program to estimate the voids existing in the structures. The results of measuring the number of voids and their sizes are reported. A conclusion about possible diffusion paths of interstitial boron, carbon, nitrogen and oxygen atoms is drawn based on the calculation results, and the solubility of these impurities in the structure of each Nb₅Si₃ modification is estimated.

An atomistic simulation of the deformation of ideal magnesium crystal along the \([11\bar 20]\) crystallographic axis has been performed. The evolution of structural defects under load at T = 300–350 K is considered in detail. It is established that the nucleation of dislocations in an ideal crystal occurs when the stress reaches a level of 0.1G (G is the shear modulus). The acting deformation modes are found to be prismatic slip of a dislocations and \(\{ 10\bar 13\} \) twinning. The formation of dislocation networks and dislocation sites in the twinning plane is observed. Some reactions are proposed to describe the dislocation evolution in the \((\bar 3034)\) plane.

The structure of tungsten-doped Nd₅Mo₃O_{16 + δ} single crystals has been investigated by X-ray diffraction analysis, energy-dispersive X-ray spectroscopy (EDXS) microanalysis, and extended X-ray absorption fine-structure (EXAFS) spectroscopy. Tungsten atom, which partially replaces molybdenum atoms in the structure, is found to be located close (at a distance of 0.57 Å) to the Mo atom site. The interstitial oxygen atom О3 shifts from the crystallographic site with coordinates (0.5, 0.5, 0) to the site with coordinates (0.43, 0.48, 0.04) and complements the tungsten coordination to octahedral. The decrease in the unit-cell parameter and conductivity with an increase in the tungsten concentration in the sample is shown to be related to the fact that the interstitial oxygen atom О3 (responsible for conductivity) is in the coordination environment of tungsten atom.

An eudialyte group mineral, found in pegmatites of the Odikhincha massif (the northern part of the Siberian platform), has been investigated using X-ray diffraction, IR spectroscopy, and Raman spectroscopy. The mineral is characterized by a high strontium content and a low chlorine content. It has a trigonal unit cell with the following parameters: a = 14.2700(6) Å and c = 30.057(1) Å; V = 5300.6(1) ų; sp. gr. R3m. The structure has been refined to R = 0.047 in the anisotropic approximation of atomic displacements using 1697F > 4σ(F). The idealized formula (Z = 3) was found to be Na₁₂Sr₂Ca₆Fe₃²⁺ Zr₃NbSi₂₅O₇₂(OH,O)₄Cl(Н₂О)_0.2. The chemical composition and structure of this mineral are close to those of taseqite; however, it differs from the holotype sample by a low chlorine content and peculiarities of cation distribution over basic structure sites. A comparative analysis of strontium-rich eudialytes has revealed their important crystallochemical feature: selective concentration of strontium in the N4 site. Thus, taseqite, along with heterophyllosilicates, may play a role of strontium concentrator in agpaitic pegmatites.

The crystal structure of the nickel(II) complex with substituted azadibenzo-14-crown-4 ether containing the embedded di(α-pyridyl)bispidone moiety having the formula [L(H₂O)Ni(NO₃) Ni(H₂O)L](ClO₄)₃ · 0.7EtOH was studied by X-ray diffraction (T = 150(2) K, R = 0.0628). In the complex cation two five-coordinate nickel complexes are bridged by the nitrate anion to form a dimer. The distorted octahedral environment of Ni atoms is formed by four nitrogen atoms of the molecule L and the oxygen atoms of the water molecule and the NO₃^- anion. In the nickel complex, like in the cobalt and copper complexes studied previously, the bispidine moiety of the molecule L adopts a chair-chair conformation.

The molecular structure of the title compound, C₁₄H₁₁ClN₂O₄, was determined by single crystal X-ray diffraction. The compound crystallizes in the monoclinic sp. gr. P2₁/c with Z = 4. The title compound, C₁₄H₁₁ClN₂O₄, is a Schiff base which adopts the phenol-imine tautomeric form in the solid state.The molecule is almost planar and the dihedral angle between the planes of two aromatic ring is 2.2(1)°. The molecular structure is stabilized by intramolecular O–H···N hydrogen bond which generates a six-membered ring. In the crystal structure, the molecules are linked together by intermolecular C–H···O interactions.

The title compound N-(Phenylthio)phthalimide has been synthesized and characterized by FT-IR, NMR, and X-ray single-crystal determination. The compound crystallizes in the triclinic sp. gr. \(P\bar 1\) with Z = 2. The title compound is not planar. The dihedral angle between the phthalimide and phenyl ring systems is 77.41(8)°. The crystal structure is stabilized by intermolecular π...π and C–H...π interactions.

Ethyl 6-amino-5-cyano-4-(4-fluorophenyl)-2,4-dihydropyrano[2,3-c]pyrazole-3-carboxylate was synthesized based on a commercially available trisodium citrate dihydrate as an inexpensive and eco-friendly catalyst for the first-time via one-pot tandem Knoevenagel-cyclocondensation of malononitrile, 4-f luorobenzaldehyde and in situ generated ethyl 5-oxo-2,5-dihydro-1H-pyrazole-3-carboxylate in aqueous ethanol at room temperature and its crystal structure is determined by X-ray structure analysis. The crystals are triclinic, sp. gr. \(P\bar 1\), a = 8.7914(7) Å, b = 11.3632(8) Å, c = 11.4005(9) Å, α = 62.278(7)°, β = 71.099(7)°, γ = 80.856(6)°, Z = 2, R = 0.0544 for 2491 observed ref lections. Pyran and pyrazole rings are almost coplanar and phenyl ring is almost perpendicular to these two rings. Pyran ring adopts boat conformation. The crystal structure is stabilized by N–H···N, N–H···O, C–H···F, and C–H···π hydrogen interactions. In addition, a number of weak π···π interactions also contribute to stabilize the crystal structure.

The coordination polymer, [MnL_0.5(H₂O)(phen)]_n (H₄L = 1,1':4',1''-terphenyl-2',4,4'',5'-tetracarboxylic acid, phen = 1,10-phenanthroline), has been solvothermal synthesized and structurally characterized by single-crystal X-ray diffraction. Complex crystallizes in triclinic sp. gr.\(P\bar 1\) with Z = 2. Two carboxylate oxygen atoms in the central phenyl rings from two μ\({u_{{6^ - }}}\)L^4– ligands doubly-bridge two Mn(II) ions to form the dinuclear \(M{n_2}{({O_{CO{O^ - }}})_2}\) unit. Each dinuclear \(M{n_2}{({O_{CO{O^ - }}})_2}\) unit links four L^4– ligands and each L^4–ligand bridges four dinuclear \(M{n_2}{({O_{CO{O^ - }}})_2}\) units to generate a 2D coordination network, which can be rationalized as a binodal (4,4) topological network by considering the dinuclear \(M{n_2}{({O_{CO{O^ - }}})_2}\) units and L^4– ligands as 4-connected nodes.

Andrographolide, C₂₀H₃₀O₅, is a labdane diterpenoid which was isolated from the leave of Andrographis paniculata. Its crystal structure is determined by single crystal X-ray diffraction: monoclinic, sp. gr. P2₁, Z = 2. Absolute configuration is determined by the refinement of the Flack parameter to 0.21(19). In the crystal, molecules are linked by O–H···O hydrogen bonds and C–H···O interactions into two dimensional network parallel to the (001) plane. Its proliferation of osteoblast cell lines is reported.

The structure of bacterial uridine phosphorylase (UPh) belonging to the NP-I family in complex with 6-methyluracil was determined for the first time at 1.17 Å resolution. The structural features of bacterial UPh from the bacterium Vibrio cholerae (VchUPh) responsible for selectivity toward 6-methyluracil acting as a pseudosubstrate were revealed. The repulsion between the hydrophilic hydroxyl group of the active-site residue Thr93 of VchUPh and the hydrophobic methyl group of 6-methyluracil prevents the oxygen atom O4' of the ribose moiety and the phosphate oxygen atom O3P of ribose 1-phosphate from forming hydrogen bonds with OG1_Thr93, which are essential for the enzymatic reaction. This, apparently, makes VchUPh inactive in the enzymatic synthesis of 6-methyluridine from 6-methyluracil. Hence, Thr93 is the residue, the modification of which will allow VchUPh to catalyze the biotechnologically important synthesis of 6-methyluridine from 6-methyluracil. Taking into account high structural homology of the functionally significant regions of bacterial UPhs, this conclusion is also true for other bacterial UPhs. It was demonstrated that bacterial thymidine phosphorylases of the NP-II family cannot bind 6-methyluracil in a proper conformation required for the catalysis because of a close contact between the 6-methyl group and Phe210.

Using an organoamine, 2,5-bis (1-imidazoly) pyridine (L), a novel inorganic-organic hybrid material based on antimony halide formulated as {(CH₃)₂L}²⁺{(Sb₄Cl₈I₈)^0.5}^2–(1) was synthesized in situ via solvothermal technique and characterized by the single-crystal X-ray diffraction. During the synthesis, the organoamine L was transformed in situ into the imidazolium ion, {(CH₃)₂L}²⁺. In the compound 1, four Sb(III) ions are linked by two \({u_{{3^ - }}}\)I^– and four u\({u_{{2^ - }}}\)I^– ligands into a (Sb₄I₈Cl₈)^4–unit, in which eight Cl^–ions and two I^–ions act as the terminal ligands. The uncoordinated {(CH₃)₂L}²⁺ organoamine moieties are linked with the (Sb₄I₈Cl₈)^4– clusters via H bonds into three-dimensional (3D) supramolecular architecture. The band structure calculation shows that the compound has an indirect band gap of 2.253 eV.

The crystal structure of potassium, rubidium, cesium, and ammonium hydrophthalates is analyzed based on the data in the literature. A relationship between their structure and elastic and mechanical properties has been established for the first time. Young’s moduli, shear moduli, and Poisson’s ratios in the (100), (010), and (001) planes of these crystals are calculated, and Knoop indentation of these planes is performed. Anisotropy of the elastic and mechanical properties of the crystals is revealed. Rubidium, cesium, and ammonium hydrophthalates are found to be partial auxetics. Ammonium hydrophthalate, whose structure contains additional (as compared with other hydrophthalates) hydrogen bonds, exhibits the highest anisotropy of properties.

Well aligned 1D ZnO nanostructures are important for optoelectronic and nanoscale electronic devices. In this report, 1D ZnO nanorods were synthesized by very simple, low cost, low temperature hydrothermal process. An effect of concentration, growth time, growth temperature, seed layer annealing, and seed layer thickness was investigated. The synthesized ZnO nanorods were characterized by scanning and transmission electron microscopies, X-ray diffraction, Raman and ultraviolet–visible spectroscopies. Growth parameters were found to influence strongly on the morphology, orientation, diameter, length, and density of the ZnO nanorod arrays. The growth temperature 80–90°C, seed layer annealing at 300–400°C, growth time 3 h, 0.025 M precursor concentration, and 0.2–0.3 M seed layer solution concentrations are more favorable conditions for better orientation and excellent crystallinity of the ZnO nanorods.

Sodium cholate is a bile acid salt, which is applied as a biological detergent. The mixed systems of phospholipid/sodium cholate are used to study the self-assembly of micelles and formation of micellar systems. The micelles consisting of a phospholipid/sodium cholate mixture are used for drug delivery through the skin. An important part of the investigations in this field is examination of the structure and properties of micelles consisting of sodium cholate molecules. The structure of sodium cholate micelles have been investigated by small-angle neutron scattering. The average radius of sodium cholate micelles in the sodium cholate concentration range of 25‒100 mM is found to be 10.14 ± 0.01 Å.

The transport of one-dimensional CuI crystals in channels of single-walled carbon nanotubes (SWCNTs) has been studied by high resolution electron microscopy. The diffusion kinetics has been investigated by counting the number of CuI atoms escaping from the nanotube channel. The diffusivity is calculated to be 6.8 × 10^–21 m²/s, which corresponds to an activation-barrier height of ~1 eV/atom. A comparison with the theoretically estimated height of the energy barrier for molecular transport through a graphene layer is indicative of mass transfer through vacancy defects in graphene.

The electrical conductivity of crystals of artificial cancrinite Na_{8 − 2x}Ca_x[Al₆Si₆O₂₄][CO₃] · 2H₂O (x ≤ 0.03) has been studied in the temperature range of 498−604 K. These crystals were grown by hydrothermal synthesis on a seed in the Na₂O–Al₂O₃–SiO₂–H₂O system (t = 380−420°С, P = 3 × 10⁷−9 × 10⁷ Pa). The ionic conductivity of a single-crystal sample (sp. gr. P6₃), measured along the crystallographic axis c, is low: σ = 8 × 10^–7 S/cm at 300°С. The electric transport activation energy is E_a = 0.81 ± 0.05 eV. The relationship between the ionic conductivity and specific features of the atomic structure of cancrinites is discussed.

The processes occurring in aqueous salt solutions have been investigated based on thermodynamic and experimental modeling. The self-organization in a drying drop of dehydrated liquids is analyzed using the fractal theory, due to which the quantitative characteristics of the crystallization processes in a small volume are obtained.

Nine ancient Egyptian mummies (dated preliminarily to the period from the 1st mill. BCE to the first centuries CE) from the collection of the State Pushkin Museum of Fine Arts have been studied at the National Research Centre “Kurchatov Institute” (NRC KI) on the base of the complex of NBICS technologies. Tomographic scanning is performed using a magneto-resonance tomograph (3 T) and a hybrid positron emission tomography/computed tomography (PET-CT) scanner. Three-dimensional reconstructions of mummies and their anthropological measurements are carried out. Some medical conclusions are drawn based on the tomographic data. In addition, the embalming composition and tissue of one of the mummies are preliminarily analyzed.