LeNeveu D M, Rand R P
Biophys J. 1977 May;18(2):209-30. doi: 10.1016/S0006-3495(77)85608-7.
We probe in two different ways the competing attractive and repulsive forces that create lamellar arrays of the phospholipid lecithin when in equilibrium with pure water. The first probe involves the addition of low molecular weight solutes, glucose and sucrose, to a system where the phospholipid is immersed in a large excess of water. Small solutes can enter the aqueous region between bilayers. Their effect is first to increase and then to decrease the separation between bilayers as sugar concentration increases. We interpret this waxing and waning of the lattice spacing in terms of the successive weakening and strengthening of the attractive van der Waals forces originally responsible for creation of a stable lattice. The second probe is an "osmotic stress method," in which very high molecular weight neutral polymer is added to the pure water phase but is unable to enter the multilayers. The polymer competes for water with the lamellar lattice, and thereby compresses it. From the resulting spacing (determined by X-ray diffraction) and the directly measured osmotic pressure, we find a force vs. distance curve for compressing the lattice (or, equivalently, the free energy of transfer to bulk water of water between bilayers. This method reveals a very strong, exponentially varying "hydration force" with a decay distance of about 2 A.
我们用两种不同的方法探究了相互竞争的吸引力和排斥力，这些力在磷脂卵磷脂与纯水达到平衡时会形成层状排列。第一种方法是向磷脂浸没在大量水中的体系中添加低分子量溶质，即葡萄糖和蔗糖。小分子溶质可以进入双层之间的水相区域。随着糖浓度的增加，它们的作用先是增加然后减小双层之间的间距。我们根据最初导致形成稳定晶格的范德华吸引力的相继减弱和增强来解释晶格间距的这种增减变化。第二种方法是“渗透压法”，即在纯水相中添加非常高分子量的中性聚合物，但该聚合物无法进入多层结构。聚合物与层状晶格竞争水，从而压缩它。根据由此得到的间距（通过X射线衍射确定）和直接测量的渗透压，我们得到了压缩晶格的力与距离曲线（或者等效地说，是双层之间水转移到大量水中的自由能）。这种方法揭示了一种非常强的、呈指数变化的“水化力”，其衰减距离约为2埃。
