Study of non-ionic monoalkyl amphiphile-cholesterol vesicles solubilization by octylglucoside

Abstract

Two populations of non-ionic surfactant vesicles (NVS) with mean diameter (MD) of 322 and 72 nm, and based on diglycerol hexadecylether (C16G2), cholesterol (CHOL), and dicetylphosphate (DCP) (47.5/47.5/5 wt%) were prepared by detergent dialysis and sonication, respectively. The solubilization of NSV, performed by the continuous and controlled addition, at different rates, of a 100 mM OG solution to vesicles was examined at 25°C by monitoring turbidity at 350 nm. The molecular composition of aggregates ([OG:lip]agg) and the OG concentration in the continuous phase ([OG]bulk) were determined from relation between total OG and lipid concentration at the break points observed on the solubilization curves. At the fastest rate of OG addition, no insertion of OG occurs until [OG]bulk = 13 mM, and when [OG]bulk = 23 mM, the solubilization mechanism of large and sonicated NSV involves a unique process through the formation of the same aggregates. At the slowest one, sonicated NSV membranes exhibit impermeability properties until [OG]bulk = 11 mM and the insertion of the detergent and, most likely, its lateral diffusion in the lipidic structures are time-dependent. Nevertheless, the amounts of OG required to solubilize the NSV membranes indicate that bilayers are particularly resistant to the action of OG molecules, probably due to the C16G2-CHOL association.