Basis Of X-ray Research Articles

Preparation and characterization of a new inorganic cation-exchanger: Zirconium (IV) iodosilicate: Analytical applications for metal content determination in pharmaceutical sample and synthetic mixture

A new inorganic cation exchanger zirconium(IV) iodosilicate was synthesized and characterized on the basis of X-ray, TGA-DTA, FTIR and SEM studies. This cation-exchanger was found to have a good ion-exchange capacity (0.85 meq g−1 for Na+), high thermal and chemical stability. The chemical composition reveals that Zr:I:Si is in the molar ratio 1:1.57: 1. The chemical stability data shows that material is quite stable in common mineral acids, bases and organic solvents of analytical interest upto 2.0 M. Thermal analysis shows that exchanger retain 80% of ion-exchange capacity upto 400°C. Effect of time and temperature on the sorption of metal ions on this material was explored. The sorption behavior of metal ions was studied in acetic acid, formic acid, DMSO, DMF and succinic acid. Some important and analytically diffi cult quantitative binary separations viz. Cd(II)-Ba(II), Cd(II)-Ni(II), Cd(II)-Cu(II), Cd(II)-Fe(III) etc. were achieved. The practical applicability of the cation-exchanger was demonstrated...

Lattice Distortion and Lithium Ionic Conduction Path in a Superionic Conductor with Perovskite Structure

Three-dimensional structure for La 2/3- x Li 3 x TiO 3 was deduced by the reverse Monte Carlo (RMC) modeling technique on the basis of X-ray and neutron diffractions to reveal the lattice distortion relating to the disorder in the distributions of La ions and the conduction path of Li ions. Our previous results focused on Li ion distribution on the average lattice structure obtained from Rietveld analysis and revealed that the Li ions were mainly situated on the La-rich layer which is completely different from the earlier works. In the present study where physical constraints on La, Ti, and O atoms forming the lattice structure have been relatively released during RMC modeling, we analyzed the distortion of TiO 6 octahedra to check the difference between our study and the earlier studies. In addition of the consistency of our structural model with the earlier studies in terms of the Ti and O positions, and the tilting angle of about 10° for TiO 6 octahedra, it has been analyzed their fluctuations from the averaged values. Furthermore, it has been suggested from the RMC model that Li ions yield a conduction path from the bottleneck to the adjacent one through the interstitial site between the O 3 triangle plane of TiO 6 octahedron and a La ion.

Preparation and properties of new materials: Solid solutions (GaSb) x (ZnTe)1−x

Solid substitutional solutions of cubic (sphalerite) lattice based on the binary semiconducting compounds GaSb and ZnTe in the range of their mutual solubility were synthesized. Their identification was performed on the basis of X-ray and electrophysical studies.

EDTA-stannic(IV)iodate: preparation, characterization and its analytical applications for metal content determination in real and synthetic samples

A new organic–inorganic cation exchanger EDTA-stannic(IV)iodate was synthesized. The materials possess good chemical and thermal stability. The exchanger was characterized on the basis of X-ray, TGA, FTIR, UV–Visible spectrophotometery and SEM studies. ion exchange capacity, pH titration, elution and distribution studies were also carried out to determine the primary ion exchange properties of the material. The SEM study confirms the fibrous nature of the material. The exchanger behaves as a monofunctional cation exchanger with ion exchange capacity of 1.30 meq/g for Na+ ions. The material can perform well upto the temperature of 500 °C and retains the 76.4% of ion exchange capacity. The material is fairly stable in dilute solutions of some common mineral acids, bases and organic solvents. The differential selectivity of metal ions on EDTA-stannic(IV)iodate has been utilized to perform analytically and industrially important binary separations.

Secondary structures in hyaluronan solutions: chemical and biological implications.

Hyaluronan behaves as an unusually stiff polymer in solution. Periodate oxidation of the hexuronic acid moiety is severely hindered, as is that of chondroitin 4-sulphates and 6-sulphates. On the basis of X-ray and computer studies a secondary structure was proposed which accounted for the known facts. NMR data obtained subsequently in dimethyl sulphoxide were completely compatible with these proposals. Results obtained in H2O suggested that the acetamido group could not be oriented in aqueous solution as it was in dimethyl sulphoxide solution. There is strong evidence that an H2O bridge between the acetamido and carboxylate groups is involved in the secondary structure in H2O. It is suggested that conversion of one structure (stable in the absence of H2O) to the other (in aqueous solution) might occur during biosynthesis, as part of the driving force that results in shedding from the H2O-poor environment of the membrane. The hydrogen-bonded secondary structures show quite large arrays of contiguous CH groups, giving a hydrophobic character to some parts of the polymer, which might be significant in self-association and for interactions with membranes.

Crystallization of amorphous Fe78Si9B13 alloy

The crystallization process of Fe78Si9B13 metallic glass was investigated by DSC, X-ray diffraction, electrical resistivity, Hall effect and TEM methods. The investigations proved two-stages crystallization. By means of non-isothermal DSC experiments the activation energy and the Avrami exponent were determined for both stages. The created phases: α-Fe(Si) and (Fe,Si)2B were identified on the basis of X-ray and TEM investigations. However, TEM observations showed also a little amount of the FeB49 phase as well as some rest of the amorphous phase. The electrical and Hall resistivities decrease abruptly after the creation of the phases out of the amorphous matrix.

Complex of Calmodulin with a Ryanodine Receptor Target Reveals a Novel, Flexible Binding Mode

Calmodulin regulates ryanodine receptor-mediated Ca(2+) release through a conserved binding site. The crystal structure of Ca(2+)-calmodulin bound to this conserved site reveals that calmodulin recognizes two hydrophobic anchor residues at a novel "1-17" spacing that brings the calmodulin lobes close together but prevents them from contacting one another. NMR residual dipolar couplings demonstrate that the detailed structure of each lobe is preserved in solution but also show that the lobes experience domain motions within the complex. FRET measurements confirm the close approach of the lobes in binding the 1-17 target and show that calmodulin binds with one lobe to a peptide lacking the second anchor. We suggest that calmodulin regulates the Ca(2+) channel by switching between the contiguous binding mode seen in our crystal structure and a state where one lobe of calmodulin contacts the conserved binding site while the other interacts with a noncontiguous site on the channel.

The Ability of the Lauge-Hansen Classification to Predict Ligament Injury and Mechanism in Ankle Fractures: An MRI Study

The Lauge-Hansen classification system was designed to predict the mechanism and ligament injury patterns of ankle fractures on the basis of x-rays. The purpose of this study was to evaluate the accuracy of these predicted injury sequences using magnetic resonance imaging (MRI) in a series of patients with ankle fractures. Retrospective cohort. Two university level 1 trauma centers. Fifty-nine patients with operative ankle fractures who were evaluated with both x-ray and MRI were included. All patients had a standard 3-view ankle x-ray series before fracture reduction, followed by an MRI. All plain x-rays were assigned to a Lauge-Hansen category by an experienced orthopedic traumatologist. MRI studies were subsequently read by an MRI musculoskeletal radiologist for the integrity of the ankle ligaments. After evaluation of the x-rays, fractures were classified according to the system of Lauge-Hansen, and the predicted presence, sequence, and mechanism of injury was determined. These were then compared to the actual injured structures on MRI in each case, and the ability of the Lauge-Hansen system to accurately predict the complete injury pattern was determined for the entire cohort. Average patient age was 59 (range: 18 to 84) years. Of the 59 ankle fractures evaluated, 37 (63%) were classified as supination external rotation, 11 (19%) were pronation external rotation, 1 (2%) was supination adduction, and 10 (17%) were not classifiable on the basis of the Lauge-Hansen system. Of the 49 fractures that fit into Lauge-Hansen categories, 26 (53%) had patterns of ligamentous injury and fracture morphology that did not coincide with the Lauge-Hansen predictions. A common fracture pattern was observed in 8 of the 10 unclassifiable fractures, which included a high spiral fracture of the fibula, vertical shear fracture of the medial malleolus, posterior malleolar fracture, and complete tears of the anterior-inferior tibiofibular ligament and the interosseous membrane. In addition, over 65% of patients in this series had complete ligamentous injury and a fracture of the malleolus to which the ligament attaches. These results demonstrate that the Lauge-Hansen classification system may have some limitations as a predictor of the mechanism of injury and the presence of soft-tissue damage associated with ankle fractures. The identification of a novel pattern of ankle fracture also illustrates how the system fails to describe all possible fracture patterns. For these reasons, we recommend that the Lauge-Hansen system be used only as a guide in the diagnosis and management of ankle fractures and not solely relied upon for treatment decisions. Although the exact clinical implications of the variety of ligamentous injuries observed on MRI are yet to be determined, this technique may be useful in individual cases in which doubt about joint stability and soft-tissue integrity exists. Additionally, MRI may be helpful in planning surgical approaches in atypical fractures in which injury patterns are less predictable solely on the basis of x-ray.

Camphor-Palladium Complexes as Catalysts for Cyclization of Alkynes

Catalytic properties of the camphor-derived complexes trans-[PdCl2(L1)2], R = Me2N (1), i-Pr (3), C6H5 (4), in PhC≡CMe cyclotrimerization are highly dependent on the characteristics of the R group. Their activity decreases in the order 1 > 3 > 4. The effects of geometric and/or electronic parameters on the catalytic activity of the complexes are evaluated on the basis of X-ray and electrochemical data.

Chemical Components of Leptopus chinensis

Six substances were isolated from the branches and leaves of the Chinese herb Leptopus Chinensis (Bunge) Pojark. by column chromatography for the first time. Their structures were elucidated as 3α-hydroxyfriedelan-2-one, saccharose, triacontanol, friedelane-2α,3β-diols, β-sitosterol-3-O-β-D-glucoside, and β -sitosterol on the basis of x-ray, chemical, and spectroscopic methods.

Antiferromagnet-ferromagnet phase transition in lightly doped manganites

Magnetic and structural phase diagrams of the La0.88MnOx, La1−xSrx(Mn1−x/2Nbx/2)O3, Nd1−xCaxMnO3, and Bi1−xCaxMnO3 series, constructed on the basis of x-ray, neutron powder diffraction, Young’s modulus, magnetization and resistivity measurements, are presented. It is shown that the main factor controlling the antiferromagnet-ferromagnet phase transition in the manganites is a type of an orbital state. The results are discussed in the framework of structurally driven magnetic phase separation model.

Stereoselective synthesis of new modified conformationally constrained l-tyrosine analogue with potential applications to SH2 domain ligands

This paper reports the stereoselective synthesis of a modified tricyclic tyrosine analogue 3 , whose conformation is constrained by the covalent bonds and designed on the basis of X-ray and solution structures of SH2 domain and its natural peptide ligand. A Michael addition followed by an alkylation in high stereoselections, a Friedel–Crafts and a Mannich reaction-based cyclization served as the key steps in the synthesis.

Enhanced Ligand Affinity for Receptors in which Components of the Binding Site Are Independently Mobile

Using calmodulin antagonism as a model, it is demonstrated that, under circumstances in which binding sites are motionally independent, it is possible to create bifunctional ligands that bind with significant affinity enhancement over their monofunctional counterparts. Suitable head groups were identified by using a semiquantitative screen of monofunctional tryptophan analogs. Two bifunctional ligands, which contained two copies of the highest-affinity head group tethered by rigid linkers, were synthesized. The bifunctional ligands bound to calmodulin with a stoichiometry of 1:1 and with an affinity enhancement over their monofunctional counterparts; the latter bound with a stoichiometry of 2:1 ligand:protein. A lower limit to the effective concentrations of the domains of calmodulin relative to each other (0.2-2 mM) was determined. A comparable effective concentration was achieved for bifunctional ligands based on higher-affinity naphthalene sulphonamide derivatives.

Liquid crystalline properties of unsymmetrical bent-core compounds containing chiral moieties

The synthesis, characterization and mesomorphic properties of new unsymmetrical bent-core compounds containing chiral moieties are reported. These compounds have been derived from either 3-hydroxybenzoic acid or 2,7-dihydroxynaphthalene as the central unit. The chiral group is incorporated either within the bent-core structure as a linking group or is appended in the terminal position. The influence of the position of the chiral moiety on the mesomorphic properties has been investigated. The bent-core compounds containing a chiral group (octan-2-ol) in the terminal chain exhibit a direct transition from chiral calamitic phases such as SmC*, SmC*γ to a polar banana phase with a two-dimensional lattice (ColobPA*) on decreasing temperature. In order to prove this phase sequence, the corresponding compound with a racemic octan-2-ol group at the terminal chain has been synthesized. The preliminary observations and investigations are presented for comparison with the chiral compound. Possible explanations for this unusual phase sequence and the models for the ColobPA* (SmSPA*) phase are also discussed on the basis of X-ray and electric field experiments.

Metal—Metal Bonding in ScTaN2. A New Compound in the System ScN—TaN.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Metal-metal bonding in ScTaN2. A new compound in the system ScN-TaN.

Gray microcrystalline powders of ScTaN(2) were prepared from solid-state reactions of delta-ScN with Ta(3)N(5) powders at T = 1770 K. According to thermal analyses the compound is stable against oxidation by O(2) up to temperatures of T = 800 K. In an Ar atmosphere ScTaN(2) decomposes above T = 1250 K and in a N(2) atmosphere above T = 2000 K under release of N(2) to form delta-ScN and beta-Ta(2)N. The crystal structure (space group P6(3)/mmc, No. 194, a = 305.34(3) pm, c = 1056.85(9) pm, Z = 2) was refined on the basis of X-ray and neutron powder diffraction data. It comprises alternating layers of ScN(6/3) octahedra and trigonal TaN(6/3) prisms, which are also observed in the binary nitrides delta-ScN and theta-TaN, respectively. A small degree of anti-site defects (about 5%) was detected. Only a small solubility of ScN in epsilon-TaN was observed, while the solubility of TaN in delta-ScN is >/=10 mol % at T = 1820 K. ScTaN(2) is a diamagnetic small gap semiconductor or a semimetal, as inferred from magnetization and electrical resistivity measurements, consistent with band structure calculations. Chemical bonding analyses with the COHP method yield significant covalent Ta-Ta interactions. Topological analyses of the electron localization function reveal unexpected Ta-Ta three-center bonding basins within seemingly empty trigonal prisms of the TaN(6/3) layers.

A study of hydrogen bond of imidazole and its 4-nitro derivative by ab initio and DFT calculated NQR parameters

Nuclear quadrupole resonance (NQR) parameters of 14N, 2H of N 2H groups are calculated for imidazole and 4-nitroimidazole using HF and B3LYP methods. These computations are performed on the basis of X-ray and neutron diffraction structural data which are collected at 100, 103, 123 and 293 K temperatures. In order to take into account intermolecular hydrogen bonds and the van der Waals effects, two different sizes of clusters have been considered. Results of calculation have been compared with that of a single molecule in each case. Calculations illustrate that for imidazole and 4-nitroimidazole octameric and trimeric clusters, respectively, suffice to generate results which are compatible with experimental data. Our calculated NQR parameters and X-ray data show no significant structural change for 4-nitroimidazole at 293 and 100 K.

A study of hydrogen bond of imidazole and its 4-nitro derivative by ab initio and DFT calculated NQR parameters

Nuclear quadrupole resonance (NQR) parameters of 14 N, 2 H of N 2 H groups are calculated for imidazole and 4-nitroimidazole using HF and B3LYP methods. These computations are performed on the basis of X-ray and neutron diffraction structural data which are collected at 100, 103, 123 and 293 K temperatures. In order to take into account intermolecular hydrogen bonds and the van der Waals effects, two different sizes of clusters have been considered. Results of calculation have been compared with that of a single molecule in each case. Calculations illustrate that for imidazole and 4-nitroimidazole octameric and trimeric clusters, respectively, suffice to generate results which are compatible with experimental data. Our calculated NQR parameters and X-ray data show no significant structural change for 4-nitroimidazole at 293 and 100 K.

Synthesis, structure and superconducting properties of the (Hg1−xRex)Sr2(Nd1−yCay)Cu2O6+δ system

The synthesis, structure and superconducting properties of the (Hg1−xRex)Sr2(Nd1−yCay)Cu2O6+δ system (with 0 ≤ x ≤ 0.2 and 0.2 ≤ y ≤ 0.6) have been investigated. Near single phase compositions with x = 0.2 and 0.2 ≤ y ≤ 0.6 may be prepared by solid state reaction at room pressure. The maximum Tc = 100 K in this system is found for the nominal composition (Hg0.8Re0.2)Sr2(Nd0.6Ca0.4)Cu2O6+δ. Rietveld analysis of time-of-flight neutron powder diffraction data from a sample with the refined composition Hg0.78Re0.22Sr2Nd0.59Ca0.41Cu2O6.88 indicates that the rhenium cation in the (Hg,Re)Oδ layer of this material is hexavalent and six coordinate. On the basis of x-ray and neutron powder diffraction data, the Hg and Re cations in the (Hg,Re)Oδ layer of Hg0.78Re0.22Sr2Nd0.59Ca0.41Cu2O6.88 appear to be randomly distributed, in contrast to the ordered nature of these cations in similar materials prepared by high pressure methods. The irreversibility field of essentially optimally doped Hg0.78Re0.22Sr2Nd0.59Ca0.41Cu2O6.88 indicates no enhancement of the kind reported in similar materials prepared under high pressure. We suggest that this difference may be associated with (dis)ordering of the Hg and Re cations in the (Hg,Re)Oδ layer of these materials.

On the internal structure of Guinier-Preston zones in Al-3 at.% Ag

High-angle annular dark-field scanning transmission electron microscopy has been employed to study partially decomposed Al-3 at.% Ag. After solutionizing at 550°C and quenching to room temperature, samples of an Al-3 at.% Ag single crystal were aged for short times at 105, 140 and 180°C. Independent of the ageing temperature for these early stages, Guinier-Preston zones with a diameter of about 3 nm are found. Most of these zones consist of a silver-depleted core surrounded by a silver-rich shell. The shell structure is not uniformly pronounced. Irregularly shaped Guinier-Preston zones are common, but the shell structure dominates. No indication of different structures of the Guinier-Preston zones in Al-3 at.% Ag was found after short ageing at the three different temperatures. The shell model for Guinier-Preston zones in aluminium-rich Al-Ag alloys, which was previously proposed on the basis of X-ray and neutron scattering experiments, is thus appropriate to describe the structure of the Guinier-Preston zones in the early stages of the decomposition.