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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    DouglasL. DorsetRequires cookie*
 Title    How Different are the Crystal Structures of Chiral and Racemic Diacylphosphatidylethanolamines?  
 Abstract    Both chiral and racemic phosphatidylethanolamines are known to crystallize in a similar poly-morphic form with nearly the same lamellar spacing; yet published lamellar X-ray diffraction intensity data for those materials do not agree with one another, even though the peak positions in Patterson maps are nearly the same. Translational structural searches based on the crystal struc-ture of the racemic compound also lead to similar packing models with both data sets, although the agreement between model and observed data is poor for the chiral compound. A separate analysis of L-DMPE based on lamellar electron diffraction data again leads to a similar lamellar structure with a better agreement between calculated and observed structure factors. The major difference seen for enantiomeric vs. racemic compounds is that, for the racemic lipid, the lateral unit cell spacings are about 3% larger than the chiral form, perhaps indicating a more stable hydrogen bonding network, in agreement with the higher melting point of the racemic compound. Attempts to explain this difference with other head group conformations, however, have not yet produced an improved structural model. 
  Reference    Z. Naturforsch. 43c, 319—327 (1988); received November 20 1987 
  Published    1988 
  Keywords    Phospholipids, X-Ray Diffraction, Electron Diffraction 
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 TEI-XML for    default:Reihe_C/43/ZNC-1988-43c-0319.pdf 
 Identifier    ZNC-1988-43c-0319 
 Volume    43 
5Author    Herbert Brunner, Reginald GruehnRequires cookie*
 Title    Synthesis and Structure of a New Polymorph of FeNb0 4  
 Abstract    Three different polymorphs of FeNbC>4 were prepared by chemical transport. One of them is a new modification, which crystallisizes in the GaNb04-type, monoclinic, space group C2, o= 12.52 A; 6 = 3.83 A; c=6.67Ä; 107.5°. The detailed structure, composed of 2 X 2 'blocks' of corner shared metal-oxygen octahedra, was investigated by electron-diffraction and two-dimensional high resolution electron microscopy. Bisherige Untersuchungen an FeNb04, 
  Reference    (Z. Naturforsch. 31b, 318—320 [1976]; eingegangen am 21. Oktober 1975) 
  Published    1976 
  Keywords    Iron Niobate, Crystal Structure, Electron Diffraction, High Resolution Electron Microscopy 
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 TEI-XML for    default:Reihe_B/31/ZNB-1976-31b-0318.pdf 
 Identifier    ZNB-1976-31b-0318 
 Volume    31