THE INFLUENCE OF THE POLAR HEADGROUPS OF ACIDIC DIACETYLENIC PHOSPHOLIPIDS ON TUBULE FORMATION, MICROSTRUCTURE MORPHOLOGY AND LANGMUIR FILM BEHAVIOR

The effect of modification of the polar headgroup of diacetylenic phospholipids on bilayer morphology and monolayer properties has been investigated. The lipids were prepared by substituting the choline -portion of 1,2-bis(10, 12-tricosadiynoyl)-sn-glycero-3-phosphocholine with the glycols HO(CH2)nOH (n = 2, 3, 4), by means of a phospholipase D catalyzed transphosphatidylation. In the presence of CuCl2 (PH 5.6 and ionic strength 0.18), the lipid with n = 2, produced a bimodal population of small diameter (0.1 mum) and large diameter (0.9 mum) tubules, the lipid for n = 3 produced a similar bimodal distribution of tubules except that the diameter of the smaller tubules increased to 0.3 mum. No small diameter tubules were formed from the lipid where n = 4. An increase or decrease either in the pH or ionic strength decreased the yield of tubules and affected the formation of the small diameter tubules, respectively. The counteranion of the metal salt present in the aqueous medium was also found to affect tubule diameter. The molecular area of the lipids was 70 A2/molecule (n = 2), 105 A2/molecule (n = 3) and 160 A2/molecule (n = 4). Monolayer studies suggested that the packing behavior of lipids at the air-water interface in the low surface pressure region was influenced by the subphase pH, ionic strength and counteranions.