Photoresponsive peptide and polypeptide systems: part II. Photochromism of poly(l-ornithine) containing various azo-contents in side chains

Cross-linking and insolubilization studies of water-soluble poly(L-ornithine)

Cross-linking and insolubilization studies of water-soluble synthetic cationic polypeptides containing ornithine residues were carried out using the organic cross-linking agents glutaraldehyde (GA) and 2,5-hexanedione (HD) in water. The cross-linking reaction was characterized by the viscosity and turbidity changes. When more than a 1:5 equimolar amount of GA or a 1:2 equimolar amount of HD was added to the ornithine polypeptide systems as organic cross-linking agents, insolubilization occurred causing turbidity. As a whole, the molecular weight of the samples, the cross-linking agent used, the molar ratios between cross-linking agents and functional residues, and the system pH were found to play roles in the insolubilization reaction and gel formation. Of these factors, a system pH of 11 is the most important in insolubilization of polyornithine (PLO)-GA and PLO-HD mixed solutions. Using PLO and polylysine (PLL) samples with almost similar degrees of polymerization, the cross-linking results of the PLO systems were compared with those of the PLL systems.