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  • 1
    Electronic Resource
    Electronic Resource
    Oxalic acid dihydrate – an accurate low-temperature structural study using high-resolution neutron powder diffraction (1994)
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 50 (1994), S. 344-348 
    Details
    ISSN: 1600-5740
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0108768193011656
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  • 2
    Electronic Resource
    Electronic Resource
    Rapid neutron-diffraction data collection for hydrogen-bonding studies: application of the Laue diffractometer (LADI) to the case study zinc (tris)thiourea sulfate (2001)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 57 (2001), S. 429-434 
    Details
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The successful application of the newly developed image-plate neutron Laue diffractometer (LADI) at the Institut Laue–Langevin (ILL), Grenoble, France, for rapid hydrogen-bonding characterization is reported. The case study concerns the promising non-linear optical material zinc (tris)thiourea sulfate (ZTS), which contains 30 atoms in the asymmetric unit and crystallizes in the orthorhombic space group, Pca21, a = 11.0616 (9), b = 7.7264 (6), c = 15.558 (1) Å [T = 100.0 (1) K]. The results from a 12 h data collection from ZTS on LADI are compared with those obtained over 135 h using the monochromatic four-circle diffractometer D9 at the same reactor source with a crystal 13 times larger in volume. Both studies reveal the extensive hydrogen bonding and other close non-bonded contacts within the material. As expected, the results from D9 are more precise than those obtained from LADI; however, the bond geometry determined from the two experiments is the same within the larger estimated standard deviations. Furthermore, the conclusions drawn from the two studies separately regarding the nature of all supramolecular features are identical. This illustrates that LADI is eminently suitable for rapid characterization of hydrogen-bonded structures by neutron diffraction, with the gain in speed compared with traditional instrumentation being several orders of magnitude.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S010876730100349X
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  • 3
    Electronic Resource
    Electronic Resource
    On the use of neutron spin-echo to separate inelastic scattering from elastic scattering at high energy resolution (1979)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 35 (1979), S. 333-336 
    Details
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Generally the measured intensity of a Bragg peak or of elastic diffuse scattering contains an inelastic component (thermal diffuse scattering, low-lying phonon branches). Theoretical corrections for such effects are only possible in the limited number of cases where appropriate data are available. An experimental correction is difficult because the high energy resolution imposed reduces the beam intensity in a conventional experiment. In the case of neutron diffraction, the spin-echo technique proposed by Mezei [Z. Phys. (1972), 255, 146-160] for neutron spectroscopy can be used as a filter for inelastic scattering without significant loss in elastic intensity. The application of the technique to an elastic neutron-scattering experiment is described, and it is shown that for a neutron wavelength of 1.5 Å an energy resolution of better than 50 μeV can be obtained. With this energy band-pass, scattering even from very soft phonons or magnons can be avoided when studying critical scattering near phase transitions. Simple estimates also imply that more than 90% of the TDS contribution can be removed even for soft materials.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0567739479000693
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  • 4
    Electronic Resource
    Electronic Resource
    Direct observation of TDS profiles from perfect silicon single crystals on a neutron diffractometer (1981)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 37 (1981), S. 863-871 
    Details
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: TDS profiles convoluted with the instrument resolution were obtained by forming differences between diffraction profiles measured with neutrons of wavelength 0.60 Å on three perfect Si crystals of different thickness. The profiles were measured with two detector apertures for the reflections 022, 004, 044, 026, 008 and 066. From these measurements TDS correction factors α and hence a correction term ΔB for the temperature parameter of Si were derived. The temperature parameter of Si was determined for two temperatures, 92 and 292 K, as B92 = 0.212 (3) Å2 and B292 = 0.422 (3) Å2, respectively, from the refinement of 100 symmetry-inequivalent reflections measured with neutrons of wavelength 0.53 Å on an imperfect Si crystal.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0567739481001885
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  • 5
    Electronic Resource
    Electronic Resource
    Protein single-crystal diffraction with 5 Å synchrotron X-rays at the sulfur K-absorption edge (1993)
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 49 (1993), S. 308-310 
    Details
    ISSN: 1399-0047
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: . Sulfur atoms, an integral part of many proteins, are possible candidates for anomalous scattering in phase determination by multiple-wavelength methods. The main difficulty encountered is that a wavelength of about 5 Å is required to obtain a large anomalous signal from these atoms, leading to very large absorption effects. Initial experiments have been carried out using a synchrotron X-ray source, evacuated beam tubes, a diffractometer inside a vacuum chamber, a special sample holder and a suitable scattering geometry. The results are encouraging, showing that Bragg reflections can be measured, and that changes in their intensities around the absorption edge are observable.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0907444992011910
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  • 6
    Electronic Resource
    Electronic Resource
    Quasi-Laue neutron-diffraction study of the water arrangement in crystals of triclinic hen egg-white lysozyme (1999)
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 55 (1999), S. 978-987 
    Details
    ISSN: 1399-0047
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Triclinic crystals of lysozyme, hydrogen–deuterium exchanged in deuterated solvent, have been studied using neutron quasi-Laue techniques and a newly developed cylinder image-plate detector. The wavelength range employed was from 2.7 to 3.5 Å, which gave 9426 significant reflections [F ≥ 2σ(F)] to a resolution limit of 1.7 Å. The deuteration states of the H atoms in the protein molecule were identified, followed by an extensive analysis of the water structure surrounding the protein. The final R factor was 20.4% (Rfree = 22.1%). In total, the 244 observed water molecules form approximately one layer of water around the protein with far fewer water molecules located further away. Water molecules covering the apolar patches make tangential layers at 4–5 Å from the surface or form C—H\cdotsO contacts, and several water-molecule sites can be identified in the apolar cavities. Many of the water molecules are apparently orientationally disordered, and only 115 out of the 244 water molecules sit in mean single orientations. Comparison of these results with quasi-elastic neutron scattering observations of the water dynamics leads to a picture of the water molecules forming an extended constantly fluctuating network covering the protein surface.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0907444998018514
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  • 7
    Electronic Resource
    Electronic Resource
    A semi-empirical potential function for the hydrogen atom in the N(sp3)–H...O hydrogen bond (1974)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 30 (1974), S. 713-720 
    Details
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The forces acting on a hydrogen atom in equilibrium in a hydrogen bond of type N(sp3)-H . . . O are determined with the use of a known potential for the nitrogen-hydrogen bond, and the assumption that the force field consists of only three forces, namely a H . . . O attractive force, FHO, a N-H stretching restoring force FNH and a N-H bending restoring force, FCNH. With crystal-structure data for the α-ammonium group in 12 α-amino acids a relationship is set up between FHO and the distance between the hydrogen and the oxygen atoms, leading to - by integration - the potential function for the H . . . O interaction. In addition the forces FCNH are correlated with the distortions in the ammonium groups and force constants are obtained for the C-N-H bend, which are in good agreement with spectroscopic values.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S056773947400177X
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  • 8
    Electronic Resource
    Electronic Resource
    Temperature dependence of thermal vibrations in lead as determined from short-wavelength neutron diffraction data (1984)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 40 (1984), S. 127-133 
    Details
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The temperature dependence of the atomic thermal motion in lead has been studied by analysis of diffraction measurements with 0.535 and 0.844 Å neutrons. Full single-crystal data sets were collected at ten temperatures ranging from 100 K to the vicinity of the melting point at 600 K. The data were interpreted in the anharmonic one-particle-potential formalism. Significant values for both isotropic and anisotropic quartic-anharmonic potential parameters were obtained, but a single temperature-independent one- particle potential was found sufficient to describe the temperature dependence of the atomic temperature factor only above 4̃θM, where θM is the Debye temperature.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0108767384000283
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  • 9
    Electronic Resource
    Electronic Resource
    Neutron Laue diffraction studies of coenzyme cob(II)alamin (1999)
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 55 (1999), S. 51-59 
    Details
    ISSN: 1399-0047
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Using a recently designed neutron single-crystal diffractometer utilizing a narrow-band Laue concept (LADI), diffraction data were collected from a crystal of the coenzyme cob(II)alamin (B12r), crystallized from a mixture of D2O and perdeuterated acetone. The instrument was placed at the end of a cold neutron guide at the Institute Laue Langevin (ILL, Grenoble, France), and data collection with neutrons of 1.8–8.0 Å wavelength to a crystallographic resolution of 1.43 Å was complete after about 36 h. This compares favourably with a previous experiment utilizing the same crystal specimen, where more than four weeks were required to collect monochromatic diffraction data to about 1 Å resolution. Using the Laue data, the structure was solved by molecular replacement with the known X-ray crystal structure. Difference density maps revealed the atomic positions (including deuterium atoms) of seven ordered solvent water molecules and two (partially disordered) acetone molecules. These density maps were compared with corresponding maps computed with monochromatic neutron-diffraction data collected to 1.0 Å resolution using the same crystal specimen, as well as to maps derived from high-resolution (0.90 Å) synchrotron X-ray data. In spite of the better definition of atomic positions in the two high-resolution maps, the 1.43 Å LADI maps show considerable power for the determination of the location of hydrogen and deuterium positions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S090744499800660X
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  • 10
    Electronic Resource
    Electronic Resource
    A method for location of the peaks in step-scan measured Bragg reflexions (1974)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 30 (1974), S. 580-584 
    Details
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: A method for location of the peak in a step-scan-measured Bragg reflexion profile is described. It leads to a ratio between the standard deviation of the intensity and the intensity, σ(I)/I, which is near minimum. The method is based on the observation that if σ(I)/I is calculated for all possible peak widths for a given profile then σ(I)/I is minimum near the true value of the peak width, and minimal σ(I)/I can thus be used as a criterion for correct location of the peak. The intensity determined this way is however in general slightly underestimated, and the bias as well as possible corrections are discussed. In addition a simple function resembling σ(I)/I, which has proved to be useful for practical applications, is given.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0567739474001379
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