Phase separations of alpha-tocopherol in aqueous dispersions of distearoylphosphatidylethanolamine.
The effect of alpha-tocopherol on the structure and thermotropic phase behaviour of distearoylphosphatidylethanolamine was examined by using synchrotron X-ray diffraction methods. There was evidence that alpha-tocopherol does not distribute randomly in the dispersed phospholipid but instead phospholipid phases enriched in alpha-tocopherol are formed. Heating codispersions from lamellar gel phase induced formation of hexagonal-II phase at temperatures below the main transition of the pure phospholipid and which were enriched in alpha-tocopherol. Codispersions containing 5 or 10 mol% alpha-tocopherol were induced to form a cubic phase at temperatures above the lamellar to hexagonal-II phase transition. Such phases were not observed in codispersions containing 2.5 or 20 mol% alpha-tocopherol in which only lamellar and hexagonal-II phases were formed. The space group of the cubic phases were tentatively assigned as Pn3m. Equilibration of codispersions at 4 degrees C results in the formation of lamellar crystalline phases enriched in alpha-tocopherol and phase separated domains of pure phospholipid. Two lamellar crystalline phases were characterized on the basis of their particular wide-angle X-ray scattering patterns. The lamellar crystalline phases were also distinguished from other lamellar phases of the pure phospholipid by the lamellar repeat. Partitioning of alpha-tocopherol into phosphatidylethanolamine domains in membranes may introduce instability into the structure.
Wang
Xiaoyuan
X
Division of Life Sciences, King's College London, 150 Stamford Street, SE1 9NN, London, UK.
Quinn
Peter J
PJ
D005782:Gels; D021962:Membrane Microdomains; D008567:Membranes, Artificial; D015394:Molecular Structure; D010714:Phosphatidylethanolamines / Q000737:chemistry* / Q000378:metabolism; D017356:Synchrotrons; D013696:Temperature; D014961:X-Ray Diffraction / Q000379:methods; D024502:alpha-Tocopherol / Q000378:metabolism / Q000494:pharmacology*
D005782:Gels; D008567:Membranes, Artificial; D010714:Phosphatidylethanolamines; C038089:1,2-distearoylphosphatidylethanolamine; D024502:alpha-Tocopherol