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1992 (1)
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1977 (1)
1Author    DouglasL. Dorset, AnthonyJ. HancockRequires cookie*
 Title    Glycerol Conformation and the Crystal Structure of Lipids. I. An Electron Diffraction Study of Tripalmitin and Conformationally Fixed Analogs  
 Abstract    Transmission electron diffraction is used as a qualitative analytical probe of poly methylene chain packing in three conformationally-restricted analogs of tripalmitin derived from configura­ tional isomers of cyclopentane-l,2,3-triol. The analysis demonstrates that the all trans "tuning-fork" conformation seen in X-ray crystal structure analyses on homologous compounds is also found in microcrystals, in contrast to a proposal by Fringeli et al. (Z. Naturforsch. 27 b, 780 [1972]) that an all cis conformation of the triglyceride exists in solvent-grown microcrystals and in multilayers. The presence of mixed polymorphs is also shown for bulk samples previously examined by X-ray powder diffraction techniques by other workers. 
  Reference    (Z. Naturforsch. 32c, 573 [1977]; received March 28 1977) 
  Published    1977 
  Keywords    Triglycerides, Crystal Structure, Electron Diffraction 
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 TEI-XML for    default:Reihe_C/32/ZNC-1977-32c-0573.pdf 
 Identifier    ZNC-1977-32c-0573 
 Volume    32 
2Author    DouglasL. Dorset, WalterA. Pangborn, AnthonyJ. Hancock, IrisS. LeeRequires cookie*
 Title    Influence of Molecular Conformation on the Solid State Packing of 1,2-Diglycerides Study of 1,2-Dipalmitin and Some Structural Analogs by Electron Diffraction, X-Ray Diffraction, and Infrared Spectroscopy  
 Abstract    Diffraction studies on natural 1,2-dipalmitin and on analogs, including those based on the configurational isomers of cyclopentane-l,2,3-triol reveal that the 1,2-diglycerides crystallize from solvent with chain methylene packing identical to the monoclinic form of even-chain alkanes. The chains probably are folded back in "hairpin" fashion as found in phospholipid crystal structures. Acyl shifts are observed to occur in the crystalline solid state at room temperature to give the 1,3-diglyceride. Analogs based on the above-mentioned cyclitols show that isomers with adjacent chains trans to the ring (possibly extended chain packing) or with chains cis to the ring ("hair­ pin") crystallize readily. Both possibly extended chain configurational isomers have the a-form as well as /?'-forms and a /5-polymorph. The hairpin isomers each give a /?'-polymorph but only the all-cts isomer gives an «-form. 
  Reference    Z. Naturforsch. 33c, 39 (1978); received July 29/October 3 1977 
  Published    1978 
  Keywords    Diglycerides, Crystal Structure, Electron Diffraction, X-Ray Diffraction 
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 TEI-XML for    default:Reihe_C/33/ZNC-1978-33c-0039.pdf 
 Identifier    ZNC-1978-33c-0039 
 Volume    33 
3Author    DouglasL. Dorset, WalterA. Pangborn, AnthonyJ. Hancock, TonC. Van Soest, S. M. GreenwaldRequires cookie*
 Title    Glycerol Conformation and the Crystal Structure of Lipids II. A Further Study of Tripalmitin and Conformationally Fixed Analogs by Small-Angle X-Ray Diffraction and Reflection Electron Diffraction  
 Abstract    The utility of analogs to glycerol-containing lipids based on the configurational isomers of cyclo-pentane-l,2,3-triol for ab initio crystal structure analysis via electron diffraction is assessed further. Such analogs of tripalmitin are examined with the natural triglyceride via low angle X-ray diffrac­ tion. The 1,3/2 (all-irarcs) and 1,2/3 (cis-trans) analogs give long spacing dimensions some 23 Ä greater than found for the ß-2 form of the natural compound, consistent with the long spacing observed for a ß-3 form. The 1,2,3/0 (all-cis) analog gives a long spacing near that of the a-form of the triglyceride. Reflection electron diffraction measurements on the 1,3/2 and 1,2/3 analogs reveal a chain tilt near 60° for both and untilted chains for 1,2,3/0. A more accurate tilt determina­ tion from X-ray long spacings of the homologous series of 1,3/2 pseudotrilaurin to 1,3/2 pseudo-tripalmitin confirm the 67° tilt expected for the ß-3 form. Therefore, given the same T,, methylene subcell, the molecular packing is very close to natural triglycerides. The subtle influences of the cyclopentane ring are overcome for 1,3/2 analogs based on stearic and arachidic acids. This emphasizes the utility of these structural analogs for ab initio crystal structure determinations of glycerol containing lipids. 
  Reference    Z. Naturforsch. 33c, 50 (1978); received October ll/November 28 1977 
  Published    1978 
  Keywords    Triglycerides, Crystal Structure, X-Ray Diffraction, Electron Diffraction 
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 TEI-XML for    default:Reihe_C/33/ZNC-1978-33c-0050.pdf 
 Identifier    ZNC-1978-33c-0050 
 Volume    33 
4Author    M. Athias, O. Senge, H. Äkon, Hope, KevinM. SmithRequires cookie*
 Title    Structure and Conformation of Photosynthetic Pigments and Related Compounds 3. Crystal Structure of ß-Carotene  
 Abstract    The crystal structure o f the title compound (C40H 56, M w = 536.8) has been redetermined by X-ray diffraction methods in order to achieve a structure at higher resolu­ tion suitable for theoretical calculations. The crystal sys­ tem is monoclinic, P2 ,/«, a = 7.656(2), b = 9.445(5), c -23.536(15) Ä , ß = 93.41(2)°, V = 1698.8(15) Ä 3, Z = 2, D = 1.050 m g/m 3, 130 K. R = 0.071, R w = 0.076. 
  Reference    Z. Naturforsch. 47c, 474 (1992); received June 4 1991/February 24 1992 
  Published    1992 
  Keywords    Crystal Structure, ß-Carotene, Carotenoids, Photosynthesis 
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 TEI-XML for    default:Reihe_C/47/ZNC-1992-47c-0474_n.pdf 
 Identifier    ZNC-1992-47c-0474_n 
 Volume    47 
5Author    U. Kreibig, C. W. EtterRequires cookie*
 Title    Light Diffraction of in vitro Crystals of Six Tobacco Mosaic Viruses  
 Abstract    Iridescent gels o f the common, tomato mosaic, para-tobacco mosaic, ribgrass mosaic, sunnhemp mosaic, and cucumber 4 tobacco mosaic virus strains were prepared using the purification method of Boedtker and Simmons (J. Amer. Chem. Soc. 1958). Macrocrystals which were stable for many months could be grown from iridescent gels of all viruses when stored at 0 -1 0 °C. The gels exhibited various structural phases (nematic and smectic) differing in density. The structure of the microcrystalline gels and of macrocrystals was investigated by means of optical diffraction. Distinct Bragg reflections were observed from which a mean periodicity of 340 nm was derived for all virus strains. The results indicate a crystalline multilayer structure as first proposed by Oster (J. Gen. Physiol. 33, 445, [1950]). The angular positions and widths of the Bragg reflections depended on the concentration of virus and the ionic strength. The periodicity decreased from 365 nm at 30 mg/ml virus to about 315 nm at 109 mg/ml virus, i.e. the periodicity approached the 300 nm length o f the virion. Model calculations taking into account Debye-Hückel repulsive and van der Waals attractive forces gave a qualitative explanation for the crystalline structure and its observed concentration dependence. The in vitro crystals resemble immature crystal forms observed in the living cell. 
  Reference    Z. Naturforsch. 35c, 750—762 (1980); received March 7 1980 
  Published    1980 
  Keywords    Tobacco Mosaic Viruses, Crystallization, Phase Transitions, Light Diffraction, Crystal Structure, Model Calculations 
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 TEI-XML for    default:Reihe_C/35/ZNC-1980-35c-0750.pdf 
 Identifier    ZNC-1980-35c-0750 
 Volume    35