Solid State NMR Characterization of Biosilicification Peptides

Abstract

Biomimetic syntheses of useful inorganic and mineral materials are the subject of much interest in the biomineralization community, as organisms can often produce materials at ambient conditions and temperatures, as opposed to the extreme conditions of commercial methods. The focus here is on biosilicication peptides, which produce silica nanoparticles out of solutions of silicic acid. Solid-state NMR (SSNMR) investigations of the R5 peptide (part of a naturally occurring sequence in diatoms) and the synthetic, model LKa14 peptide are detailed here, utilizing 1D and 2D 13C,15N and 29Si CPMAS and DARR experiments and culminating in the elucidation of secondary structures for both peptides in their neat (lyophilized) form, and their form when complexed to biosilica. Additional relaxation experiments (13C CP T1IR) probe dynamics of side chains. It is shown that secondary structure alone is not responsible for the morphology of the resulting silica nanoparticles, and the importance of larger scale aggregation is emphasized. Several self-assembly and silica templating models for the R5 and LKa14 peptide are proposed, with supporting SSNMR results and incorporating a review of relevant current literature in the field.