Synthesis,characterization, and mesomorphic investigation of vinyl ester-substituted chalcones and effect of lateral ‒NO2 and ‒OCH3 group

A novel homologous series of α-4-(4′-n-alkoxy cinnamoyloxy) phenyl β-2″-nitro, 3″–4″ di methoxy benzoyl ethylenes, H_2n+1CnO?C₆H₄?CH?CH?COO?C₆H₄?CO?CH?CH?C₆H₂(NO₂) (OCH₃)₂ (n = 1–8, 10, 12, 14, 16, 18) has been synthesized. All these compounds have been characterized by suitable spectroscopic techniques. C₁ homologue is nonmesogenic, while C₂ homologue shows enantiotropic nematogenic property and the rest of the homologous (C₃?C₁₈) displayed enantiotropically smectogenic plus nematogenic phase. Phase transition temperatures and textures of the LC phase were determined by an optical polarizing microscopy (POM) equipped with a heating stage. The mesomorphic properties of these compounds were confirmed by differential scanning calorimetry (DSC) analysis.     

Investigation of the Mechanism of Influence of Stress Corrosion on the Development of Macroplastic Instabilities of Aluminum–Magnesium Alloy

Crystallography Reports - Macroscopic jumps of plastic deformation (few percent in amplitude) on creep curves of aluminum–magnesium alloy, caused by a local effect of concentrated solution of...     

Peculiarities of the microstructure of a nanoscale modification of η-TiO2

Samples with nanoscale η-TiO₂ phase have been obtained by sulfate and modified sulfate methods and are characterized by a complex of techniques: X-ray diffraction, electron diffraction, small-angle X-ray scattering (SAXS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy, and X-ray energy-dispersive analysis. The effect of sample formation conditions on the size and shape of crystallites, content of the amorphous component in the samples, and their elemental composition has been established. A significant change (depending on the synthesis conditions) in the parameters of the diffraction reflection with d ～ 17–21 Å (intensity and interplanar spacing d, Å), pronounced for η-TiO₂, is revealed. This change is most likely related to the variation in the content of water molecules in the interlayer space of η-TiO₂ structure and/or the change in crystallite shape.     

Incorporation of group III,IV and V elements in 3C–SiC(1 1 1) layers grown by the vapour–liquid–solid mechanism

We report on a comparative investigation of the incorporation of group III, IV and V impurities in 3C–SiC heteroepitaxial layers grown by the vapour–liquid–solid (VLS) mechanism on on-axis α-SiC substrates. To this end, various Si-based melts have been used with addition of Al, Ga, Ge and Sn species. Homoepitaxial α-SiC layers grown using Al-based melts were used for comparison purposed for Al incorporation. Nitrogen incorporation depth profile systematically displays an overshoot at the substrate/epilayer interface for all the layers. Ga and Al incorporations follow the same distribution shape as N whereas this is not the case for the isoelectronic impurities Ge and Sn. This suggests some interaction between Ga/Al and N coming from the high bonding energy between the group III and V elements, which does not exist with Ge and Sn. This is why both incorporate as a cluster. A model of incorporation is proposed taking into account metal-N and metal-C bonding energies together with the solid solubility of the corresponding nitrides.     

Crystallization of mutant forms of the γ subunit of archaeal translation initiation factor 2

Archaeal translation initiation factor 2 (aIF2) is homologous to its eukaryotic counterpart (eIF2). It is a heterotrimeric protein consisting of α, β, and γ subunits. The protein e/aIF2 forms a ternary complex with guanosine 5′-triphosphate and the initiator methionyl-tRNA (Met-tRNA_i) and delivers the latter to the ribosome. In archaea, translation initiation factor 2 has an additional function. The γ subunit of aIF2 binds mRNAs with a triphosphate at the 5′-end and prevents 5′-to-3′ directional mRNA decay. To determine the mRNA-binding site on the surface of aIF2γ, mutations were introduced into the protein sequence at sites of possible interactions with mRNA. The crystals of the mutant forms of aIF2γ were obtained, and X-ray diffraction data sets suitable for structure determination at atomic resolution were collected.     

The crystal and molecular structure of one of the possible conformers of “the smallest piece of ice”—A solid-state isolation of a hydrogen bonded water hexamer trapped within channels of a crystal of a dirhodium molecule

Reexamination of our study of [Rh₂(HNOCCH₃)₄(2H₂O)] 3H₂O (Ahsan, M.Q.; Bernal, I.; Bear, J.L. Inorg. Chem. 1986, 26 260) showed it to be interesting not just because the dirhodium molecule is an antineoplastic but because it contains a hexameric cluster of waters trapped in Rh–Rh lattice cavities. It may well provide an interesting model for the smallest piece of ice (Nauta, K.; Miller, R.E. Science 2000, 287, 293).     

Morphology prediction of crystals grown in the presence of impurities and solvents — An evaluation of the state of the art

Computational methods enable to calculate relative face growth rates and crystal shape from structural information alone. Even if these models are sufficient for the calculation of the habit of a vapor grown crystal, most of them fail to correctly reproduce the habit of crystal growth from solution. In recent years, new approaches have been proposed based on the substitution of additive molecules in the crystal lattice or on the surface of the crystal. The new computer-based approaches provide a fundamental understanding of processes of crystal growth from solution. The number of methods proposed in morphology prediction is enormous. Herein, an overview of these methods and approaches is provided.     

Electron Microscopy of the Microstructure of Nb–Ti Tapes

Crystallography Reports - The microstructure of a cold-rolled tape made of Nb–50 wt % Ti superconducting alloy before and after heat treatment has been investigated by transmission electron...     

Positronium study of porous structure of sol–gel prepared SiO2: influence of pH

Positron annihilation lifetime and Doppler broadening of annihilation line techniques have been used to obtain information about the small-pore structure of SiO₂ prepared by the alkoxide method in different experimental conditions. Samples prepared in strong acidic environment (pH = 2) contain only small pores with mean radius R∼5 Å, while those prepared at pH = 6 and pH = 9 contain pores of two sizes, R∼5 and R∼17–26 Å. The influence of pH, water/alkoxide molar ratio and temperature of heat-treatment of the samples on their pore structure has been studied.     

Molecular and crystal structures of the products of crystallization of (N′-furfurylidene)isonicotinoylhydrazide from aqueous solutions of hydrochloric and acetic acids

Crystals of (N′-furfurylidene)isonicotinoylhydrazide (I), which have been isolated from a water-methanol solution of hydrochloric acid (Ia) and an aqueous solution (～50%) of acetic acid (Ib), are studied by X-ray diffraction. In Ia, the nitrogen atom of the pyridine ring is protonated. In the crystal, the intermolecular C=O?HN(Py) hydrogen bonds link the I · H⁺ cations into chains which are bound through centrosymmetric NH?W?Cl^??W′?H′N′ bridges. In molecule Ib, no protonation occurs; however, its pyridine N atom is blocked by the hydroxyl H atom of a solvate molecule of acetic acid. Crystals Ib have a layered structure. The crystallization water molecule is involved in the formation of three intermolecular hydrogen bonds, namely, those with the H atom of the amide group and the carbonyl O atoms of molecule I and an acetic acid molecule of the neighboring layer.     

A review of: “Molecular Dynamics of Liquid Crystals”

Abstract

Editors: G.R. Luckhurst and C.A. Veracini NATO ASI Series C: Mathematical and Physical Sciences - Vol. 431 Proceedings of the NATO Advanced Study Institute on The Molecular Dynamics of Liquid Crystals. II Ciocco. Borga. Italy. 11 - 23 September 1989 ISBN 0-7923-2809-4     

Detailed study of surface and interface properties of μc-Si films

The properties of surfaces and interfaces of microcrystalline films deposited by radio-frequency plasma enhanced chemical vapor deposition (RF-PECVD) were studied by spectroscopic ellipsometry. The effect of the low-power reactive ion etching (RIE) on the properties of the films was investigated. The surface properties could be effectively improved using RIE to eliminate of the top porous part of the films, without deterioration of bulk layer properties. Ellipsometric measurements from both film and substrate sides were used for the study of the interface properties of the various samples deposited on fused silica substrates. We show that the crystalline fraction that determined from modeling of ellipsometric spectra measured from the film side could be overestimated.     

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.     

Supramolecular Architecture of Two Modifications of Flavone-6,2′-dicarboxylic acid

Abstract  

Two crystalline forms of flavone-6,2′-dicarboxylic acid (fla): one N,N-dimethylformamide (DMF) solvate (modification 1) and one without any solvate molecules (modification 2), have been obtained and their structures were determined by X-ray diffraction technique. Modification 1 crystallized in the orthorhombic space group Pbca; and modification 2 crystallized in the monoclinic space group P2(1)/c. In 1 and 2 fla molecules are both joined to helix chain structures via O–H···O hydrogen-bonds between carboxylic group of B ring and carbonyl oxygen atom of C ring, however, in 1 helix chains are further joined by DMF molecules; and in 2 helix chains are further linked via rich hydrogen-bonds between fla molecules, which result in different packing of modifications 1 and 2.     

Anisotropy of microhardness of β-BaB2O4 single crystals

The anisotropy of microhardness of β-barium borate single crystals β-BaB₂O₄ (BBO) is studied by the sclerometry method on the (0001) basal plane, the $(10\bar 10)$ plane of the hexagonal prism, and the $(11\bar 20)$ plane of the trigonal prism. It is shown that the anisotropy observed in the crystal is determined by the directions of covalent B-O bonds. It is established that the anisotropy of microhardness correlates with the system of cleavage planes.     

Structure of a liquid crystal of 4-cyano-4′-n-octyloxybiphenyl

The structure of a liquid crystal of 4-cyano-4′-n-octyloxybiphenyl (C₂₁H₂₅NO) is determined by X-ray diffraction analysis. The compound crystallizes in the triclinic crystal system with unit cell parameters a = 7.322(1) Å, b = 12.693(3) Å, c = 20.393(2) Å, α = 92.45(1)°, β = 99.96(1)°, γ = 99.35(2)°, and space group $P\bar 1$ . The structure is solved by the direct method and refined to R = 0.057. Two independent molecules are located in the asymmetric unit. No short intermolecular contacts are observed in the crystal packing.     

Growth of CuSO4 · 5H2O single crystals and study of some of their properties

Large single crystals of copper sulfate pentahydrate CuSO₄ · 5H₂O of optical quality have been grown; they can be applied as broadband UV optical filters. Their transmission spectra are measured. The crystal thermal stability is investigated and the onset temperature of dehydration is determined to be 46°C.     

A study of the crystallization of two non-crystalline CuZr alloys

Two CuZr alloys, Cu-50 at% Zr and Cu-54 at% Zr, were splat quenched to the non-crystalline state using a piston and anvil device. The glass transition and crystallization temperatures, as well as the enthalpy releases observed during crystallization were measured using differential scanning calorimetry of as-splat specimens and specimens aged below T_g. Transmission electron microscopy and X-ray diffraction experiments were utilized to monitor phase and structural changes in the alloys as they were transformed to the crystalline state.The results of the investigation indicated that the non-crystalline to crystalline transformation of these two alloys in constant heating rate experiments above T_g was a two-step process. The initial step, which is associated with a large exothermic reaction, results in the appearance of crystallites in a matrix of non-crystalline material. The final step, associated with a smaller exothermic reaction, results in the total transformation of glass to the crystalline state and the formation of the equilibium crystalline phases.The effect of aging these splat-quenched non-crystalline alloys at temperatures below T_g was also investigated. It was determined from these experiments that crystallization does occur when the non-crystalline alloys are aged ～ 15°C below T_g. However, the incubation time for crystalline nucleus formation was found to be substantially greater for the Cu₅₀Zr₅₀ glass. Finally, it was determined that the thermal stability of the aged glass relative to the spontaneous crystallization observed during the constant heating rate experiments above T_g decreases as a function of aging time.