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  • Cambridge University Press (CUP)
  • International Union of Crystallography (IUCr)
  • 2000-2004  (393)
  • 1955-1959  (190)
  • 1935-1939
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  • 1
    Electronic Resource
    Electronic Resource
    The XMaS beamline at ESRF: instrumental developments and high-resolution diffraction studies (2001)
    Chester : International Union of Crystallography (IUCr)
    Journal of synchrotron radiation 8 (2001), S. 1172-1181 
    Details
    ISSN: 1600-5775
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The beamline, which is situated on a bending magnet at ESRF, comprises a unique combination of instrumentation for high-resolution and magnetic single-crystal diffraction. White-beam operation is possible, as well as focused and unfocused monochromatic modes. In addition to an eleven-axis Huber diffractometer, which facilitates simple operation in both vertical and horizontal scattering geometries, there is an in-vacuum polarization analyser and slit system, mirrors for harmonic rejection, sub 4.2 K and 1 Tesla magnetic field sample environment, plus a diamond phase plate for polarization conditioning. The instrumentation developed specifically for this beamline is described, and its use illustrated by recent scientific results.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0909049501015394
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  • 2
    Electronic Resource
    Electronic Resource
    Estimating nanoparticle size from diffraction measurements (2000)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 33 (2000), S. 1335-1341 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Nanometre-sized particles are of considerable current interest because of their special size-dependent physical properties. Debye–Scherrer diffraction patterns are often used to characterize samples, as well as to probe the structure of nanoparticles. Unfortunately, the well known `Scherrer formula' is unreliable at estimating particle size, because the assumption of an underlying crystal structure (translational symmetry) is often invalid. A simple approach is presented here which takes the Fourier transform of a Debye–Scherrer diffraction pattern. The method works well on noisy data and when only a narrow range of scattering angles is available.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889800010888
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  • 3
    Electronic Resource
    Electronic Resource
    Structure of the C123S mutant of dienelactone hydrolase (DLH) bound with the PMS moiety of the protease inhibitor phenylmethylsulfonyl fluoride (PMSF) (2000)
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 56 (2000), S. 1376-1384 
    Details
    ISSN: 1399-0047
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The structure of DLH (C123S) with PMS bound was solved to 2.5 Å resolution (R factor = 15.1%). PMSF in 2-propanol was delivered directly to crystals in drops and unexpectedly caused the crystals to dissolve. New crystals displaying a different morphology emerged within 2 h in situ, a phenomenon that appears to be described for the first time. The changed crystal form reflected altered crystal-packing arrangements elicited by structural changes to the DLH (C123S) molecule on binding inhibitor. The new unit cell remained in the P212121 space group but possessed different dimensions. The structure showed that PMS binding in DLH (C123S) caused conformational changes in the active site and in four regions of the polypeptide chain that contain reverse turns. In the active site, residues with aromatic side chains were repositioned in an edge-to-face cluster around the PMS phenyl ring. Their redistribution prevented restabilization of the triad His202 side chain, which was disordered in electron-density maps. Movements of other residues in the active site were shown to be related to the four displaced regions of the polypeptide chain. Their implied synergy suggests that DLH may be able to accommodate and catalyse a range of compounds unrelated to the natural substrate owing to an inherent coordinated flexibility in its overall structure. Implications for mechanism and further engineering studies are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0907444900010647
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  • 4
    Electronic Resource
    Electronic Resource
    A test of crystal structure prediction of small organic molecules (2000)
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 56 (2000), S. 697-714 
    Details
    ISSN: 1600-5740
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: A collaborative workshop was held in May 1999 at the Cambridge Crystallographic Data Centre to test how well currently available methods of crystal structure prediction perform when given only the atomic connectivity for an organic compound. A blind test was conducted on a selection of four compounds and a wide range of methodologies representing the principal computer programs currently available were used. There were 11 participants who were allowed to propose at most three structures for each compound. No program gave consistently reliable results. However, seven proposed structures were close to an experimental one and were classified as `correct'. One compound occurred in two polymorphs, but only one form was predicted correctly among the calculated structures. The basic problem with lattice energy based methods of crystal structure prediction is that many structures are found within a few kJ mol−1 of the global minimum. The fine detail of the force-field methodology and parametrization influences the energy ranking within each method. Nevertheless, present methods may be useful in providing a set of structures as possible polymorphs for a given molecular structure.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0108768100004584
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  • 5
    Electronic Resource
    Electronic Resource
    N-(6-Amino-3,4-dihydro-3-methyl-5-nitroso-4-oxopyrimidin-2-yl) derivatives of glycine, valine, serine, threonine and methionine: interplay of molecular, molecular–electronic and supramolecular structures (2000)
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 56 (2000), S. 882-892 
    Details
    ISSN: 1600-5740
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: In each of N-(6-amino-3,4-dihydro-3-methyl-5-nitroso-4-oxopyrimidin-2-yl)valine, C10H15N5O4 (3) (orthorhombic, P212121), N-(6-amino-3,4-dihydro-3-methyl-5-nitroso-4-oxopyrimidin-2-yl)serine monohydrate, C8H11N5O5·H2O (4) (orthorhombic, P212121), and N-(6-amino-3,4-dihydro-3-methyl-5-nitroso-4-oxopyrimidin-2-yl)threonine, C9H13N5O5(5) (monoclinic, P21), the C-nitroso fragments exhibit almost equal C—N and N—O bond lengths: the C—N range is 1.315 (3)–1.329 (3) Å and the N—O range is 1.293 (3)–1.326 (3) Å. In each compound there are also very short intermolecular O—H...O hydrogen bonds, in which carboxyl groups act as hydrogen-bond donors to the nitrosyl O atoms: the O...O distances range from 2.440 (2) to 2.504 (4) Å and the O—H...O angles lie between 161 and 163°. An interpretation of the relationship between the unusual intramolecular bond lengths and the very short intermolecular hydrogen bonds has been developed based on database analysis and computational modelling. In each of (3)–(5) there is an extensive network of intermolecular hydrogen bonds, generating three-dimensional frameworks in (3) and (5), and two-dimensional sheets in (4).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0108768100005437
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  • 6
    Electronic Resource
    Electronic Resource
    10-(4-Fluorophenyl)-3,3,6,6,9-pentamethyl-3,4,6,7,9,10-hexahydroacridine-1,8(2H,5H)-dione and 10-(4-fluorophenyl)-3,3,6,6-tetramethyl-9-propyl-3,4,6,7,9,10-hexahydroacridine-1,8(2H,5H)-dione (2001)
    Oxford [u.a.] : International Union of Crystallography (IUCr)
    Acta crystallographica 57 (2001), S. 821-824 
    Details
    ISSN: 1600-5759
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: 10-(4-Fluorophenyl)-3,3,6,6,9-pentamethyl-3,4,6,7,9,10-hexahydroacridine-1,8(2H,5H)-dione, C24H28FNO2, (I), crystallizes with two crystallographically independent molecules (which differ slightly in conformation), while 10-(4-fluorophenyl)-9-propyl-3,3,6,6-tetramethyl-3,4,6,7,9,10-hexahydroacridine-1,8(2H,5H)-dione, C26H32FNO2, (II), crystallizes with one molecule per asymmetric unit. In both structures, the central ring in the acridine moiety is in a sofa conformation, while the outer rings adopt intermediate half-chair/sofa conformations. The central pyridine ring is orthogonal to the substituted phenyl ring. In both structures, the packing of the crystal is stabilized by C—H...O intermolecular hydrogen bonds.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0108270101005662
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  • 7
    Electronic Resource
    Electronic Resource
    Aminoguanidinium hexafluorozirconate: a new ferroelectric (2001)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 34 (2001), S. 47-54 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Analysis of the atomic arrangement in anhydrous aminoguanidinium hexafluorozirconate, CN4H8ZrF6, reported by Bukvetskii, Gerasimenko & Davidovich [Koord. Khim. (1990), 16, 1479–1484], led to the prediction that it is a new ferroelectric [Abrahams, Mirsky & Nielson (1996). Acta Cryst. B52, 806–809]. Initial attempts to verify the prediction were inconclusive because of the variety of closely related materials produced under the original preparation conditions. Clarification of these conditions led to the formation of pure CN4H8ZrF6 and the growth of single crystals with dimensions as large as 7 × 7 × 2 mm. Highly reproducible calorimetric and dielectric permittivity anomalies reveal the Curie temperature Tc = 383 (1) K. At this temperature, the heat capacity Cp exhibits an entropy change of 0.7 (1) J mol−1 K−1, while the relative permittivity εr exhibits an inflection and the dielectric loss a distinct peak; the dielectric anomaly at Tc is observed only at the lowest (0.1–1 kHz) frequencies used. Dielectric hysteresis is demonstrable at 295 K under the application of ∼1 MV m−1 alternating fields and remains observable at all T 〈 Tc but not at T ≥ Tc; the prediction of ferroelectricity is hence confirmed. The value of the spontaneous polarization Ps is 0.45 (9) × 10−2 C m−2 at 298 K, with piezoelectric coefficient d33 = 1.9 (5) pC N−1 and pyroelectric coefficient p3 = 4 (1) µC m−2 K−1. Tilts of less than ∼11° by the two symmetry-independent CN4H{}_{8}^{2+} ions, combined with rotations of ∼20° or less by the N—NH3 and C—(NH2)2 groups about the central C—N bond in each cation, as all H atoms rotate into or become symmetrically distributed about the planes at z = 0 or ½, allow them to conform to mirror symmetry via polar atomic displacements of ∼0.4 Å or less by N or C, and of 0.7 Å or less by H. Corresponding displacements of less than 0.08 Å within the two symmetry-independent ZrF{}_{6}^{2-} anions also result in mirror symmetry, satisfying the structural criteria required for the development of ferroelectricity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889800015508
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  • 8
    Electronic Resource
    Electronic Resource
    High-energy X-ray diffuse scattering using Weissenberg flat-cone geometry (2000)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 33 (2000), S. 1046-1050 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: A technique for the measurement of diffuse X-ray scattering on individual reciprocal-space planes using high-energy X-ray photons is described. The method is demonstrated using a disordered crystal of the compound TlSbOGeO4 and compared to data collected with a sealed-tube Cu anode source. Measurements were made on a synchrotron undulator beamline at an energy of 45 keV using Weissenberg flat-cone geometry and a storage phosphor (image) plate to detect the scattered X-rays. Advantages of the method include: extension of the accessible diffraction space to both higher and lower wavevectors, the ability to use crystals of irregular shape without the need for complicated absorption corrections, less need to prepare sample surfaces carefully, and the ability to filter fluorescence simply.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889800005318
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  • 9
    Electronic Resource
    Electronic Resource
    Dynamics of dense, charge-stabilized suspensions of colloidal silica studied by correlation spectroscopy with coherent X-rays (2000)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 33 (2000), S. 424-427 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The dynamics of concentrated, charge-stabilized colloidal silica suspensions was studied over a wide range of wave-vectors. The short-time diffusion coefficient, D(Q), was measured for concentrated suspensions up to their solidification points by photon correlation spectroscopy with coherent X-rays and compared to free particle diffusion D0, studied by Dynamic Light Scattering (DLS) in the dilute case. Small angle X-ray scattering (SAXS) was used to determine the static structure factor S(Q). D0/D(Q) peaks for Q values corresponding to the maximum of the static structure factor showing that the mostly likely density fluctuations decay the slowest. The data allow one to estimate the diffusion coefficient D(Q) in the Q → 0 and Q → ∞ limits. Thus, hydrodynamic functions can be derived free from any modeling of the static or dynamic properties. The effects of hydrodynamic interactions on the diffusion coefficient in charge-stabilized suspensions are presented for volume fractions 0.075 〈 Φ 〈 0.28.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889800099994
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  • 10
    Electronic Resource
    Electronic Resource
    X-ray diffraction from perfect silicon crystals distorted by surface acoustic waves (2000)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 33 (2000), S. 1019-1022 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: High-resolution X-ray diffraction measurements were carried out on ZnO/Si devices under surface acoustic wave excitation and revealed some very clear satellite diffraction peaks that are obtained from the sinusoidal modulation of the near-surface region. This experiment shows that the propagation of a Rayleigh surface acoustic wave in a perfect crystal acts as a dynamical diffraction grating. The variation of the acoustic velocity has been followed across the crystal surface from the acoustic source region (beneath the ZnO film) to the far field region (not covered by the ZnO film).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889800006828
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