Enzyme-Mimicking Peptides to Catalytically Grow ZnO Nanocrystals in Non-Aqueous Environments

The application of enzymes for biomimetic material growth is a potential path to breakthroughs in catalytic inorganic nanocrystal synthesis because the biocatalytic functions of proteins can lead to highly efficient growth of materials with accurate structures at low temperature. However, many metal nanocrystals are grown in organic solvents, which is not an ideal environment for biomineralization with enzymes due to denaturing of catalytic pocket structures. Here, we applied a catalytic CP4 peptide, optimized for protease reactions such as amide and ester hydrolysis, to test the catalytic ZnO nanocrystal growth in non-aqueous environments and the performance was compared with the enzyme subtilisin. We demonstrated that the CP4 catalytic peptide, evolved by the hydrogel-based combinatory phage display library, could grow ZnO nanoparticles from zinc acetate precursors in higher crystallinity and yield, as compared to the protease enzyme, in an organic solvent by catalyzing ester-elimination of precursors at room temperature. This result indicates that catalytic oligopeptides, which possess no rigid 3D structures but are rather flexible, could fold into the catalytically active conformation more frequently in harsh environments such as organic solvents.