Max Planck Institute of Colloids and Interfaces, Science Park Golm, 14424 Potsdam, Germany.
University of Bergen, Department of Chemistry, 5007 Bergen, Norway.
Soft Matter. 2023 Sep 20;19(36):6929-6944. doi: 10.1039/d3sm00351e.
Biological and biomimetic membranes are based on lipid bilayers, consisting of two monolayers or leaflets. One important but challenging physical parameter of these membranes is their tension. For a long time, this tension was explicitly or implicitly taken to be the bilayer tension, acting on the whole bilayer membrane. More recently, it has been realized that it is useful to decompose the bilayer tension into two leaflet tensions and that these tensions are accessible to molecular dynamics simulations. To divide the bilayer up into two leaflets, it is necessary to introduce a midsurface that defines the spatial extent of the two leaflets. In previous studies, this midsurface was obtained from the density profiles across the bilayer and was then used to compute the molecular per lipid. Here, we develop an alternative approach based on three-dimensional Voronoi tessellation and molecular per lipid. Using this volume-based approach, we determine the reference states with tensionless leaflets as well as the optimal volumes and areas per lipid. The optimal lipid volumes have practically the same value in both leaflets, irrespective of the size and curvature of the nanovesicles, whereas the optimal lipid areas are different for the two leaflets and depend on the vesicle size. In addition, we introduce lateral volume compressibilities to describe the elastic response of the lipid volume to the leaflet tensions. We show that the outer leaflet of a nanovesicle is more densely packed and less compressible than the inner leaflet and that this difference becomes more pronounced for smaller vesicles.
生物和仿生膜基于脂质双层，由两个单层或叶瓣组成。这些膜的一个重要但具有挑战性的物理参数是它们的张力。长期以来，这种张力被明确或隐含地视为作用于整个双层膜的双层张力。最近，人们已经意识到，将双层张力分解为两个叶瓣张力并使这些张力可用于分子动力学模拟是很有用的。为了将双层分成两个叶瓣，有必要引入一个中间表面来定义两个叶瓣的空间范围。在以前的研究中，这个中间表面是从双层的密度分布中得到的，然后用于计算每个脂质的分子。在这里，我们开发了一种基于三维 Voronoi 细分和每个脂质的分子的替代方法。使用这种基于体积的方法，我们确定了无张力叶瓣的参考状态以及每个脂质的最佳体积和面积。在两种叶瓣中，最优脂质体积的实际值几乎相同，而与纳米囊泡的大小和曲率无关，而两个叶瓣的最优脂质面积不同，取决于囊泡的大小。此外，我们引入了侧向体积压缩性来描述脂质体积对叶瓣张力的弹性响应。我们表明，纳米囊泡的外叶瓣比内叶瓣更密集和压缩性更小，并且对于较小的囊泡，这种差异变得更加明显。
