GEOMETRICAL ASPECTS OF THE FRUSTRATION IN THE CUBIC PHASES OF LYOTROPIC LIQUID-CRYSTALS
GEOMETRICAL ASPECTS OF THE FRUSTRATION IN THE CUBIC PHASES OF LYOTROPIC LIQUID-CRYSTALS
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DOI：
10.1073/pnas.85.15.5364
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发表时间：
1988-08-01
影响因子：
11.1
通讯作者：
LEIBLER, S
中科院分区：
文献类型：
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作者：
ANDERSON, DM;GRUNER, SM;LEIBLER, S
双连续立方相，由排列在周期性极小表面的几何形状的双层组成，被发现在各种不同的脂质/水系统。最近有人提出，这些立方结构到达作为两个自由能之间的竞争的结果：每个单层的曲率能和脂质链的拉伸能。这种情况下，非常类似的一个解释的起源的六方相，这里调查通过简单的几何计算。首先假设脂质双层是恒定的厚度和分布的磷脂-水界面的（本地）平均曲率计算。然后，假设这些界面的平均曲率为常数，计算双层的厚度分布。这两种计算都量化了两个能量项受挫且不能同时满足的事实。然而，对于立方相，挫折的量可以小于对于层状和六方结构。因此，这个相可以出现在其他两个之间的相图中，正如在许多最近的实验中所观察到的那样。
Bicontinuous cubic phases, composed of bilayers arranged in the geometries of periodic minimal surfaces, are found in a variety of different lipid/water systems. It has been suggested recently that these cubic structures arrive as the result of competition between two free-energy terms: the curvature energy of each monolayer and the stretching energy of the lipid chains. This scenario, closely analogous to the one that explains the origin of the hexagonal phases, is investigated here by means of simple geometrical calculations. It is first assumed that the lipid bilayer is of constant thickness and the distribution of the (local) mean curvature of the phospholipid-water interfaces is calculated. Then, assuming the mean curvature of these interfaces is constant, the distribution of the bilayer's thickness is calculated. Both calculations quantify the fact that the two energy terms are frustrated and cannot be satisfied simultaneously. However, the amount of the frustration can be smaller for the cubic phase than for the lamellar and hexagonal structures. Therefore, this phase can appear in the phase diagram between the other two, as observed in many recent experiments.