Incorporation of saturated fatty acids into phosphatidylcholine bilayers

The transition temperature of dipalmitoylglycerophosphocholine in multi-lamellar aqueous suspensions, as observed by high-sensitivity differential scanning calorimetry, is raised from 41.4 to 61.5 degrees C by addition of palmitic acid at a mole fraction of 0.67. It appears that the fatty acid chains pack in the hexagonal lattice with the lipid chains in a one-to one ratio, thereby eliminating the destabilizing crowding of the phosphatidylcholine head groups. A similar effect on dilauroylglycerophosphocholine is produced by lauric acid. The stabilizing effect is not produced in full measure by acids of different chain lengths, nor by alcohols or saturated hydrocarbons of the same chain length.