Preparation and characterization of conjugates of silk fibroin and chitooligosaccharides

With the aim of the functionalization of silk fibroin (SF), conjugates of SF and polycationic chitooligosaccharides (COS) were prepared by the chemical modification of SF with cyanuric chloride (CY)-activated COS (COS-CY). The ¹H NMR spectrum of the reaction product between a model compound D-glucosamine and CY suggested that the COS-CY modifier was synthesized by the reaction of the amino group and the terminal anomeric hydroxyl group in COS, with the chlorine atom of CY. The ¹H NMR spectrum and amino acid analysis of the conjugates (COS-CY-SF) clarified that the tyrosine and lysine residues of SF reacted with a second chlorine atom of the triazine ring of the modifier. On the basis of the results of the hexosamine determination and the amino acid analysis of COS-CY-SF, it is estimated that COS-CY-SF consists of 38 wt% COS, 8 wt% CY, and 54 wt% SF. The absorbance at 600 nm as a function of pH for COS-CY-SF and SF indicated that the introduction of a large amount of hexosamine made SF amphiphilic and more water-soluble at lower pH values. The COS-CY-SF conjugates retarded the growth of Escherichia coli after incubation for 24 h at a conjugate concentration of 0.6% (w/v), while SF did not retard the growth at a SF concentration of 0.7% (w/v).