Theoretical study on microdomains in biomembranes

为了理解生物膜中的“筏”，我们提出了饱和和不饱和脂质混合物以及脂质加胆固醇混合物的现象学模型。我们考虑了局部组成和内部膜结构之间的简单耦合，以及它们对液膜和凝胶膜相之间转变的影响。假设饱和脂的凝胶转变温度因不饱和脂的存在而发生移位，且胆固醇作为链融化转变的外场，得到了各种相图。我们的结果也适用于脂质/脂质/胆固醇系统三元相图中的区域。我们提出了溶性片层在表面活性剂溶液中的一阶解结合跃迁模型。考虑了表面活性剂体积分数与弹性自由度之间的耦合作用，从而增强了表面活性剂分子间的净吸引相互作用。弹性自由度可以是(i)膜弹性自由度，或（ii）体弹性自由度。分析了这两种模型的相行为。对于这两种情况，当耦合足够强时，解绑定跃迁变为一阶跃迁。我们确定了分离具有不同重复距离的两个层状相的相关预解结线。

In an effort to understand "rafts" in biological membranes, we propose phenomenological models for saturated and unsaturated lipid mixtures, and lipid plus cholesterol mixtures. We consider simple couplings between the local composition and internal membrane structure, and their influence on transitions between liquid and gel membrane phases. Assuming that the gel transition temperature of the saturated lipid is shifted by the presence of the unsaturated lipid, and that cholesterol acts as an external field on the chain melting transition, a variety of phase diagrams are obtained. Our results also apply to regions in the ternary phase diagram of lipid/lipid/cholesterol systems.We propose models for the first-order unbinding transition of lyotropic lamellae in surfactant solutions. The coupling between the surfactant volume fraction and the elastic degree of freedom is considered so that the net attractive interaction between the surfactant molecules is enhanced. The elastic degree of freedom can be either (i) a membrane elastic degree of freedom, or (ii) a bulk elastic degree of freedom. The phase behaviors of these two models are analyzed. For the both cases, the unbinding transition becomes first-order when the coupling is strong enough. We determine the associated preunbinding line which separates two lamellar phases having different repeat distances.