Supramolecular chiral self-assembled peptide nanostructures

Abstract

Self-assembly process is an easy and convenient bottom-up technique for designing novel functional materials. Self-assembled peptide amphiphile (PA) molecules are remarkable building blocks for a wide-range of applications due to their easy synthesis, biocompatibility, biodegradabability and dynamic nature in aqueous conditions. Controlling self-assembly behavior still remains complex, since it can be affected by multiple factors. Chirality is an important parameter for designing and controlling self-assembled supramolecular nanomaterials. In this thesis, self-assembly mechanism of chiral peptide molecules was studied with different driving forces in order to develop new methodsfor producing self-assembled nanomaterials. In addition to self-assembly mechanism, different morphologies and chiral behaviors of the self-assembled supramolecular chiral peptide amphiphile nanostructureswere monitored with variouscharacterization methods. pH is a significant contributor for the self-assembly process and this effect was studied in detail to elucidate pH dependency of supramolecular conformation. According to morphological characterizations, histidine containing PA molecules form nanosheet like structures under acidic pH.At the isoelectric point of imidazole, they have a tendency to form twisted fiber or ribbon structures. Athigh pH iv conditions, pH 10, they form nanotubes due to the neutralization of imidazole groups and π-π interactionsat theside chain of histidine moiety.When another aromatic ring is included in the sequence, in this case phenylalanine residue, different nanostructures were observed. In addition to histidine PA, lysine and glutamic acid containing peptide building blocks were also studied to understand the effect of electrostatic interactions. Phenylalanine containing PAs and valine containing PAs were compared in terms of their chiral self-assembly behaviors. As a result of self-assembly of the positively charged and negatively charged peptides, well defined nanostructures were obtained. While valine containing PA molecules form straight nanofibers, phenyl alanine containing PAs form well ordered rigid twisted fibers and twisted ribbon structures.