Silicification and biosilicification - Part 4. Effect of template size on the formation of silica

Silicification at neutral pH and under ambient conditions is of growing interest due to its close relationship with biosilicification. In diatoms biosilicification has been reported to occur at ( or close to) neutral pH and it has been shown that protein molecules act as catalysts / templates / scaffolds for this elegant materials chemistry. In this investigation various catalysts / templates have been studied for their role in silicification in vitro. We have used functionalized C-60 fullerene, R5 (an important polypeptide from the amino acid sequence of a silaffin protein), poly-l-lysine (PLL) and two poly(allylamine hydrochloride) (PAH) samples having different molecular weights. An aqueous silica precursor was used and ordered silica structures were produced in each of the systems studied. The sizes of the silica structures appear to correlate with the size, in solution, of the templating / scaffolding agents. Biological systems exhibit hierarchical structures with remarkable control of morphologies over different length scales. The use of templating / scaffolding agents having different sizes and shapes is one possible paradigm for the production of such structures in vivo.