Department of Physics , University of Washington , Seattle , Washington 98195-1560 , United States.
J Phys Chem B. 2018 Apr 5;122(13):3251-3258. doi: 10.1021/acs.jpcb.7b08890. Epub 2017 Nov 2.
I consider a model of a bilayer characterized by two order parameters, one in each leaf. That of the inner leaf represents the difference in mole fractions of lipids with large spontaneous curvature, phosphatidylethanolamine (PE), and those with small spontaneous curvatures, phosphatidylcholine (PC) and phosphatidylserine (PS). Similarly, the order parameter in the outer leaf represents the difference in mole fractions of lipids with small spontaneous curvature, PC, and large curvature, sphingomyelin (SM). Each order parameter is coupled to the variations in the height of the membrane that is assumed to be of constant thickness. The couplings are of different strength. I show that, with reasonable parameters, a microemulsion is formed in each leaf, and that the two microemulsions are strongly coupled. Their characteristic size of domains is found to be on the order of 75 nm. In this picture, rafts consist of regions of SM in the outer leaf and PC and PS in the inner leaf, floating in a sea of PC in the outer leaf and PE in the inner leaf. I argue that microemulsions have been observed, but not identified as such, in model systems.
我考虑了一种由两个序参量表征的双层模型，每个叶层一个。内层叶层的序参量代表具有大自发曲率的脂质（如磷脂酰乙醇胺（PE））与具有小自发曲率的脂质（如磷脂酰胆碱（PC）和磷脂酰丝氨酸（PS））之间的摩尔分数差异。同样，外层叶层的序参量代表具有小自发曲率的脂质（PC）与大曲率的脂质（鞘磷脂（SM））之间的摩尔分数差异。每个序参量都与膜的高度变化相关联，而膜被假定为具有恒定厚度。这些耦合的强度不同。我表明，在合理的参数下，每个叶层都会形成微乳液，并且这两个微乳液之间存在强烈的耦合。它们的特征域大小被发现约为 75nm。在这种情况下，筏由外层的 SM 区域和内层的 PC 和 PS 区域组成，漂浮在具有 PC 的外层和具有 PE 的内层的海洋中。我认为，已经在模型系统中观察到了微乳液，但尚未将其识别为微乳液。
