Biomimetic templates for the synthesis of nanostructured and nanocomposite silica materials.

摘要

Unicellular eukaryotic planktons, known as diatoms, are able to biomineralize siliceous cell structures in a vast array of diverse nanopatterns. Contrasting with current harsh industrial methods of silica nanopatterning, diatoms form the silica under the ambient conditions of their environment. Recently, short chained highly modified peptides named silaffins and other polyamines have been implicated as the structural catalyst upon which the diatoms biogenically form silica. The lysines of the peptide are modified with long chain polyamines and the serine residues are phosphorylated upon which the peptide is able to self-assemble into larger structures which possess localized areas of high concentrations of amines to drive silica production from monosilicic acid. The non modified peptide named R5 (H2N-SSKKSGSYSGSKGSKRRIL-CO2H) has also been shown to produce silica in similar methods to that of the modified silaffin. Through a synthetic site directed mutagenesis study, we have shown that the R5 peptide is able to self-assemble upon the RRIL subunit into larger structures to drive the condensation reaction for silica production as the silaffin peptide does upon the phosphoserines. Under standard conditions, the R5 produces nanospherical particles of silica. To mimic the side chain modifications, we have also used amine-terminated PAMAM and PPI dendrimers as a template for silica production in vitro to understand the important factors of the polyamine modifications to the silaffin peptide. We have shown that the dendrimers react in an amine concentration dependent fashion producing silica nanospheres of a distinct size distribution and morphology. The particle size distributions can be controlled by judicious choice of reaction conditions leading to size selective precipitation of the material. Furthermore, we have shown that the dendrimer templates are encapsulated by the growing silica nanospheres leading to the production of novel multicomponent systems.