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'Crystal Structure' in keywords Facet   section ZfN Section C:Volume 033  [X]
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1978 (2)
1Author    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 
2Author    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