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

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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.