Photoresponsive Peptide and Polypeptide Systems. 13. Photoinduced Cross-Linked Gel and Biodegradation Properties of Copoly(l-lysine) Containing ε-7-Coumaryloxyacetyl-l-lysine Residues

Copoly[LysLys(Cou)] containing ε-7-coumaryloxyacetyl- l -lysine [Lys(Cou)] residues were synthesized by the N -carboxyanhydride method. When the aqueous solutions of copoly[LysLys(Cou)] containing 5−10 mol % of Lys(Cou) are irradiated by light, the photo-cross-linking reaction proceeds slowly between coumarin moieties in the side chains to give a cis head-to-head cyclocoumarin, and after 6−24 h the solutions become transparent hydrogels. The gels exhibit solvent-induced reversible expansion and contraction behavior in water and in ethanol. The biodegradation of the hydrogels by some proteolytic enzymes and soil filamentous fungi has been investigated using photo-cross-linked copoly[LysLys(Cou)] gels. The photo-cross-linked copoly[Lys 90-95 Lys(Cou) 10-5 ] gels are degradable by trypsin and protease type XXIII or two microorganisms, Aspergillus oryzae and Penicillium citrinum, suggesting potential for a controlled biodegradation by the different cross-linking densities in the gel matrixes upon the controlled irradiation.