Chemical modification of silk fibroin with N-acetyl-chito-oligosaccharides.

N-Acetyl-chito-oligosaccharides (NACOS)-silk fibroin (SF) conjugates (NACOS-CY-SF) were prepared by the reaction of solubilized SF and cyanuric chloride (CY)-activated NACOS modifier (NACOS-CY). N-Acetyl-D-glucosamine (NAG), as a model compound, was reacted with CY to clarify the chemical structure of the modifier. The 1H- and 13C-NMR spectra of the reactant suggest that the anomeric hydroxyl group of NACOS reacted with the chlorine atom of CY. The content of NACOS in the NACOS-CY-SF conjugates was calculated by comparing the integral values of the signals in the 1H-NMR spectra of the conjugates and the mixture of NACOS and SF. As the 1H-NMR spectrum of the conjugates showed a downfield shift of the aromatic protons of the tyrosine residue, the tyrosine residue in SF reacted with another chlorine atom of the triazine ring of the modifier. The result of the amino acid analysis of the conjugates suggests that lysine residues also reacted with the modifier.