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Crystal Quality (crystal + quality)
Selected AbstractsCrystal quality and differential crystal-growth behaviour of three proteins crystallized in gel at high hydrostatic pressureACTA CRYSTALLOGRAPHICA SECTION D, Issue 6 2005A. Kadri Pressure is a non-invasive physical parameter that can be used to control and influence protein crystallization. It is also found that protein crystals of superior quality can be produced in gel. Here, a novel crystallization strategy combining hydrostatic pressure and agarose gel is described. Comparative experiments were conducted on hen and turkey egg-white lysozymes and the plant protein thaumatin. Crystals could be produced under up to 75,100,MPa (lysozymes) and 250,MPa (thaumatin). Several pressure-dependent parameters were determined, which included solubility and supersaturation of the proteins, number, size and morphology of the crystals, and the crystallization volume. Exploration of three-dimensional phase diagrams in which pH and pressure varied identified growth conditions where crystals had largest size and best morphology. As a general trend, nucleation and crystal-growth kinetics are altered and nucleation is always enhanced under pressure. Further, solubility of the lysozymes increases with pressure while that of thaumatin decreases. Likewise, changes in crystallization volumes at high and atmospheric pressure are opposite, being positive for the lysozymes and negative for thaumatin. Crystal quality was estimated by analysis of Bragg reflection profiles and X-ray topographs. While the quality of lysozyme crystals deteriorates as pressure increases, that of thaumatin crystals improves, with more homogeneous crystal morphology suggesting that pressure selectively dissociates ill-formed nuclei. Analysis of the thaumatin structure reveals a less hydrated solvent shell around the protein when pressure increases, with ,20% less ordered water molecules in crystals grown at 150,MPa when compared with those grown at atmospheric pressure (0.1,MPa). Noticeably, the altered water distribution is seen in depressurized crystals, indicating that pressure triggers a stable structural alteration on the protein surface while its polypeptide backbone remains essentially unaltered. [source] Size Selection During Crystallization of Oppositely Charged NanoparticlesCHEMISTRY - A EUROPEAN JOURNAL, Issue 9 2009Bartlomiej Kowalczyk Dr. Abstract Opposites attract (selectively): Oppositely charged nanoparticles characterized by different size distributions form 3D supracrystals (see figure) only if the distributions overlap. Crystal quality decreases rapidly with decreasing degree of overlap, and, irrespective of the ratio of particle diameters/charges, no crystals are observed for non-overlapping distributions. [source] Growth, etching morphology and spectra of LiAlO2 crystalCRYSTAL RESEARCH AND TECHNOLOGY, Issue 8 2008Taohua Huang Abstract ,-LiAlO2 single crystal was successfully grown by Czochralski method. The crystal quality was characterized by X-ray rocking curve and chemical etching. The effects of air-annealing and vapor transport equilibration (VTE) on the crystal quality, etch pits and absorption spectra of LiAlO2 were also investigated in detail. The results show that the as-grown crystal has very high quality with the full width at half maximum (FWHM) of 17.7-22.6 arcsec. Dislocation density in the middle part of the crystal is as low as about 3.0×103 cm,2. The VTE-treated slice has larger FWHM value, etch pits density and absorption coefficient as compared with those of untreated and air-annealed slices, which indicates that the crystal quality became inferior after VTE treatment. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Growth and characterization of magneto-optical YFeO3 crystalsCRYSTAL RESEARCH AND TECHNOLOGY, Issue 10 2007Hui Shen Abstract The floating zone growth of magneto-optical crystal YFeO3 has been investigated. The polycrystalline feed rod was prepared by a pressure of 250MPa and sintering at about 1500°C. A crack- free YFeO3 single crystal has been successfully grown. The crystal preferred to crystallize along <100> direction with about 10° deviation. The X-ray rocking curve of the crystal has a FWHM of 24 arcsec, confirming the high crystal quality of the sample. The (100) plane was etched by hot phosphoric acid and the dislocation density was about 104/cm2. A thin outer layer with Y2O3 -rich composition was found at the periphery of as-grown crystals, which was attributed to the Fe2O3 evaporation during growth. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Large area lateral overgrowth of mismatched InGaP on GaAs(111)B substratesCRYSTAL RESEARCH AND TECHNOLOGY, Issue 12 2005S. Uematsu Abstract Application of InGaAs/InGaP double-heterostructure (DH) lasers increases the band offset between the cladding layer and the active layer more than the use of conventional 1.3 µm InGaAsP/InP lasers. As a first step in realizing 1.3 µm InGaP/InGaAs/InGaP DH lasers, we proposed InGaP lattice-mismatched epitaxial lateral overgrowth (ELO) technique and successfully carried out the InGaP growth on both GaAs (100), (111)B and InP (100) substrates by liquid phase epitaxy. In this work, we grew the InGaP crystal on GaAs (111)B substrate by adjusting Ga and P composition in In solution, to obtain In0.79Ga0.21P (, = 820 nm) virtual substrate for 1.3 µm InGaAs/InGaP DH lasers. To grow the InGaP all over the lateral surface of the substrate, the growth time was extended to 6 hours. The amount of InGaP lateral growth up to 2 hours was gradually increased, but the lateral growth was saturated. The InGaP lateral width was about 250 µm at the growth time of 6 hours. We report the result that optical microscope observation, CL and X-ray rocking curve measurements and reciprocal lattice space mapping were carried out to evaluate the crystal quality of the grown InGaP layers. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] New Developments in Vertical Gradient Freeze Growth,ADVANCED ENGINEERING MATERIALS, Issue 7 2004O. Pätzold The Vertical Gradient Freeze (VGF) technique is an important method for growing high quality compound semiconductors such as GaAs. Results obtained with a novel VGF set-up developed for the growth under influence of a rotating magnetic field (RMF) and under vapour pressure control are presented in this paper. The RMF is shown to be a powerful tool to affect the heat and mass transport within the melt in a definite way. In GaAs:Si growth, RMF induced flow results in a decreased curvature of a nominally concave-shaped interface, i.e., it contributes to an axial heat transfer at the solid-liquid interface. The axial dopant segregation of Ga in Ge is found to be improved under continuous RMF action due to better mixing of the melt. The set-up also allowed to determine the influence of carbon and the arsenic vapour pressure on the dopant incorporation and crystal quality. [source] Automated seeding for the optimization of crystal qualityJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 4 2010Sahir Khurshid With the advent of structural genomics a variety of crystallization techniques have been automated and applied to high-throughput pipelines, yet seeding, which is the most common and successful optimization method, is still being performed predominantly manually. The aim of this study was to devise simple automated seeding techniques that can be applied in a routine manner using existing robots and not requiring special tools. Two alternative protocols for automated seeding experiments are described. One involves the delivery of microcrystals from stock to target wells using the robot dispensing tip as a seeding tool. The second harnesses an animal whisker as the seeding tool. Larger and better ordered crystals were obtained using both techniques. [source] Autolabo: an automated system for ligand-soaking experiments with protein crystalsJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 4 2010Michihiro Sugahara Ligand soaking of protein crystals is important for the preparation of heavy-atom derivative crystals for experimental phasing as well as for large-scale ligand screening in pharmaceutical developments. To facilitate laborious large-scale ligand screening, to reduce the risk of human contact with hazardous ligand reagents and to increase the success rate of the soaking experiments, a protein crystallization robot `Autolabo' has been developed and implemented in the high-throughput crystallization-to-structure pipeline at RIKEN SPring-8 Center. The main functions of this robotic system are the production of protein crystals for experiments, the ligand soaking of these crystals and the observation of soaked crystals. The separate eight-channel dispensers of Autolabo eliminate the cross-contamination of reagents which should be strictly avoided in the ligand-soaking experiment. Furthermore, the automated approach reduces physical damage to crystals during experiments when compared with the conventional manual approach, and thereby has the potential to yield better quality diffraction data. Autolabo's performance as a ligand-soaking system was evaluated with a crystallization experiment on ten proteins from different sources and a heavy-atom derivatization experiment on three proteins using a versatile cryoprotectant containing heavy-atom reagents as ligands. The crystallization test confirmed reliable crystal reproduction in a single condition and the capability for crystallization with nucleants to improve crystal quality. Finally, Autolabo reproducibly derivatized the test protein crystals with sufficient diffraction quality for experimental phasing and model building, indicating a high potentiality of this automated approach in ligand-soaking experiments. [source] Morphological study of Czochralski-grown lanthanide orthovanadate single crystals and implications on the mechanism of bulk spiral formationJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 2 2010Hengjiang Cong Single crystals of monoclinic Nd:LaVO4 with dimensions up to Ø28 × 21,mm have been grown from the near-stoichiometric melt by the Czochralski method, making use of various seed orientations that are perpendicular to the (010), (10), (001) and (00) crystal planes. A sample was also prepared with the seed orientation in an arbitrary direction relative to the crystal. The anisotropic properties of the crystal are manifested in the growth morphology of the as-grown crystals, where different degrees of bulk spiral growth were observed. It was also found that employing the (001) or (00) seed faces severely suppressed the bulk spiral growth, and thus high quality and large-scale Nd:LaVO4 crystals were obtained. The constituent segregation coefficients and high-temperature stability, including the melting point, were determined and evaluated. Based on the attachment energy model of Hartman,Perdok theory, morphology predictions were made for monoclinic LaVO4 and tetragonal YVO4 orthovanadate single crystals. Correlating with the as-grown morphology of both crystals developed along different seed orientations, a theoretical explanation is provided for the influences of seed crystals on bulk spiral formation, crystal quality and utilization ratio. It suggests that breaking the axial symmetry of the ideal atomic level interface between crystal and melt plays a crucial triggering role in bulk spiral formation in the Czochralski growth of lanthanide orthovanadate single crystals. Selecting a proper seed orientation that yields such a highly axially symmetric surface structure consisting of a series of large-area facets with similar growth velocities can greatly reduce bulk spiral formation and thus is preferable in the Czochralski growth of large-sized low-symmetry oxide crystals. [source] Optical properties of InN grown on templates with controlled surface polaritiesPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 10 2010Ronny Kirste Abstract The structural and optical properties of InN layers grown on GaN/sapphire templates with controlled Ga-/N-polar surfaces are investigated. Raman spectroscopy and XRD reciprocal space map analysis suggest that the InN layers were grown strain free with a high crystal quality. A line shape analysis of the A1(LO) Raman mode yields to a decreasing carrier concentration for the sample grown on Ga-polar substrate. Low temperature photoluminescence measurements exhibit a shift to lower energies of the luminescence maximum for the sample grown on Ga-polar GaN probably due to a reduced carrier concentration and thus, a decreased Burstein,Moss shift. Following this, we demonstrate that the use of polarity controlled GaN/sapphire substrates leads to unstrained layers with good structural and optical properties. [source] Annealing experiments of the GaP based dilute nitride Ga(NAsP)PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 1 2008B. Kunert Abstract The post-growth annealing behaviour of Ga(NAsP) multi quantum well heterostructures (MQWHs) grown pseudomorphically strained to GaP substrate has been investigated. The optical properties as well as the structural crystal quality of the novel dilute nitride show an obvious dependence on the applied annealing temperature. Photoluminescence (PL) measurements reveal a step-like blue shift of the PL peak position in line with an increase of PL intensity with rising annealing temperature. The PL line width decreases to a mini- mal value for an optimized heating temperature around 800 °C. This annealing behaviour of the Ga(NAsP)/GaP-MQWHs up to 850 °C is quite typical for a dilute nitride, however, the functional dependence of the integrated intensity above 850 °C is unusual. The increase of the PL line width above 850 °C suggests a deterioration of the crystalline MQW quality, but transmission electron microscopy (TEM) and high resolution X-ray diffraction (XRD) prove the opposite. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Growth and characterization of ZnMgTe/ZnTe layered structures grown by molecular beam epitaxyPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 6 2010S. Imada Abstract ZnMgTe/ZnTe layered structures were grown on ZnTe substrates by molecular beam epitaxy, and the crystal structures were characterized using X-ray diffraction methods. This structure would be the waveguide for various optoelectronic devices. Therefore, the crystal quality of this layered structure would be very crucial for the realization of high performance devices. ZnMgTe is lattice mismatched to ZnTe, and the increase of the ZnMgTe layer thickness or Mg mole fraction ratio would result in the crystal quality deterioration of the layered structure. The critical layer thickness (CLT) was theoretically derived, and various structures with various ZnMgTe layer thickness and Mg mole fraction were grown. The lattice mismatch strain relief and crystal quality of those samples were investigated by means of X-ray reciprocal space mapping (RSM) and cross sectional transmission electron microscopy (TEM). The dislocation formation and the lattice mismatch relaxation were confirmed for various samples and it was revealed that the calculated CLT values could be used as an appropriate guideline to design the dislocation free and high performance device structures (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Electron microscopy of InGaN nanopillars spontaneously grown on Si(111) substratesPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 5 2010Th. Kehagias Abstract The mopholological, structural and chemical properties of InxGa1,xN nanopillars directly grown on Si (111) substrates, by molecular beam epitaxy, were investigated employing transmission electron microscopy related techniques. Single crystalline, single phase nanopillars were observed exhibiting a low density of crystal defects, which contribute to good crystal quality. Initial nanostructures merge through subgrain boundaries to form final nanopillars. Energy dispersive X-ray analysis revealed a very low InN mole fraction near the interface with the substrate, owing to high desorption rates from the elevated growth temperature, and gradually higher In incorporation rates near the tips of the nanopillars. This compositional fluctuation is maintained due to poor segregation of indium adatoms along the c-axis of the nanopillars towards the Si interface. A second species of long and narrow nanopillars was found In-free. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Improvement of crystal quality of GaN grown on AlN template by MOCVD using HT-AlN interlayerPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue S2 2009Tao Yuebin Abstract Two GaN samples, with and without high temperature (HT)-AlN interlayer (labelled as sample A and B, respectively) grown by MOCVD on AlN template, were investigated by double-crystal X-ray diffraction (DC-XRD), photoluminescence (PL), and atomic force microscope (AFM) measurements. It was found that the crystal quality of GaN could be greatly improved by the HT-AlN interlayer. The full width at half maximum (FWHM) of (102) reflection in XRD rocking curve was narrower for sample A than that for sample B. However, the FWHMs of (002) reflections were almost the same for the two samples. In addition, the tilt degree which reflected screw dislocation density was almost the same, while the twist degree which reflected edge dislocation density changed from 0.214° to 0.152° when the HT-AlN interlayer was used. Both the intensities of (102) reflection in XRD and band edge emission in PL for sample A were stronger too. In the AFM images, the atomic growth steps of sample A were clearer than those of sample B. According to the results of the in situ optical reflectivity spectra and the atomic force microscope (AFM) images, the above results were attributed to the three-dimensional (3D) growth mode of the HT-AlN interlayer. The HT-AlN interlayer may work as a kind of "micro-area" seed for epitaxial lateral overgrowth (ELOG) resulting in bending some dislocations. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Effects of initial conditions and growth temperature on the properties of nonpolar a -plane AlN grown by LP-HVPEPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue S2 2009Jie-Jun Wu Abstract AlN was grown on r - and c -plane sapphire substrates by low-pressure hydride vapor phase epitaxy (LP-HVPE). Nitridation and buffer methods were used and compared. Results show that the buffer method is appropriate for the growth of a-plane AlN. In-plane stresses were measured and found to be different in the two in-plane directions parallel and perpendicular to the AlN c -axis. In-plane stress anisotropy is reduced at high temperature leading to a smoother surface, partly owing to a decreased difference in the growth rates between two in-plane directions. However, too high a temperature decreases the crystal quality of a-plane AlN. Thus, there exists an optimal temperature range for the growth of a-plane AlN, in which improved crystal and surface qualities can both be obtained. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Self-organized growth of InN-nanocolumns on p-Si(111) by MBEPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 6 2008Christian Denker Abstract InN-nanocolumns are an attractive system for light harvesting applications. To understand the mechanism of self organized growth of nanocolumns in plasma assisted MBE, InN samples were produced under various conditions on p-Si(111). Depending on the growth parameters different growth regimes for nanocolumns were identified according to their final shape. High-resolution TEM pictures show a very good crystal quality. This is also confirmed by Raman and PL measurements. Nanocolumns with diameters of 20-200 nm and lengths of up to 2 mm were produced. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] High temperature growth of AlN film by LP-HVPEPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7 2007K. Tsujisawa Abstract AlN films were grown on AlN/sapphire templates at 1400,1500 °C using low-pressure hydride vapor phase epitaxy (LP-HVPE). Compared to the step-flow growth of AlN film at 1200 °C with growth rate of 2.1 ,m/h, AlN films with atomic steps were obtained at 1400,1500 °C even with high growth rate. For the AlN film grown at 1450 °C with growth rate of 14.3 ,m/h, the RMS value is 0.75 nm and the FWHM values of (0002) and (10-12) X-ray rocking curve (XRC) are 351 and 781 arcsec, respectively. Since the FWHM value of (10-12) XRC for the AlN/sapphire template is 1492 arcsec, the crystal quality of HVPE-grown AlN is greatly improved compared with the AlN/sapphire template, which is also confirmed by TEM observation. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Blue light emitting diode fabricated on a-plane GaN film over r-sapphire substrate and on a-plane bulk GaN substratePHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7 2007Y. Naoi Abstract We studied the growth technique for the dislocation reduction in a-plane GaN grown by metal organic chemical vapour deposition (MOCVD) using AlInN buffer layer, high temperature atomic layer epitaxy, and trenched r-sapphire technique. By using these techniques, the crystal quality was much improved. We also fabricated blue light emitting diodes (LEDs) on a-plane GaN film over r-sapphire substrate and on a-plane bulk GaN substrate. The electroluminescence (EL) characteristics of the LED samples were examined, and we found that the EL near field pattern from homo-epitaxially grown a-GaN based LED was spatially uniform, although the pattern from the LED on r-sapphire substrate was not uniform. The output power at the wavelength of 430nm was 0.72mW at the 20mA injection current for the sample on a-plane bulk GaN. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Doping efficiency and segregation of Si in AlN grown by molecular beam epitaxyPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 6 2006V. Lebedev Abstract The growth of Si-doped 2H-AlN thin films by plasma-induced molecular-beam epitaxy is reported. We have found that Si positively affects the epitaxy being an effective surfactant for AlN growth with a remarkable impact on the crystal quality. It was also observed that heavy doping conditions result in the volume segregation of Si at the threading dislocation network and in the formation of an amorphous (AlO)(SiO)N cap layer caused by post-growth surface oxidation of the accumulated Al and segregated Si. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Laser diodes with highly strained InGaAs MQWs and very narrow vertical far fieldsPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 3 2006F. Bugge Abstract The effect of variation of the number of highly strained InGaAs quantum wells embedded in GaAs layers on the crystal quality of the epitaxial layers and AlGaAs/GaAs laser diodes was investigated. With four quantum wells and very thick waveguide layers, reasonable efficient laser diodes emitting above 1100 nm with a narrow vertical far field (FWHM = 15°) were obtained. Broad area laser diodes with 200 µm stripe width and an optimised doping profile emit nearly 20 W cw output power. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Epitaxial Growth of AlN Layers on SiC Substrates in a Hot-Wall MOCVD SystemPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 1 2003A. Kakanakova-Georgieva Abstract In this study we report the successful growth of AlN and AlN/GaN on SiC substrates in a MOCVD process based on a hot-wall susceptor design. Different features of AlN growth are established depending on the total reactor pressure, temperature, off-cut SiC substrate orientation and V-to-III gas-flow ratio. The feasibility of the hot-wall MOCVD concept is demonstrated by the performance of AlN/GaN structures with state-of-the-art properties with strong potential for further optimization. A narrower X-ray rocking curve over the asymmetric 10.4 than the symmetric 00.2 reflection clearly underlines the high overall crystal quality of the GaN layers on AlN buffers grown in this type of MOCVD reactor. [source] Electron diffraction, X-ray powder diffraction and pair-distribution-function analyses to determine the crystal structures of Pigment Yellow 213, C23H21N5O9ACTA CRYSTALLOGRAPHICA SECTION B, Issue 2 2009Martin U. Schmidt The crystal structure of the nanocrystalline , phase of Pigment Yellow 213 (P.Y. 213) was solved by a combination of single-crystal electron diffraction and X-ray powder diffraction, despite the poor crystallinity of the material. The molecules form an efficient dense packing, which explains the observed insolubility and weather fastness of the pigment. The pair-distribution function (PDF) of the , phase is consistent with the determined crystal structure. The , phase of P.Y. 213 shows even lower crystal quality, so extracting any structural information directly from the diffraction data is not possible. PDF analysis indicates the , phase to have a columnar structure with a similar local structure as the , phase and a domain size in column direction of approximately 4,nm. [source] De-icing: recovery of diffraction intensities in the presence of ice ringsACTA CRYSTALLOGRAPHICA SECTION D, Issue 6 2010Michael S. Chapman Macromolecular structures are routinely determined at cryotemperatures using samples flash-cooled in the presence of cryoprotectants. However, sometimes the best diffraction is obtained under conditions where ice formation is not completely ablated, with the result that characteristic ice rings are superimposed on the macromolecular diffraction. In data processing, the reflections that are most affected by the ice rings are usually excluded. Here, an alternative approach of subtracting the ice diffraction is tested. High completeness can be retained with little adverse effect upon the quality of the integrated data. This offers an alternate strategy when high levels of cryoprotectant lead to loss of crystal quality. [source] Systematic study on crystal-contact engineering of diphthine synthase: influence of mutations at crystal-packing regions on X-ray diffraction qualityACTA CRYSTALLOGRAPHICA SECTION D, Issue 10 2008Hisashi Mizutani It is well known that protein crystallizability can be influenced by site-directed mutagenesis of residues on the molecular surface of proteins, indicating that the intermolecular interactions in crystal-packing regions may play a crucial role in the structural regularity at atomic resolution of protein crystals. Here, a systematic examination was made of the improvement in the diffraction resolution of protein crystals on introducing a single mutation of a crystal-packing residue in order to provide more favourable packing interactions, using diphthine synthase from Pyrococcus horikoshii OT3 as a model system. All of a total of 21 designed mutants at 13 different crystal-packing residues yielded almost isomorphous crystals from the same crystallization conditions as those used for the wild-type crystals, which diffracted X-rays to 2.1,Å resolution. Of the 21 mutants, eight provided crystals with an improved resolution of 1.8,Å or better. Thus, it has been clarified that crystal quality can be improved by introducing a suitable single mutation of a crystal-packing residue. In the improved crystals, more intimate crystal-packing interactions than those in the wild-type crystal are observed. Notably, the mutants K49R and T146R yielded crystals with outstandingly improved resolutions of 1.5 and 1.6,Å, respectively, in which a large-scale rearrangement of packing interactions was unexpectedly observed despite the retention of the same isomorphous crystal form. In contrast, the mutants that provided results that were in good agreement with the designed putative structures tended to achieve only moderate improvements in resolution of up to 1.75,Å. These results suggest a difficulty in the rational prediction of highly effective mutations in crystal engineering. [source] Post-crystallization treatments for improving diffraction quality of protein crystalsACTA CRYSTALLOGRAPHICA SECTION D, Issue 9 2005Begoña Heras X-ray crystallography is the most powerful method for determining the three-dimensional structure of biological macromolecules. One of the major obstacles in the process is the production of high-quality crystals for structure determination. All too often, crystals are produced that are of poor quality and are unsuitable for diffraction studies. This review provides a compilation of post-crystallization methods that can convert poorly diffracting crystals into data-quality crystals. Protocols for annealing, dehydration, soaking and cross-linking are outlined and examples of some spectacular changes in crystal quality are provided. The protocols are easily incorporated into the structure-determination pipeline and a practical guide is provided that shows how and when to use the different post-crystallization treatments for improving crystal quality. [source] Effects of macromolecular impurities and of crystallization method on the quality of eubacterial aspartyl-tRNA synthetase crystalsACTA CRYSTALLOGRAPHICA SECTION D, Issue 6 2005A. Moreno Although macromolecular purity is thought to be essential for the growth of flawless protein crystals, only a few studies have investigated how contaminants alter the crystallization process and crystal quality. Likewise, the outcome of a crystallization process may vary with the crystallization method. Here, it is reported how these two variables affect the crystallogenesis of aspartyl-tRNA synthetase from the eubacterium Thermus thermophilus. This homodimeric enzyme (Mr = 130,000) possesses a multi-domain architecture and crystallizes either in a monoclinic or an orthorhombic habit. Minute amounts of protein impurities alter to a different extent the growth of each crystal form. The best synthetase crystals are only obtained when the crystallizing solution is either enclosed in capillaries or immobilized in agarose gel. In these two environments convection is reduced with regard to that existing in an unconstrained solution. [source] The influence of an internal electric field upon protein crystallization using the gel-acupuncture methodACTA CRYSTALLOGRAPHICA SECTION D, Issue 9 2003N. Mirkin In this work, the influence of an internal electric field upon the crystallization of lysozyme and thaumatin is explored using a modified design of the gel-acupuncture setup. From a crystallographic point of view, the orientation of crystals that grow preferentially over different types of electrodes inside capillary tubes is also evaluated. Finally, the crystal quality and the three-dimensional structure of these proteins grown with and without the electric field influence are analyzed by means of X-ray diffraction methods. [source] Dramatic improvement of crystal quality for low-temperature-grown rabbit muscle aldolaseACTA CRYSTALLOGRAPHICA SECTION F (ELECTRONIC), Issue 5 2010HaJeung Park Rabbit muscle aldolase (RMA) was crystallized in complex with the low-complexity domain (LC4) of sorting nexin 9. Monoclinic crystals were obtained at room temperature that displayed large mosaicity and poor X-ray diffraction. However, orthorhombic RMA,LC4 crystals grown at 277,K under similar conditions exhibited low mosaicity, allowing data collection to 2.2,Å Bragg spacing and structure determination. It was concluded that the improvement of crystal quality as indicated by the higher resolution of the new RMA,LC4 complex crystals was a consequence of the introduction of new lattice contacts at lower temperature. The lattice contacts corresponded to an increased number of interactions between high-entropy side chains that mitigate the lattice strain incurred upon cryocooling and accompanying mosaic spread increases. The thermodynamically unfavorable immobilization of high-entropy side chains used in lattice formation was compensated by an entropic increase in the bulk-solvent content owing to the greater solvent content of the crystal lattice. [source] Crystallization and preliminary X-ray crystallographic analysis of ,-galactosidase from Kluyveromyces lactisACTA CRYSTALLOGRAPHICA SECTION F (ELECTRONIC), Issue 3 2010Ángel Pereira-Rodríguez ,-Galactosidase from Kluyveromyces lactis catalyses the hydrolysis of the ,-galactosidic linkage in lactose. Owing to its many industrial applications, the biotechnological potential of this enzyme is substantial. This protein has been expressed in yeast and purified for crystallization trials. However, optimization of the best crystallization conditions yielded crystals with poor diffraction quality that precluded further structural studies. Finally, the crystal quality was improved using the streak-seeding technique and a complete diffraction data set was collected at 2.8,Å resolution. [source] The taming of small heat-shock proteins: crystallization of the ,-crystallin domain from human Hsp27ACTA CRYSTALLOGRAPHICA SECTION F (ELECTRONIC), Issue 12 2009E. V. Baranova Small heat-shock proteins (sHsps) are ubiquitous molecular chaperones. sHsps function as homooligomers or heterooligomers that are prone to subunit exchange and structural plasticity. Here, a procedure for obtaining diffraction-quality crystals of the ,-crystallin domain of human Hsp27 is presented. Initially, limited proteolysis was used to delineate the corresponding stable fragment (residues 90,171). This fragment could be crystallized, but examination of the crystals using X-rays indicated partial disorder. The surface-entropy reduction approach was applied to ameliorate the crystal quality. Consequently, a double mutant E125A/E126A of the 90,171 fragment yielded well ordered crystals that diffracted to 2.0,Å resolution. [source] | ||||||||||||||||