A cooling rate dependent structure of amorphous (AuxCu1−x)91La9

A novel class of metallic glasses of the form (Au_xCu_1?x)₉₁La₉ (x = 0.5, 0.25, 0.6) and (Au_0.5Cu_0.5)_1?yLa_y (y = 10, 11) have been prepared by rapid cooling from the melt. Investigation by means of X-ray diffraction and TEM shows a dependence of the structure on the cooling rate and suggests a phase separated amorphous structure. For sufficiently low cooling rates, crystallization seems to follow phase separation.     

Structure of a new crystal modification of the bacterial NAD-dependent formate dehydrogenase with a resolution of 2.1 Å

Formate dehydrogenase (FDG) from methylotrophic bacteria Pseudomonas sp. 101 catalyzes the reaction of oxidation of the formate ion to carbon dioxide, which is accompanied by the reduction of nicotinamid adenine dinucleotide (NAD⁺). The structures of the apo and holo (enzyme-NAD-azide triple complex) forms of the enzyme were determined earlier. In an attempt to prepare a complex of FDG with the product of the enzymatic reaction (NADH), a new crystal modification of FDG is obtained (space group P4₂2₁2, a = b = 93.3 Å, c = 103.05 Å). The FDG structure is solved by the molecular replacement method and refined to R = 20.7%. The asymmetric part of the unit cell contains one FDG molecule. In contrast to the previously studied FDG structures, the biologically active dimer is formed by the crystallographic rotation axis. A comparative structural analysis of the studied form with the apo and holo forms of the enzyme is performed. The influence of the molecular structure on the environment in the crystal is investigated.     

Structural investigations of <Emphasis Type="Italic">E. Coli</Emphasis> dihydrolipoamide dehydrogenase in solution: Small-angle X-ray scattering and molecular docking

Dihydrolipoamide dehydrogenase from Escherichia coli (LpD) is a bacterial enzyme that is involved in the central metabolism and shared in common between the pyruvate dehydrogenase and 2-oxoglutarate dehydrogenase complexes. In the crystal structure, E. coli LpD is known to exist as a dimer. The present work is focused on analyzing the solution structure of LpD by small-angle X-ray scattering, molecular docking, and analytical ultracentrifugation. It was shown that in solution LpD exists as an equilibrium mixture of a dimer and a tetramer. The presence of oligomeric forms is determined by the multifunctionality of LpD in the cell, in particular, the required stoichiometry in the complexes.     

Growth and structure of epitaxial Pb1 − x Mn x Se(Ga) films

The growth and structure of Pb_{1 ? x} Mn _x Se (Ga) (N_Ga = 0.8 at %) films with thicknesses of 0.3–0.5 μm, grown on single-crystal PbSe_{1 ? x} S _x (100) substrates by molecular-beam epitaxy, have been studied. It is established that films grow in a face-centered cubic lattice with the (100) orientation, reproducing the substrate orientation. The optimal conditions for obtaining photosensitive epitaxial films with perfect crystal structure are determined (W _1/2 = 70–80″).

     

Molecular structural flexibility dependence of mesomorphism through ortho-substituted bromo group

A novel series of liquid crystal (LC) materials of Schiff's bases viz. RO-C₆H₄?CH?CH?COO?C₆H₄?N?CH?C₆H₄?Br (ortho) is synthesized and studied with a views to understanding and establishing the effect of molecular structure on liquid crystal properties and to provide novel thermotropic LC material to the scientific and technological community of research interest. The novel series consists of thirteen members (C₁ to C₈, C₁₀, C₁₂, C₁₄, C₁₆ &; C₁₈). All the members of a series are enantiotropic liquid crystals. Smectic (C₁₀?C₁₈) and nematic (C₁?C₁₈) property commence from C₁₀ and C₁ homologue respectively. Transition temperatures and the textures of homologues were determined using a polarizing optical microscope (POM) equipped with a heating stage. Transition curves Cr-M, Sm-N and N-I of a phase diagram behaved in normal manner. Odd–even effect is absent for Sm-N transition curve, but it is present for N-I curve. Sm-N transition curve is extrapolated to C₈ and C₆ nonsmectogenic homologues to determine and predict their latent ability for exhibition of smectic property. Analytical and spectral data confirms the molecular structures of homologues. Thermal stabilities of smectic and nematic are 85.4°C and 130.1°C °C whose upper and lower total mesophase length vary from 58.0°C to 06.0°C at the C₁₀ and C₁ = C₅ = C₆ homologue, respectively. Textures of nematic phase are threaded or Schlieren and smectic phase are of type A or C. LC properties of present novel series are compared with structurally series known series. Thus, present novel series is predominantly nematogenic and partly smectogenic with middle ordered melting type and considerable total mesophase length range.     

1,3,5-trichlorotricyanobenzene complexes with mesitylene (1/1) and benzene (1/3)

Trichlorotricyanobenzene-mesitylene (1/1) is monoclinic, space group P2₁/n; at ?88°Ca=10.509(3),b=14.863(7),c=11.518(3) Å, β=99.38(2)⁰,V=1775(2) ų,D _x =1.409(2) g cm^?3,Z=4. Trichlorotricyanobenzene-benzene (1/3) is hexagonal, space group $P\bar 6$ ; at ?99°Ca=17.3914(3),c=7.2673(1) Å,V=1903.6(1) ų,D _x =1.2844(1) g cm^?3,Z=3. In both complexes there are stacks of alternating trichlorotricyanobenzene and hydrocarbon molecules. In both complexes there are sheets of molecules perpendicular to the stacks. In the mesitylene complex these sheets contain equal numbers of both kinds of molecules with the trichlorotricyanobenzene molecules arranged in tapes. In the benzene complex the sheets contain only one kind of molecule or the other. The sheets containing the trichlorotricyanobenzene molecules have approximately linear C?N...Cl?C intermolecular interactions with N...Cl distances about 3.02 å.     

Metamagnetic phase transition in Nd1−x TbxCo2 compounds

The electric resistivity and neutron diffraction measurements of the intermetallic compounds Nd_1?x Tb_xCo₂ (x = 0, 0.2, 0.3, 0.5, 0.7, or 1) have been performed. All compounds have a cubic structure at room temperature and a rhombohedral structure at 4.2 K. The magnetic structure of these compounds is described by the wave vector k = 0. The magnetizations of the rare earth and cobalt sublattices increase with increasing x. The concentration dependence of the cobalt sublattice magnetization is explained on the basis of the model of metamagnetic band subsystem in compounds of the RCo₂ type.     

The amorphous Sb1−xTex system

Amorphous films of Sb_1?xTe_x, where 0.11 ? x ? 0.86, have been prepared by coevaporation. Crystallization temperatures occur near room temperature for all compositions and appear to depend on film thickness. The optical and transport properties have been investigated as a function of temperature. Optical band gaps at room temperature, E_g, ranged between 0.3 and 0.7 eV and decreased non-linearly with temperature. For the composition Sb₂Te₃, E_g ≈ 0.7 eV, in contrast to the semimetallic character of the crystalline form. All compositions were p-type with the Fermi level close to the middle of the gap. The results have been interpreted in terms of the chemical bonding.     

ZnO hexagonal prisms grown onto p-Si (1 1 1) substrate from poly (vinylpyrrolidone) assisted electrochemical assembly

Nonionic polymer poly (vinylpyrrolidone) (PVP) was firstly mixed into oxygenated zinc chloride electrolyte to modulate the crystal growth and morphology of ZnO from electrodeposition. Arrays of ZnO hexagonal prisms with well-defined (0 0 0 1) end facets and side facets were grown perpendicularly onto p-type Si substrates using the simple and economic route. It was observed that the concentration of PVP played an important role in the final morphology and size of ZnO crystals. The optical studies indicated that the addition of PVT not only influenced crystal growth habit but also improved the optical properties of ZnO.     

Crystal structure of hydrazine 5-amino-1-benzyl-1,2,3-triazole-4-carboxylate hexafluorosilicate trihydrate

Hydrazine 5-amino-1-benzyl-1,2,3-triazole-4-carboxylate hexafluorosilicate trihydrate (I) is synthesized. The crystal structure of the compound synthesized is determined. Crystals I are monoclinic, a = 13.353(1) Å, b = 21.094(2) Å, c = 20.233(2) Å, β = 94.05(3)°, space group P2₁/c, and R = 0.0584 for 16 601 reflections with I > 2σ(I). In the asymmetric part of the unit cell, four organic cations protonated at the terminal hydrazine nitrogen atoms, two hexafluorosilicate anions, and six water molecules are linked into a three-dimensional framework through hydrogen bonds of the N-H?F, N-H?O, and O-H?F types.     

Structural analysis of models for AsxS1−x glasses

The structural models of chalcogenide glasses As_xS_1?x for x = 0.2 and 0.5 have been constructed by the three-step procedure and the characteristic dependence of atomic scale structure on the As content has been analysed. The AsS bonds are most favorable and the distributions of bond lengths and bond angles are very narrow around their minimum energy configurations. The glass of x = 0.2 consists of cross-linked linear chains and the number of molecular units increases drastically in the range of x = 0.4 ≈ 0.5. Furthermore, the two-dimensional network cannot be seen for x = 0.2 and 0.5, which is the essential difference from the glass with x = 0.4.     

Investigation into the evolution of the structure of K1−x LixTa1−y NbyO3 single crystals under variations in temperature

The evolution of the structure of K_1?x Li_xTa_1?y Nb_yO₃ single crystals with x = 0.001, y = 0.026, and 1900 ppm Cu (KLTN277) and with x = 0.0014 and y = 0.024 (KLTN123), which exhibit an extremely high permittivity (up to 4 × 10⁵ in the quasi-static regime for the KLTN277 crystal), is investigated in the range from room temperature to 20 K. It is demonstrated that, upon cooling to the lowest temperatures, both crystals retain their cubic structure, but the lattice parameters pass through a minimum at the temperature of the observed anomalies of the dielectric response (～50 K). In the neutron diffraction pattern of the KLTN123 sample, satellites appear in the vicinity of the (hhh) reflections at temperatures below ～50 K. These satellites can be associated with the nucleation of the rhombohedral phase.     

Molecular flexibility dependence on mesogenic behaviors of isomeric and nonisomeric series

A novel homologous series containing vinyl ester and azomethane central bridges and n-alkoxy as well as 3″,4″-dimethyl groups as flexible terminal/lateral groups viz. RO?C₆H₄?CH = CH?COO?C₆H₄?N?CH?C₆H₃-(CH₃)₂ have been synthesized and studied with a view to establishing the relation between molecular structure and thermotropic liquid crystal (LC) properties with reference to molecular flexibility within the series. The series consists of twelve homologues (C₁ to C₁₆). C₆ and C₇ homologues are smectogenic plus nematogenic and C₈ to C₁₆ homologues are only smectogenic, and the rest of the homologues (C₁ to C₅) are nonmesomorphic. Transition temperatures and the textures of the homologues were determined using an optical polarizing microscope equipped with a heating stage (POM). The textures of a nematic phase are threaded or Schlieren and that of a smectic phase are of the A or C type. Analytical, thermal and spectral data support the molecular structures. Smectic and nematic thermal stabilities are 116.85°C and 147.5°C, respectively. Whose Sm?N/I and N-I mesophase lengths are varied between 15°C to 21°C and 25°C to 62°C, respectively. The novel compounds are compared with structurally-similar series.     

Influence of the VPE parameters on the epitaxial film properties for the (Pb1−xSnx)1+yTe1−y system

Epitaxial films have been produced for 0 ? x ? 1 by steps of 0.1. The growth rate, crystalline quality, carrier concentration and composition have been measured as a function of source, substrate and Te₂ source temperature. The growth rate is adjustable between 0.1 and 36 μm h^-1 and the films have smooth and shiny surfaces. The crystalline quality, conduction type and carrier concentration is mainly determined by the Te₂ pressure. It is possible to choose the type and the carrier concentration in the stable region for a source composition x ? 0.2. The films are always p-type if x ? 0.3. The composition of the films is varied by the source and by the substrate temperature. It is possible to vary the film composition compared to the source composition in the range of ±20% by varying the substrate temperature.     

The 1:1 crystal complex of salicylic acid and urea

The 1∶1 crystal complex of salicylic acid (C₇H₆O₃) and urea (CH₄N₂O), mp 121° C, is monoclinic, with space groupC2/c (C ₂ ⁶ h, No. 15) and unit cell dimensionsa=22.206(3),b=5.108(1),c=17.177(2) Å,β=106.18(1)°.d _calc=1.407 g cm^?3,d _meas=1.41 g cm^?3 forZ=8. The structure was determined by direct methods and refined by a full-matrix least-squares procedure to giveR=0.057 andR _w =0.050 for 1652 integrated intensities above 2σ(I). The structure contains a strong OH?O hydrogen bond with O?O distance 2.54 Å in which the carboxyl OH group is donor and urea oxygen atom is acceptor. There are two NH?O intermolecular hydrogen bonds with N?O distances of 2.90 and 2.96 Å. Additionally, the salicyclic acid contains an intramolecular OH?O hydrogen bond of 2.56 Å.     

Structure of adamantan-1-ammonium 1-adamantanecarboxylate

Adamantan-1-ammonium 1-adamantanecarboxylate, C₂₁H₃₃NO₂ (I) is a novel dispiro-type compound. Aminoadamantane derivatives, in which the spiro carbon atoms are part of heterocyclic rings, are of potential interest as biological active substances and antiviral agents. Complex (I) crystallizes in the centrosymmetric space group C2/c (No. 15) with eight molecules in the unit cell with a = 25.227(4), b = 6.527(1), c = 22.489(4) Å, and = 90.75(1)°. The two spiro units are a 1-adamantylammonium cation and a 1-adamantane carbonyloxy anion. The complex units are stabilized by a network of intermolecular carbonyloxy-to-amine hydrogen bonding and van der Waals cohesive forces. Germane bond lengths are: C—N = 1.479(9) and C—O (mean) = 1.25(2) Å.     

Error estimates in the determination of rigid body displacements in protein crystals

We report the estimation of random errors in the refinement of the rigid body displacements of the -helices of the enzyme 6-phosphogluconate dehydrogenase. Least-squares refinement of the TLS parameters of the helices has been carried out using X-ray reflection data of 2.1 Å resolution, resulting in anR-factor of 19.5%. Standard deviations were estimated from the normal matrix. The results show that the translational mean-square displacements of nearly all the helices are significant at this resolution. However the libration parameters are only significant when the helices have at least four turns. Screw-rotation tensor values cannot be determined at this resolution.     

Conversion of CuS thin films to structured nanosheet CuyS (1 < y ≦ 2) by vacuum annealing

In this study, large‐area and uniform thickness novel nano‐sheet structured CuS thin films on ITO glass have been prepared by the one‐step electrodeposition method from a dimethyl sulfoxide solution. Thin films of completely preserved nano‐sheet like morphology of Cu_yS (y = 1.75, 1.8, 1.95, and 2.0) are grown by vacuum annealing CuS thin films at 500 °C for different lengths of time. The 500 °C sample heated for 10 hours was nearly converted to single phase of Cu₂S with y ∼ 2. The optical direct band gaps of nano‐sheet Cu_yS thin films annealed at 500 °C of 2, 6, and 10 hours in vacuum were found to be 1.94, 1.68, and 1.44 eV, respectively.     

Crystal structure of the supramolecular system of indole-2,3-dione 1-(2-oxopropyl)-3-ethylene ketal and its thiosemicarbazone

The crystal structure of a supramolecular system consisting of indole-2,3-dione 1-(2-oxopropyl)-3-ethylene ketal (I) and indole-2,3-dione 1-(2-oxopropyl)-3-ethylene ketal thiosemicarbazone (II) molecules that are linked together by hydrogen bonds is determined using X-ray diffraction. The crystal is monoclinic, and the unit cell parameters are as follows: a = 12.8360(3) Å, b = 10.7330(3) Å, c = 19.4610(3) Å, β = 99.566(1)°, space group P2₁/c, and Z = 4 (C₂₇H₂₉N₅O₇S). In molecules I and II, the indole-2,3-dione 3-ethylene ketal fragments have a virtually identical structure. The pyrrole and dioxolane fragments are spiro-linked through the carbon atom with a dihedral angle close to 90°. The adjacent pyrrole and benzene rings are coplanar to within 4.4°. In molecule II, the oxygen atom of the dioxolane fragment and the terminal nitrogen atom of the thiosemicarbazide fragment are involved in the N-HïO intramolecular hydrogen bond [3.294(2) Å]. The key role in the formation of the crystal structure is played by intermolecular hydrogen bonds of the N-H?dO, C-H?O, C-H?N, and N-H?S types.     

Growth of single crystals of the new double perovskite Ba2HoRu1−xCuxO6 from high temperature solutions

Single crystals of Ba₂HoRu_1−xCu_xO₆ have been grown from high temperature solutions using PbO–PbF₂ as solvent in the temperature range 1150–1250 °C. Crystals with a six sided plate like morphology measuring up to 3 mm across and 0.5 mm thick and polyhedral habit measuring up to 2 and 1 mm in thick mass were obtained. Powder X-ray diffraction patterns obtained on the crystals were indexed to give a monoclinic space group P2₁/n with lattice parameters a=5.875(2), b=5.874(3), c=8.960(1) and β=89.995(2)°. The crystals with x=0 show a single anomaly at 6.5 K corresponding to an antiferromagnetic phase with . The crystals containing Cu show additional anomalies at 18 and 48 K. The SEM and EDS analysis reveals a 2116 phase.