Peptide-based bioinspired functional materials

Ability of nature to build complex systems via step-by-step addition of small building blocks with distinctive qualities and multi-functionalities has garnered massive attention which gave a rise to biomimetic or biologically inspired synthesis concept. Biomimetic synthesis mimics nature’s approach and design principles offering various combinations of new concepts and designs to adapt them in synthetic materials or processes.[1] Up to date, many efforts have been made to mimic nature’s approach for the development and fabrication of more effective synthetic systems and structures to compensate drawbacks and overcome reported challenges in existing models.[2] In the first part of this thesis, development of a bioinspired, heterogeneous and recyclable Cu-complex catalyst for [3+2] Huisgen cycloaddition reaction, also known as click reaction, is described. A copper binding peptide sequence, human tripeptide Gly-His-Lys (GHK), is utilized for such purpose.[3] GHK sequence is linked with an alkyl tail comprising 6, GHK-6-abx, or 11, GHK-11-adx, carbons to the polystyrene ring amide resin where it is used as a solid support and complexed with Cu(II). The catalyst provides better catalytic activities in aqueous solvent rather than organic solvents which is a desirable property for green chemistry point of view. Accordingly, an enzyme-like catalyst is described where alkyl tail offers hydrophobic regions for organic reagents to be immobilized closer to the Cu(II), catalytic site of the molecule, and increases reaction yields. 80% yield can be obtained from GHK-11-adx-Cu complex catalyst in water using Cu(II) loadings as low as 0.5 mol% and catalytic activity can be retained up to three cycles of reactions. In the second study of this thesis, we developed a versatile system to induce self-assembly of peptide amphiphiles by using light which is a readily available and cheap reagent allowing precise stimulation and providing quick response. For this purpose, a photo-labile calcium chelator, Nitr-T, which releases free Ca2+ ions upon irradiation is mixed with a negatively charged E2-PA. E2-PA, a negatively charged PA molecule, self-assembles to form a hydrogel in the presence of free Ca2+ ions provided by the NitrT-Ca2+ complex, and goes back to its solution state when free Ca2+ ions are removed from the medium by the addition of EDTA solution. Consequently, swelling characteristics and mechanical properties of any negatively charged Peptide-Amphiphile (PA) can be controlled by using light as stimuli by simply mixing PA solution with NitrT-Ca2+ complex without any further modification or covalent modification in the molecule’s structure. In overall, peptide-based, bioinspired functional materials for various applications like catalysts and tissue engineering was reported in the scope of this thesis. Peptides and peptide-amphiphiles present a very useful member in number of biomimetic applications as they are indispensable part of many biological processes capable of performing very complicated tasks.