Construct And Applications Of Small Molecular Gels Formed By Modified Peptides

Supramolecular hydrogels based on peptide self-assembly are important bio-compatible functional material with diverse applications. With increasing research interest on stimuli-responsive biomaterials in recent years, peptide-based supramolecular hydrogels have been designed as "smart" materials with response to various stimuli such as pH, heat, light, enzyme etc.In this thesis, we found that short peptides appropriately linked with azobenzene as conformational switch were motif and pH dependant supramolecular hydrogelators. Hydrogelation property of the short peptides linked with conformation switch was studied in detail with respect to dependence on amino acid residue and pH. The presence of amino acids with aromatic side chains such as Phe and Tyr was found to be favorable for the short peptides to gel water at appropriate pH range. The cryo-gel SEM showed tangle fiber structure in the hydrogel, and CD P-sheet-like superstucture in the gel state. A series of short peptides with bioactive sequences were linked with the conformation switch and their hydrogelation properties were investigated. The hydrogel had potential application in biological engineering.Photo-responsive supramolecular hydrogels were realized based on the trans-lcis-transition of the conformation switch upon light irradiation. The UV-Vis and HPLC of the hydrogel before and after UV irradiation showed the process. Change on the viscoelastic properties of the hydrogel before and after UV irradiation had also been confirmed by oscillatory rheology, and SEM also showed the change of nanofiber. We have constructed photo-responsive supramolecular hydrogels based on azobenzene link with peptide.Photo-responsive supramolecular hydrogels formed by different azobenzene have different photo-sensitivities to UV irradiation. For example, Azo-Gly-Phe-Ala hydrogel began to collapse after 5 minutes'irradiation, while Azo-Glu-Phe-Ala hydrogel didn't have any phase change even after 50 hours' irradiation. The hydrogel formed by Azo-Lys-D-Phe-D-Ala indicated to show multiple responses like light, heat and ligand-receptor interaction. The photoresponsive supramolecular hydrogel Azo-Gln-Phe-Ala can be used in controlled release of drug molecular, which has been demonstrated by an experimental release of Vitamin B12. Preliminary theoretical study was performed on the self-assembly system before and after photo-irradiation.Recent research shows that intramolecular or intermolecular non-covalent interaction such as hydrogen bond could be applied to induce asymmetric selectivity in organic reactions. It is also possible to use these non-covalent interactions to induce asymmetric selectivity of certain photoreactions. Preliminary study on the possibility of asymmetric photoreaction induced by the microenviroment presented in the gel formed by peptide derivatives was conducted. We designed and synthesized naphthalene-peptide Naph-Ala-Ala-O'Bu, which could form transparent organogel in benzene. Difference on the photoreactions betweenN-acetylisatin (IS) and alkenes in solution and in gel media were studied preliminarily using HPLC monitoring on the distribution of the products. The results showed that IS and cyclopropylidenecyclobutane (CPCB) had different selectivities in solution and gel media. While the reactions of IS with bycyclopropylidene (BCP) and IS with cyclopropylidenecyclohexane (CPCH) didn't show significant difference in the solution and gel media. Also we have designed and synthesized stearic acid peptide SA-Phe-Ala-O'Bu, which could form transparent gel in acetonitrile, which could be used in our future study on different photoreactions in gel medium.