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Biomimetic synthesis of ordered silica structures mediated by block copolypeptides

Abstract

In biological systems such as diatoms and sponges, the formation of solid silica structures with precisely controlled morphologies is directed by proteins and polysaccharides and occurs in water at neutral pH and ambient temperature1,2,3,4. Laboratory methods, in contrast, have to rely on extreme pH conditions and/or surfactants to induce the condensation of silica precursors into specific morphologies or patterned structures5,6,7,8,9,10. This contrast in processing conditions and the growing demand for benign synthesis methods that minimize adverse environmental effects have spurred much interest in biomimetic approaches in materials science4,5. The recent demonstration that silicatein—a protein found in the silica spicules of the sponge Tethya aurantia11—can hydrolyse and condense the precursor molecule tetraethoxysilane to form silica structures with controlled shapes at ambient conditions12,13,14 seems particularly promising in this context. Here we describe synthetic cysteine-lysine block copolypeptides that mimic the properties of silicatein: 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 sulphydryl groups, which is known to affect the assembly of the block copolypeptide15, allows us to produce different structures: hard silica spheres and well-defined columns of amorphous silica are produced using the fully reduced and the oxidized forms of the copolymer, respectively.

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Figure 1: Synthesis strategy to produce block copolypeptides.
Figure 2: Different ordered silica shapes obtained using block copolypeptide 6.

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Acknowledgements

We thank M. Brzezinski and B. Chmelka for suggestions, and E. Skogen for the light microscopy pictures. This work was supported by the US Army Research Office Multidisciplinary University Research Initiative, the US Office of Naval Research, the NOAA National Sea Grant College Program, the US Department of Commerce, the California Sea Grant College System, the MRSEC Program of the NSF to the UCSB Materials Research Laboratory, and the Dow Corning Corporation.

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Correspondence to Timothy J. Deming.

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Cha, J., Stucky, G., Morse, D. et al. Biomimetic synthesis of ordered silica structures mediated by block copolypeptides . Nature 403, 289–292 (2000). https://doi.org/10.1038/35002038

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