Controlled biomimetic silica formation using star-shaped poly(l-lysine)

A novel star-shaped copolymer PEI10 000-g-PLL20, with a hyperbranched polyethylenimine (PEI) core and multiple linear poly(L-lysine) (PLL) peripheral chains was designed and synthesized. The star-shaped peptide, along with multiple counterions, was used as an organic template to direct the biomimetic synthesis of silica under mild conditions. Various biosilica morphologies, such as spherical, clubbed, and hexagonal shapes, were transformed using a specific TEOS/lysine residue ratio (δ) in a peptide/phosphate/silicic acid system. Individual silica spheres were obtained when δ was smaller than 10, whereas clubbed (δ = 11) and hexagonal (δ = 18) particles formed when δ was larger than 10. However, only clubbed biosilica was obtained when the counterions were carbonates or sulfates. Transmission electron microscopy and circular dichroism spectroscopy results suggest that the presence of counterions was necessary but not sufficient to produce ordered silica morphologies. Thus, the nature of peptide/anion complex, TEOS/lysine residue ratio, and pH changes in the biomimetic system played important roles in determining the silica morphologies.