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  • 1
    Electronic Resource
    Electronic Resource
    On the quantitative determination of triplet phases by X-ray three-beam diffraction (1990)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 46 (1990), S. 387-393 
    Details
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Calculations of the integrated diffracted intensity for Renninger experiments, i.e. calculations of ψ-scan profiles scanning through three-beam positions, are reported. The fundamental equations of the dynamical theory are solved by means of an eigenvalue procedure and boundary conditions consistent with the diffraction geometry. It is shown that for noncentrosymmetric structures the three-beam ψ-scan profiles bear information on both the magnitude, defined in the range 0 ≤ |φ| ≤ 180°, and the sign of the triplet phase involved in the three-beam interference. In general, the ψ-scan profiles can be separated into two parts: a phase-dependent part ('ideal' profile) due to the interference effect and a symmetric phase-independent Umweganregung or Aufhellung profile due to the mean energy flow in a three-beam case. Both parts can be calculated by summing up the ψ-scan profiles for + φ and -φ, one profile being reversed with respect to the three-beam point. As a result, the experimentally best suited three-beam cases for triplet phase determination should involve structure factors of nearly equal magnitude.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0108767389013863
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  • 2
    Electronic Resource
    Electronic Resource
    Direct measurements of triplet phase relationships of organic non-centrosymmetric structures using synchrotron radiation (1990)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 46 (1990), S. 393-402 
    Details
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Recent progress in experimental triplet phase determination by the method of three-beam diffraction for non-centrosymmetric light-atom structures is reported. The measurements were carried out with a special ψ-circle diffractometer installed at the DORIS II storage ring in Hamburg. Experimental results confirm the theoretical considerations. In general, the ψ-scan profiles consist of a phase-independent Umweganregung or Aufhellung part superimposed on a phase-dependent part due to the three-beam interference, which contains the phase information. Experimentally, Umweganregung and Aufhellung effects can be evaluated by comparison of the two centrosymmetrically related three-beam cases. It is shown that with moderate phase-independent effects the triplet phase can be determined with an accuracy of about 45°.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0108767389013875
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  • 3
    Electronic Resource
    Electronic Resource
    Improvements in lysozyme protein crystal perfection through microgravity growth (1995)
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 51 (1995), S. 1099-1102 
    Details
    ISSN: 1399-0047
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Microgravity offers an environment for protein crystallization where there is an absence of convection and sedimentation. We have investigated the effect of microgravity conditions on the perfection of protein crystals. The quality of crystals for X-ray diffraction studies is characterized by a number of factors, namely size, mosaicity and the resolution limit. By using tetragonal lysozyme crystals as a test case we show, with crystal growth in two separate Space Shuttle missions, that the mosaicity is improved by a factor of three to four over earth-grown ground control values. These microgravity-grown protein crystals are then essentially perfect diffraction gratings. As a result the peak to background of individual X-ray diffraction reflections is enhanced by a similar factor to the reduction in the mosaicity. This then offers a particularly important opportunity for improving the measurement of weak reflections such as occur at high diffraction resolution. These microgravity results set a benchmark for all future microgravity and earth-based protein crystallography procedures.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0907444995012170
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  • 4
    Electronic Resource
    Electronic Resource
    Partial Improvement of Crystal Quality for Microgravity-Grown Apocrustacyanin C1 (1997)
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 53 (1997), S. 231-239 
    Details
    ISSN: 1399-0047
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The protein apocrustacyanin C1 has been crystallized by vapour diffusion in both microgravity (the NASA space shuttle USML-2 mission) and on the ground. Rocking width measurements were made on the crystals at the ESRF Swiss-Norwegian beamline using a high-resolution ψ-circle diffractometer from the University of Karlsruhe. Crystal perfection was then evaluated, from comparison of the reflection rocking curves from a total of five crystals (three grown in microgravity and two earth controls), and by plotting mosaicity versus reflection signal/noise. Comparison was then made with previous measurements of almost `perfect' lysozyme crystals grown aboard IML-2 and Spacehab-I and reported by Snell et al. [Snell, Weisgerber, Helliwell, Weckert, Hölzer & Schroer (1995). Acta Cryst. D51, 1099–1102]. Overall, the best diffraction-quality apocrustacyanin C1 crystal was microgravity grown, but one earth-grown crystal was as good as one of the other microgravity-grown crystals. The remaining two crystals (one from microgravity and one from earth) were poorer than the other three and of fairly equal quality. Crystal movement during growth in microgravity, resulting from the use of vapour-diffusion geometry, may be the cause of not realising the `theoretical' limit of perfect protein crystal quality.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0907444996013996
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  • 5
    Electronic Resource
    Electronic Resource
    Direct determination of triplet phases and enantiomorphs of non-centrosymmetric structures. II. Experimental results (1989)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 45 (1989), S. 182-187 
    Details
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Direct measurements of triplet phase relationships for non-centrosymmetric light-atom organic structures with medium-size unit cells are reported. The phase information can be extracted from the three- beam profiles of a Renninger ψ-scan experiment. The measurements were carried out with a special ψ-circle diffractometer installed on a rotating Cu-anode generator. The incident-beam divergence is reduced to 0.02°. The experimental results confirm the theoretical considerations of paper I of this work [Hümmer & Billy (1986). Acta Cryst. A42, 127-133]. As triplet phases of +90° can be distinguished, the absolute structure can be determined unambiguously. The measurements show that the triplet-phase-dependent interference effects may be superposed on phase-independent Umweganregung or Aufhellung effects. By a comparison of the ψ-scan profiles of two centrosymmetrically related three-beam cases, the triplet phases of which have opposite signs, it is possible to evaluate the phase-independent effects and to determine the value of the triplet phase with an accuracy of at least 90°.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0108767388011067
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  • 6
    Electronic Resource
    Electronic Resource
    Synthesis and structural characterization of an AI 77 cluster (1997)
    [s.l.] : Nature Publishing Group
    Nature 387 (1997), S. 379-381 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] In the experiments described here our aim was to prepare polyhedral Al(i) compounds containing more than four Al atoms using N(SiMe3)2 ligands for protection. A solution of aluminium(i) iodide5 in a solvent mixture of toluene and diethyl ether was added to a solution of base-free LiN(SiMe3)2 at -78 ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/387379a0
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  • 7
    Electronic Resource
    Electronic Resource
    The absolute configuration of chiromodine
    Amsterdam : Elsevier
    Phytochemistry 31 (1992), S. 2170-2172 
    Details
    ISSN: 0031-9422
    Keywords: Croton megalocarpus ; Euphorbiaceae ; X-ray crystal structure. ; absolute configuration ; chiromodine ; clerodane diterpene
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Biology , Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://linkinghub.elsevier.com/retrieve/pii/0031-9422(92)80393-S
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  • 8
    Electronic Resource
    Electronic Resource
    The absolute configuration of kinoin C
    Amsterdam : Elsevier
    Phytochemistry 33 (1993), S. 447-448 
    Details
    ISSN: 0031-9422
    Keywords: 3α-16α-dihydroxy-4,4,9,14-tetramethyl-(9β,10α)-19-norpregn-5-ene-11,20-d ; Cucurbitaccae ; Ibervillea sonorae ; X-ray crystal structure. ; absolute configuration ; hexanorcucurbitacin ; kinoin C
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Biology , Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://linkinghub.elsevier.com/retrieve/pii/0031-9422(93)85536-Z
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  • 9
    Electronic Resource
    Electronic Resource
    4,4'-Bis(2,4,6-trimethylbenzenesulfonamido)diphenylmethane (1996)
    Oxford [u.a.] : International Union of Crystallography (IUCr)
    Acta crystallographica 52 (1996), S. 2303-2305 
    Details
    ISSN: 1600-5759
    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/S0108270196002016
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  • 10
    Electronic Resource
    Electronic Resource
    The absolute configuration of (+)-2-benzyl-2-[N-(α-phenylethyl)amino]cyclohexanone hydrochloride (1993)
    Oxford [u.a.] : International Union of Crystallography (IUCr)
    Acta crystallographica 49 (1993), S. 307-310 
    Details
    ISSN: 1600-5759
    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/S0108270192008965
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