Biomimetic Sol–Gel Synthesis of TiO₂ and SiO₂ Nanostructures

Abstract

We report the heptapeptide-mediated\nbiomineralization of titanium\ndioxide nanoparticles from titanium alkoxides. We evaluated the influence\nof pH on the biomineralized products and found that nanostructured\nTiO₂ was formed in the absence of external ions (water\nonly) at pH ∼ 6.5. Several variants (mutants) of the peptides\nwith different properties (i.e., different charges, isoelectric points\n(p<i>I</i>s), and sequences) were designed and tested in\nbiomineralization experiments. Acid-catalyzed experiments were run\nusing the H1 (HKKPSKS) peptide at room temperature, which produced\nanatase nanoparticles (∼5 nm in size) for the first time via\na heptapeptide and sol–gel approach. In addition, the peptide\nH1 was used to synthesize SiO₂ nanoparticles. The influence\nof the pH and the added ions were monitored: at higher pH levels (8–9),\nSiO₂ nanoparticles (20–30 nm in size) were obtained.\nIn addition, whereas borate and Tris ions allowed the formation of\ncolloidal systems, phosphate ions were unable to produce sols. The\nresults presented here demonstrate that biomineralization depends\non the sequence and charge of the peptide, and ions in solution can\noptimize the formation of nanostructures.