Mechanistic Processes Underlying Biomimetic Synthesis of Silica Nanotubes from Self-Assembled Ultrashort Peptide Templates

This work reports a mechanistic study of template-directed synthesis of silica nanomaterials utilizing self-assembled peptide nanotubes as scaffolds. An ultrashort amphiphilic peptide (I 3 K) underwent self-assembly in aqueous solution under ambient conditions to form long and uniform nanotubes. The assembled peptide nanotubes then were used as templates for the subsequent fabrication of silica nanotubes from tetraethoxysilane (TEOS), also under ambient conditions. In order to gain better insight into the mediation of peptide self-assembly on the formation of silica nanostructures, we have carefully investigated environmental influences including the concentrations of peptide and silica precursor, solution pH, and reaction time, with the full screening of the processes by TEM, SEM, 29 Si MAS NMR, FTIR, and TG-MS. The results revealed that, while peptide nanotubes worked as scaffolds for the formation of tubular silica structures, the surfaces of these peptide nanotubes served as catalytic sites for both hydrolysis and condensation of TEOS, thereby working as templates for directing silica deposition. Because the electrostatic attraction of the negatively charged silica intermediates onto the positively charged surface of peptide nanotubes drove the templating process, tuning of such an interaction by adjusting the solution conditions (such as pH) affected silica morphological structures. Silica tended to deposit along the exterior surface of the template at undersaturation over weak acidic and neutral pH ranges, while silica intermediates overcame diffusion resistance and moved inside the tubular template over mild basic pH ranges, enabling silica precipitation along the interior surface. This work has thus demonstrated that the morphological nanostructures of silica can be controlled by adjusting the silicification conditions (such as peptide concentration and solution pH) under an ambient environment, thus avoiding harsh chemicals or extreme reaction conditions.