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Neutron Diffraction Data (neutron + diffraction_data)
Selected AbstractsA neutron crystallographic analysis of T6 porcine insulin at 2.1,Å resolutionACTA CRYSTALLOGRAPHICA SECTION D, Issue 10 2009Wakari Iwai Neutron diffraction data for T6 porcine insulin were collected to 2.1,Å resolution from a single crystal partly deuterated by exchange of mother liquor. A maximum-likelihood structure refinement was undertaken using the neutron data and the structure was refined to a residual of 0.179. The hydrogen-bonding network of the central core of the hexamer was observed and the charge balance between positively charged Zn ions and their surrounding structure was interpreted by considering the protonation and/or deprotonation states and interactions of HisB10, water and GluB13. The observed double conformation of GluB13 was essential to interpreting the charge balance and could be compared with the structure of a dried crystal of T6 human insulin at 100,K. Differences in the dynamic behaviour of the water molecules coordinating the upper and lower Zn ions were observed and interpreted. The hydrogen bonds in the insulin molecules, as well as those involving HisB10 and GluB13, are discussed. The hydrogen/deuterium (H/D) exchange ratios of the amide H atoms of T6 porcine insulin in crystals were obtained and showed that regions highly protected from H/D exchange are concentrated in the centre of a helical region of the B chains. From the viewpoint of soaking time versus H/D-exchange ratios, the amide H atoms can be classified into three categories. [source] High-resolution neutron protein crystallography with radically small crystal volumes: application of perdeuteration to human aldose reductaseACTA CRYSTALLOGRAPHICA SECTION D, Issue 10 2005I. Hazemann Neutron diffraction data have been collected to 2.2,Å resolution from a small (0.15,mm3) crystal of perdeuterated human aldose reductase (h-AR; MW = 36,kDa) in order to help to determine the protonation state of the enzyme. h-AR belongs to the aldo,keto reductase family and is implicated in diabetic complications. Its ternary complexes (h-AR,coenzyme NADPH,selected inhibitor) provide a good model to study both the enzymatic mechanism and inhibition. Here, the successful production of fully deuterated human aldose reductase [h-AR(D)], subsequent crystallization of the ternary complex h-AR(D),NADPH,IDD594 and neutron Laue data collection at the LADI instrument at ILL using a crystal volume of just 0.15,mm3 are reported. Neutron data were recorded to 2,Å resolution, with subsequent data analysis using data to 2.2,Å. This is the first fully deuterated enzyme of this size (36,kDa) to be solved by neutron diffraction and represents a milestone in the field, as the crystal volume is at least one order of magnitude smaller than those usually required for other high-resolution neutron structures determined to date. This illustrates the significant increase in the signal-to-noise ratio of data collected from perdeuterated crystals and demonstrates that good-quality neutron data can now be collected from more typical protein crystal volumes. Indeed, the signal-to-noise ratio is then dominated by other sources of instrument background, the nature of which is under investigation. This is important for the design of future instruments, which should take maximum advantage of the reduction in the intrinsic diffraction pattern background from fully deuterated samples. [source] Self-Propagating High-Temperature Synthesis of Ti3SiC2: II.JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 10 2008Kinetics of Ultra-High-Speed Reactions from In Situ Neutron Diffraction In situ neutron diffraction data at 0.9-s time resolution during the self-propagating high-temperature synthesis of Ti3SiC2 from stoichiometric 3Ti+SiC+C mixtures have been further analyzed to give the phase quantities during all five stages of the identified reaction [(i) preheating, (ii) ,,, phase transformation in Ti, (iii) preignition reactions, (iv) intermediate phase formation, and (v) rapid nucleation and growth of Ti3SiC2]. The phase quantities thus determined have been used, in conjunction with temperatures estimated from lattice parameters and thermal expansion data, to determine the kinetic parameters for the nucleation and growth stage using a nonisothermal form of the Avrami kinetic equation. The analysis gave an Avrami exponent, n, close to 3 in agreement with nucleation and the observed two-dimensional growth of Ti3SiC2 crystals. An activation energy of ,45 kJ/mol was also estimated. [source] DFT LCAO and plane wave calculations of SrZrO3PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 2 2005R. A. Evarestov Abstract The results of the density functional (DFT) LCAO and plane wave (PW) calculations of the electronic and structural properties of four known SrZrO3 phases (Pm3m, I4/mcm, Cmcm and Pbnm) are presented and discussed. The calculated unit cell energies and relative stability of these phases agree well with the experimental sequence of SrZrO3 phases as the temperature increases. The lattice structure parameters optimized in the PW calculations for all four phases are in good agreement with the experimental neutron diffraction data. The LCAO and PW results for the electronic structure, density of states and chemical bonding in the cubic phase (Pm3m) are discussed in detail and compared with the results of previous PW calculations. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Simultaneous fitting of X-ray and neutron diffuse scattering dataACTA CRYSTALLOGRAPHICA SECTION A, Issue 1 2007D. J. Goossens Conventional crystallographic refinement uses the Bragg-peak intensities and gives the single-site average crystal structure. Information about short-range order and local order is contained in the diffuse scattering that is distributed throughout reciprocal space. Models of the short-range order in materials can now be automatically refined. The complementarity of X-ray and neutron diffraction data, and the value of simultaneously refining a structural model against both types of data, has long been known. This paper presents the first refinement of a short-range-order model against comprehensive X-ray and neutron diffuse scattering data simultaneously. The sample is the organic molecular crystal benzil, C14H10O2 (for neutron work H is replaced by D). The technique gives new insights into local order in crystalline materials, including the dynamic correlation structure indicative of the dynamics of molecules in the crystalline state, and successfully overcomes limitations of using only the X-ray data set. [source] Bond lengths in organic and metal-organic compounds revisited: X,H bond lengths from neutron diffraction dataACTA CRYSTALLOGRAPHICA SECTION B, Issue 3 2010Frank H. Allen The number of structures in the Cambridge Structural Database (CSD) has increased by an order of magnitude since the preparation of two major compilations of standard bond lengths in mid-1985. It is now of interest to examine whether this huge increase in data availability has implications for the mean bond-length values published in the late 1980s. Those compilations reported mean X,H bond lengths derived from rather sparse information and for rather few chemical environments. During the intervening years, the number of neutron studies has also increased, although only by a factor of around 2.25, permitting a new analysis of X,H bond-length distributions for (a) organic X = C, N, O, B, and (b) a variety of terminal and homometallic bridging transition metal hydrides. New mean values are reported here and are compared with earlier results. These new overall means are also complemented by an analysis of X,H distances at lower temperatures (T, 140,K), which indicates the general level of librational effects in X,H systems. The study also extends the range of chemical environments for which statistically acceptable mean X,H bond lengths can be obtained, although values from individual structures are also collated to further extend the chemical range of this compilation. Updated default `neutron-normalization' distances for use in hydrogen-bond and deformation-density studies are also proposed for C,H, N,H and O,H, and the low-temperature analysis provides specific values for certain chemical environments and hybridization states of X. [source] Neutron and electron diffraction studies of La(Zn1/2Ti1/2)O3 perovskiteACTA CRYSTALLOGRAPHICA SECTION B, Issue 4 2006Yi Hu The crystallography and microwave dielectric properties of La(Zn1/2Ti1/2)O3 (LZT) ceramics prepared via the mixed-oxide route were investigated in this study. While samples were largely single phase, small amounts of ZnO impurity were detected in sintered pellets. Observed reflections in electron and neutron diffraction patterns indicate that the symmetry of LZT is P21/n. The B site is ordered on {110} or pseudocubic {111}, but the presence of the pseudocubic (111) reflection is in itself insufficient to indicate the existence of such order. Rietveld refinements of the neutron diffraction data yield an excellent fit for such a model. The structure is highly twinned, with variants related through common {211} composition planes and 90° rotations about ,011,. The microwave dielectric properties measured were ,r = 34, Qf = 36,090 and ,f = ,70,MK,1. [source] Migration of the proton in the strong O,H,O hydrogen bond in urea,phosphoric acid (1/1)ACTA CRYSTALLOGRAPHICA SECTION B, Issue 3 2001Chick C. Wilson The structure of urea,phosphoric acid is reported at a large number of temperatures in the range 150,335,K from neutron diffraction data collected using a novel multiple single-crystal data collection method. The work focuses on the behaviour of the H atom involved in the short strong O,H,O hydrogen bond in this material. The position of this atom is shown to vary significantly, by around 0.035 ,Å, as a function of temperature, becoming effectively centred at the highest temperatures studied. This result, only accessible due to the accurate determination of H-atom parameters by neutron diffraction, has implications for the potential governing the hydrogen bond. [source] A new layered perovskite, KSrNb2O6F, by powder neutron diffractionACTA CRYSTALLOGRAPHICA SECTION C, Issue 8 2007Chung-Yul Yoo The structure of a new layered oxyfluoride, viz. potassium strontium diniobium hexaoxide fluoride, KSrNb2O6F, was refined from powder neutron diffraction data in the orthorhombic space group Immm. The oxyfluoride compound is an n = 2 member of the Dion,Jacobson-type family of general formula A[A,n,1BnX3n+1], which consists of double layered perovskite slabs, [SrNb2O6F],, between which K+ ions are located. Within the perovskite slabs, the NbO5F octahedra are significantly distorted and tilted about the a axis. A bond-valence-sum calculation gives evidence for O/F ordering in KSrNb2O6F, with the F, ions located in the central sites of the corner-sharing NbO5F octahedra along the b axis. All atoms lie on special positions, namely Nb on m, Sr on mmm, K on m2m, F on mm2, and O on sites of symmetry m and m2m. [source] Preliminary neutron and X-ray crystallographic studies of equine cyanomethemoglobinACTA CRYSTALLOGRAPHICA SECTION F (ELECTRONIC), Issue 4 2010A. Y. Kovalevsky Room-temperature and 100,K X-ray and room-temperature neutron diffraction data have been measured from equine cyanomethemoglobin to 1.7,Å resolution using a home source, to 1.6,Å resolution on NE-CAT at the Advanced Photon Source and to 2.0,Å resolution on the PCS at Los Alamos Neutron Science Center, respectively. The cyanomethemoglobin is in the R state and preliminary room-temperature electron and neutron scattering density maps clearly show the protonation states of potential Bohr groups. Interestingly, a water molecule that is in the vicinity of the heme group and coordinated to the distal histidine appears to be expelled from this site in the low-temperature structure. [source] A preliminary neutron diffraction study of rasburicase, a recombinant urate oxidase enzyme, complexed with 8-azaxanthinACTA CRYSTALLOGRAPHICA SECTION F (ELECTRONIC), Issue 3 2006Monika Budayova-Spano Crystallization and preliminary neutron diffraction measurements of rasburicase, a recombinant urate oxidase enzyme expressed by a genetically modified Saccharomyces cerevisiae strain, complexed with a purine-type inhibitor (8-azaxanthin) are reported. Neutron Laue diffraction data were collected to 2.1,Å resolution using the LADI instrument from a crystal (grown in D2O) with volume 1.8,mm3. The aim of this neutron diffraction study is to determine the protonation states of the inhibitor and residues within the active site. This will lead to improved comprehension of the enzymatic mechanism of this important enzyme, which is used as a protein drug to reduce toxic uric acid accumulation during chemotherapy. This paper illustrates the high quality of the neutron diffraction data collected, which are suitable for high-resolution structural analysis. In comparison with other neutron protein crystallography studies to date in which a hydrogenated protein has been used, the volume of the crystal was relatively small and yet the data still extend to high resolution. Furthermore, urate oxidase has one of the largest primitive unit-cell volumes (space group I222, unit-cell parameters a = 80, b = 96, c = 106,Å) and molecular weights (135,kDa for the homotetramer) so far successfully studied with neutrons. [source] | ||||||||||