Control of the incorporation and release of guest molecules by photodimerization in liposomes.

In a drug-delivery system using liposomes, the use of guest molecules bearing hydrophilic moieties results in some leakage from lipid membranes. We suppressed the leakage of coumarins (used as model guest molecules in a drug-delivery system) from lipid membranes by photodimerization at 365 nm. The reason for this phenomenon could be ascribed to an increase in the hydrophobicity of the dimers of the coumarins. The formation of the dimers was detected by 1H NMR, UV-vis absorption, and mass spectra and the leakage percentages of the coumarins were determined by 1H NMR spectra based on the peak intensities. In contrast, when the dimer reverted to a monomer by ultraviolet (254 nm) irradiation, the resulting monomer was released from liposomes.