Small-Angle Neutron Scattering Studies of Mixed Bile Salt-Lecithin Colloids

Abstract

Small-angle neutron scattering is used to analyze the morphology of particles formed in aqueous colloids of glycocholate with lecithin mixed at different lecithin to glycocholate molar ratios. Of interest are the transformations which occur when the system is diluted in aqueous solution. These are presumed to model the changes that occur in the formation of bile and when the colloid mixtures are used as novel drug delivery systems. It is observed that substantial changes in particle morphology occur with dilution. At high total lipid concentrations the particles are globular. As the system is diluted they elongate and at certain dilutions long rods are formed. At lower total lipid concentrations large bilayer sheets of undetermined shape and size are formed. Bilayer vesicles are observed at still lower total lipid concentrations, and become smaller with further dilution. The formation of rods with dilution is not in accord with the current theory of micelle structure and the mechanism of micelle growth in these systems. The relatively large solubility of glycocholate compared to that of lecithin may cause the former to repartition into the bulk solvent upon dilution, and thus induce the structural transformations noted above.