Photoresponsive peptide and polypeptide systems. 13. Photoinduced cross-linked gel and biodegradation properties of copoly(L-lysine) containing epsilon-7-coumaryloxyacetyl-L-lysine residues

Copoly[LysLys(Cou)] containing epsilon-7-coumaryloxyacetyl-L-lysine [Lys(Co u)] residues were synthesized by the N-carboxyanhydride method. When the aq ueous solutions of copoly[LysLys(Cou)] containing 5-10 mol % of Lys(Cou) ar e irradiated by light, the photo-cross-linking reaction proceeds slowly bet ween coumarin moieties in the side chains to give a cis head-to-head cycloc oumarin, and after 6-24 h the solutions become transparent hydrogels. The g els exhibit solvent-induced reversible expansion and contraction behavior i n water and in ethanol. The biodegradation of the hydrogels by some proteol ytic enzymes and soil filamentous fungi has been investigated using photo-c ross-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 o r two microorganisms, Aspergillus oryzae and Penicillium citrinum, suggesti ng potential for a controlled biodegradation by the different cross-linking densities in the gel matrixes upon the controlled irradiation.