Liposomes composed of dioleoylphosphatidylethanolamine and 2-(hexadecyloxy)cinnamic acid: effects of UV irradiation and pH value on release.

Novel liposomes composed of dioleoylphosphatidylethanolamine (DOPE) and 2-(hexadecyloxy) cinnamic acid (HOCA) were prepared by a detergent removal method. When the molar ratio of DOPE to HOCA was 4:1, 3:2, and 2:3, the florescence quenching degree of 5(6)-carboxylic fluorescein (CF, a fluorescence marker) loaded in the assemblies was 62.4%, 68.9%, and 72.5%, respectively. The quenching degree was fairly high, indicating the assemblies were closed bilayer vesicles (liposomes). The release degree in 60 min of CF from the DOPE/HOCA liposomes was 9.6% to 15.7%, when the liposomes were subjected to the irradiation of a UV light (e.g., lambda = 254 nm). The photo-dimerization of the cinnamic acid residue of HOCA may destabilize the liposomal membrane, leading to a significant release. In addition, DOPE/HOCA (4/1) liposome exhibited a pH-sensitive release. It showed almost 100% of release degree in a few seconds under an acidic condition (e.g., pH 5.0), but it was stable at neutral and alkali conditions.