Design of Nanostructured Materials via Protein Engineering
Controlled biomineralization of hybrid metal oxide using affinity peptides
Some organisms such as sponges and diatoms can produce minerals under physiological conditions through the use of specific biomolecules. Inspired by this exquisite phenomenon, many research efforts have been directed toward harnessing these natural proteins for biomimetic synthesis of inorganic materials. In view of synthesizing a remarkably diverse range of inorganic materials using the precursor available in the biosphere by biological system, the biomolecules were used to induce inorganic materials under the ambient condition in these days. In addition, biomolecule such as proteins and peptides can control the size, shape, chemistry and crystal structure of the inorganic product in material synthesis. In our previous study, screened constraint heptapeptide STB1 (-CHKKPSKSC-) with specific affinity to TiO2 surface was demonstrated to facilitate biomineralization of TiO2 nanoparticles in thermodynamically unfavorable condition. It was found out that major deriving force enabling the nanoparticle synthesis is electrostatic interaction between the peptide and precursor. TiO2 is commonly used as a photocatalyst as it is non-toxic, chemically stable, inexpensive, and highly efficient. However, it has a relatively large band gap (~3.2 eV), which renders it usable only under UV light. By coupling two metal oxides (e.g. TiO2 and WO3) the reduction of band gap energy is expected, thereby making it possible to use the hybrid metal oxide in the visible light region. In this project, STB1 and its engineered derivatives are explored to synthesize both TiO2 and WO3 from their precursors. Since STB1 was screened against TiO2, it is not surprising to see low efficiency of STB1-mediated WO3 synthesis. However, it was found that a designer peptide RSTB1 with three lysine residues in STB1 replaced by arginine could render the biomineralization of both TiO2 and WO3. Furthermore, RSTB1 was demonstrated to synthesize TiO2-WO3 hybrid metal oxide with uniform distribution of titanium and tungsten elements at molecular level. It is anticipated that further engineering of STB1 and/or RSTB1 will enable the controlled biomineralization of hybrid metal oxides of various compositions, sizes and morphologies. This study provides interesting insights to understanding biomimetic synthesis of inorganic materials and their potential usages as novel energy materials.