The molecular self-assembly of aromatic peptide amphiphiles has raised interest through the last decades due to the possibility to form different nanostructures in aqueous medium, depending on the sequence, kinetics and established non-covalent interactions. Enzyme triggered self-assembly gives an extra spatiotemporal control over the assembling process when initiating, e.g., fibre formation and consequent gelation under physiological unchanged conditions. The development of natural alternative types of emulsifiers is critical and more recently sought within the cosmetic/food industries. Peptides can act as surfactants if they are designed to present an amphiphilic nature, and can also be switchable if designed to respond to stimuli, which would be attractive for different applications. An alkaline phosphatase is used to transform phosphorylated precursors into self-assembling aromatic-capped dipeptide amphiphiles, providing a route to trigger self-assembly of nanofibrous networks and hydrogels in aqueous medium. The same mechanism is proven for unprotected tripeptides, where the kinetic control, tuned by the amount of enzyme used, is shown to play a key role in dictating the morphology of the nanofibrous networks produced and consequent hydrogel stiffness. When the aromatic dipeptide amphiphiles or amphiphilic tripeptides are used in biphasic systems, nanofibrous networks are shown to self-assemble preferentially at the aqueous/organic interface or vicinity, thereby stabilising the oil-in-water droplet dispersions. Alkaline phosphatase is shown to be active in aqueous-organic solvent systems, in approximately the same extent as in aqueous buffer. Different experimental and computational techniques are used to obtain further insight on the supramolecular interactions responsible for the self-assembly process, in both aqueous and biphasics systems. The ability of on-demand emulsification is shown by the addition of the enzyme to the biphasic de-emulsified mixture after storage for different times, proving these two kinds of peptidic systems can be used as responsive emulsifiers. In addition, the possibility of controlling the emulsification extent by taking advantage of the dephosphorylation kinetics and consequent formation of different stabilising fibrous networks is shown.The use of a non-covalent trigger for the formation of a specific structure can also be attractive for various applications. The possibility of achieving innovative functional materials through co-assembly of tripeptides and dipeptides is also studied. A computational screening approach has been developed for the creation of design rules to produce hydrogelators and better emulsifiers. In this work, the possibility of on-demand emulsification when using biocatalytically-triggered self-assembly of short peptide amphiphiles was shown for the first time. The time control and tuning over the emulsifying ability extent was also proved. Additionally, design methods allow for the identification of promising candidates for numerous types of materials. Co-assembled tripeptides and dipeptides can be carefully designed to give rise to hydrogels and effective emulsifiers, which can be highly attractive for different applications.
|Date of Award||2 Jun 2017|
- University Of Strathclyde
|Supervisor||Tell Tuttle (Supervisor) & Rein Ulijn (Supervisor)|