Biomimetic Construction Of Ordered Silica Nanostructures Based On Ultrashort Peptides

In natural world, biosilic exist in some organisms such as diatonms, sponge spicules andsome plants, and they exhibit obvious advantages over the current artificial silicananostructures both in complexity and controbility. Especially, these refined structures ofbiosilica are formed in physiological conditions, needless of high temperature, high pressureand chemical reagents necessary in artificial synthetic techniques. It therefore become anattractive to biomimetic prepares well controlled silica nanostructures because it is help toweaken the energy and environmental problems.Amphiphilic ultrashort peptides ImKn(m=3-5, n=1-2, K: lysine) which contain4-6aminoacid residues were designed and synthesized. One hand, hydrophilic head groups provide thedriving force for self-assembly with the intermolecular hydrogen bonds and the hydrophobicinteraction derived from isoleucine (I). On the other hand, researches had confirmed thatlysine play a significant role in promoting silicification reaction. Spatical arrangement,morphology and size parameters of assmble and silica deposition rate were studied by varyingthe number of hydrophobic amino acid residues (I) and functional amino acid residues (K)density. The results indicated that the assembly diameter decreases with hydrophobic aminoacid residues, and silica deposition rate was controlled by the size of assembly. When the I3Kwas used as the substrate, the interior and exterior surface of assembly were both deposited bysilica, as to I4K or I5K, silica could only deposite on the exterior surface of template. However,increasing the density of fuctinal amino acid residues, such as I4K2, could also achievemineralization both in interior and exterior surfaces even in a smaller assembly size.The ultrashort peptide assembly can functioned as the catalytic site and the template forsilica deposition. Furthermore, the formation of silica nanostructures was also affected by theformation rate of inorganic particles and their assembly rate on the organic template surface. The random silica deposition was presented when replacing TEOS with TMOS whichhydrolyze faster in the same mineralization condition. Little influence on mineral morphologywas observed by diluting the concentration of reactants or decreasing the reaction temperature.Finally, ordered nano-tubular structures were obtained by increasing the concentration ofpeptide and electricity of peptide (I4K2as the substrate). Further experiments confirmed thatthe silica growed under the regulation of organic template only when the interaction betweenorganic particles and the organic interface exceeded the growth rate of organic particles,resulting silica nanostructures dependent on the template.With the increasing of the deposition thickness of silica on the ultrashort peptide, thecatalytic and assembly ability for silica gradually weakened and finaly disappeared. Thus thesilica structure and their size can only be controlled in a limited scale. Silica nanostructureswith larger size and morphology-contralled could be obtained by the introduction of a specialsilicon precusor (aminopropyltriethoxysilane) in the reaction system, for the amino of APTEScould catalyze silicide reaction while alkoxy could react with the hydroxyl groups of silica onthe template surface. Synergistic growth mechanism of silica competition from the two siliconsources was discussed through the study of the impact of mineralization and morphology byvarying the ratio of reactants, feeding orders, etc. In addition, silica nanotubes grafting vinylgroup on the surface were obtained by using vinyl triehoxysilane as co-silica precusors.What’s more, after loading Pt on the nano-silica by hybridizing with chloroplatinic acid, thecatalytic properties in hydrosilylation was investigated. The complex containing Pt not onlyhad a considerable catalytic capability with Karstedt catalyst, and as the heterogeneouscatalysts they could be easily removed after the end of the reaction.