DIRECT MEASUREMENT OF FORCES BETWEEN MEMBRANES OR MACROMOLECULES

能够直接测量膜之间或膜与膜之间的力， 大分子正在创造一种新的逻辑来思考分子 识别和折叠。 互动的突出特点是 当分子或膜接近接触时， 方法涉及从对置溶液中除去有机水溶剂， 表面。 这些“水化力”现在被认为是在 各种各样的材料，如脂质双层，蛋白质，DNA双螺旋， 和硬多糖。 在本年度，我们已经测量了分子间的力量，在本地 并在不同温度、pH、离子浓度 条件下，并在几个小溶质的存在下。 已经表明，盐不会完全渗入空间 胶原蛋白三螺旋之间。 从外部施加的渗透压 由排除盐是胶原纤维的重要组成部分 组装件. 力测量表明，温度有利的组装 的纤维是由水介导的氢键之间的驱动， 通过极性残基而不是通过疏水作用，通常 用来解释蛋白质的组装 现在可以想到一个 排斥力和吸引力之间的竞争， 蛋白质表面的匹配程度 DNA分子间水合力对小分子溶质的依赖性 对溶液中存在的问题进行了研究。 一个不寻常的再入液-胶-液相变序列， 在测量磷酸双十二烷基酯之间的力期间观察到 bilayers，已经解释过了。 一种用于测量球体间力的渗透应力技术 粒子已经被开发出来。

The ability to measure directly the forces between membranes or between macromolecules is creating a new logic for thinking about molecular recognition, and folding. The outstanding feature of interaction is that as molecules or membranes approach contact, the important work of approach involves removal of organized water solvent from the apposing surfaces. These "hydration forces" are now recognized to act in materials as diverse as lipid bilayers, proteins, DNA double helices, and stiff polysaccharides. During the current year we have measured intermolecular forces in native and reconstituted collagen fibers at various temperatures, ph, ionic condiitons, and in the presence of several small solutes. It has been shown that salt does not fully penetrate into the space between collagen triple helices. Osmotic pressure applied from outside by the excluded salt is an important component of collagen fiber assembly. Force measurements have demonstrated that temperature-favored assembly of the fibers is driven by water-mediated hydrogen bonding between the apposing polar residues rather than by the hydrophobic effect, usually invoked to explain assembly of proteins. One can now think of a competition between repulsive and attractive hydration forces, depending on how well protein surfaces match each other. A dependence of hydration forces between DNA molecules on small solutes present in the solution has been studied. An unusual re-entrant liquid-gel-liquid phase transition sequence, observed during measurement of forces between didodecylphosphate bilayers, has been explained. An osmotic stress technique for measuring forces between spherical particles has been developed.