PHOTO-SENSITIVE LIPID-MEMBRANE PERTURBATION BY A SINGLE-CHAIN LIPID HAVING TERMINAL SPIROPYRAN GROUP

The synthesis a novel single chain lipid (SP-16A), containing a photo- sensitive spiropyran group at its hydrophobic terminus is described. T he photoisomerization behavior of SP-16A has been studied by UV-Vis sp ectroscopy. The lipid has been incorporated into small unilamellar ves icles (SUVs) in quantities up to 10 mol% by mixing with dipalmitoylpho sphatidylcholine (DPPC) and consequent sonication. The photo-induced m embrane perturbation of the SP-16A/DPPC mixed SUV liposome was observe d by monitoring of leakage of carboxyfluorescein(CF), a water soluble fluorescent dye, from the interior aqueous phase of the SUV. SUVs cont aining 5-10 mol% of SP-16A showed drastic leakage of CF by UV irradiat ion at 465 nm, however, neither liposome rupture nor release of the li pid from the SUV was observed after the UV irradiation. On/off switchi ng of the leakage of interior material from the vesicle could also be demonstrated. In order to discuss the mechanism and kinetics of the ph oto-sensitive membrane perturbation behavior for the SP-16A/DPPC mixed SUV, the isomerization behavior of the SP-16A molecule and the leakag e of CF from the SUV over time were investigated using a pulsed excime r laser. These experiments suggested that the main factor involved in membrane perturbation by SP-16A is a conformational change of the lipi d in the membrane, which occurs after isomerization of the molecule. T his new lipid molecule is thus a novel and useful photo-sensitive swit ching system, and may have future applications in drug delivery system s. (C) 1998 Elsevier Science Limited.