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During the last decade, a great deal of efforts has been put in explaining the mechanism by which biological antifreeze proteins (AFGPs) bind to ice and inhibit its growth. The macromolecular mechanism has been described initially as an adsorption-inhibition process in which the AFGPs bind irreversibly on the surface of ice. However, there is a strong debate as to which is the dominant force for adsorption of AFGPs on ice. The hydrophilic interactions between polar hydroxyl groups on the disaccharides and the water molecules on the ice surface are extremely important, but the entropic and enthalpic contributions from hydrophobic residues might be crucial in the binding of an AFGP to the ice surface. These questions prompted a direct study of protein-surface interactions under various conditions. The specificity of protein-surface interactions led us to test the applicability of AFGPs to guide crystal growth. This concept of biomineralization strategies for the synthesis of materials has become one of the most important areas in nano-biotechnology. Biological antifreeze proteins provide an impressive example of macromolecules with specific recognition capabilities for inorganic structures. The use of such molecules in organizing non-biological inorganic objects, like nanoparticles, into functional materials is an important new frontier in material and surface chemistry. Moreover, patterning surfaces with this type of macromolecules could serve as nucleation templates for controlling nucleation crystal growth, including precise localization of particles, crystal sizes and shapes.
In the present work, we focus on the spontaneous pattern formation of antifreeze glycoprotein fraction 8 (AFGP8) deposited on mica. During solution-droplet evaporation, single proteins have been identified and patterns of single-proteins-lines were observed. The single protein height was measured as 8.1±2.5 Ǻ. The line spacing directly depends on the concentration of the protein solution. A two-dimensional single-protein-thick grid was also observed. Imaging under solution conditions showed the high affinity of the proteins for the surface leading to monolayer formation.
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