Synthesis and polymorphic phase behaviour of polyunsaturated phosphatidylcholines and phosphatidylethanolamines.
A series of phosphatidylcholines and phosphatidylethanolamines was synthesized containing two acyl chains of the following polyunsaturated fatty acids: linoleic acid (18:2), linolenic acid (18:3), arachidonic acid (20:4) and docosahexaenoic acid (22:6). In addition two phospholipids with mixed acid composition were synthesized: 16:0/18:1c phosphatidylcholine and 16:0/18:1c phosphatidylethanolamine. The structural properties of these lipids in aqueous dispersions in the absence and in the presence of equimolar cholesterol were studied using 31P-NMR, freeze fracturing and differential scanning calorimetry (DSC). The phosphatidylcholines adopt a bilayer configuration above 0 degrees C. Incorporation of 50 mol% of cholesterol in polyunsaturated species induces a transition at elevated temperatures into structures with 31P-NMR characteristics typical of non-bilayer organizations. When the acyl chains contain three or more double bonds, this non-bilayer organization is most likely the hexagonal HII phase. 16:0/18:1c phosphatidylethanolamine shows a bilayer to hexagonal transition temperature of 75 degrees C. The polyunsaturated phosphatidylethanolamines exhibit a bilayer to hexagonal transition temperature below 0 degrees C which decreases with increasing unsaturation and which is lowered by approximately 10 degrees C upon incorporation of 50 mol% of cholesterol. Finally, it was found that small amounts of polyunsaturated fatty acyl chains in a phosphatidylethanolamine disproportionally lower its bilayer to hexagonal transition temperature.
D002151:Calorimetry; D055598:Chemical Phenomena; D002627:Chemistry, Physical; D002784:Cholesterol; D005231:Fatty Acids, Unsaturated; D005614:Freeze Fracturing; D009682:Magnetic Resonance Spectroscopy; D008563:Membrane Lipids; D010713:Phosphatidylcholines / Q000138:chemical synthesis*; D010714:Phosphatidylethanolamines / Q000138:chemical synthesis*; D013329:Structure-Activity Relationship; D013696:Temperature
D005231:Fatty Acids, Unsaturated; D008563:Membrane Lipids; D010713:Phosphatidylcholines; D010714:Phosphatidylethanolamines; D002784:Cholesterol