Molecular Interactions between Phospholipid and Nonionic Surfactants in a Lipid Bilayer

Abstract

Molecular interactions between dipalmitoylphosphatidylcholine (DPPC) and long polyoxylated nonionic surfactants in a lipid bilayer were investigated by dynamic light scattering, ultracentrifuge, differential scanning calorimetry (DSC), ζ-pontential and fluorescence.Particle size and encapsulation efficiency of the liposomes decreased rapidly with increasing concentrations of the nonionic surfactants possessing a long oxyethylene chain (C16POE20, and C16POE40), but showed virtually no change in the case of a short chain C16POE10. The cooperative effect on the physical properties of bilayer caused by interaction among DPPC molecules decreased with increasing concentration of the nonionic surfactants. Surface charge density of the liposomes also decreased following the addition of nonionic surfactants. Microviscosity of the liposome decreased with increasing concentrations of C16POE20 and C16POE40, but remained essentially unchanged in the case of C16POE10.The addition of a long polyoxylated nonionic surfactant to a solution containing DPPC molecules caused structural change of molecular aggregation and in particular, in the presence of large amounts of C16POE20 and C16POE40, the DPPC liposome with nonionic surfactants did not form. A molecular aggregate such as a micelle was obtained instead.