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Structural Study (structural + study)
Selected AbstractsStructural Study of Novel Graphite,Lithium,Calcium Intercalation CompoundsEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 8 2004Sébastien Pruvost Abstract Three new layered compounds were synthesised by immersing a pyrographite platelet in a molten Ca,Li alloy creating a new graphite intercalation compound family. The samples were studied by X-ray and neutron diffraction, revealing that the intercalated sheets are polylayered. The study of the 00l reflections allowed us to establish the c -axis stacking of these three phases. The ,-phase exhibits a five-layered intercalated sheet which has something in common with a Li,Ca,Li,Ca,Li slice cut in the CaLi2 structure (ThMn2 Laves phase type). The ,-phase, which is richer in metallic elements and with a greater repeat distance, possesses seven-layered intercalated sheets due to the splitting of the middle lithium plane in three. The third phase is a pseudo-binary compound, containing monolayered sheets and with a formula close to CaC6. Electron microdiffraction allowed us to determine the 2D unit cell for each compound, all of which were commensurate with that of graphite. Charge transfer from the intercalate to the host lattice was evaluated for the three phases from hk0 data, leading to high values. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source] Multimaterial Photodetecting Fibers: a Geometric and Structural Study,ADVANCED MATERIALS, Issue 22 2007F. Sorin We report in this communication on structure property relations, specifically focusing on geometric scaling and its effect on the performance of one dimensional distributed photodetecting fibers. Envisioned applications include large area optoelectronic systems, remote sensing and multifunctional fabrics. [source] Structural Study on Water-induced Phase Transitions of Poly(ethylene imine) as Viewed from the Simultaneous Measurements of Wide-Angle X-ray Diffractions and DSC ThermogramsMACROMOLECULAR SYMPOSIA, Issue 1 2006Tomoko Hashida Abstract Thermal behavior of poly(ethylene imine) [PEI] has been studied using simultaneous WAXD/DSC measurement system. PEI exhibits water-induced and thermally-induced phase transitions among four kinds of crystalline hydrates: anhydrate (EI/water,=,1/0), hemihydrate (1/0.5), sesquihydrate (1/1.5), and dihydrate (1/2). The chain conformation changes from a double helix in the anhydrate to a planar zigzag form in the three hydrates. The anhydrate melts at 60,°C while the hydrates melt differently in the temperature region of 70,110,°C. By means of the simultaneous WAXD/DSC measurements, complex DSC thermograms of PEI hydrates were characterized on the basis of X-ray diffractions obtained concurrently. [source] ChemInform Abstract: Structural Study of the Semimagnetic Semiconductor Zn0.5Mn0.5In2Te4.CHEMINFORM, Issue 15 2009G. E. Delgado Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] Synthesis and Structural Characterization of C(OTeF5)4 and a Comparative Structural Study of the Isoelectronic B(OTeF5)4 - Anion.CHEMINFORM, Issue 35 2007Matthew D. Moran Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source] Synthesis and Structural Study of 3-Anisyl-4-(4,-pyridyl)(pyridinium)thieno[2,3-b]thienophenes.CHEMINFORM, Issue 19 2005Sabir H. Mashraqui Abstract For Abstract see ChemInform Abstract in Full Text. [source] Structural Study of the Dehydration of Templated Zirconium Phosphate Fluorides.CHEMINFORM, Issue 15 2003Martin Wloka Abstract For Abstract see ChemInform Abstract in Full Text. [source] Structural Study of the Cation Ordering in the Ternary Oxide Ba8Ti3Nb4O24.CHEMINFORM, Issue 3 2003Nicolas Teneze Abstract For Abstract see ChemInform Abstract in Full Text. [source] Structural study of the semimagnetic semiconductor Zn0.5Mn0.5In2Te4CRYSTAL RESEARCH AND TECHNOLOGY, Issue 2 2009G. E. Delgado Abstract The semimagnetic semiconductor alloy Zn0.5Mn0.5In2Te4 was refined from an X-ray powder diffraction pattern using the Rietveld method. This compound crystallizes in the space group I42m (Nº 121), Z = 2, with unit cell parameters a = 6.1738(1) Å, c = 12.3572(4) Å, V = 471.00(2) Å3, c/a = 2.00. This material crystallizes in a stannite-type structure. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Structural study of monoclinic KGd(WO4)2 and effects of lanthanide substitutionJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 1 2001M. C. Pujol The crystal structure of monoclinic KGd(WO4)2 (KGW) has been refined at room temperature by using single-crystal X-ray diffraction data. The unit-cell parameters are a = 10.652,(4), b = 10.374,(6), c = 7.582,(2),Å, , = 130.80,(2)°, with Z = 4, in space group C2/c. The linear thermal expansion tensor has been determined and the principal axes are [302], [010] and [106]. The principal axis with maximum thermal expansion ( = 23.44 × 10,6,K,1), , was located 12° from the c axis. Undoped crystals of KGW and crystals that were partially doped by Pr, Nd, Ho, Er, Tm and Yb were grown by the top-seeding-solution growth slow-cooling method. The effect of doping on the KGW structure was observed in the cell parameters and in morphological changes. The changes in parameters follow the changes in lanthanide ionic radii. The doped crystals show {021} and {21} faces in addition to the {110}, {11}, {010}, {130} and {310} faces which basically follow the habit of the undoped KGW crystals. The development of the faces is related to the number of the most important periodic bond chains parallel to them. [source] Structural study of ethyl 3-arylcarbamoyl-2,3-diazabicyclo[2.2.1]hept-5-ene-2-carboxylates: conformation and transmission of substituent effects across the diazabicycloheptene ring,JOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 11 2001A. Perjéssy Abstract Nine new ethyl 3-arylcarbamoyl-2,3-diazabicyclo[2.2.1]hept-5-ene-2-carboxylates were prepared by a [4,+,2] cycloaddition and their FTIR, 1H, 13C and 15N NMR spectra were measured and assigned. Single crystals were grown for five compounds and their X-ray data were obtained. The electronic structure and the conformations were calculated by the semi-empirical AM1 method. Using correlations between the spectral, empirical and theoretical structural data, the transmission of substituent effects and the preferential conformation connected with the consecutive double nitrogen inversion and regarding the mutual orientation of NH and CO bonds were investigated. The results are compared with those for a previously reported series of analogous ethyl 2-arylcarbamoyl-4,5-dimethyl-1,2,3,6-tetrahydropyridazine-1-carboxylates. Copyright © 2001 John Wiley & Sons, Ltd. [source] Structural study on the crystallization behavior of Sb3Te2 alloy for phase change memoryPHYSICA STATUS SOLIDI - RAPID RESEARCH LETTERS, Issue 1 2007Chang Woo Sun Abstract The atomic crystal structure of the Sb3Te2 binary alloy has been investigated with high-resolution transmission electron microscopy (HR-TEM) and fast Fourier transform patterns. As a result, there is inconsistency between the previous theoretical model and the experimental result. But, from the calculations of lattice parameters and the number of layers in the unit cell, it is found that the Sb3Te2 alloy can be crystallized into the Sb2Te structure with Pm1 space group and the difference between stacking sequences of the Sb3Te2 and the Sb2Te structures has been discussed with the proposed atomic arrangement model of unit cells. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Structural study of ferroelectric and paraelectric phases in PbK2LiNb5O15PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 11 2004Y. Gagou Abstract The structures of PbK2LiNb5O15 showing the ferroelectricity below about 640 K have been studied in the paraelectric and ferroelectric phases by means of synchrotron X-ray powder diffraction. The data are analyzed with a Rietveld refinement method. It is found that the paraelectric structure and the ferroelectric one are of tetragonal and orthorhombic symmetry with P4/mbm and Pba2, respectively. The Pba2 structure gives a polar displacement along c -axis, whose direction is consistent with that deduced from dielectric measurements. The refined chemical occupancies of the cations Pb, K and Nb give the site-situation of these ions in the tunnels with square sections and pentagonal sections in each phase. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Structural study of NaNO2 embedded into porous glassPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 3 2007E. Rysiakiewicz-Pasek Abstract Temperature-dependent Raman study of NaNO2 confined within porous glass with a pore size of 46 nm has been performed. It is demonstrated that the bandwidths and frequencies of the Raman bands as a function of temperature show similar behaviour, but not identical, as those observed for bulk NaNO2. This result indicates that the first-order phase transition mechanism is only slightly modified by embedding NaNO2 into the porous glass. It seems that formation of "premelted state" is not significant in the studied material, at least up to 40-50 K above Tc. At higher temperatures, however, a significant increase of bandwidth of the 1326 cm,1 band is observed, which could indicate appearance of "premelted" state. The dielectric measurements are consistent with this view since they show large increase of dielectric permittivity above 480 K, well below the NaNO2 melting temperature (554 K). (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Structural study of KxNa1,,,xNbO3 (KNN) for compositions in the range x = 0.24,0.36ACTA CRYSTALLOGRAPHICA SECTION B, Issue 1 2009D. W. Baker The structure of the A -site substituted perovskite KxNa1,,,xNbO3, x = 0.24,0.36, where a phase boundary was previously reported, has been determined by high-resolution X-ray powder and neutron powder diffraction studies. The structure of the x = 0.3 compound was refined in the monoclinic space group Pm at 293,K and in P4mm at 523,K. The Glazer tilt system of the room-temperature monoclinic phase is a0b+c0, which has implications for the nature of the next symmetry change with composition towards pure potassium niobate. A phase-coexistence region at the transition between monoclinic and tetragonal phases was also identified, consistent with a first-order phase boundary. There is also evidence for an intermediate oxygen-octahedra tilted tetragonal phase. [source] Structural study of the low-temperature phase of TlH2PO4 at 180,KACTA CRYSTALLOGRAPHICA SECTION B, Issue 5 2002E. Álvarez-Otero The low-temperature phase of TlH2PO4 has been studied by X-ray diffraction. A structural model is proposed with space group P. This model is compared with the structure of the antiferroelectric phase of TlD2PO4 at room temperature to analyze the expected isomorphism at low temperature. Given the structural distortion of TlH2PO4, such isomorphism present in the common high-temperature phase is not recovered in this phase. Through the analysis of the displacements of the PO4 groups there is some evidence that the ordering of the H atoms responsible for the appearance of antiferroelectricity seems to be incomplete. An exhaustive study of the detected ferroelastic domains is also performed. [source] Structural study and thermodynamic characterization of inhibitor binding to lumazine synthase from Bacillus anthracisACTA CRYSTALLOGRAPHICA SECTION D, Issue 9 2010Ekaterina Morgunova The crystal structure of lumazine synthase from Bacillus anthracis was solved by molecular replacement and refined to Rcryst = 23.7% (Rfree = 28.4%) at a resolution of 3.5,Å. The structure reveals the icosahedral symmetry of the enzyme and specific features of the active site that are unique in comparison with previously determined orthologues. The application of isothermal titration calorimetry in combination with enzyme kinetics showed that three designed pyrimidine derivatives bind to lumazine synthase with micromolar dissociation constants and competitively inhibit the catalytic reaction. Structure-based modelling suggested the binding modes of the inhibitors in the active site and allowed an estimation of the possible contacts formed upon binding. The results provide a structural framework for the design of antibiotics active against B. anthracis. [source] Molecular structure, conformational analysis and charge distribution of pralidoxime: Ab initio and DFT studiesINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 3 2002Alexandre T. Castro Abstract A detailed structural study of pralidoxime (2-PAM), the main antidote against organophosphate intoxication, was performed using Hartree-Fock, Möller,Plesset (MP2), and density functional theory (Becke, Lee, Yang, and Paar [B3LYP]) methods. Rotational barriers, equilibrium geometries, and charge distributions were calculated, showing important differences between the two forms available in physiological conditions, namely with the oxime group protonated or unprotonated. For the protonated form, conjugation between the side chain and the pyridinium ring, although present, has little importance, resulting in a flexible structure. On the other hand, the unprotonated form has a more rigid structure and a smaller charge density on the oxime oxygen. Contrary to the common belief, those results strongly suggest that it may be the protonated form of 2-PAM, instead of the unprotonated form, that is responsible for the antidote activity of this compound. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002 [source] Solid Composite Polymer Electrolytes with High Cation Transference NumberISRAEL JOURNAL OF CHEMISTRY, Issue 3-4 2008Hadar Mazor This work presents the electrochemical and structural study of the dual modified composite LiBOB-based polymer electrolyte. Modification has been carried out by calix[6]pyrrole (CP) anion trap and nanosize silica filler. The main advantage of the use of LiBOB salt is the high ionic conductivity at near-ambient temperatures and low solid-electrolyte interphase (SEI) resistance. The conductivity of LiBOB:PEO20:CP0.125 with SiO2 is slightly lower than 10,5 Scm,1 at 30 °C, a value higher by about two orders of magnitude than that of the semi-crystalline LiCF3SO3 (LiTf)-PEO system. At 75 to 90 °C the bulk ionic conductivity of modified LiBOB polymer electrolyte approaches 1 mScm,1. The transference number of dual-modified LiBOB-polymer electrolyte is about 0.8 at 75 °C. Cyclic voltammetry tests showed a wide electrochemical stability window of the composite polymer electrolyte. The peak power of Li/MoOxSy cell with the polymer electrolyte film containing CP and SiO2 reaches 2.2 mW/cm2 and 3.0 mW/cm2 at 90 and 110 °C, respectively. [source] Protein,protein docking dealing with the unknownJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 2 2010Irina S. Moreira Abstract Protein,protein binding is one of the critical events in biology, and knowledge of proteic complexes three-dimensional structures is of fundamental importance for the biochemical study of pharmacologic compounds. In the past two decades there was an emergence of a large variety of algorithms designed to predict the structures of protein,protein complexes,a procedure named docking. Computational methods, if accurate and reliable, could play an important role, both to infer functional properties and to guide new experiments. Despite the outstanding progress of the methodologies developed in this area, a few problems still prevent protein,protein docking to be a widespread practice in the structural study of proteins. In this review we focus our attention on the principles that govern docking, namely the algorithms used for searching and scoring, which are usually referred as the docking problem. We also focus our attention on the use of a flexible description of the proteins under study and the use of biological information as the localization of the hot spots, the important residues for protein,protein binding. The most common docking softwares are described too. © 2009 Wiley Periodicals, Inc. J Comput Chem, 2010 [source] Experimental and theoretical structural study of 2-pyridyl- and 4-hydroxyphenyl-1,4-dihydropyridine derivativesJOURNAL OF HETEROCYCLIC CHEMISTRY, Issue 6 2000Héctor Novoa De Armas A series of substituted 1,4-dihydropyridines (1,4-DHPs) has been synthesised following the well-known Hantzsch's procedure for symmetrical 1,4-DHP. The structures of these compounds have been thoroughly studied by X-ray crystallographic analysis and semiempirical (AMI) calculations. A good agreement is found between the theoretical and experimental results. In all cases, the most stable conformation fulfils all the requirements needed for exhibiting an antagonist calcium effect. [source] High-resolution H/D exchange studies on the HET-s218,295 prion proteinJOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 5 2005Alexis Nazabal Abstract In a search for improved resolution of hydrogen/deuterium (H/D) exchange experiments analyzed by mass spectrometry (HXMS), we evaluated two methodologies for a detailed structural study of solvent accessibility in the case of the HET-s218,295 prion protein. For the first approach, after incubation in the deuterated solvent, aggregated HET-s218,295 was digested with pepsin and the generated peptides were analyzed by nanospray mass spectrometry in an ion trap, with and without collision-induced dissociation (CID). We compared deuterium incorporation in peptides as determined on peptide pseudomolecular ions and on b and y fragments produced by longer peptides under CID conditions. For both b and y fragment ions, an extensive H/D scrambling phenomenon was observed, in contrast with previous studies comparing CID-MS experiments and 1H NMR data. Thus, the spatial resolution of HXMS experiments could not be improved by means of MS/MS data generated by an ion trap mass spectrometer. In a second approach, the incorporation of deuterium was analyzed by MS for 76 peptides of the HET-s218,289 peptide mass fingerprint, and the use of shared boundaries among peptic peptides allowed us to determine deuteration levels of small regions ranging from one to four amino acids. This methodology led to evidence of highly protected regions along the HET-s218,295 sequence. Copyright © 2005 John Wiley & Sons, Ltd. [source] Folding in solution of the C-catalytic protein fragment of angiotensin-converting enzymeJOURNAL OF PEPTIDE SCIENCE, Issue 8 2009Sotirios-Spyridon M. Vamvakas Abstract Angiotensin-converting enzyme (ACE) is a key molecule of the renin,angiotensin,aldosterone system which is responsible for the control of blood pressure. For over 30 years it has become the target for fighting off hypertension. Many inhibitors of the enzyme have been synthesized and used widely in medicine despite the lack of ACE structure. The last 5 years the crystal structure of ACE separate domains has been revealed, but in order to understand how the enzyme works it is necessary to study its structure in solution. We present here the cloning, overexpression in Escherichia coli, purification and structural study of the Ala959 to Ser1066 region (ACE_C) that corresponds to the C-catalytic domain of human somatic angiotensin-I-converting enzyme. ACE_C was purified under denatured conditions and the yield was 6 mg/l of culture. Circular dichroism (CD) spectroscopy indicated that 1,1,1-trifluoroethanol (TFE) is necessary for the correct folding of the protein fragment. The described procedure can be used for the production of an isotopically labelled ACE959,1066 protein fragment in order to study its structure in solution by NMR spectroscopy. Copyright © 2009 European Peptide Society and John Wiley & Sons, Ltd. [source] Solution structure of nociceptin peptidesJOURNAL OF PEPTIDE SCIENCE, Issue 9 2002Pietro Amodeo Abstract Peptides embedded in the sequence of pre-pro-nociceptin, i.e. nociceptin, nocistatin and orphanin FQ2, have shed light on the complexity of the mechanisms involving the peptide hormones related to pain and have opened up new perspectives for the clinical treatment of pain. The design of new ligands with high selectivity and bioavailability, in particular for ORL1, is important both for the elucidation and control of the physiological role of the receptor and for their therapeutic importance. The failure to obtain agonists and antagonists when using, for nociceptin, the same substitutions that are successful for opioids, and the conformational flexibility of them all, justify systematic efforts to study the solution conformation under conditions as close as possible to their natural environment. Structural studies of linear peptides in solution are hampered by their high flexibility. A direct structural study of the complex between a peptide and its receptor would overcome this difficulty, but such a study is not easy since opioid receptors are membrane proteins. Thus, conformational studies of lead peptides in solution are still important for drug design. This review deals with conformational studies of natural pre-nociceptin peptides in several solvents that mimic in part the different environments in which the peptides exert their action. None of the structural investigations yielded a completely reliable bioactive conformation, but the global conformation of the peptides in biomimetic environments can shed light on their interaction with receptors. Copyright © 2002 European Peptide Society and John Wiley & Sons, Ltd. [source] Probing the influence of stereoelectronic effects on lithium affinity in 1,3- and 1,4-dioxa systemsJOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 7 2001Bishwajit Ganguly Abstract A combined computational and structural study of the lithium affinity (LA) of O,C,O systems exhibiting the anomeric effect and of O, C,C,O systems exhibiting the gauche effect is presented. QM ab initio calculations using the MP2/6,31G* basis set were carried out on the gas-phase lithium affinities of dimethoxymethane (DMOM), dimethoxyethane (DMOE), 1,3-dioxane (DOX) and cis - and trans -tetraoxadecalin (TOD), along with that of dimethyl ether and of its dimer as reference compounds. Structural parameters were retrieved from the Cambridge Structural Database (CSD) for diethyl ether dimer and O,C,C,O lithium complexes and these agreed well with the calculated data. The computed lithium affinities of dimethoxymethane and dimethoxyethane were found to be conformationally dependent. The LAs are conformationally dependent (wherever applicable) and decrease in the order: (Me2O)2 >,DMOE >,DMOM >,DOD >,DOX >,trans -TOD, but cis -TOD restores the high LA (better than DMOE) by virtue of multiple coordination. Copyright © 2001 John Wiley & Sons, Ltd. [source] Synchrotron techniques for metalloproteins and human disease in post genome eraJOURNAL OF SYNCHROTRON RADIATION, Issue 1 2004S. Samar Hasnain Metalloproteins make up some 30% of proteins in known genomes. Metalloproteins are a special class of proteins that utilise the unique properties of metal atoms in conjunction with the macromolecular assembly to perform life-sustaining processes. A number of metalloproteins are known to be involved in many disease states including ageing processes. The incorporation of the metal ion is a very tightly regulated process that, in vivo, very often requires specific chaperons to deliver and help incorporate the metal atom in the macromolecule. The lack of or inappropriate incorporation of metals along with genetic factors can lead to the mis-function of these proteins leading to disease. The mis-functions due to genetic alterations that lead to diseases like ALS (amyotrophic lateral sclerosis or motor neuron disease) and Creutzfeld Jacob disease (CJD) are now well recognised. Synchrotron radiation sources provide a unique set of structural tools, which in combination can prove extremely powerful in providing a comprehensive picture of these complex biological systems. In particular for metalloproteins, the combined use of X-ray crystallography, X-ray solution scattering and X-ray spectroscopy (XAFS) is extremely useful. We are currently engaged in a structural study where our aim is to characterize structurally and functionally metalloproteins and then transfer this knowledge to afford the problem of the mis-function of metalloproteins that lead to these terminal illnesses, either due to a gain of function/property or a loss of function/property. In this context, the benefits of adopting the `philosophy' being developed for the structural genomics effort are highlighted. [source] Facile synthesis and characterization of star-shaped polystyrene: self-condensing atom transfer radical copolymerization of N -[4-(,-bromoisobutyryloxy)phenyl]maleimide and styrenePOLYMER INTERNATIONAL, Issue 10 2008Yun Cao Abstract BACKGROUND: Generation of stars around in situ formed cores provides a facile approach to star-shaped polymers. Therefore the self-condensing atom transfer radical copolymerization (SCATRCP) of N -[4-(,-bromoisobutyryloxy)phenyl]maleimide (BiBPM) and a large excess of styrene (St) was investigated. RESULTS: BiBPM and St formed a charge transfer complex (CTC), which underwent the SCATRCP, leading to the branched core initiating the atom transfer radical polymerization of St, finally giving star-shaped polystyrene (PS). Kinetic and structural study showed that a higher dosage of BiBPM resulted in an enhanced polymerization rate, a higher degree of branching and a larger number of short PS arms. Differential scanning calorimetry suggested that the glass transition temperature of the star-shaped PS decreased with molecular weight. Melt rheometry showed that even a slightly branched architecture of the PS led to a significantly lower viscosity; both the melt flow index and the activation energy increased with the degree of branching. CONCLUSION: Due to the preferential consumption of BiBPM and formation of a CTC, even a very low dosage of BiBPM could lead to star-shaped PS, which, in comparison with linear analogues, could possess much better melt fluidity. Copyright © 2008 Society of Chemical Industry [source] A conformational polymorphic transition in the high-temperature ,-form of chlorpropamide on cooling: a new ,,-formACTA CRYSTALLOGRAPHICA SECTION B, Issue 6 2009Tatiana N. Drebushchak Structural changes in the high-temperature ,-polymorph of chlorpropamide, 4-chloro- N -(propylaminocarbonyl)benzenesulfonamide, C10H13ClN2O3S, on cooling down to 100,K and on reverse heating were followed by single-crystal X-ray diffraction. At temperatures below 200,K the phase transition into a new polymorph (termed the ,,-form) has been observed for the first time. The polymorphic transition preserves the space group Pna21, is reversible and is accompanied by discontinuous changes in the cell volume and parameters, resulting from changes in molecular conformation. As shown by IR spectroscopy and X-ray powder diffraction, the phase transition in a powder sample is inhomogeneous throughout the bulk, and the two phases co-exist in a wide temperature range. The cell parameters and the molecular conformation in the new polymorph are close to those in the previously known ,-polymorph, but the packing of the z-shaped molecular ribbons linked by hydrogen bonds inherits that of the ,-form and is different from the packing in the ,-polymorph. A structural study of the ,-polymorph in the same temperature range has revealed no phase transitions. [source] Disorder in Ag7GeSe5I, a superionic conductor: temperature-dependent anharmonic structural studyACTA CRYSTALLOGRAPHICA SECTION B, Issue 1 2008Stéphanie Albert A temperature-dependent structural investigation of the substituted argyrodite Ag7GeSe5I has been carried out on a single crystal from 15 to 475,K, in steps of 50,K, and correlated to its conductivity properties. The argyrodite crystallizes in a cubic cell with the space group. The crystal structure exhibits high static and dynamic disorder which has been efficiently accounted for using a combination of (i) Gram,Charlier development of the Debye,Waller factors for iodine and silver, and (ii) a split-atom model for Ag+ ions. An increased delocalization of the mobile d10 Ag+ cations with temperature has been clearly shown by the inspection of the joint probability-density functions; the corresponding diffusion pathways have been determined. [source] Order,disorder transition in monoclinic sulfur: a precise structural study by high-resolution neutron powder diffraction.ACTA CRYSTALLOGRAPHICA SECTION B, Issue 5 2007Corrigendum Revised lattice parameters for Table 1 of the paper by David et al. (2006), Acta Cryst. B62, 953959, are given. [source] | ||||||||||||||||||||||||||||||||||