Serine-Lysine Peptides as Mediators for the Production of Titanium Dioxide: Investigating the Effects of Primary and Secondary Structures Using Solid-State NMR Spectroscopy and DFT Calculations.

A biomimetic approach to the formation of titania (TiO2 ) nanostructures is desirable because of the mild conditions required in this form of production. We have identified a series of serine-lysine peptides as candidates for the biomimetic production of TiO2 nanostructures. We have assayed these peptides for TiO2 -precipitating activity upon exposure to titanium bis(ammonium lactato)dihydroxide and have characterized the resulting coprecipitates using scanning electron microscopy. A subset of these assayed peptides efficiently facilitates the production of TiO2 nanospheres. Here, we investigate the process of TiO2 nanosphere formation mediated by the S-K peptides KSSKK- and SKSK3 SKS using one-dimensional and two-dimensional solid-state NMR (ssNMR) on peptide samples with uniformly 13 C-enriched residues. ssNMR is used to assign 13 C chemical shifts (CSs) site-specifically in each free peptide and TiO2 -embedded peptide, which are used to derive secondary structures in the neat and TiO2 coprecipitated states. The backbone 13 C CSs are used to assess secondary structural changes undergone during the coprecipitation process. Side-chain 13 C CS changes are analyzed with density functional theory calculations and used to determine side-chain conformational changes that occur upon coprecipitation with TiO2 and to determine surface orientation of lysine side chains in TiO2 -peptide composites.