2-DIMENSIONAL POLYMERIZATION OF SUPRAMOLECULAR ASSEMBLIES - SYNTHESISAND BILAYER POLYMERIZATION OF LIPIDS CONTAINING ALPHA-METHYLENE-SUBSTITUTED ACYL CHAINS

Polymerization of lipid assemblies may be usefully employed to alter t he properties of the assemblies. The possible locations of the reactiv e group in the lipids include (1) the chain terminus, (2) the head gro up, and (3) near the lipid backbone. The third strategy yields polymer ized assemblies which retain their head group functionality and lipid chain motion. We have designed and synthesized new members of this lat er category by the use of 2-methylene-substituted acyl chains. The mai n transition temperature (T(m)) from gel to liquid crystalline phase o f hydrated bilayers of (2-methylene)palmitoyl-sn-glycero-3-phosphochol ine (1) and the disubstituted 1,2-bis (2-methylenepalmitoyl) -sn-glyce ro-3-phosphocholine (2) were 33.6 and 25.3-degrees-C, respectively. Th e T(m) of the mono-substituted (2-methylene)palmitoyl-sn-glycero-3-pho sphocholine (3) bilayers was detected in a range from -15 to -10-degre es-C by x-ray diffraction. Hydrated bilayers of each individual lipid were successfully polymerized with a water-soluble initiator, azobis ( 2-amidinopropane) dihydrochloride (AAPD). These results indicate the l ipid 2-methylene groups are accessible to the water interface. Thermal polymerization of the mono-substituted lipids in aqueous suspensions with AAPD, yielded oligomers. However the bis-2-methylene PC (2) was s uccessfully polymerized to yield stabilized crosslinked bilayers. (C) 1994 John Wiley & Sons, Inc.