Tabaei Seyed R, Jackman Joshua A, Kim Seong-Oh, Liedberg Bo, Knoll Wolfgang, Parikh Atul N, Cho Nam-Joon
School of Materials Science and Engineering, Nanyang Technological University , 50 Nanyang Avenue, Singapore 639798, Singapore.
Langmuir. 2014 Nov 11;30(44):13345-52. doi: 10.1021/la5034433. Epub 2014 Oct 27.
This paper describes the application of a solvent-exchange method to prepare supported membranes containing high fractions of cholesterol (up to ∼57 mol %) in an apparent equilibrium. The method exploits the phenomenon of reverse-phase evaporation, in which the deposition of lipids in alcohol (e.g., isopropanol) is followed by the slow removal of the organic solvent from the water-alcohol mixture. This in turn induces a series of lyotropic phase transitions successively producing inverse-micelles, monomers, micelles, and vesicles in equilibrium with supported bilayers at the contacting solid surface. By using the standard cholesterol depletion by methyl-β-cyclodextrin treatment, a quartz crystal microbalance with dissipation monitoring assay confirms that the cholesterol concentration in the supported membranes is comparable to that in the surrounding bulk phase. A quantitative characterization of the biophysical properties of the resultant bilayer, including lateral diffusion constants and phase separation, using epifluorescence microscopy and atomic force microscopy establishes the formation of laterally contiguous supported lipid bilayers, which break into a characteristic domain-pattern of coexisting phases in a cholesterol concentration-dependent manner. With increasing cholesterol fraction in the supported bilayer, the size of the domains increases, ultimately yielding two-dimensional cholesterol bilayer domains near the solubility limit. A unique feature of the approach is that it enables preparation of supported membranes containing limiting concentrations of cholesterol near the solubility limit under equilibrium conditions, which cannot be obtained using conventional techniques (i.e., vesicle fusion).
本文描述了一种溶剂交换法的应用，该方法用于制备在表观平衡状态下含有高比例胆固醇（高达约57摩尔%）的支撑膜。该方法利用了反相蒸发现象，即在醇（如异丙醇）中沉积脂质后，从水-醇混合物中缓慢除去有机溶剂。这反过来又引发了一系列溶致相变，依次产生与接触固体表面的支撑双层处于平衡状态的反胶束、单体、胶束和囊泡。通过使用甲基-β-环糊精处理标准胆固醇耗竭法，一种带有耗散监测分析的石英晶体微天平证实了支撑膜中的胆固醇浓度与周围本体相中的胆固醇浓度相当。使用落射荧光显微镜和原子力显微镜对所得双层的生物物理性质进行定量表征，包括横向扩散常数和相分离，确定了横向连续支撑脂质双层的形成，该双层以胆固醇浓度依赖的方式分解为共存相的特征性畴图案。随着支撑双层中胆固醇比例的增加，畴的尺寸增大，最终在溶解度极限附近产生二维胆固醇双层畴。该方法的一个独特之处在于，它能够在平衡条件下制备含有接近溶解度极限的极限胆固醇浓度的支撑膜，而这是使用传统技术（即囊泡融合）无法获得的。
