Chemical and biophysical studies of ionic protein fluids

许多纯物质，例如金属，受热时会熔化而形成液体。熔化发生的原因之一是因为金属原子的大小与它们之间的力作用的距离相似。然而，对于大的生物分子如蛋白质，加热干燥的蛋白质粉末导致分解和气体的形成，即没有液相。然而，聚合物也是大分子，在加热时会熔化（如熔化的塑料），这部分是由于聚合物分子之间的力作用的距离更大。在这里提出的研究中，我们希望将聚合物附着在蛋白质表面，使蛋白质可以形成没有水的液体。将聚合物附着到蛋白质上的方法包括对蛋白质表面进行化学修饰，使其高度带电。聚合物带相反电荷，因此它们以静电方式结合到蛋白质表面。实际上，表面的聚合物表现为流化区域，并且需要仔细选择这些分子，使得修饰的蛋白质表现为单一实体，并且可以被分类为真正的液体。在最近的研究中，我们通过修饰蛋白质以提供高度带正电荷的表面，然后添加带负电荷的聚合物表面活性剂来实现这一点。然后，我们去除未结合的表面活性剂，冷冻样品，并通过冷冻干燥小心地去除所有的水，以产生在29 ℃左右熔化的粉末，产生液体蛋白质。我们现在希望将这种方法扩展到生产各种不同性质的液体蛋白质。我们将研究形成的每种蛋白质液体的内部结构和流体性质。获得的关于内部结构的信息将用于帮助确定蛋白质的天然特性是否仍然存在于液态中。在我们了解了这些液体蛋白质的结构以及形成的方式和原因之后，我们将利用这些信息开发使用液体蛋白质的新型智能材料，例如用于生物传感器和新型伤口敷料材料。

When heated, many pure substances, for example metals, will melt and form liquids. One of the reasons that melting occurs is because the metal atoms are of a similar size to the distance over which the forces between them act. For large biological molecules like proteins however, heating the dry protein powder results in decomposition and the formation of a gas, i.e. there is no liquid phase. Polymers however, are also large molecules that do melt when heated (like melting plastic), and this is due in part to the greater distances over which the forces between the polymer molecules act. In the research proposed here, we wish to attach polymers to the surface of proteins so that proteins can form liquids with no water. The method for attaching the polymer to the protein involves the chemical modification of the protein surface to make it highly charged. The polymers are oppositely charged and as a result they bind electrostatically to the protein surface. Effectively, the polymers at the surface behave as a fluidization region and these molecules need to be selected carefully so that the modified proteins behave as a single entity and can be classified as true liquids. In recent studies we have achieved this by modifying the protein to give a highly positively charged surface, and then adding a negatively charged polymer surfactant. We then remove the unbound surfactant, freeze the sample, and carefully remove all the water by freeze-drying to produce a powder that melts at around 29 C, producing a liquid protein. We now wish to extend this method to produce a wide range of liquid proteins with different properties. We will study both the internal structure and the fluid properties of each protein liquid formed. The information gained about the internal structure will be used to help determine if the natural properties of the proteins are still present in the liquid state. After we understand the structure and how and why these liquid proteins form, we will use this information to develop new types of smart' materials using liquid proteins, e.g. for biosensors and for new types of wound dressing materials.