Solid-Supported Assembly Composed of n-Octyl-β-D-glucopyranoside and 1,2-Dioleoyl-sn-glycero-3-phosphocholine in Equilibrium with Its Ambient Aqueous Solution System Including Dispersed Assembly.

Abstract

In the last few decades, the preparation of solid-supported lipid bilayers by immersing a solid substrate in an aqueous solution where the lipid is dissolved with the aid of a surfactant, followed by dilution of the solution, has been reported. In this study, we attempted to interpret the evolution of supported surfactant/lipid assemblies towards the supported lipid bilayer in terms of a phase equilibrium between the supported assembly phase and its ambient solution system consisting of the dispersed surfactant/lipid assembly phase and the bulk solution phase comprising monomeric surfactant and lipid. We characterized the supported assembly formed on hydrophilized Ge or mica substrates in equilibrium with aqueous solutions containing various concentrations of the nonionic surfactant, n-octyl-β-D-glucopyranoside (OG) and the amphoteric phospholipid, 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC), using interaction-force-profile measurements by atomic force microscopy (AFM), and attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR). We also investigated the ambient solution system using equilibrium dialysis to obtain the partition equilibrium profile of OG between the bulk solution and dispersed assembly phases in the micellar or vesicular states. These studies indicate that the properties of the supported assembly depend on the composition of the dispersed assembly and concentration of monomerically dissolved OG. Further, a type of micellar-bilayer state transition occurs in the supported assembly, roughly synchronized with that in the dispersed assembly.