The steric stabilization of small unilamellar vesicles

Abstract

Steric stabilization of small unilamellar vesicles composed of dipalmitoyl phosphatidylglycerol (DPPG) is achieved by the incorporation of nonylphenol poly(ethylene oxide) ethers at varying mol%. Nonylphenol poly(ethylene oxide) ethers with an average of either 10.8 (NP 10 or 50 (NP 50 ethylene oxide groups are incorporated into vesicles at between 2.5 and 10 mol%. Vesicle aggregation is induced by the addition of either NaCl or CaCl 2 with the effective diameter of the vesicle dispersion measured as a function of time using photon correlation spectroscopy. The addition of between 5 and 20 mol% NP 10 to DPPG vesicles increases dispersion stability 10-fold in the presence of NaCl but only 2-fold in the presence of CaCl 2. Dispersion stability is increased 100-fold with the addition of 10–20 mol% NP 50 in NaCl and 1000-fold in the presence of CaCl 2. Vesicle aggregation is found to be reversible with 5 mol% added NP 50 in NaCl but only partially reversible in the presence of CaCl 2. The hydrophobic nonylphenol moiety of NP 50 is found to be critical for imparting dispersion stability when compared to the addition of pure poly(ethylene oxide) to vesicles.