Silica Biomineralization Of Amphiphilic Peptides And Formation Mechanism

Peptides are the fundamental building units of biological systems. De novo synthesized amphiphilic peptides are attracted rapidly rising attention because they are easy to be designed and synthesized. Moreover, because of their amphiphilic and chiral nature, the self-assembly and biomineralization of amphiphilic peptides can find applications in the fields of bioengineering, therapeutics and nanotechnology. People have designed various kinds of amphiphilic peptides, and studied their self-assembly and biomineralization process. However, the structures of biomineralized peptides were only resulted in lamellar structure or disordered. Herein, amphiphilic peptides were designed with different strength of intramolecular hydrogen bonds, different hydrophilicity and different kinds of hydrophobic tails to study the biomineralization process through structures, morphologies and energy, etc as well as synthesis of novel materials.In Chapter 2, amphiphilic peptides were designed with proline residues into the backbone to control the nanostructures of the biomineralization assemblies. Amphiphilic peptides with different conformations, but have the similar sequence(Ac-FFFFPTTPTTE-COOH and Ac-FFFFTTTTE-COOH; Ac: acetyl group, F: phenylalanine, T: threonine, P: proline, E: glutamic acid) were precisely designed, for synthesizing a highly ordered two-dimensional(2D) hexagonal and lamellar chiral silica mesostructure, and studied the role of the proline units. The geometry of the peptide was designed by adding proline residues into the hydrophobic chain of the peptide to break the β-sheet conformation by weakening the intermolecular hydrogen bonds; this led to the mesophase transformation from the most general lamellar structure to the 2D hexagonal p6 mm mesostructure by increasing the amphiphilic molecules packing parameter g. The biomineralization process was taken out through a co-structure directing agent(CSDA) route. A proper peptide–silicate interaction was developed by introducing quaternised aminosilane N-trimethoxysilylpropyl-N,N,N-trimethylammonium chloride(TMAPS) as the CSDA into the synthesis system to synthesize silica materials with highly ordered structures. Enantiomerically pure chiral mesostructures were formed thanks to the intrinsic chirality and relatively strong intermolecular hydrogen bonds of peptides.In Chapter 3, amphiphilic peptides were designed with different hydrophilicity to control the nanostructures of the biomineralization assemblies. A series of amphiphilic peptides with different hydrophilicity(Ac-FFFFSSSSEE-COOH, Ac-FFFSSSSE-COOH, Ac-FFFFSSSSD-COOH and Ac-FFFFFSSSE-COOH; S: serine, D: aspartic acid) was designed for mimicking natural biomineralization to synthesize chiral silica materials that have controllable chiral morphologies and mesostructures. by control the hydrophilicity of the amphiphilic peptides, we found(i) by decreasing the hydrophilicity, the morphologies changed from helical nanofibers to helical nanoribbons, and the extent of the helicity decreased due to less twisting of the β-sheets;(ii) by decreasing the hydrophilicity, the mesostructures changed from 2D-hexagonal structures to lamellar structures because of the increase in the surfactant packing parameter g. The geometry, energy and formation mechanism of the system were further discussed.In Chapter 4, amphiphilic peptides were designed with different hydrophobic tails to control the nanostructures of the biomineralization assemblies.to figure out the structural roles of the tails, these peptides with different hydrophobic tails(Ac-FFFFSSSSSE-COOH, C16-SSSSSE-COOH and Ac-SSSSSE-COOH) were designed for mimicking natural biomineralization. It was found that by changing the hydrophobic tails of the amphiphilic peptides(i) the conformations of peptides turned from the type II β-turn to α-helix and random coil;(ii) the morphologies of silica materials changed from twisted nanoribbons to twisted nanofibers and hollow nanospheres. The biomineralization process was conducted through CSDA route that allow the negatively charged peptide surface to be interacted with silica source under ambient condition, and thus for a better self-assembly and biomineralization.In Chapter 5, synthesis of amphiphilic peptide/metal nanoparticle/silica complex.(1) Amphiphilic peptide was designed to induce an easy approach to synthesize complex materials of amphiphilic peptide/metal nanoparticle/silica. The metal nanoparticles in the material not only have a spatial superstructure, but also have good stability under high temperature.(2) Silver nanoparticles were embedded into amphiphilic peptide induced silica material with helical morphology, chiral pore structure and enantiomerical purity, and synthesized complex materials of metal nanoparticle/silica with a special photonic property of asymmetric surface plasmon resonance.