We study material transport and permeation through a lamellar stack of multi-component lipid membranes by performing Monte Carlo simulations of a stacked two-dimensional Ising model in presence of permeants. In the model, permeants are transported through the stack via in-plane lipid clusters, which are inter-connected in the vertical direction. These clusters are formed transiently by concentration fluctuations of the lipid mixture, and the permeation process is affected, especially close to the critical temperature of the binary mixture. We show that the permeation rate decays exponentially as function of temperature and permeant lateral size, whereas the dependency on the characteristic waiting time obeys a stretched exponential function. The material transport through such lipid clusters can be significantly affected around physiological temperatures.
Molecular simulation analysis of structural variations in lipoplexes
我们使用一个粗粒度的分子模型来研究阳离子和中性脂质与DNA分子的复合物（“lipoplexes”）的自组装过程-一种有前途的非病毒DNA载体用于基因治疗。我们通过直接可视化的分子排列和通过计算相应的散射图来确定所得到的结构。后一种方法提供了一种手段，从X射线散射实验与公布的数据进行比较。与实验结果一致，我们发现，在增加的脂质材料的刚度，系统往往形成层状结构。从层状复合物的散射图中可以提取两个特征距离-层状（层间）间距和每层内的DNA间距。我们发现这两个量的计算值与实验数据之间有很好的一致性[J.O.雷德勒岛Koltover，T. Salditt和C. R. Safinya，Science Vol.275，810（1997）]在实验研究的带电脂质（CL）的摩尔分数的整个范围内。对模拟系统的目视检查表明，对于非常高分数的CL，自发形成由结合到小膜片段的DNA分子组成的无序结构。这些非层状无序复合物的衍射图似乎非常相似的层状结构，这使得解释的X射线数据模糊。层状秩序的损失可能是所观察到的脂质复合物作为基因递送载体在高电荷密度下的效率增加的起源。
Gel-state nucleation in multilamellar vesicles of dimyristoylphosphatidylcholine and its relation to the critical temperature: A lattice model and microcalorimetry
