gamma-ray irradiation of liposomes of polymerizable phospholipids containing octadeca-2,4-dienoyl groups and characterization of the irradiated liposomes

The synthesis of a variety of polymerizable phospholipids containing the oc tadeca-2,4-dienoyl moiety on 2-acyl chains and the characteristics of lipos omes containing those phospholipids of the gamma-irradiation are described. We synthesized three different polymerizable phosphocholines that have dif ferent 1-acyl chain lengths with the octadeca-2,4-dienoyl moiety on the 2-a cyl chain: myristoyl (MODPC), palmitoyl (PODPC) and stearoyl (SODPC). The l iposomes were prepared by extrusion through polycarbonate filters with a po re size of 0.2 mu m, and were polymerized by gamma-irradiation with various dose rates. The polymerization rate increased in the order SODPC > MODPC > PODPC. The mechanism of the polymerization of SODPC was the same as that o f 1,2-bis-[(E,E)-octadeca-2,4-dienoyl]-sn-glycero-3-phosphocholine (DODPC), but differed from that of MODPC and PODPC. Freeze-thaw testing was used to evaluate the stability of the polymerizable liposomes. The MODPC liposome was more stable than other monofunctional liposomes. For similar irradiatio n, the polymerization behavior of the liposomes was significantly affected by the 1-acyl length.