Phase metastability and supercooled metastable state of diundecanoylphosphatidylethanolamine bilayers.
Aqueous dispersons of L-alpha-phosphatidylethanolamine (PE) with identical saturated acyl chains are known to exhibit gel-state metastability. It is also known that the metastability in PE becomes more pronounced with decreasing acyl chain-length. In an attempt to study the metastable phase behavior of PE, we have synthesized diundecanoylphosphatidylethanolamine (diC11PE) and examined its polymorphic phase behavior. A single endothermic transition at 38 degrees C is detected between 10 and 55 degrees C by DSC for the nonheated sample of diC11PE in excess water. An immediate second heating scan done after cooling slowly of the same sample from the liquid-crystalline state shows a smaller endothermic transition at a lower temperature, 18 degrees C. However, the high-temperature transition at 38 degrees C can be detected, if the sample which has been heated above 38 degrees C is quench cooled from the liquid-crystalline to a temperature between 18 and 38 degrees C. Furthermore, two endothermic transitions at 18 and 38 degrees C and an exothermic transition at 19 degrees C are recorded for diC11PE after quench supercooling of the sample from the liquid-crystalline state to an appropriate temperature below 10 degrees C. The gel-state metastability of diC11PE can be most appropriately explained in terms of changes in interbilayer headgroup-headgroup interactions. It is suggested that the kinetically trapped supercooled metastable state may be a multilamellar structure with melted acyl chains but with strong interbilayer headgroup-headgroup interactions.
Xu
H
H
Department of Biochemistry, University of Virginia School of Medicine, Charlottesville 22908.
Stephenson
F A
FA
Lin
H N
HN
Huang
C H
CH
D002151:Calorimetry; D008051:Lipid Bilayers / Q000378:metabolism*; D009682:Magnetic Resonance Spectroscopy; D010714:Phosphatidylethanolamines / Q000378:metabolism*; D013696:Temperature
D008051:Lipid Bilayers; D010714:Phosphatidylethanolamines; C056766:1,2-diundecanoylphosphatidylethanolamine