A biomembrane sample system where millimolar changes of cations induce reversible large scale (≥ 200 Å) changes in the membrane-to-surface distance is described. The system composes of a free-floating bilayer (FFB), formed adjacent to a self-assembled monolayer (SAM). To examine the membrane movements, differently charged FFBs in the presence and absence of Ca2+ and Na+, respectively, were examined using neutron reflectivity (NR) and quartz crystal microbalance (QCM) measurements, alongside molecular dynamics (MD) simulations. In NR the variation of Ca2+ and Na+ concentration enabled precision manipulation of the FFB-to-surface distance. Simulations suggest that Ca2+ ions bridge between SAM and bilayer whereas the more diffuse binding of Na+, especially to bilayers, is unable to fully overcome the repulsion between anionic FFB and anionic SAM. Reproduced NR results with QCM demonstrate the potential of this easily producible sample system to become a standard analysis tool for e.g. investigating membrane binding effects, endocytosis and cell signalling.

中文翻译：

---

阳离子开关引起的大规模膜运动

描述了一种生物膜样品系统，其中阳离子的毫摩尔变化引起膜到表面距离的可逆大规模变化（≥200Å）。该系统由与自组装单层（SAM）相邻形成的自由浮动双层（FFB）组成。为了检查膜的运动，使用中子反射率（NR）和石英晶体微天平（QCM）测量以及分子动力学（MD）模拟，分别检查了存在和不存在Ca2 +和Na +时带不同电荷的FFB。在NR中，Ca2 +和Na +浓度的变化使得可以精确控制FFB至表面的距离。模拟表明，Ca2 +离子在SAM与双层膜之间架起了桥梁，而Na +的弥散结合（尤其是与双层的结合）无法完全克服阴离子FFB与阴离子SAM之间的排斥。