Identification and design of peptides for the rapid, high-yield formation of nanoparticulate TiO2 from aqueous solutions at room temperature

Titania (TiO2) nanoparticles are widely used, or are under active development, for a range of applications in (photo)catalysis, photovoltaics, enzyme support, energy storage, and photonics. The peptide-directed room-temperature formation of titania nanoparticles can be an attractive alternative to higher-temperature synthetic methods. However, the influence of the peptide primary structure on the titania precipitation activity at room temperature is not well understood. Through the selective binding of phage-displayed 12-mer peptides to TiO2 substrates, we have identified 20 peptides with an affinity for titania. The average numbers of arginine, lysine, and histidine residues present in these 20 peptides were distinctly higher than for the overall peptide-bearing phage library. Synthetic 16-mer versions of four of these peptides (i.e., 12-mer peptides with C-terminal tetrapeptide tags for quantitative spectrophotometry) induced the formation of 8.1-38.7 mol TiO2/mol peptide after exposure for only 10 min to an otherwise water-stable Ti(IV) complex at room temperature and a pH of 6.3. X-ray diffraction analyses, electron diffraction analyses, and high-resolution transmission electron microscopy revealed that the peptide-induced titania contained fine (< 10 nm) anatase and monoclinic beta-TiO2 nanocrystals, along with an amorphous phase. The titania yield increased with the number of positive charges carried by these peptides. On the basis of these results, a peptide was designed that exhibited the highest titania formation activity reported to date for a peptide (82.9 mol TiO2/mol peptide), as well as a reduced pH dependence for such titania formation.