The vesicle-to-micelle transition of phosphatidylcholine vesicles induced by nonionic detergents: effects of sodium chloride, sucrose and urea.

The vesicle-to-micelle transition of egg phosphatidylcholine LUVs induced by octylglucoside was studied in buffers with 0-4 M sodium chloride, sucrose or urea. We used both light scattering and fluorescent probes to follow the lipid-detergent complexes in these buffers. The vesicle-to-micelle transition process was fundamentally the same in each solute. However, the detergent-to-lipid ratio required for micelle formation shifted in ways that depended on the aqueous solute. The partitioning of octylglucoside between the vesicles and the aqueous phase was primarily determined by the change in its critical micelle concentration (cmc) induced by each solute. Specifically, the cmc decreased in high salt and sucrose buffers but increased in high concentrations of urea. Cmc for two additional nonionic detergents, decyl- and dodecyl-maltoside, and three zwittergents (3-12, 3-14 and 3-16) were determined as a function of concentration for each of the solutes. In all cases NaCl and sucrose decreased the solubility of the detergents, whereas urea increased their solubilities. The effects clearly depended on acyl chain length in urea-containing solutions, but this dependence was less clear with increasing NaCl and sucrose concentrations. The contributions of these solutes to solubility and to interfacial interactions in the bilayers, pure and mixed micelles are considered.