Stearylamine Changes the Liposomal Shape from MLVs to LUVs

The shape of mixed dipalmitoylphosphatidylcholine (DPPC)/stearylamine (SA) liposomes prepared by the Bangham method was examined using freeze-fracture electron microscopy. The shape of the mixed DPPC/SA liposomes (XSA = 0.05) was not that of multilamellar vesicles (MLVs) but large unilamellar vesicles (LUVs) with a diameter of approximately 1.0 μm. These facts overthrow the preconceived idea that the shape of the DPPC/SA liposomes prepared by the Bangham method is that of MLVs. The trapping efficiency of the mixed DPPC/SA liposomes (XSA = 0.05) was ten times greater than that of the DPPC liposomes, since the DPPC liposomes were MLVs. The data of the DSC peak for the DPPC/SA liposomes also indicated that the shape of the DPPC/SA liposomes is that of LUVs. We emphasize that the shape of the DPPC liposomes changes from that of MLVs to LUVs by the mixing of a small amount of SA into the DPPC liposomes.