Biomimetic synthesis of ordered silica structures mediated by block copolypeptides

In biological systems such as diatoms and sponges, the formation of solid s ilica structures with precisely controlled morphologies is directed by prot eins and polysaccharides and occurs in water at neutral:pH and ambient temp erature(1-4). Laboratory methods, in contrast, have to rely on extreme pH c onditions and/or surfactants to induce the condensation of silica precursor s into specific morphologies or patterned structures(5-10), This contrast i n processing conditions and the growing demand for benign synthesis methods that minimize adverse environmental effects have spurred much interest in biomimetic approaches in materials science(4,5), The recent demonstration t hat silicatein-a protein found in the silica spicules of the sponge Tethya aurantia(11)-can hydrolyse and condense the precursor molecule tetraethoxys ilane to form silica structures with controlled shapes at ambient condition s(12-14) seems particularly promising in this context, Here we describe syn thetic cysteine-lysine block copolypeptides that mimic the properties of si licatein: the copolypeptides self-assemble into structured aggregates that hydrolyse tetraethoxysilane while simultaneously directing the formation of ordered silica morphologies. We find that oxidation of the cysteine sulphy dryl groups, which is known to affect the assembly of the block copolypepti de(15), allows us to produce different structures: hard silica spheres and well-defined columns of amorphous silica are produced using the fully reduc ed and the oxidized forms of the copolymer, respectively.