THE STABILIZATION OF TUBULES FORMED FROM HETEROBIFUNCTIONAL PHOSPHOLIPIDS

The formation properties of hollow, cylindrical microstructures or tub ules (0.4-0.5 mum diameter and length up to 300 mum) and their stabili zation from phospholipids equipped with heterobifunctional groups are reported. Two phospholipids, a-10,12-diyn-22-enoyl)-sn-glycero-3-phosp hocholine (1) and -diyn-24-methacryloyl)-sn-glycero-3-phosphocholine ( 2), were synthesized. These lipids contain an olefinic or methacryloyl group at the acyl chain terminus in addition to diacetylenic group to provide additional polymerization in lipid bilayers. Tubule formation was observed from 1 and 2 and from mixtures of 1 with tricosa-10,12-d iynoyl)-sn-glycero-3-phosphocholine (3). Differential scanning calorim etry and Langmuir film studies demonstrated that phospholipids 1 and 3 were miscible. Polymerization of tubules from 1 and 2 by UV and gamma radiation (Co-60) was characterized by thin layer chromatography, FT- IR, and NMR. Polymerization by gamma radiation disrupted the morpholog y of tubules formed from 1. The effect of polymerization on tubules fo rmed from 2 was dependent on temperature. Tubule formation properties and the effect of polymerization on the resultant morphology of tubule s formed from mixtures of 1 and 3 depended on the lipid ratio in the m ixtures. At 1:2 and 1:1 molar ratios of 1 to 3, complete conversion of lipid into 20-30 mum and 30-40 mum tubules was observed by optical an d transmission electron microscopy. Tubules polymerized by a combinati on of UV and gamma radiation retained the tubule morphology and were s table to ultrasonic agitation, and lyophilization followed by redisper sion. At 3:1 molar ratio of 1 to 3, 15-20 mum long tubules were observ ed. The lipids were only partially polymerized by UV and gamma radiati on and some disruption of tubule morphology was observed.