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Crystals Used (crystal + used)
Selected AbstractsOn-line optical and X-ray spectroscopies with crystallography: an integrated approach for determining metalloprotein structures in functionally well defined statesJOURNAL OF SYNCHROTRON RADIATION, Issue 5 2008Mark J. Ellis X-ray-induced redox changes can lead to incorrect assignments of the functional states of metals in metalloprotein crystals. The need for on-line monitoring of the status of metal ions (and other chromophores) during protein crystallography experiments is of growing importance with the use of intense synchrotron X-ray beams. Significant efforts are therefore being made worldwide to combine different spectroscopies in parallel with X-ray crystallographic data collection. Here the implementation and utilization of optical and X-ray absorption spectroscopies on the modern macromolecular crystallography (MX) beamline 10, at the SRS, Daresbury Laboratory, is described. This beamline is equipped with a dedicated monolithic energy-dispersive X-ray fluorescence detector, allowing X-ray absorption spectroscopy (XAS) measurements to be made in situ on the same crystal used to record the diffraction data. In addition, an optical microspectrophotometer has been incorporated on the beamline, thus facilitating combined MX, XAS and optical spectroscopic measurements. By uniting these techniques it is also possible to monitor the status of optically active and optically silent metal centres present in a crystal at the same time. This unique capability has been applied to observe the results of crystallographic data collection on crystals of nitrite reductase from Alcaligenes xylosoxidans, which contains both type-1 and type-2 Cu centres. It is found that the type-1 Cu centre photoreduces quickly, resulting in the loss of the 595,nm peak in the optical spectrum, while the type-2 Cu centre remains in the oxidized state over a much longer time period, for which independent confirmation is provided by XAS data as this centre has an optical spectrum which is barely detectable using microspectrophotometry. This example clearly demonstrates the importance of using two on-line methods, spectroscopy and XAS, for identifying well defined redox states of metalloproteins during crystallographic data collection. [source] A preliminary neutron crystallographic study of an A-DNA crystalACTA CRYSTALLOGRAPHICA SECTION F (ELECTRONIC), Issue 3 2009Ricardo M. F. Leal The LADI-III diffractometer at the Institut Laue,Langevin has been used to carry out a preliminary neutron crystallographic study of the self-complementary DNA oligonucleotide d(AGGGGCCCCT)2 in the A conformation. The results demonstrate the viability of a full neutron crystallographic analysis with the aim of providing enhanced information on the ion,water networks that are known to be important in stabilizing A-DNA. This is the first account of a single-crystal neutron diffraction study of A-DNA. The study was carried out with the smallest crystal used to date for a neutron crystallographic study of a biological macromolecule. [source] Azeotropic Binary Solvent Mixtures for Preparation of Organic Single CrystalsADVANCED FUNCTIONAL MATERIALS, Issue 22 2009Xiaoran Li Abstract Here, a new approach is introduced to prepare large single crystals of ,-conjugated organic molecules from solution. Utilizing the concept of azeotropism, single crystals of tri-isopropylsilylethynyl pentacene (TIPS-PEN) with dimensions up to millimeters are facilely self-assembled from homogeneous solutions comprising two solvents with opposing polarities and a positive azeotropic point. At solvent compositions close to the azeotropic point, an abrupt transition of morphology from polycrystalline thin-films to large single crystals is found. How to adjust the initial ratio of the binary solvents so that the change in solvent composition during evaporation favors the specific H-aggregation and promotes an efficient self-assembly of TIPS-PEN is explained. The charge-carrier (hole) mobilities are substantially enhanced by a factor of 4 from the morphology of thin-films to large single crystals used as active layer in field-effect transistors. Additionally, this approach is extended to other ,,, stacked organic molecules to elucidate its broad applicability. [source] Anatase Titanium Dioxide Crystallization by a Hydrolysis Reaction of Titanium Alkoxide without AnnealingJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 8 2006Kunio Funakoshi The crystallization of anatase titanium dioxide (TiO2) was achieved by a hydrolysis reaction of titanium alkoxide without annealing. The hydrolysis reaction rates of tetraethyl orthotitanate were indicated by a function of the concentration of acetylacetone added. The degree of crystallinity of the product particles was influenced by the amounts of acetylacetone and seed crystals. Anatase TiO2 was crystallized by restraining the rapid increase in supersaturation of TiO2 and the consequent nucleation of amorphous TiO2. The degree of crystallinity of the product particles also changed with the types of seed crystals used, and was strongly influenced by the specific surface areas of the seed crystals. [source] Melt Crystallization and Morphology of Poly(p -phenylene sulfide) under High PressureMACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 4 2007Jun Lu Abstract The high-pressure melt-crystallization behaviors of poly(p -phenylene sulfide) (PPS) were investigated using WAXD, DSC, TEM and SEM. PPS extended-chain crystals with c -axis thickness exceeding 4.5 µm were formed at high pressure. The DSC results showed that the melting temperature and melting enthalpy of high-pressure crystallized PPS samples were up to 327.53,°C and 94.96 J,·,g,1, respectively, which were higher than the values of ideal PPS perfect crystals used by some researchers, and the melting enthalpy of the samples fluctuated regularly during the thickening growth of the PPS crystals. Other characteristic morphologies obtained at high pressure, i.e. spherulites and rod-like crystals, were also presented with the SEM measurements. [source] MAD phasing using the (Ta6Br12)2+ cluster: a retrospective studyACTA CRYSTALLOGRAPHICA SECTION D, Issue 5 2008Oliwia Pasternak The crystal structure of cytokinin-specific binding protein (CSBP) containing four independent molecules with 4 × 155 = 620 residues in the asymmetric unit of the P64 unit cell has been solved by three-wavelength MAD using 1.8,Å resolution data recorded from a crystal derivatized with the dodecabromohexatantalum cation (Ta6Br12)2+. The diffraction data contained a very strong anomalous signal (allowing successful phasing even using peak SAD data alone) despite the fact that the five (Ta6Br12)2+ clusters found in the asymmetric unit have low occupancy (about 0.3). The derivative structure has been successfully refined to R = 0.158, providing interesting details on the geometry of the (Ta6Br12)2+ cluster, its interactions with the protein and on the backsoaking of a cytokinin ligand that was originally part of a CSBP,cytokinin complex in the native crystals used for (Ta6Br12)2+ derivatization. A simulation analysis of the phasing power of the (Ta6Br12)2+ ions at artificially imposed resolution limits shows that it is not possible to resolve the individual Ta atoms if the dmin limit of the data is higher than 2.9,Å. Additionally, for successful Ta identification the (Ta6Br12)2+ complex should be specifically bound and ordered. Good binding at the protein surface is facilitated by the presence of acidic groups, indicating higher pH buffer conditions to be preferable. In addition, the water channels in the crystal should be sufficiently wide (at least 11,Å) to allow free diffusion of the (Ta6Br12)2+ ions on soaking. A retrospective look at the initial molecular-replacement calculations provides interesting insights into how the peculiar packing mode and strong bias of the molecular-replacement-phased electron-density maps had hindered successful solution of the structure by this method. [source] | |||||||||||||