Environmental issues in the synthesis and purification of 5-nitrotetrazole sodium salt

“Green” laboratory procedures have been developed for the synthesis and purification of 5-nitrotetrazole sodium salt, a key precursor of promising energetic compounds. The procedures can be safely scaled up.     

Perspectives for thiamin as a preparation for correction of free radical states of different origin

Аntioxidant capacity of thiamin has been investigated, Liposome suspension being the standard biological test-system has been used for this purpose Antioxidant capacity of thiamin has been investigated. Liposome suspension being the standard biological test-system has been used for this purpose. Thiamin usually being not included in the list of antioxidant substances is able to interfere the processes of lipid peroxidation. Such effects give the possibility to extend the scale of thiamine practical application and to recommend it for correction different free radical states including environmentally induced free radical diseases.     

Cluster self-organization of silicate and germanate systems: Suprapolyhedral precursor clusters and self-assembly of orthotetrahedral structures in Na,TR-germanates (silicates)

The geometrical and topological analysis of all known types of the orthotetrahedral structures of Na,TR-germanates and their silicon analogues has been carried out using computer methods (TOPOS 4.0 program package). The full 3D reconstruction of the self-assembly mechanism of crystal structures has been performed as follows: precursor cluster-primary chain-microlayer-microframework (supraprecursor). For Na₂HLaSiO₅, NaHo₄(GeO₄)₂O₂OH, NaScGeO₄, and NaSm₃Ge₂O₈(OH)₂, the same type of 2D TR, T-network has been recognized: 433334 + T 4433. For Na₂HScGeO₅, network TR 44444 + T 444 has been recognized. The coordination number (CN) of a precursor cluster in 2D networks is six. In all structures, the invariant type of cyclic four-polyhedral precursor clusters built of tetrahedron-linked TR-polyhedra has been identified with CNs being eight, seven, or six. In the Na₅Y₄Si₄O₁₆F structure, a tubular-type primary chain in which precursor clusters are tetrahedron-linked TR polyhedra with CN = 8 has been recognized. Their stacking in a layer is characterized by the network TR 8 8 4 + T 8 4 8, where 8 corresponds to the cross section of the primary chain. In a 3D network, the total number of neighboring tubular primary chains linked to the main chain is four. In the structures with TR: T = 1: 1 or 1.5: 1, the positions above and below the center of the precursor cluster are occupied by Na atoms; in NaHo₄(GeO₄)₂O₂(OH), where TR: T = 2: 1, these positions are occupied by an Na atom and a TR atom.     

Cluster self-organization of Li- and TR-Containing silicate systems: Suprapolyhedral precursors and self-assembly of LiY<Superscript>[7]</Superscript>SiO<Subscript>4</Subscript> and LiTR<Superscript>[6]</Superscript>SiO<Subscript>4</Subscript> (TR = Y,Sc, Tm) dimorphic crystal structures

The combinatorial and topologic analysis (the TOPOS 4.0 program package, the coordination sequences method) is carried out for silicates LiY^[7]SiO₄ (a synthetic phase (SIN), space group P2₁/b) and LiTR^[6]SiO₄ (TR = Y, Sc, Tm; the olivine structure type (OLI), space group Pnma). The framework of these silicates is built of polyhedral structural units YO₇ + SiO₄ and YO₆(ScO₆, TmO₆) + SiO₄, respectively. The framework structures TRTO₄, built of Y,O- and Si,O-polyhedra in SIN and OLI, respectively, are represented as three-dimensional (3D) Y,Si-nets with distal oxygen atoms. The crystal-forming 2D Y,Si-net is the four-nodal net Y(1) (43333) + Y(2) (4334334) + Si(1) (434) + Si(2) (3343) for SIN and the two-nodal net Y 443333 + Si 4433 for OLI. In the 2D Y,Si, nets, equivalent chains of four-nodal precursor clusters Y-Si-Y-Si with three shared bonds are identified. In the dimorphic crystals structures of LiTRTO₄, polyhedral precursor clusters Li₂TR₂T₂ are linked into a ring with two Li atoms lying one above the other below the center of the ring, thus retaining the center of symmetry\(\bar 1\). Precursor clusters Li₂TR₂T₂ through the matrix self-assembly mechanism control the evolution of high-level crystal-forming clusters. Cluster coordination numbers in layers are equal to six.     

Computer simulation of the self-assembly of paulingite crystal structure from suprapolyhedral nanocluster precursors K6, K16, and K20

A combinatorial and topological analysis of the paulingite crystal structure (a = 35.093 Å, V = 43 217 ų; sp. gr. Im \(\bar 3\) m) has been performed by computational methods using the TOPOS program package. The application of the complete expansion of the 3D factor graph into nonintersecting substructures of a cluster type has revealed three types of nanocluster precursors in the tetrahedral T framework: K6, K16, and K20; they consist of 6T, 16T, and 20T tetrahedra, which are involved in the matrix self-assembly of the crystal structure. The translated cell contains 44 clusters (8 K6+ 24 K16 + 12 K20). None of the clusters have shared T tetrahedra. Three cluster precursors form a crystallochemically complex structure with extraframework Na⁺/Ca²⁺ and K⁺/Ba²⁺ cations which carry out two structural functions as templates (stabilizing nanocluster precursors) and as spacers (filling the voids between precursors). The self-assembly code of the 3D structure from complementary bound nanocluster precursors is completely reconstructed in the form primary chain → microlayer → microframework → … framework.     

Microwave Radiometric Sensing of Cumulus Cloudiness from Space

Radiophysics and Quantum Electronics - We consider the Planck model for generating random discontinuous cloud fields in a three-dimensional computation domain. An algorithm for calculating a...     

New icosahedral nanoclusters in crystal structures of intermetallic compounds: Topological types of 50-atom deltahedra D50 in samson phases β-Mg2Al3 and ?-Mg23Al30

A database of intermetallic compounds has been compiled using the TOPOS program package. This database includes 514 topological types, containing 12- and 13-atom icosahedral i clusters. An isolated group of 1649 i clusters is described by 14 point groups and their maximum symmetry D _3d ( $\bar 3$ m) and T _h (m $\bar 3$ ) is established, respectively, in 47 and 25 types of crystal structures. A structural analysis of the outer quasispherical shells showed that local 63-atom i configurations 1@12@50, which contain 50 atoms in the second layer, are implemented in 8 out of 19 cases. Examples of new topologically different types of 50-atom D50 deltahedra in the Samson phases ?-Mg₂₃Al₃₀ and ??-Mg₂Al₃ are presented. Four topologically different sites with coordination numbers of 5, 6, 6, or 7 are established in the ? shell and seven sites with coordination numbers of 5, 5, 6, 6, 6, 6, or 7 are found in the ?? shell. The inner i clusters for the ??-Mg₂Al₃ structure (with the symmetry $\bar 3$ m) and the ?-Mg₂₃Al₃₀ structure (with the symmetry $\bar 3$ ) have a similar chemical composition, i.e., Mg₇Al₆ and Mg₆Al₇, and their 50-atom shells are chemically identical to 18Mg + 32Al. The configurations found supplement the series of known two-layer icosahedral Bergman and Mackay clusters in the form of deltahedra with 32- and 42-atom shells.     

Hydrothermal crystallization in the KF-ZrO2-SiO2-H2O system at 40°C: Phase equilibria and modeling of ZrSiO4, K2ZrSi6O15, K2ZrSi3O9, K3ZrF7, and ZrO2 crystal structures

The phase equilibria in the KF-ZrO₂ (nanocrystals)-SiO₂-H₂O system are studied for the ZrO₂: SiO₂ molar ratio ranging from 2: 1 to 1: 6 and the KF concentration C _KF ranging from 3 to 36 wt % under 0.1 GPa at 40°C. We established crystallization of three silicates—ZrSiO₄ (zircon), K₂ZrSi₆O₁₅ (deleite), K₂ZrSi₃O₉ (wadeite)—and K₃ZrF₇ fluoride and ZrO₂ and SiO₂ oxides. The structures of K-and Zr-based silicates obtained can be represented as an open framework formed by M octahedra (ZrO₆) that share vertices with T tetrahedra (SiO₄). With the increase of KF concentration, silicates “substitute” each other in the following sequence: ZrSiO₄ ?K₂ZrSi₆O₁₅ ? K₂ZrSi₃ O₉. Depending on the ZrO₂: SiO₂ ratio and C _KF concentration, K₃ZrF₇ fluoride is formed simultaneously with K₂ZrSi₃O₉ and K₂ZrSi₃O₉ + K₂ZrSi₆O₁₅. The characteristic features of formation of Zr-containing phases are discussed in the framework of the model of the matrix assembly of crystal structures from subpolyhedral structural units—clusters of cyclic type. The features of the phase formation in the system are compared with the characteristics determined earlier for the KOH-ZrO₂ (nanocrystals)-SiO₂-H₂O system at 40°C.     

Mössbauer studies of the atomic distributions and hyperfine interactions in Mn-Fe alloys with β-Mn structure

Mn_20?x Fe_x alloys (x=1–6.4) with β-Mn structure are studied by Mössbauer spectroscopy. The electric field gradient tensor for the crystallographically nonequivalent sites 8(c) and 12(d) are calculated. Partial Mössbauer spectra are identified, and the ⁵⁷Fe hyperfine-interaction parameters determined. Iron atoms substituting for manganese in the Mn_20?x Fe_x system exhibit strong preference for occupying 8(c) sites. With increasing iron concentration, the longrange order parameter in the Fe atom arrangement increases, and the degree of order, decreases.