Biomimetic silicification to mimic 3D ornate diatom structures - a myth or a reality?

Conventional methods of making silica structures involve high temperatures, pressures, and pH. In contrast, biosilicification process in living organisms such as diatoms proceeds under physiological conditions and is triggered via hydrolysis of silicic acid by cationic proteins/peptides that act as a scaffold/catalyst/template. Although in vitro studies using these biomolecules have demonstrated biosilica formation, the ability to produce 3D ornate silica structures still remains an open challenge. To this end, biomimetic studies have so far only been explored in aqueous solvents, which do not necessarily mimic the natural biosilicification environment. Ionic liquids (ILs) have recently attracted significant attention as environmentally-benign solvents due to their unique physico-chemical properties. ILs can, in principle, act as supersaturated salt solutions and mimic the marine conditions where biosilicification takes place. To the best of our knowledge, the potential of ILs as designer solvents for performing biomimetic reactions has not hitherto been explored, more so, in the context of biosilicification. In this study, we show the role of amino acids in controlling the growth of silica structures in IL 1-butyl-3-methylimidazolium tetrafluroborate ([BMIM][BF4]). Our studies show that amino acids an form diatoms-like 3D silica structures when reactions are undertaken in ILs. The specificity of amino acids towards attaining unique 3D silica morphologies in this study suggests that the diversity in biosilica morphology seen in different diatom species might possibly be due to the compositional differences in polypeptide building blocks responsible in biosilicification, wherein amino acids have been found to be present in different proportions