The Construction Of Photoresponsive Short Peptides And Their Applications

Photoresponsive organic molecules are widely used in material sciences and biological systems since their structure and properties are subject to external regulation through light irradiation. Hydrogel as a special "soft matter" has been widely developed into am important bio-functional material with applications in cell culture and tissue engineering etc. Constuction of hydrogel using short peptide which can be easily synthesized has advantages such as excellent biological compatibility, easy degradation inside body and non-toxic metabolites. We used synthetic short peptides as building blocks of self-assembling systems. Modification of the short peptides using photoresponsive organic molecules resulted in photo-responsive short peptides whose properties could be regulated through light irradiation. Supramolecular hydrogels formed by the photoresponsive short peptide thus showed photo-response through disturbance of the self-assebling properties.First part of this dissertation described photoresponsive short peptides based on the spiropyran moiety. The self-assembly properties of the photosensitive peptide were studied arid photoresponsive supramolecular hydrogel system based on spiropyran dipeptides were constructed. The photoisomerization of the spiropyran form and meracyanine form was used as a switch to regulate the strength of intermolecularπ-πstacking. When the short peptide was linked to the ring-open meracyanine moiety, delicate balance betweent theπ-πstacking from the meracyanine moiety and hydrogen bonding from the peptide bond was achieved. The modified short peptide could self-assemble into nanofibers which then form three dimensianl network to form hydrogel. The self-assembling system was disturbed upon visible light irradiation since the planar merocyanine form turned into spiropyran form to destroy theπ-πstacking. The relative position of the spiropyran moiety to the peptide backbone as well as the amino acid residues in the peptide was found to be an important factor for the hydrogelation property of the modified peptides. The scanning electron microscopy of the hydrogels formed by spriopyran-linked dipeptides showed entangled nanofibers formed the matrice of the hydrogel. Hydrogel with dual responses was realized by spriopyran-D-Ala-D-Ala. It not only responds to photo-irradiation, but also to the specific ligand-receptor interaction between D-Ala-D-Ala and the antibiotics vancomycin.The second part of this dissertation describes photoresponsive short peptides based on the 2,5-diaryl tetrazole moiety. The self-assembly properties of the photosensitive peptide were studied and photoresponsive supramolecular hydrogel system based on 2,5-diaryl tetrazole short peptides were constructed. Two types of tetrazole-based dipeptides and some functional peptides were synthesized. And photosensitive peptide were constracted by the photoactived 1,3-dipolar cycloaddition between tetrazole-based short peptides and alkene.. Their self-assembled properties were well studied. We found that the amino acid connected to tetrazole have a great impact on its gelation ability. Tetrazole-based dipeptides could not self-assemble into hydrogel when the amino acid connected to tetrazole was alanine. We believed that the side-chain of alanine affected the balance of hydrogen bonds and theπ-πaccumulation, thus detrimental to their self-assembly. If a linker, like succinic acid, were inserted between short peptide and tetrazole, we received different kinds of short peptides that could self-assemble into hydrogel at different pH and different concentration. The scanning electron microscopy of the hydrogels formed by tetrazole-based peptides also showed that nano-fiber structure formed. Photosensitivity of hydrogels formed by TetⅡwas better than that formed by TetⅠ.In this paper, photoresponsive short peptides constructed by some of other photoactive molecules and their applications were also investigated, including dipeptieds based on photo-induced cis-trans isomerization of azobenzene moieties and short peptides based on the "cage compounds" whose photo-labile group can be removed upon photo-irradiation. We investigated pH effect and salt effects on the hydrogelation properties of azo-dipeptides and the results showed that low pH and high concentration of salt were beneficial to their self-assembly. The results of Gel test on short peptides modified by "caged" groups showed that most of them were not stable under basic condition and hydrolysis of the ester bond could happen not only upon photo-irradition, but also under basic condition.