Partitioning of hydrophobic molecules to liposome membranes can induce variations in their micro-polarity and micro-viscosity

The micro-polarity and micro-viscosity of liposome membranes were evaluated to develop a platform for the localization of hydrophobic substrates in aqueous solution. The distribution ratios of benzaldoxime (BO) onto the zwitterionic 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) liposome and onto the cationic 1,2-dioleoyl-3-trimethylammonium-propane (DOTAP) liposome were almost the same, while those of benzonitrile oxide (BNO) onto DOTAP liposomes were higher than those of BO. Through the analysis of a polarity-sensitive 6-lauroyl-2-dimethylaminonaphthalene, the membrane surface of the DOTAP liposome was found to be dehydrated in the presence of substrates. Using a fluorescent probe 1,6-diphenyl-1,3,5-hexatriene, we found that the micro-viscosity of the DOTAP liposome membrane increased with BNO. These results indicate that the interaction of hydrophobic substrates induce variations in the microscopic membrane environment.