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Quality Crystals (quality + crystal)
Selected AbstractsCombined effects of crucible geometry and Marangoni convection on silicon Czochralski crystal growthCRYSTAL RESEARCH AND TECHNOLOGY, Issue 8 2009F. Mokhtari Abstract In order to understand the influence of crucible geometry combined with natural convection and Marangoni convection on melt flow pattern, temperature and pressure fields in silicon Czochralski crystal growth process, a set of numerical simulations was conducted. We carry out calculation enable us to determine temperature, pressure and velocity fields in function of Grashof and Marangoni numbers. The essential results show that the hemispherical geometry of crucible seems to be adapted for the growth of a good quality crystal and the pressure field is strongly affected by natural and Marangoni convection and it is more sensitive than temperature. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Growth and characterization of semiorganic NLO crystals of LAHClBrCRYSTAL RESEARCH AND TECHNOLOGY, Issue 12 2006P. C. Thomas Abstract Single crystals of non-linear optical (NLO) LAHClBr were grown by slow evaporation technique from its aqueous solution. Good optical quality crystals having dimensions up to 12 × 9 × 7 mm3 were obtained. The lattice parameters and morphology for the grown crystals were determined using single crystal XRD. The crystals were characterized by FT-Raman, optical absorption, thermal (DTA and TGA) and dielectric studies. LAHClBr was found to be thermally stable up to 124.3°C. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Synthesis and characterization of 4,4,-dihydroxy-,-methylstilbene crystalCRYSTAL RESEARCH AND TECHNOLOGY, Issue 7 2006K. Rameshbabu Abstract 4,4,-dihydroxy-,-methylstilbene (DHAMS) was synthesized by condensation reaction with chloroacetone and phenol in the presence of concentrated sulfuric acid, and has been successfully grown by solution growth technique. This is the first report in the literature on the crystallization of DHAMS and exhibited the birefringent melt (liquid crystal property) of the optical properties. FTIR and FTNMR studies are in accordance with the structure. Good quality crystals were grown by slow evaporation technique by acetone as solvent. A transmission spectrum of the crystal was obtained in the region of 285 nm. The structural and optical properties were studied. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Recent developments in modelling of liquid phase electroepitaxy under applied magnetic fieldCRYSTAL RESEARCH AND TECHNOLOGY, Issue 4-5 2005S. Dost Abstract Growth of single crystals under magnetic field is of interest for suppressing the adverse effect of natural convection and for better mixing in the liquid solution, which are the favorable conditions for prolonged growth and high quality crystals. In this short review article, recent developments in the modelling of electroepitaxy under magnetic field are presented. An application is given for the liquid phase electroepitaxial growth of GaAs bulk single crystals under a static magnetic field. Experimental results, that have shown that the growth rate under an applied static magnetic field is proportional to the applied magnetic field, and increases with the field intensity level, are predicted from the present model. The model also predicts growth interface shapes accurately. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] A synergistic approach to protein crystallization: Combination of a fixed-arm carrier with surface entropy reductionPROTEIN SCIENCE, Issue 5 2010Andrea F. Moon Abstract Protein crystallographers are often confronted with recalcitrant proteins not readily crystallizable, or which crystallize in problematic forms. A variety of techniques have been used to surmount such obstacles: crystallization using carrier proteins or antibody complexes, chemical modification, surface entropy reduction, proteolytic digestion, and additive screening. Here we present a synergistic approach for successful crystallization of proteins that do not form diffraction quality crystals using conventional methods. This approach combines favorable aspects of carrier-driven crystallization with surface entropy reduction. We have generated a series of maltose binding protein (MBP) fusion constructs containing different surface mutations designed to reduce surface entropy and encourage crystal lattice formation. The MBP advantageously increases protein expression and solubility, and provides a streamlined purification protocol. Using this technique, we have successfully solved the structures of three unrelated proteins that were previously unattainable. This crystallization technique represents a valuable rescue strategy for protein structure solution when conventional methods fail. [source] l -2-Aminobutyric acid: two fully ordered polymorphs with Z, = 4ACTA CRYSTALLOGRAPHICA SECTION B, Issue 2 2010Carl Henrik Görbitz The crystal structure of l -2-aminobutyric acid, an l -alanine analogue with an ethyl rather than a methyl side chain, has proved elusive owing to problems growing diffraction quality crystals. Good diffraction data have now been obtained for two polymorphs, in space groups P21 and I2, revealing surprisingly complex, yet fully ordered crystalline arrangements with Z, = 4. The closely related structures are divided into hydrophilic and hydrophobic layers, the latter being the thinnest ever found for an amino acid (other than ,-glycine). The hydrophobic layers furthermore contain conspicuous pseudo-centers-of-symmetry, leading to overall centrosymmetric intensity statistics. Uniquely, the four molecules in the asymmetric unit can be divided into two pairs that each forms an independent hydrogen-bond network. [source] Development of an automated large-scale protein-crystallization and monitoring system for high-throughput protein-structure analysesACTA CRYSTALLOGRAPHICA SECTION D, Issue 9 2006Masahiko Hiraki Protein crystallization remains one of the bottlenecks in crystallographic analysis of macromolecules. An automated large-scale protein-crystallization system named PXS has been developed consisting of the following subsystems, which proceed in parallel under unified control software: dispensing precipitants and protein solutions, sealing crystallization plates, carrying robot, incubators, observation system and image-storage server. A sitting-drop crystallization plate specialized for PXS has also been designed and developed. PXS can set up 7680 drops for vapour diffusion per hour, which includes time for replenishing supplies such as disposable tips and crystallization plates. Images of the crystallization drops are automatically recorded according to a preprogrammed schedule and can be viewed by users remotely using web-based browser software. A number of protein crystals were successfully produced and several protein structures could be determined directly from crystals grown by PXS. In other cases, X-ray quality crystals were obtained by further optimization by manual screening based on the conditions found by PXS. [source] Reproducible growth of well diffracting ribosomal crystalsACTA CRYSTALLOGRAPHICA SECTION D, Issue 6 2005Tamar Auerbach-Nevo The crystallization of ribosomal particles is associated with extraordinary challenging demands. This originates mainly from the ribosome's natural tendency to deteriorate and from its multi-conformational heterogeneity, both of which stem from its functional flexibility. To increase the level of homogeneity of ribosomal preparations, systematic searches for conditions yielding populations of fully defined chemical compositions were employed and the variables essential for high functional activity were analyzed and optimized. These include temperature, cell-growth duration and media, the cell-harvesting stage, ribosomal purification and storage. The functional state that is most suitable to yield quality crystals was identified as that of the polysome and it was found that this fraction reproducibly yielded crystals of superior properties. [source] How the CO in myoglobin acquired its bend: lessons in interpretation of crystallographic dataACTA CRYSTALLOGRAPHICA SECTION D, Issue 5 2001Boguslaw Stec Contrary to the expectation of chemists, the first X-ray structures of carbon monoxide bound to myoglobin (Mb) showed a highly distorted Fe,C,O bond system. These results appeared to support the idea of a largely steric mechanism for discrimination by the protein against CO binding, a lethal act for the protein in terms of its physiological function. The most recent independently determined high-resolution structures of Mb,CO have allowed the 25,year old controversy concerning the mode of CO binding to be resolved. The CO is now seen to bind in a roughly linear fashion without substantial bending, consistent with chemical expectations and spectroscopic measurements. Access to deposited diffraction data prompted a reevaluation of the sources of the original misinterpretation. A series of careful refinements of models against the data at high (1.1,Å) and modest resolutions (1.5,Å) have been performed in anisotropic versus isotropic modes. The results suggest that the original artifact was a result of lower quality crystals combined with anisotropic motion and limited resolution of the diffraction data sets. This retrospective analysis should serve as a caution for all researchers using structural tools to draw far-reaching biochemical conclusions. [source] Crystallization and preliminary X-ray analysis of the matrix protein from Ebola virusACTA CRYSTALLOGRAPHICA SECTION D, Issue 6 2000Andréa Dessen The matrix protein from Ebola virus is a membrane-associated molecule that plays a role in viral budding. Despite its functional similarity to other viral matrix proteins, it displays no sequence similarity and hence may have a distinct fold. X-ray diffraction quality crystals of the Ebola VP40 matrix protein were grown by the hanging-drop vapour-diffusion method. The crystals belong to the monoclinic space group C2, with unit-cell parameters a = 64.4, b = 91.1, c = 47.9,Å, , = 96.3°. A data set to 1.9,Å resolution has been collected using synchrotron radiation. The unit cell contains one molecule of molecular weight 35,kDa per asymmetric unit, with a corresponding volume solvent content of 35%. [source] Improved crystals of Thermus thermophilus prolyl-tRNA synthetase complexed with cognate tRNA obtained by crystallization from precipitateACTA CRYSTALLOGRAPHICA SECTION D, Issue 2 2000Anna Yaremchuk The complex between Thermus thermophilus prolyl-tRNA synthetase (ProRSTT) and its cognate tRNA has been crystallized using two different isoacceptors of tRNAPro. Similar bipyramidal crystals of the complexes of ProRSTT with the two different tRNAPro isoacceptors grow within two weeks from 32% saturated ammonium sulfate solution. They belong to space group P43212, with unit-cell parameters a = 143.1, b = 143.1, c = 228.6,Å. The crystals diffract weakly to a maximum resolution of 3.1,Å. Superior quality crystals were obtained by growing slowly from precipitate over 5,6 months. These are of the same space group but have slightly altered unit-cell parameters, a = 140.8, b = 140.8, c = 237.0,Å. These crystals diffract more strongly to at least 2.8,Å resolution and a complete data set to 2.85,Å resolution has been collected from a single crystal. Comparison of the packing in the two crystal forms shows that domain flexibility contributes to the presence of different crystal contacts in the two forms. [source] Laser-improved protein crystallization screeningACTA CRYSTALLOGRAPHICA SECTION F (ELECTRONIC), Issue 8 2010Neela Yennawar Screening of proteins for crystallization under laser irradiation was investigated using six proteins: ribonuclease B, glucose dehydrogenase, lysozyme, sorbitol dehydrogenase, fructose dehydrogenase and myoglobin. Shining 532,nm green circularly polarized laser light with a picosecond pulse and 6,mW power for 30,s on newly set-up protein drops showed a marked improvement in the number of screen conditions amenable for crystal growth compared with control drops under identical conditions but without laser exposure. For glucose dehydrogenase and sorbitol dehydrogenase, larger and better quality crystals were formed and the resolution of X-ray diffraction was improved. The speed of crystallization increased in the case of ribonuclease B, lysozyme and sorbitol dehydrogenase. During laser irradiation, the amount of precipitation in the screened drops increased, indicating a transient decrease in protein solubility. At the optimized laser settings, there was no deleterious effect of the laser on crystal growth or on the protein. In the cases of ribonuclease B and lysozyme the crystal packing did not change owing to the laser exposure. [source] Ring-Borylated 15-Electron and 17-Electron ansa -Chromocene Complexes, their Physical Properties and Molecular StructuresCHEMISTRY - A EUROPEAN JOURNAL, Issue 21 2007Pamela Abstract A detailed study of the thermal decomposition of the zwitterionic, ring-borylated ansa -chromocene hydrido carbonyl complex [Cr(CO)H{Me4C2(C5H4)[C5H3B(C6F5)3]}] (2) is described. This complex is formed in the reaction between [Cr(CO){Me4C2(C5H4)2}] (1) and B(C6F5)3 in toluene at ,78,°C. Above ,25,°C, 2 decomposes to a 50:50 mixture of the low-spin, 17,e CrIII complexes [Cr(CO){Me4C2(C5H4)[C5H3B(C6F5)3]}] (3,b) and [Cr(CO){Me4C2(C5H4)2}][HB(C6F5)3] (4). Carbon monoxide elimination from 3,b generates high-spin, 15,e [Cr{Me4C2(C5H4)[C5H3B(C6F5)3]}] (3,a), which coordinates two other electron-donating ligands, such as xylyl isocyanide, PMe3, and PPh2Me to form the low-spin, 17,e electron complexes 3,c, 3,d, and 3,e, respectively. High-spin, 15,e [Cr{Me4C2(C5H4)2}][HB(C6F5)3] (5) is generated by heating 3,b in toluene at 100,°C and periodically removing the evolved CO. Efforts to isolate more than a few X-ray quality crystals of 5 were thwarted by its tendency to form an insoluble precipitate (6) with the same molecular formula. Heating the solution of 5 at 120,°C results in its partial conversion (ca. 28,%) to 3,a, thereby allowing the formation of 3,a in yields as high as 74,% from the reaction between 1 and B(C6F5)3. The X-ray crystal structures of 3,b,e and 5 are described. Cyclic voltammetry measurements on 3,a,e reveal a dramatic reduction in the redox potentials of the complexes relative to their non-borylated analogues. DFT calculations show that this is due primarily to electrostatic stabilization of the oxidized species by the negatively charged borylate group. EPR and 19F,NMR spectroscopy allow 3,a to be distinguished from its Lewis base adducts 3,b,e and reveal the relative affinities of different Lewis bases for the chromium. [source] | ||||||||||