Molten Proteins: synthesis and design of novel biomolecule-based liquid nanomaterials and their application in bionanochemistry

在传感、数据存储、电子和催化等广泛的应用中，制造具有小尺寸结构和多部件的新材料预计将具有重要意义。小尺度结构可能取得重大突破的一个新领域是蛋白质的使用，蛋白质是具有多种特性的大型生物分子。因此，人们对制备包含生物成分的纳米材料越来越感兴趣，因为蛋白质和酶等分子具有精细调节的活性，而这些活性在合成对偶物中是不易获得的。蛋白质与许多其他形式的纳米级物体相似，因为它们具有持久的三维结构，可以以干粉的形式制备，或者更常见的是，作为水溶液中的分散体。然而，有趣的是，纯液态的蛋白质是未知的；它们在环境温度和压力下根本不存在。因此，存在一种有待发现和探索的生物分子物质的缺失状态。在没有溶剂的情况下，液体蛋白相的缺失是纳米颗粒通常遇到的一个问题，并且提出了关于纳米级物体中这种物质状态的潜在存在的基本问题。问题出现了，因为液态是由分子间的力稳定的，与单个分子的大小相比，分子间的力在很大程度上扩大了范围，但这种关系对于蛋白质来说就不成立了，因为蛋白质通常比力场的范围更大。因此，在常压下加热传统的固体通常会产生液态，因为增加的热能会通过分子之间的相关运动消散，而加热干燥的蛋白粉会导致热降解。也就是说，蛋白质分子在很短的距离内紧紧地结合在一起，在较长的距离内几乎不相互作用，以至于热能的增加破坏了分子结构，或者在非常低的压力下，将分子直接推向气相（升华），在那里分子间的作用力非常弱或不存在。提出的研究旨在通过生产液体蛋白质的第一个例子来解决生物分子物质的这种缺失状态。我们打算通过改变几种不同类型蛋白质的表面特性来实现这一点，这样分子就可以在更远的距离上继续相互作用。实际上，我们要做的是在没有溶剂的情况下，将基团化学地附着在蛋白质表面，使其表现为流化层。需要仔细设计这些基团，使修饰后的蛋白质表现为单一组分，这样才能制备出真正的液体。在我们的初步研究中，我们首先使蛋白质表面带高度正电，然后添加带负电的聚合物表面活性剂，使其静电结合到阳离子位点上，从而实现了这一点。然后，我们通过冷冻干燥技术仔细地除去所有的水分，得到一种软固体，在27度左右融化，产生液体蛋白质。我们提出的工作旨在发展这种新方法来发现各种具有不同功能的液体蛋白。在每种情况下，我们将研究液体的内部结构，以及它们的组成和性质，如粘度。我们还将确定蛋白质的自然性质在液体状态下是否仍然具有活性。最后，一旦我们了解了这些系统是如何工作的，那么就有可能利用这些结果开始开发基于液体蛋白质的新型材料。例如，我们有兴趣探索蛋白质熔体作为智能液体、生物传感器和用于伤口敷料的新型材料。

Making new materials that have small-scale structures and multiple components is expected to be of great importance in a wide range of applications such as sensing, data storage, electronics and catalysis. One new area where small-scale structures could make a significant breakthrough is in the use of proteins, which are large biological molecules with a wide range of properties. There is therefore a growing interest in preparing nanomaterials that include biological components because molecules such as proteins and enzymes have finely tuned activities not readily available in synthetic counterparts. Proteins are similar to many other forms of nanoscale objects in that they have persistent 3-D structures that can be prepared in the form of dry powders, or more usually, as dispersions in aqueous solutions. However, it is interesting to note that proteins in the pure liquid state are not known; they simply do not exist at ambient temperature and pressure. As a consequence there is a missing state of biomolecular matter that remains to be discovered and explored.The absence of a liquid protein phase in the absence of solvent is a problem that is encountered with nanoparticles in general, and raises fundamental questions concerning the potential existence of this state of matter in nanoscale objects. The problem arises because the liquid state is stabilized by inter-molecular forces that extend considerably in range compared with the size of the individual molecules, but this relationship breaks down for proteins, which are generally larger than the range of the force field. So, whilst heating a conventional solid under atmospheric pressure usually produces the liquid state because the increased thermal energy is dissipated by correlated motions between the molecules, heating a dried protein powder results in thermal degradation. That is, the protein molecules are so firmly held together at a very short range and hardly interact at a longer distance that the increase in thermal energy destroys the molecular structure, or when under very low pressure, drives the molecules directly into the gas phase (sublimation), where the intermolecular forces are very weak or non-existent.The proposed research aims to address this missing state of biomolecular matter by producing the first examples of liquid proteins. We intend to do this by modifying the surface properties of several different types of proteins such that the molecules will continue to interact at longer distances. Effectively what we will do is chemically attach groups to the protein surface that behave as a fluidization layer in the absence of a solvent. These groups need to be designed carefully so that the modified proteins behave as a single component so that true liquids can be prepared. In our preliminary studies we have achieved this by first making the protein surface highly positively charged, and then adding a negatively charged polymer surfactant that electrostatically binds to the cationic sites. We then meticulously remove all the water by freeze drying techniques to give a soft solid that melts at around 27 degress to produce a liquid protein. Our proposed work intends to develop this new approach to discover a wide range of liquid proteins with different functions. In each case we will investigate the internal structure of the liquids, as well as their composition and properties such as viscosity. We will also determine if the natural properties of the proteins are still active in the liquid state. Finally, once we understand how these systems work, then it should be possible to use the results to start to develop new types of materials based on liquid proteins. For example, we are interested in exploring the protein melts as smart liquids, biosensors and as new types of materials for use as wound dressings.