Diffusion Rearrangement Crystallization And Application Of Protein Film At Gas-liquid Interface

The controllable crystallization process is essential for scientific research and practical applications,so it is imperative to study the mechanism of nucleation and growth of crystal.The nucleation can be divided into two parts:phase separation and phase transition.Phase separation refers to the formation of a solid/liquid phase interface that is driven by super saturation;and phase transition refers to the transformation of a metastable phase into a stable crystalline phase.Since two-step nucleation is often called as the non-classical nucleation.The non-classical nucleation theory has been widely used for studying nucleation process because it's more consistent with the real situation.The non-classical nucleation theory suggests that the amorphous preclusters appear before the formation of crystal nucleus.However,people cannot give a clear conclusion until now whether preclusters themselves transform into crystal nucleus or provide an environment for nucleation of molecules in solution,because such two-step nucleation process takes place so fast and in one aqueous phase.Thus,a predictive description that connects molecular details with ensemble behavior is lacking,particularly for macromolecule that is difficult to be crystallized.Furthermore,many protein crystallization and nucleation process involving in important biological functions often occur at surface and interface,such as S-layer protein,protein storage and release.Therefore,more research is needed to develop bio-macromolecular two-step nucleation at interface.For the above challenges,based on unfolded lysozyme assembly system,we construct a new two-step crystallization system at air/water interface successfully in which the phase separation and phase transition can be separated.The new crystallization system sheds new light on understanding the two-step nucleation and provides a new method for analyzing the macromolecular crystallization.In addition,the crystallization system can be used to induce the ordered arrangement of 2D particles,which can be developed into a new and simple method to prepare 2D colloid crystal.The research outline is as follows:(1)A new two-step crystallization system in which phase separation and phase transition can be separated.We construct a new two-step crystallization system successfully based on the unfolded lysozyme assembly system.In this crystallization system,phase separation process refers to the preparation process of free-floating unfolded lysozyme film in which we can observe solid phase separated from liquid;and phase transition process refers to the diffusion and further assembly of unfolded lysozyme film into ?-sheet-rich crystal after transferring the film on the ultrapure water surface.In our research,we found the surface tension and the surface spatial degrees of freedom are determined to the diffusion and assembly of the film.The new crystallization system is different from traditional two-step crystallization system because it occurs on the air/water interface and has clear differentiation of phase transition and phase separation.Meanwhile,the function of interfacial force was emphasized in crystallization process.(2)The application to induce ordered arrangement of 2D particlesWe prepared a single layer particle/unfolded lysozyme hybrid film by introducing the PS into the preparing process of the unfolded lysozyme film.We found that the hybrid film also can diffuse and the PS particles arrange orderly when the hybrid film is transferred on the ultrapure water surface.The hybrid system provides a research fundation and new method to prepare 2D colloid crystal.