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  • 1
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 41 (1985), S. 571-577 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The probabilistic theory of the three-phase structure invariants for a pair of isomorphous structures [Hauptman (1982). Acta Cryst. A38, 289-294] is reexamined. The analysis leads to distributions capable of estimating cosine invariants in the full range of -1 to +1. In particular, it is shown that heavy-atom substructure information can be incorporated easily into the distributions. The initial applications, using calculated diffraction data from the protein cytochrome c550, MR ∼ 14 500, and its PtCl2-4 derivative show that a remarkable increase in accuracy results from the use of the revised distributions, particularly after the incorporation of heavy-atom substructure information. Finally, it is shown that in the individual phase determinations the redundant cosine invariants play a role identical to that of the multiple isomorphous derivatives and thus provide the basis for the solution of the phase problem in the single isomorphous replacement case.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
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  • 2
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 42 (1986), S. 149-156 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The theoretical basis for the integration of direct methods into the single-wavelength anomalous dispersion technique is reexamined. The analysis shows that the approximations responsible for the ability to obtain unique estimates of the two- and three-phase structure invariants [Hauptman (1982). Acta Cryst. A38, 632-641; Giacovazzo (1983). Acta Cryst. A39, 585-592] or twofold estimates of the three-phase structure invariants [Kroon, Spek & Krabbendam (1977). Acta Cryst. A33, 382-385] are also responsible for the substantial errors observed in the applications. It is shown that, in the general case, the method of joint probability distributions leads to twofold estimates of the two-phase invariants and eightfold estimates of the three-phase invariants. Finally, it is shown that more accurately determined three-phase invariant estimates can be obtained by the use of anomalous scatterer substructure information, when available, and the use of a strategy that recognizes cases in which the eight estimates are clustered around one or two values. These cases are then distinguished from those where the eight estimates are widely scattered by a weighting function.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Oxford [u.a.] : International Union of Crystallography (IUCr)
    Acta crystallographica 41 (1985), S. 411-413 
    ISSN: 1600-5759
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
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