Homogeneous sulfation of silk fibroin in an ionic liquid

Ionic liquid, 1-butyl-3-methylimidazolium chloride, was used as the solvent of silk fibroin (SF) polymer for its homogeneous chemical modification by chlorosulfonic acid in a non-aqueous system. The sulfation of SF in the ionic liquid possesses several obvious advantages, such as mild reaction condition, high modification degree, low degradation and requiring no dialysis process. The incorporation of sulfate groups was confirmed by infrared spectroscopy and its amount was measured by elemental analysis. 1H NMR spectra revealed that the sulfation occurred mainly at tyrosine and serine residues. The coagulation time tests showed the anticoagulant activity of SF which was induced by the incorporated group.