A Comparative Study of Secondary Structure and Interactions of the R5 Peptide in Silicon Oxide and Titanium Oxide Co-precipitates using Solid-state NMR Spectroscopy.

A biomimetic, peptide-mediated approach to inorganic nanostructure formation is of great interest as an alternative to industrial production methods. To investigate the role of peptide structure on silica (SiO2) and titania (TiO2) morphologies, we use the R5 peptide domain derived from the silaffin protein to produce uniform SiO2 and TiO2 nanostructures from the precursor silicic acid and titanium bis(ammonium lactato)dihydroxide, respectively. The resulting biosilica and biotitania nanostructures are characterized using scanning electron microscopy. To investigate the process of R5-mediated SiO2 and TiO2 formation, we carry out 1D and 2D solid-state NMR (ssNMR) studies on R5 samples with uniformly C-13- and N-15-labeled residues to determine the backbone and side-chain chemical shifts. C-13 chemical shift data are in turn used to determine peptide backbone torsion angles and secondary structure for the RS peptide neat, in silica, and in titania. We are thus able to assess the impact of the different mineral environments on peptide structure, and-we can further elucidate from C-13 chemical shifts change the degree to which various side chains are in close proximity to the mineral phases. These comparisons add to the understanding of the role of R5 and its structure in both SiO2 and TiO2 formation.