Allender David W, Schick M
Department of Physics, Kent State University, Kent, Ohio; Department of Physics, University of Washington, Seattle, Washington.
Department of Physics, University of Washington, Seattle, Washington.
Biophys J. 2017 Oct 17;113(8):1814-1821. doi: 10.1016/j.bpj.2017.08.033.
We address questions posed by experiments that show small-chain alcohols reduce the miscibility transition temperature when added to giant plasma membrane vesicles (GPMVs), but increase that temperature when added to giant unilamellar vesicles. In giant unilamellar vesicles the change in temperature displays a definite minimum, between decanol and tetradecanol, as a function of alcohol chain length; in GPMVs there is no such minimum. To emphasize the competition between internal entropies of the components and the interactions between them, we model the system as consisting of three different linear polymers. Two of them are the constituents of a liquid, one that can undergo a miscibility transition. To this liquid is added the third polymer component, which represents the short-chain alcohol. We show that, within Flory-Huggins theory, the addition of alcohol causes an increase or decrease of the miscibility transition temperature depending upon the competition of two effects. The first is the dilution of the interactions between the two components of the liquid caused by the introduction of the alcohol. This tends to lower the transition temperature. The second effect is the preferential partitioning of the alcohol into one phase of the liquid or the other. This tends to raise the transition temperature irrespective of which phase the alcohol prefers. This second effect is the smallest, and the decrease in transition temperature the largest, when the alcohol partitions equally between the two phases. Such equal partitioning occurs when the effect of the entropic excluded volume interactions (which cause the alcohol to prefer one phase) just balances the effect of the direct interactions, which cause it to prefer the other. These results allow us to make several predictions, and to propose an explanation for the different behavior of the transition temperature in GPMVs and giant unilamellar vesicles that results from the addition of alcohols.
我们探讨了一些实验所提出的问题。这些实验表明，当向巨型质膜囊泡（GPMV）中添加短链醇时，会降低混溶转变温度，但当添加到巨型单层囊泡中时，则会升高该温度。在巨型单层囊泡中，温度变化在癸醇和十四烷醇之间呈现出明确的最小值，该最小值是醇链长度的函数；而在GPMV中则不存在这样的最小值。为了强调组分的内部熵之间的竞争以及它们之间的相互作用，我们将该系统建模为由三种不同的线性聚合物组成。其中两种是一种液体的成分，该液体可发生混溶转变。向这种液体中添加第三种聚合物成分，它代表短链醇。我们表明，在弗洛里 - 哈金斯理论范围内，添加醇会导致混溶转变温度升高或降低，这取决于两种效应的竞争。第一种效应是由于引入醇而导致液体中两种组分之间相互作用的稀释。这往往会降低转变温度。第二种效应是醇在液体的一个相或另一个相中的优先分配。这往往会升高转变温度，而与醇偏好哪个相无关。当醇在两个相之间平均分配时，第二种效应最小，转变温度的降低最大。当熵排斥体积相互作用（导致醇偏好一个相）的效应恰好平衡直接相互作用（导致它偏好另一个相）的效应时，就会发生这种平均分配。这些结果使我们能够做出一些预测，并对添加醇后GPMV和巨型单层囊泡中转变温度的不同行为提出一种解释。
