From Diatom Biomolecules to Bioinspired Syntheses of Silica- and Titania-Based Materials
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tules have amazed natural scientists for more than two centuries.8 However, only during the past decade have initial insights into the molecular mechanisms of diatom silica nanofabrication been gained. Here we describe how understanding of the molecular mechanism of silica formation by diatom biomolecules has been utilized to develop novel methods for synthesizing oxide/organic hybrid structures.
Biomolecules to Bioinspired Syntheses of Silica- and Titania-Based Materials
Silica Formation In Vitro Using Biomolecules from Diatoms
Nils Kröger and Kenneth H. Sandhage Abstract Amorphous silica is (next to CaCO3) the second most abundant biologically produced inorganic material. A certain group of photosynthetic microalgae, called diatoms, forms complex 3D silica architectures (frustules) containing regularly arranged nanoscale features (pores, channels, protuberances). Recently, biomolecules involved in diatom silica formation have been characterized, and first insights into their structure-function correlations have been obtained. This has spurred the development of synthetic (bio)polymers capable of directing the in vitro formation of silica and other inorganic materials from aqueous precursor solutions under mild conditions. Here we present a summary of current insight into the mechanism of silica formation by diatom biomolecules and provide examples of synthetic (bio)polymers for the formation of silica and titania materials with complex structures.
Introduction Nature provides impressive examples of organisms that produce intricate inorganic structures (biominerals). For example, certain bacteria produce magnetic nanocrystals, many mollusks build calcium carbonate shells, and mammals form bone and teeth.1 A remarkable characteristic of biomineral formation (biomineralization) is precise 3D control of complex mineral structures over several orders of magnitude in length scale (from a few nanometers up to millimeters or more). This is achieved by the action of highly organized assemblies of cellular macromolecules enabling mineral formation to proceed under physiological reaction con122
ditions.2,3 Hence, understanding the molecular mechanisms of biomineralization may potentially provide novel routes for synthesizing complex inorganic materials under mild conditions. The present review is focused on materials syntheses inspired by diatoms, a fascinating group of biomineral-forming organisms that have been receiving increased attention from the materials science community.4–7 Diatoms are single-celled algae that produce cell walls (frustules) of amorphous, hydrated silica with intricate, species-specific, 3D morphologies (Figure 1). The nano- to microstructured, highly symmetric, porous architectures of diatom frus-
Diatom biosilica is an organic-inorganic hybrid material containing biomolecules tightly attached/encapsulated within amorphous hydrated silica.9–12 Over the past decade, three groups of biosilicaassociated biomolecules (silaffins, silacidins, long-chain polyamines) have been identified that exhibit
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