Polymorphic behavior of 1,2-dipalmitoyl-3-lauroyl(PP12)- and 3-myristoyl(PP14)-sn-glycerols

D. R. Kodali, D. Atkinson, D. M. Small

Research output: Contribution to journalArticle

28 Scopus citations

Abstract

The polymorphic behavior and molecular packing in different polymorphic forms of stereospecific triacylglycerols, 1,2-dipalmitoyl-3-lauroyl-sn-glycerol (PP12) and 1,2-dipalmitoyl-3-myristoyl-sn-glycerol (PP14) were examined by X-ray diffraction, differential scanning calorimetry, infrared and Raman spectroscopy techniques. The molecular packing and the polymorphic behavior of the metastable forms of these two compounds are very similar. In both compounds the isotropic liquid, on quenching, crystallizes into a hexagonally packed α-phase. The long spacing periodicity of the α-phase indicates a tilted bilayer structure to compensate the voids created by the short acyl chains. Upon heating, the α-phase converts into an orthorhombic perpendicular (O is perpendicular to) β'2-phase. The β'2-phase, on further heating, exothermally converts to β'1-phase with slightly different O is perpendicular to subcell. On incubation of PP12 near the melting temperature of β'1-phase, there is a slow (hours) conversion to a β-phase with triclinic parallel (T//) packing. However the β'1-phase of PP14 is the most stable structure and the β-phase is absent. The thermodynamic parameters of the O is perpendicular to packings of these compounds compared to those of the higher homologue, tripalmitoylglycerol, suggest that the O is perpendicular to subcell is more stable in PP12 and PP14. The X-ray diffraction long spacings indicate that all the polymorphic forms of these compounds pack in a bilayer structure. The vibrational spectra confirm the lateral chain packing and inter- and intra-molecular order/disorder in the various polymorphic forms. The Raman and infrared spectra further indicate pertrubation in the carbonyl and the end methyl plane regions of the β'-phases.

Original languageEnglish (US)
Pages (from-to)1853-1864
Number of pages12
JournalJournal of lipid research
Volume31
Issue number10
StatePublished - 1990

Keywords

  • X-ray diffraction
  • differential scanning calorimetry
  • infrared and Raman spectroscopy
  • molecular packing
  • phase behavior

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