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X-ray Diffraction Data (x-ray + diffraction_data)
Kinds of X-ray Diffraction Data Terms modified by X-ray Diffraction Data Selected AbstractsDipole Moment Enhancement in Molecular Crystals from X-ray Diffraction DataCHEMPHYSCHEM, Issue 14 2007Mark A. Spackman Prof. Abstract Although reliable determination of the molecular dipole moment from experimental charge density analyses on molecular crystals is a challenging undertaking, these values are becoming increasingly common experimental results. We collate all known experimental determinations and use this database to identify broad trends in the dipole moment enhancements implied by these measurements as well as outliers for which enhancements are pronounced. Compelling evidence emerges that molecular dipole moments from X-ray diffraction data can provide a wealth of information on the change in the molecular charge distribution that results from crystal formation. Most importantly, these experiments are unrivalled in their potential to provide this information in such detail and deserve to be exploited to a much greater extent. The considerable number of experimental determinations now available has enabled us to pinpoint those studies that merit further attention, either because they point unequivocally to a considerable enhancement in the crystal (of 50,% or more), or because the experimental determinations suggest enhancements of 100,% or more,much larger than independent theoretical estimates. In both cases further detailed experimental and theoretical studies are indicated. [source] Crystal structure of a polar nematogen 4-(trans- 4-undecylcyclohexyl) isothiocyanatobenzeneCRYSTAL RESEARCH AND TECHNOLOGY, Issue 10 2007S. Biswas Abstract Crystal and molecular structures of a nematogenic compound 4-(trans- 4-undecylcyclohexyl) isothiocyanatobenzene (11CHBT) have been determined by direct methods using single crystal X-ray diffraction data. The compound (C24H37N1S1) crystallizes in the monoclinic system with the space group P21/c and Z = 4. The unit cell parameters are a = 5.5539(11) Å, b = 8.1341(10) Å, c = 51.494(5) Å, and (= 91.127(14)0. The structure was refined to Rw = 0.051. The molecule is found to be slightly bow-shaped though the alkyl chain is in all- trans conformation. The phenyl ring and the alkyl chain are planar and the cyclohexyl group is in chair conformation. The isothiocyanato groups are almost linear. Parallel imbricated mode of packing of the molecules is found in the crystalline state which is precursor to the nematic phase structure. There are many van der Waals' interactions particularly in the isothiocyanato benzene part of the molecule. Of the various associated pairs of molecules the one having anti-parallel configuration with overlaps in the isothiocyanato phenyl group probably exists in both the crystalline and the nematic phases. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Preparation and characterization of powders and crystals of Vn-xTixO2n-1 Magneli oxidesCRYSTAL RESEARCH AND TECHNOLOGY, Issue 10-11 2005D. Calestani Abstract Vn-xTixO2n-1 Magnéli phases have been synthesized under vacuum in powder form (n = 4, 0 , x , 0.4) and crystals (n = 4 and 5, x = 0.5 and 1.4, respectively), grown by chemical vapour transport in closed ampoules. TeCl4 and NH4Cl were used as transporting agents. Needle-shaped crystals as long as 200-300 micrometers or 2-3 mm were obtained when in presence of NH4Cl or TeCl4, respectively. The powder and crystal structures were examined by X-ray diffraction and the transport and magnetic characteristics were measured.. The powders resulted to be single-phase and the relevant composition was assumed to be equal to the nominal one. The overall stoichiometry of compounds, n, was determined from single crystal X-ray diffraction data. The Ti content, x, was deduced from the elementary cell volume, by applying the Végard law. Crystals were mainly untwinned and of good quality. The elementary cell of both, powders and crystals, was triclinic (P-1) and did not change with doping. DC electrical resistivity of the crystals was measured in a four-points (van der Pauw) configuration. DC magnetic susceptibility of the powders was measured in a SQUID magnetometer. The Ti doping was found to progressively smooth and finally to suppress the magnetic transitions occurring in the V4O7. The metal-insulator transitions observed in V4O7 and V5O9, at around 235 and 125 K respectively, were not observed in the doped crystals, thus indicating some significant change of the electronic structure of the V oxides. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Synthesis and Crystal Structure of Mercury-Substituted Type-I Clathrates A8Hg4Sn42 (A = K, Rb, Cs)EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 4 2008Andreas Kaltzoglou Abstract The mercury-substituted type-I clathrates A8Hg4Sn42,with A = K, Rb or Cs, were obtained by fusion of the pure elements at high temperatures. The crystal structures of the compounds were refined from single-crystal X-ray diffraction data. They crystallize in the space group Pmn (No. 223), Z = 1 with a = 12.1255(4) Å for K8Hg4Sn42 (1), a = 12.1838(4) Å for Rb8Hg4Sn42 (2) and a = 12.2130(4) Å for Cs8Hg4Sn42 (3). The 3D framework of four-bonded atoms defines two types of polyhedral cages of different size that are fully occupied by the alkali-metal atoms. All three compounds are considered as formally charge-balanced Zintl phases without any homogeneity range. Differential thermal analysis (DTA) indicates that the stability of the clathrates significantly depends on the size of the encaged cations. The thermal stability of the title compounds and the binary phases A8Sn44 (A = K, Rb, Cs) is discussed. Temperature-dependent magnetic measurements for compound 3 show also the expected diamagnetic behaviour. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source] Solid-State Photodimerization of Guest Molecules in Inclusion CompoundsEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 18 2006Irena Zouev Abstract Photochemical dimerization reactions of 1,3-diphenyl-1-propen-3-one (chalcone), 9-acetylanthracene, and 9-(methoxycarbonyl)anthracene as guest molecules in inclusion compounds with 1,1,6,6-tetraphenyl-2,4-hexadiyne-1,6-diol were studied. The irradiation of a single crystal containing chalcone was carried out in a single step and resulted in a single crystal containing the photodimer in full occupancy. In the case of the crystal containing 9-acetylanthracene, X-ray diffraction data were collected after irradiation for different periods of time. Only one of the two crystallographically independent pairs of 9-acetylanthracene underwent solid-state photodimerization at ca. 11,% conversion to the head-to-tail dimer. Photodimerization of the 9-(methoxycarbonyl)anthracene inclusion compound led, after irradiation for 2.5 h, to ca. 37,% conversion. It was found that the molecules that were arranged in stacks had undergone photodimerization in two different ways, so that on the average it looked as if all the guest molecules had polymerized. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] Syntheses, characterizations, and crystal structures of phosphonopeptidesHETEROATOM CHEMISTRY, Issue 1 2007Fang Hua ,-Aminophosphonic acids and their derivatives, as phosphorus analogs of amino acids, have attracted much attention as they show a range of biological activities. In this paper, dialkyl phenyl(4-pyridylcarbonylamino)methylphosphonates were synthesized via the Mannich reaction (Yuan et al., Synthesis 1990, 3, 256) and peptide coupling. Their structures were confirmed by elemental analysis, IR, 1H NMR, 13C NMR, and MS. X-ray diffraction data of compounds (2a, 2b, 2c) were reported respectively. The antibacterial and antitumor activities of these compounds are first reported in this paper. © 2007 Wiley Periodicals, Inc. Heteroatom Chem 18:9,15, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.20244 [source] Substituted 1,3,2,4-benzodithiadiazines: Novel derivatives, by-products, and intermediates,HETEROATOM CHEMISTRY, Issue 7 2001Alexander Yu. The synthesis of the title compounds 1 by 1:1 condensation of ArNSNSiMe3 2 with SCl2 followed by intramolecular ortho-cyclization of each [ArNSNSCl] intermediate is complicated by further reaction of 1 with SCl2 to give Herz salts 3. With the 2:SCl2 ratio of 2:1, the formation of by-products 3 is reduced and novel compounds 1 are accessible. With ortho-I containing starting material 2j, the parent compound 1s is obtained as the result of an unexpected I, not H, substitution. The rate of the 1 + SCl2 reaction depends upon a substituent's position, and the minor 8-R isomers 1l,p (R = Br, I) are isolated for the first time from mixtures with the major 6-R isomers due to reduced reactivity toward SCl2. The synthesized compounds 1,3 are characterized by multinuclear (including nitrogen) NMR and X-ray crystallography. According to the X-ray diffraction data, 1j (6-Br) and 1k (7-Br) derivatives are planar, whereas 1i (5-Br) and 1l (8-Br) are bent along the S1···N4 line by ,5° and ,4°, respectively, and the 1r (7-OCH3) derivative is planar in contrast to the known 5-OCH3 isomer, which possesses a significantly folded heterocycle. The distortion of the planar geometry of some compounds 1 is interpreted in terms of a pseudo-Jahn-Teller effect as the result of ,-highest occupied molecular orbital (HOMO) ,*-(LUMO) lowest unoccupied molecular orbital + 1 mixing in a planar conformation. The 2p compound is the first structurally defined Ar,N = S = N,SiMe3 azathiene. The compound Ar,N = S = N,S,NH-Ar 6 modeling the aforementioned intermediate has been isolated and structurally characterized. We describe the attempts to synthesize compounds 1 from 2-aminobenzenethiols and (SN)4 and from salts 3 and Me3SiN3, and we discuss the reaction pathways. © 2001 John Wiley & Sons, Inc. Heteroatom Chem 12:563,576, 2001 [source] A discrete tomography algorithm for improving the quality of three-dimensional X-ray diffraction grain mapsJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 4 2006A. Alpers A discrete tomography algorithm is presented for the reconstruction of grain maps based on X-ray diffraction data. This is the first algorithm for this task, inherently exploiting the discrete structure of grain maps. Gibbs potentials serve to characterize the statistics of the local morphology of the grain boundaries. A Monte Carlo based algorithm is applied as a restoration method for improving the quality of grain maps produced by a classical (non-discrete) tomography algorithm (ART). The quality of the restored maps is demonstrated and quantified by simulation studies. The robustness of the algorithm with respect to the choice of Gibbs potentials is investigated. [source] A simple and low-cost solution for the automation of X-ray powder diffractometers with chart recorder outputJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 4 2006M. Jayaprakasan X-ray powder diffraction is an established method for the qualitative identification of crystalline materials and their quantitative analysis. The new generation of X-ray diffraction systems are based on expensive digital/embedded control technology and computer interfaces. Yet many laboratories use conventional manual-controlled systems with XY strip-chart recorders. Since the output spectrum is a strip chart (hard copy), raw data, essential for structural and qualitative analysis, are not readily available for further analysis. Upgrading to modern computerized diffractometers is very expensive. The proposed automation design described here is intended to enable the conventional diffractometer user to collect, store and analyze data quickly. The design also improves the resolution by five times compared with the conventional setup. For the automation, a PC add-on card has been designed to control and collect the timing and intensity counts from the conventional X-ray diffractometer, and suitable software has been developed to collect, process and present the X-ray diffraction data for both qualitative and quantitative analysis. Moreover, a major advantage of this design is that it does not warrant any physical modification of the hardware of the conventional setup; it is simply an extension to enhance the performance of collecting raw data with a higher resolution at desired intervals/timings. [source] Microradian X-ray diffraction in colloidal photonic crystalsJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 2 2006J. H. J. Thijssen Ultra-high-resolution small-angle X-ray scattering in various colloidal photonic crystals is reported. It is demonstrated that an angular resolution of about two microradians is readily achievable at a third-generation synchrotron source using compound refractive optics. The scheme allows fast acquisition of two-dimensional X-ray diffraction data and can be realised at sample,detector separations of only a few metres. As a result, diffraction measurements in colloidal crystals with interplanar spacings larger than a micrometre, as well as determination of the range of various order parameters from the width of the Bragg peaks, are made possible. [source] Structural redetermination, thermal expansion and refractive indices of KLu(WO4)2JOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 2 2006M. C. Pujol The crystal structure of monoclinic KLu(WO4)2 (KLuW) crystals was determined at room temperature by using single-crystal X-ray diffraction data. The unit-cell parameters were a = 10.576,(7), b = 10.214,(7), c = 7.487,(2),Å, , = 130.68,(4)°, with Z = 4, in space group C2/c. The unit-cell parameters of KLu1,xYbx(WO4)2 were determined in relation to Yb concentration. Vickers micro-indentations were used to study the microhardness of KLuW. The linear thermal expansion tensor was determined and the principal axis with maximum thermal expansion ( = 16.72 × 10,6,K,1), , was located 13.51° from the c axis. The room-temperature optical tensor was studied in the near-infrared (NIR) and visible range. The principal optical axis with maximum refractive index (ng = 2.113), Ng, was located 18.5° from the c axis at 632.8,nm. Undoped and ytterbium-doped KLuW crystals were grown by the TSSG (top-seeded-solution growth) slow-cooling method. The crystals show {110}, {}, {010} and {310} faces that basically constitue the habit of the KLuW crystals. [source] Cationic disorder, microstructure and dielectric response of ferroelectric SBT ceramicsJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 3-2 2003Ch. Muller Polycrystalline samples of SrBi2Ta2O9 (acronym SBT) have been prepared by means of solid-state reaction either using a classical route or by mechanochemical activation. For each compound, a structural analysis of the ferroelectric orthorhombic phase (space group A21am) has been performed from the fitting of neutron and/or X-ray powder diffraction data using the Rietveld method. A cationic disorder on Bi3+ and Sr2+ crystallographic sites has been revealed, the Sr atoms occupying the Bi sites and vice versa. From diffraction peak broadening analyses of high-resolution synchrotron X-ray diffraction data, it has been shown that the two grinding methods (manual or mechanical) induce local strains, the average apparent strain being three times larger for the mechanically ground sample. In order to link microstructure and ferroelectric properties, the dielectric constant has been measured as a function of the temperature. It appears that the position and the shape of the dielectric anomaly strongly depend upon the composition and the route used to elaborate the powders. More exactly, for the mechanically ground powder, the large apparent strain, probably correlated to the strong cation exchange revealed by the structural refinement, leads to a significantly enhanced dielectric response. [source] Structure, crystal growth and physical anisotropy of KYb(WO4)2, a new laser matrixJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 1 2002M. C. Pujol The crystal structure of monoclinic KYb(WO4)2 (KYbW) crystals has been refined (in space group C2/c) at room temperature by using single-crystal X-ray diffraction data. KYbW undoped crystals were grown by the TSSG (top-seeded-solution growth) slow-cooling method. The crystals show {110}, {11}, {010} and {310} faces, which basically define their habit. The linear thermal expansion tensor has been determined and the principal axis with maximum thermal expansion ( = 16.68 × 10,6,K,1), , was located 12° from the c axis. Its principal , and axes are [302], [010] and [106] directions, respectively, in the crystallographic system. The optical tensor has been studied at , = 632.8,nm at room temperature; two principal axes, Ng and Nm, are located in the ac plane, while the other, Np, is parallel to [010]. The principal axis with maximum refractive index (ng = 2.45), Ng, was located 19° from the c axis. [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] Corrections for surface X-ray diffraction measurements using the Z -axis geometry: finite size effects in direct and reciprocal spaceJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 4 2000O. Robach X-ray diffraction data have to be corrected by geometrical correction factors prior to any quantitative analysis. Here the case of grazing incidence X-ray diffraction measurements is considered, including the case of high exit angles. First, an approach taking into account the evolution of the diffracting area during an , scan is presented. From the calculation of the effective part of the sample surface that participates in the diffraction phenomena at each step of the scan, a more accurate correction factor than those commonly used is derived and the evolution of the line shape along a zero-width rod is explained. Secondly, the case of finite-width rods, under the point-like sample approximation, is considered: the influence of the partial integration, as a result of the detector in-plane acceptance, of a rod with an anisotropic in-plane shape, is studied and leads to an analytical expression for the corresponding correction factor. Finally, a full numerical simulation is presented, which provides an alternative method for correcting the experimental intensities and shows in which conditions the previous formulae are no longer valid. [source] Wave functions derived from experiment.JOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 4 2003Abstract The constrained Hartree,Fock method using experimental X-ray diffraction data is extended and applied to the case of noncentrosymmetric molecular crystals. A new way to estimate the errors in derived properties as a derivative with respect to added Gaussian noise is also described. Three molecular crystals are examined: ammonia [NH3], urea [CO(NH2)2], and alloxan [(CO)4(NH)2]. The energetic and electrical properties of these molecules in the crystalline state are presented. In all cases, an enhancement of the dipole moment is observed upon application of the experimental constraint. It is found that the phases of the structure factors are robustly determined by the constrained Hartree,Fock model, even in the presence of simulated noise. Plots of the electron density, electrostatic potential, and the electron localization function for the molecules in the crystal are displayed. In general, relative to the Hartree,Fock model, there is a depletion of charge around hydrogen atoms and lone pair regions, and a build-up of charge within the molecular framework near nuclei, directed along the bonds. The electron localization function plots reveal an increase in the pair density between vicinal hydrogen atoms. © 2003 Wiley Periodicals, Inc. J Comput Chem 24: 470,483, 2003 [source] Properties of Arrowroot Starch Treated with Aqueous HCl at Ambient TemperatureJOURNAL OF FOOD SCIENCE, Issue 1 2002J.K. John Arrowroot starch was acid-treated using 2.2 M HCl at 29 to 30° C for durations of 0 to 72 h, and properties of the control and modified samples were compared. Increasing length of acid treatment produced a progressive decline in amylose blue value, intrinsic viscosity, and swelling power, as well as an increase in free sugars and solubility. Differential scanning calorimetry (DSC) studies highlighted changes effected by acid-treatment in the gelatinization behavior of the starch samples. Gel permeation chromatography (GPC) studies on 32- and 72-h acid-treated samples indicated a greater proportion of dextrins with a higher percentage of reducing sugars, compared to the control. While X-ray diffraction data suggested minor changes in the crystal phase impacted by acid-treatment, in vitro digestibility of both control and acid-treated samples did not show any appreciable change in overall patterns. [source] Synthesis and structure of new 5-(arylidene)-3-(4-methylbenzoyl)thiazolidine-2,4-dionesJOURNAL OF HETEROCYCLIC CHEMISTRY, Issue 1 2010Katarina M. Popov-Pergal The derivatives of 5-substituted-2,4-thiazolidinedione have a broad spectrum of biological activities. In this article, new 5-(arylidene)-3-(4-methylbenzoyl)thiayolidine-2,4-diones 3a,k, with arylidene groups such as 4-phenylbenzylidene 3a, 3,4-dimethoxybenzylidene 3b, 2-hydroxybenzylidene 3c, 4-ethoxybenzylidene 3d, 5-methyl-2-furfurylidene 3e, 4-dimethylaminobenzylidene 3f, 1-naphthylidene 3g, 3,4-methylenedioxybenzylidene 3h, 4-benzyloxybenzylidene 3i, benzylidene 3j, and 4-methoxybenzylidene 3k, were synthesized by direct acylation of alkali metal salts of 5-arylidene-2,4-thiazolidinediones with 4-methylbenzoylchloride. Their structures were confirmed by elemental analysis, IR, 1H NMR and MS spectroscopy. In addition, crystal structure of the compound 3d was determined using single-crystal X-ray diffraction data. J. Heterocyclic Chem., 2010. [source] Comparison of the three-dimensional structures of a human Bence-Jones dimer crystallized on Earth and aboard US Space Shuttle Mission STS-95,JOURNAL OF MOLECULAR RECOGNITION, Issue 2 2003Simon S. Terzyan Abstract Crystals of a human (Sea) Bence-Jones dimer were produced in a capillary by vapor diffusion under microgravity conditions in the 9 day US Space Shuttle Mission STS-95. In comparison to ground-based experiments, nucleation was facile and spontaneous in space. Appearance of a very large (8,×,1.6,×,1.0,mm) crystal in a short time period is a strong endorsement for the use of microgravity to produce crystals sufficiently large for neutron diffraction studies. The Sea dimer crystallized in the orthorhombic space group P212121, with a,=,48.9,Å, b,=,85.2,Å, and c,=,114.0,Å. The crystals grown in microgravity exhibited significantly lower mosaicities than those of ground-based crystals and the X-ray diffraction data had a lower overall B factor. Three-dimensional structures determined by X-ray analysis at two temperatures (100 and 293,K) were indistinguishable from those obtained from ground-based crystals. However, both the crystallographic R factor and the free R factor were slightly lower in the models derived from crystals produced in microgravity. The major difference between the two crystal growth systems is a lack of convection and sedimentation in a microgravity environment. This environment resulted in the growth of much larger, higher-quality crystals of the Sea Bence-Jones protein. Structurally, heretofore unrecognized grooves on the external surfaces of the Sea and other immunoglobulin-derived fragments are regular features and may offer supplementary binding regions for super antigens and other elongated ligands in the bloodstream and perivascular tissues. Copyright © 2003 John Wiley & Sons, Ltd. [source] Synthesis and preliminary characterization of sulfamethazine-theophylline co-crystalJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 9 2010Jie Lu Abstract Co-crystals containing active pharmaceutical ingredients (APIs) represent a new type of pharmaceutical materials. In this work, sulfamethazine (STH) and theophylline (TP) were employed as the co-crystal formers. Neat cogrinding, solvent-drop cogrinding and slow evaporation were applied to synthesize the sulfamethazine,theophylline co-crystal (hereafter STH,TP co-crystal). The co-crystalline phase was characterized by DSC, TGA, Raman, PXRD, and dynamic vapor sorption (DVS) techniques. The STH,TP co-crystal structure was determined from single crystal X-ray diffraction data. The results show that, the STH,TP co-crystal, obtained in a 2:1 molar ratio of sulfamethazine and theophylline only by slow evaporation, possesses unique thermal, spectroscopic, and X-ray diffraction properties. Besides, in the STH,TP co-crystal, the sulfamethazine molecules form a dimer through the intermolecular hydrogen bonding (O ··· H N), and two intermolecular hydrogen bonds (O ··· H N and N ··· H N) keep the theophylline attached the dimer. © 2010 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 99:4042,4047, 2010 [source] Crystal structure prediction for eniluracilJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 8 2001Mark Sacchetti Abstract State-of-the-art molecular modeling tools were used to predict the crystal structure of eniluracil, a compound for which it has not been possible to grow a single crystal. Two methods were used, one that incorporates molecular structure and powder X-ray diffraction data and another that employs molecular structure and lattice energy calculations into the search algorithm. Two structures were identified, one with P21/c and the other with P21 symmetry, both of which are consistent with the infrared and Raman spectra. A detailed analysis of the simulated and experimental powder X-ray diffraction patterns indicates that the P21/c structure is the best representation of the crystal structure. © 2001 Wiley-Liss, Inc. and the American Pharmaceutical Association J Pharm Sci 90:1049,1055, 2001 [source] Comparison of the organometallic copolymerizations of thiophene with 4-alkylthiazole and 3-alkylthiophene: The control of regioregularity in the copolymerization with 4-alkylthiazoleJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 10 2003Takakazu Yamamoto New ,-conjugated copolymers consisting of thiophene and thiazole units have been synthesized by organometallic polycondensation. The obtained polymers are thought to have a regioregular structure on the basis of their 1H NMR and X-ray diffraction data. [source] Organic cyclic difluoramino-nitramines: infrared and Raman spectroscopy of 3,3,7,7-tetrakis(difluoramino)octahydro 1,5-dinitro-1,5-diazocine (HNFX)JOURNAL OF RAMAN SPECTROSCOPY, Issue 8 2009Philippe F. Weck Abstract We present the first vibrational structure investigation of 3,3,7,7-tetrakis(difluoramino)octahydro-1,5-dinitro- 1,5-diazocine (HNFX),and, more generally, of a member of the new class of gem -bis(difluoramino)-substituted heterocyclic nitramine energetic materials,using combined theoretical and experimental approaches. Optimized molecular structure and vibrational spectra of the Ci, symmetry conformer constituting the HNFX crystal were computed using density functional theory methods. Fourier transform infrared and Raman spectra of HNFX crystalline samples were also collected at ambient temperature and pressure. The average deviation of calculated structural parameters from X-ray diffraction data is ,1% at the B3LYP/6-311 + + G(d,p) level of theory, suggesting the absence of significant molecular distortion induced by the crystal field. Very good agreement was found between simulated and measured spectra, allowing reliable assignment of the fundamental normal modes of vibration of the HNFX crystal. Detailed analysis of the normal modes of the C,(NF2)2 and N,NO2 moieties was performed due to their critical importance in the initial steps of the molecular homolytic fragmentation process. Copyright © 2009 John Wiley & Sons, Ltd. [source] Synthesis and Characterization of Silver Nanoparticles and Titanium Oxide Nanofibers: Toward Multifibrous NanocompositesJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 9 2010Fredrick O. Ochanda A new method was investigated to produce new multiscale fibrous nanocomposites comprised of titanium oxide (TiO2) nanofibers and silver (Ag) nanoparticles (NPs). The process involved electrospinning TiO2 precursor solution containing colloidal solution of Ag NPs, and organic solvent (dimethyl- n,n -formamide) to fabricate a porous, nonwoven, free-standing nanofiber mesh. Postprocess heating of the electrospun nanofibers entailed calcination in air environment at 500°C for 3 h. Microemulsion processing was used to generate NPs of Ag in a monodispersed distribution throughout the colloidal solution. X-ray diffraction data were consistent with the anatase phase of TiO2, while transmission electron microscopy and hydrogen desorption measurements revealed a very porous microstructure. It was demonstrated that NP colloidal stability is solvent dependent. It is anticipated that incorporation of metal particles in nanofibers will lead to enhanced photocurrent generation, when used in functional devices. [source] Physical and Electrical Properties of Nanosized Mn- and Cr-Doped Strontium Y-Type Hexagonal FerritesJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 2 2010Muhammad Javed Iqbal Nanometer-sized crystallites of Y-type strontium hexaferrite, Sr2Ni2Fe12O22 and its Mn- and Cr-doped derivatives have been synthesized by the sol,gel method. Y-type phase formation was achieved at a considerably lower temperature of 950°C than is required in the traditional solid-state method (1200°C). The effect of doping of manganese at the tetrahedral site, Sr2Ni2,xMnx Fe12O22 (x=0.0,2.0), and chromium at octahedral site, Sr2Ni2 Fe12,yCryO22 (y=0.0,1.5), has been studied. The crystal structure remains unaffected by the substitutions. The crystallite size in the range of 13,45 nm is calculated from the X-ray diffraction data. The energy-dispersive X-ray fluorescence analysis shows that Y-type hexaferrites can be prepared with a base of strontium. The extent of doped Cr+3 ions at the octahedral site has been increased from the reported maximum value of y=1.5. Scanning electron micrographs of the samples showed a homogenous microstructure. The dc electrical resistivity studies show that these hexaferrites exhibit high resistivity at room temperature. Cr-doped samples have comparatively higher resistivity than Mn-doped samples. The doubly doped (Cr+Mn) samples possess high resistivity (7.37 × 109,-cm), a low dielectric constant (33.88 at 3000 Hz), and a high Curie temperature (>698 K). The dielectric energy losses are minimized by increasing the Mn and Cr contents of the synthesized samples. [source] Polymorphic behavior of nylon 6/saponite and nylon 6/montmorillonite nanocompositesPOLYMER ENGINEERING & SCIENCE, Issue 6 2002Tzong-Ming Wu X-ray diffraction methods and DSC thermal analysis have been used to investigate the structural change of nylon 6/clay nanocomposites. Nylon 6/clay has prepared by the intercalation of ,-caprolactam and then exfoliaton of the layered saponite or montmorillonite by subsequent polymerization. Both X-ray diffraction data and DSC results indicate the presence of polymorphism in nylon 6 and in nylon 6/clay nanocomposites. This polymorphic behavior is dependent on the cooling rate of nylon 6/clay nanocomposites from melt and the content of saponite or montmorillonite in nylon 6/clay nanocomposites. The quenching from the melt induces the crystallization into the , crystalline form. The addition of clay increases the crystallization rate of the , crystalline form at lower saponite content and promotes the heterophase nucleation of , crystalline form at higher saponite or montmorillonite content. The effect of thermal treatment on the crystalline structure of nylon 6/clay nanocomposites in the range between Tg and Tm is also discussed. [source] Diffractive imaging for periodic samples: retrieving one-dimensional concentration profiles across microfluidic channelsACTA CRYSTALLOGRAPHICA SECTION A, Issue 4 2007Oliver Bunk A technique has been developed that allows determination of the concentration profiles of colloidal solutions or any kind of fluid under confinement. Currently, submicrometre-wide channels are sampled with a resolution in the 10,nm range. The method comprises regular arrays of microfluidic channels and one-dimensional X-ray phase-retrieval techniques for the analysis of small-angle X-ray diffraction from the array structures. Recording the X-ray diffraction data requires a low dose on each individual channel since the sum of the signals from all channels is detected. The determined concentration profiles represent the ensemble average rather than individual entities and are obtained in a model-independent way. As an example, amplitude and phase of the exit field and concentration profiles for a colloidal fluid within confining channels of different widths are shown. [source] On the application of an experimental multipolar pseudo-atom library for accurate refinement of small-molecule and protein crystal structuresACTA CRYSTALLOGRAPHICA SECTION A, Issue 2 2007Bartosz Zarychta With an increasing number of biomacromolecular crystal structures being measured to ultra-high resolution, it has become possible to extend to large systems experimental charge-density methods that are usually applied to small molecules. A library has been built of average multipole populations describing the electron density of chemical groups in all 20 amino acids found in proteins. The library uses the Hansen & Coppens multipolar pseudo-atom model to derive molecular electron density and electrostatic potential distributions. The library values are obtained from several small peptide or amino acid crystal structures refined against ultra-high-resolution X-ray diffraction data. The library transfer is applied automatically in the MoPro software suite to peptide and protein structures measured at atomic resolution. The transferred multipolar parameters are kept fixed while the positional and thermal parameters are refined. This enables a proper deconvolution of thermal motion and valence-electron-density redistributions, even when the diffraction data do not extend to subatomic resolution. The use of the experimental library multipolar atom model (ELMAM) also has a major impact on crystallographic structure modelling in the case of small-molecule crystals at atomic resolution. Compared to a spherical-atom model, the library transfer results in a more accurate crystal structure, notably in terms of thermal displacement parameters and bond distances involving H atoms. Upon transfer, crystallographic statistics of fit are improved, particularly free R factors, and residual electron-density maps are cleaner. [source] Reconstruction of a yeast cell from X-ray diffraction dataACTA CRYSTALLOGRAPHICA SECTION A, Issue 4 2006Pierre Thibault Details are provided of the algorithm used for the reconstruction of yeast cell images in the recent demonstration of diffraction microscopy by Shapiro, Thibault, Beetz, Elser, Howells, Jacobsen, Kirz, Lima, Miao, Nieman & Sayre [Proc. Natl Acad. Sci. USA (2005), 102, 15343,15346]. Two refinements of the iterative constraint-based scheme are developed to address the current experimental realities of this imaging technique, which include missing central data and noise. A constrained power operator is defined whose eigenmodes allow the identification of a small number of degrees of freedom in the reconstruction that are negligibly constrained as a result of the missing data. To achieve reproducibility in the algorithm's output, a special intervention is required for these modes. Weak incompatibility of the constraints caused by noise in both direct and Fourier space leads to residual phase fluctuations. This problem is addressed by supplementing the algorithm with an averaging method. The effect of averaging may be interpreted in terms of an effective modulation transfer function, as used in optics, to quantify the resolution. The reconstruction details are prefaced with simulations of wave propagation through a model yeast cell. These show that the yeast cell is a strong-phase-contrast object for the conditions in the experiment. [source] Determination of depth-dependent diffraction data: a new approachACTA CRYSTALLOGRAPHICA SECTION A, Issue 1 2005A. Broadhurst A direct method for determining powder diffraction data at specific depths from angle-dependent diffraction data is described. The method is non-destructive and only traditional data collections, where the angle of incidence is varied, are required. These angle-dependent spectra are transformed to give diffraction data arising from different depths, which may then be exploited using any conventional method. This is a novel approach as traditional methods are forced to tolerate the inherent depth averaging of grazing-angle diffraction, or only examine specific structural characteristics. In order to obtain depth-dependent X-ray diffraction data, a Fredholm integral equation of the first kind is solved using regularization techniques. The method has been validated by the generation of pseudo-experimental data having known depth profiles and solving the Fredholm integral equation to recover the solution. The method has also been applied to experimental data from a number of thin film systems. [source] | ||||||||||||||||||||||||||||