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Single-crystal Diffraction Data (single-crystal + diffraction_data)
Selected AbstractsCombining solution wide-angle X-ray scattering and crystallography: determination of molecular envelope and heavy-atom sitesJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 2 2009Xinguo Hong Solving the phase problem remains central to crystallographic structure determination. A six-dimensional search method of molecular replacement (FSEARCH) can be used to locate a low-resolution molecular envelope determined from small-angle X-ray scattering (SAXS) within the crystallographic unit cell. This method has now been applied using the higher-resolution envelope provided by combining SAXS and WAXS (wide-angle X-ray scattering) data. The method was tested on horse hemoglobin, using the most probable model selected from a set of a dozen bead models constructed from SAXS/WAXS data using the program GASBOR at 5,Å resolution (qmax = 1.25,Å,1) to phase a set of single-crystal diffraction data. It was found that inclusion of WAXS data is essential for correctly locating the molecular envelope in the crystal unit cell, as well as for locating heavy-atom sites. An anomalous difference map was calculated using phases out to 8,Å resolution from the correctly positioned envelope; four distinct peaks at the 3.2, level were identified, which agree well with the four iron sites of the known structure (Protein Data Bank code 1ns9). In contrast, no peaks could be found close to the iron sites if the molecular envelope was constructed using the data from SAXS alone (qmax = 0.25,Å,1). The initial phases can be used as a starting point for a variety of phase-extension techniques, successful application of which will result in complete phasing of a crystallographic data set and determination of the internal structure of a macromolecule to atomic resolution. It is anticipated that the combination of FSEARCH and WAXS techniques will facilitate the initial structure determination of proteins and provide a good foundation for further structure refinement. [source] Automated profile analysis for single-crystal diffraction dataJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 2 2003R. J. Angel An integration method for step-scanned single-crystal intensity data based upon fitting of the individual diffraction profiles by a pseudo-Voigt function is presented. Algorithms for both the recovery of weak intensities from data sets and the rejection of aberrant peak profiles are discussed. The ideas presented in this paper have been implemented in a software package for Microsoft Windows, WinIntegrStp, which is available at http://www.crystal.vt.edu/. [source] Dynamics of molecules in crystals from multi-temperature anisotropic displacement parameters.ACTA CRYSTALLOGRAPHICA SECTION A, Issue 5 2000The temperature evolution of atomic anisotropic displacement parameters (ADP's) of perdeuterobenzene and of urea in the temperature range between 12 and 123,K is investigated in terms of the model presented in paper I. For the benzene molecule, the temperature-dependent contributions to the ADP's are well described by three molecular librations and three molecular translations. For the urea molecule, the analysis revealed a low-frequency high-amplitude normal mode (~64,cm,1), which combines out-of-plane deformations of the NH2 groups with molecular libration. The pyramidalization motion allows the hydrogen-bonding pattern to be retained quite well, whereas this pattern is heavily distorted in the higher-frequency molecular librations. The results presented for urea go a step beyond those obtainable in a conventional rigid-body or segmented-rigid-body analysis because they show how correlations of atomic displacements in molecular crystals can be determined from the temperature evolution of ADP's. For both molecules, the analysis reveals temperature-independent contributions to the ADP's accounting for the high-frequency internal vibrations. It is the first time that such contributions have been extracted directly from single-crystal diffraction data for light atoms like hydrogen and deuterium as well as for heavier atoms like carbon, nitrogen and oxygen. These contributions agree well with those calculated from independent spectroscopic information. [source] Re-investigation of the structure and crystal chemistry of the Bi2O3,W2O6 `type (Ib)' solid solution using single-crystal neutron and synchrotron X-ray diffractionACTA CRYSTALLOGRAPHICA SECTION B, Issue 2 2010Neeraj Sharma Single crystals of composition Bi35.66W4.34O66.51 (or Bi8.2WO15.3, bismuth tungsten oxide), within the type (Ib) solid-solution region of the Bi2O3,WO3 system, were synthesized using the floating-zone furnace method. Synchrotron X-ray and neutron single-crystal diffraction data were used to confirm the previously tentative assignment of the room-temperature space group as I41. Fourier analysis of the combined X-ray and neutron datasets was used to elucidate and refine fully the cation and anion arrays for the first time. The mixed cation site M1 is shown to be coordinated by eight O atoms in an irregular cube when M = Bi, and by six O atoms in an octahedron when M = W. The resulting disorder in the average structure around M1 is discussed in the context of experimentally observed oxide-ion conductivity. [source] Pitfalls of data mining: triclinic polymorph of 2,2-aziridinedicarboxamide revisitedACTA CRYSTALLOGRAPHICA SECTION B, Issue 1 2007Marcin Podsiad Several procedures have been employed for validating structural models refined on poor quality single-crystal diffraction data. Analysis of intra- and intermolecular distances in the structures of 2,2-aziridinedicarboxamide polymorphs proved to be a robust means, and a means independent of the chosen unit cell and symmetry, of detecting several incorrect atom-type assignments in the reported structure of the triclinic polymorph of 2,2-aziridinedicarboxamide [Brückner (1982). Acta Cryst. B38, 2405,2408]. The corrected model, refined in the space group , rules out the existence of any conformational polymorphism in this compound. Small differences in the powder-diffraction patterns calculated for the original and corrected structures of the triclinic polymorph illustrate the sensitivity of the above method for polymorph validation. [source] `Segmented' crystals solved using synchrotron radiation: (2S,3R,4S,5R)-4-(10,10-dimethyl-3,3-dioxo-3,6 -thia-4-azatricyclo[5.2.1.01,5]decan-4-ylcarbonyl)-2,6-diphenylperhydropyrrolo[3,4- c]pyrrole-1,3-dioneACTA CRYSTALLOGRAPHICA SECTION C, Issue 7 2009Graeme J. Gainsford The title compound, C29H31N3O5S, forms needle-shaped `segmented' crystals, thereby inhibiting successful single-crystal data collection using conventional laboratory facilities. One crystallite of dimensions 0.15 × 0.03 × 0.01,mm yielded sufficent single-crystal diffraction data on the Australian Synchrotron PX1 beamline. The two independent molecules in the asymmetric unit are nearly superimposable and show only minor conformational deviations from closely related compounds. The molecules pack using one N,H...O hydrogen bond and several phenyl C,H...O(=S), phenyl C,H...O(=C) and methylene C,H...O(=C) hydrogen bonds and weak C,H..., interactions. [source] | ||||||||||