DIRECT MEASUREMENT OF FORCES BETWEEN MEMBRANES OR MACROMOLECULES

能够直接测量膜之间或膜之间的力 大分子正在创造一种思考分子的新逻辑 认同感和折叠感。交互的突出特点是 当分子或膜接近接触时，重要的工作是 方法包括从对立物中去除有组织的水溶剂 表面。这些“水合力量”现在被认为在 材料多种多样，如脂双层，蛋白质，DNA双螺旋， 和硬多糖。 在本年度，我们测量了天然分子间的作用力 和重组的胶原纤维在不同的温度，ph值，离子 条件，并在几个小溶质存在的情况下。 已经证明，盐不能完全渗入太空。 胶原蛋白三股螺旋之间。从外部施加的渗透压 被排除的盐分是胶原纤维的重要组成部分 集合。 力的测量已经证明了温度有利的装配 是由水介导的氢键驱动的， 相反的极性残基，而不是疏水效应，通常 用来解释蛋白质组装的。人们现在可以想到一种 排斥力和吸引力水合力之间的竞争，取决于 蛋白质表面相互匹配的程度。 DNA分子间水合力对小分子溶质的依赖性 对溶液中存在的物质进行了研究。 一种不同寻常的重入液体-凝胶-液体相变序列， 在测量十二烷基磷酸之间的作用力时观察到的 双层，已经解释过了。 一种测量球面间作用力的渗透应力技术 粒子已经被开发出来了。

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.