Amenitsch Heinz, Rappolt Michael, Teixeira Cilâine V, Majerowicz Monika, Laggner Peter
Institute of Biophysics and X-ray Structure Research, Austrian Academy of Sciences, Schmiedlstrasse 6, 8042 Graz, Austria.
Langmuir. 2004 May 25;20(11):4621-8. doi: 10.1021/la036319p.
The influence of LiCl solutions on liposomal and surface-supported phosphatidylcholine/water systems (dipalmitoylphosphatidylcholine (DPPC) and 1-palmitoyl-2-oleoylphosphatidylcholine (POPC), respectively) has been studied by small-angle X-ray techniques. In liposomal dispersions of DPPC, an osmotically stressed liquid-crystalline phase, denoted as Lalpha osm, forms readily after rapid mixing with salt solutions. The transition from Lalpha -->Lalpha osm proceeds in two steps. The first step takes place within seconds and is due to water diffusion from the liposome into the bulk solution. The second, slower process (minutes) can be attributed to the relaxation of initially deformed intermediate liposomes into spherical ones. In experiments with aligned lipid bilayers supported on silicon wafers, it was possible to reproducibly exchange different concentrations of LiCl solutions on a single sample and to determine the lattice changes by time-resolved X-ray scattering at grazing incidence. Independently of the deposition technique (spray- or spin-coating, respectively), none of the investigated POPC samples displayed an osmotically stressed liquid-crystalline phase. While liposomes can be considered nearly defect-free, supported bilayer stacks show a high abundance of defects, such as oily streaks typical of the Lalpha phase. Thus, the alkali ions are free to diffuse into the interbilayer water regions and to cause a slight increase of the bilayer separation (about 1 Angstroms). It is concluded that low to medium concentrations of Li+ ions partially screen the attractive van der Waals force between adjacent membrane layers. However, upon annealing the defect regions or regions of high curvature in the oriented lipid matrix, e.g. by low amounts of oleyl alcohol (OA), the system is able to sense osmotic stress upon addition of a salt solution.
通过小角X射线技术研究了LiCl溶液对脂质体和表面支持的磷脂酰胆碱/水体系（分别为二棕榈酰磷脂酰胆碱（DPPC）和1-棕榈酰-2-油酰磷脂酰胆碱（POPC））的影响。在DPPC的脂质体分散体中，与盐溶液快速混合后，很容易形成一种渗透压应激液晶相，记为Lα osm。从Lα到Lα osm的转变分两步进行。第一步在几秒钟内发生，是由于水从脂质体扩散到本体溶液中。第二步较慢（几分钟），可归因于最初变形的中间脂质体松弛成球形。在用硅片上支持的排列脂质双层进行的实验中，可以在单个样品上可重复地交换不同浓度的LiCl溶液，并通过掠入射时的时间分辨X射线散射确定晶格变化。与沉积技术（分别为喷涂或旋涂）无关，所研究的POPC样品均未显示出渗透压应激液晶相。虽然脂质体可被认为几乎无缺陷，但支持的双层堆叠显示出大量缺陷，例如Lα相典型的油条纹。因此，碱金属离子可自由扩散到双层间水区域，并导致双层间距略有增加（约1埃）。得出的结论是，低至中等浓度的Li +离子部分屏蔽了相邻膜层之间有吸引力的范德华力。然而，通过对取向脂质基质中的缺陷区域或高曲率区域进行退火处理，例如通过少量油醇（OA），该系统在加入盐溶液后能够感知渗透压应激。
