Liposomes from ionic, single-chain amphiphiles

Abstract

In studies of the minimum physicochemical requirements for lipid membrane formation, made liposomes were made from dilute, aqueous dispersions of C(8)-C(18) single-chain amphiphiles. In general, membrane formation from ionic soaps and detergents requires the presence of uncharged amphiphiles. Vesicles were characterized by phase-contrast microscopy, by trapping of ionic dyes, as well as by negativestain and freeze-fracture EM. They were typically heterogeneous in size, but the average diameter could be experimentally varied in some cases over the range of 1-100 .mu.m. Uni-, oligo- and multilamellar vesicles were observed. Membrane permeability to various solutes was determined in part by a new technique which utilized phase-contrast microscopy; when impermeable vesicles exclude added solutes such as sucrose, refractive index differences are created between vesicle contents and surrounding medium, so that the vesicles appear bright in the phase microscope. Permeant solutes do not produce this effect. Spectrophotometric permeability determinations confirmed the results of this technique and provided quantitative measures of permeability. Monoalkyl liposomes have potential uses as models of biomembranes and in drug delivery. They are also relevant to the prebiotic origin of biomembranes.