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  • 1
    Electronic Resource
    Electronic Resource
    Direct determination of polymer crystal structures by electron crystallography – isotactic poly(1-butene), form (III) (1994)
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 50 (1994), S. 201-208 
    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/S0108768193009140
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  • 2
    Electronic Resource
    Electronic Resource
    Electron Crystallography of Small Organic Molecules: Criteria for Data Collection and Strategies for Structure Solution (1998)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 31 (1998), S. 544-553 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: By crystallization onto an organic substrate such as naphthalene, thin microcrystals of a small organic molecule, such as triphenylene, can be grown. These crystals are less perturbed by shear and erratic bend disorder than the samples produced by rapid growth from dilute solutions. Selected-area electron diffraction intensities are consistent from specimen to specimen, show the symmetry expected for the crystalline projection and, furthermore, correspond to the Fourier transform of the entire unit cell. However, under sampling of the three-dimensional reciprocal lattice by goniometry can frustrate structure determination if conventional direct methods are used. Nevertheless, the crystal structure may still be solved quite accurately by energy minimization.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S002188989701618X
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  • 3
    Electronic Resource
    Electronic Resource
    Disorder and the molecular packing of C60 buckminsterfullerene: a direct electron-crystallographic analysis (1994)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 50 (1994), S. 344-351 
    Details
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The crystal structure of C60 buckminsterfullerene was determined at room temperature by a direct phasing analysis of single-crystal electron-diffraction intensity data. The initial electrostatic potential map is well fit by a regular icosahedron of C atoms but with an average rotational disorder corresponding to Fm3m symmetry. The static appearance of this directly determined map, however, does not refute the notion of uncorrelated molecular positions in the crystal lattice, indicated earlier by nuclear-magnetic resonance spectroscopy and neutron scattering. Although the direct determination of crystallographic phases is correct, the occurrence of strong axial h00 reflections in the electron diffraction patterns appears to be a result of secondary scattering. Correction for this perturbation produces a good fit of the intensities to an isotropic spherical shell of C atoms. In fact, the static appearance of the initial potential map is artificial, owing to the use of only a limited set of phased structure factors in the Fourier transform carried out after the ab initio structure analysis.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0108767393012607
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    Paper (German National Licenses)
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  • 4
    Electronic Resource
    Electronic Resource
    Automated structure analysis in electron crystallography: phase determination with the tangent formula and least-squares refinement. Erratum (1994)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 50 (1994), S. 793-793 
    Details
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: A typesetting error is corrected in the paper by Dorset & McCourt [Acta Cryst. (1994), A50, 287–292]. In Table 2 on page 290, the x coordinate for Cl after least-squares refinement should read −0.181.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0108767394009530
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  • 5
    Electronic Resource
    Electronic Resource
    Automated structure analysis in electron crystallography: phase determination with the tangent formula and least-squares refinement (1994)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 50 (1994), S. 287-292 
    Details
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The tangent formula (computer program QTAN) is used as an automated phasing technique to solve the crystal structure of 2,5-piperazinedione from published electron-diffraction intensity data. Unlike the case of the thiourea polymorphs studied previously, the correct phase set does not correspond to the lowest value of NQEST, so that four potential maps must be calculated before a chemically recognizable structure is seen. Even though dynamical scattering presents some difficulty in identifying the correct structure by changing some low-magnitude |Eh| `cross terms', hence affecting the NQEST figure of merit, it is still possible to refine the atomic coordinates found on the potential map by full-matrix least squares, leading to a structure similar to the earlier X-ray determination.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S010876739300916X
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  • 6
    Electronic Resource
    Electronic Resource
    Electron diffraction from phospholipids – an approximate correction for dynamical scattering and tests for a correct phase determination (1993)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 26 (1993), S. 778-786 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: An approximate experimental correction of electron diffraction intensities from an epitaxically crystallized phospholipid bilayer for dynamical scattering is described. This correction, which is useful for certain low-angle centrosymmetric data sets, compares intensities recorded at high and low electron-accelerating voltages to ascertain which reflections are most affected by n-beam interactions. When applied to experimental intensity data from 1,2-dihexadecyl-sn-glycerophosphoethanolamine (DHPE), the correction facilitates a direct phase determination based on the probabilistic estimate of three-phase invariants because a more accurate estimate of the hierarchy of |El| values is obtained. When a multisolution technique is used, incorporating algebraic unknowns for certain phase values, the best phase assignment can be assessed by comparison of the single convolution of phased structure factors to the observed structure-factor magnitudes for the low-voltage data. This approach exploits an approximate analogy made earlier by Moodie between the Sayre equation and the phase grating series and is valid as long as the single convolution adequately models experimental low-voltage data (a condition favored by light-atom structures in a low-angle region of reciprocal space). In real space, the correct structure can also be readily identified as the one having the smoothest density profile.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889893005394
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    Paper (German National Licenses)
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