Characterization of photopolymerized diacetylenic phospholipids in liposomes and reconstituted systems

Photosensitive phospholipids have been employed to probe the molecular structure and motional dynamics of biological membranes and their models. The presence of a small photolabile group permits the generation of reactive species with minimal perturbation of the structure of the membrane in which they reside. In contrast to their use as photoaffinity labels, our approach toward photosensitive phospholipids has been the preparation of polymers. Recently, lipid polymers have been generated by the incorporation of diacetylenic, butadienic, vinylic, acryloylic and methacryloylic moieties into the fatty acyl chains of synthetic lipids. The biosynthetic incorporation of diacetylenic fatty acids into the membrane glycolipids and phospholipids of auxotrophic organisms permits the isolation of polymerizable lipids whose structures are difficult to obtain by synthetic routes. Thus, a wide assortment of synthetic and biosynthetic membrane lipids are available for the preparation of novel polymers. We have synthesized phospholipids which contain diacetylene groups in one or both of their acyl chains. These phospholipid molecules form crystalline polymers upon irradiation with ultraviolet light. We have used polymeric phospholipids as models of biological membranes and in biomedical applications. In this brief review, we will discuss the physicochemical properties of monomeric diacetylenes and their phospholipid polymers in biological membranes and liposomes; recent results obtained with reconstituted systems will also be presented