The selectivity of Mannich-reaction-based modification on amino acid residues in silk fibroin

Abstract

The study investigates the selectivity and mechanism of Mannich reaction modification on the side groups of silk fibroin with dyes containing an aromatic primary amine group. A series of peptides was designed and synthesized as a simulation of protein in order to find the reaction site on silk fibroin and describe the reaction selectivity of the Mannich reaction for different amino acid residues. The mechanism of the Mannich reaction on peptides was revealed by means of ESI-MS and Gauss Computation. The results showed that both the tryptophan and tyrosine residues were the reaction sites for the modification of peptides, and the tryptophan residues showed stronger reactivity and tended to be modified more easily. In addition, the arginine residue has some negative influences on the selective modification of the Mannich reaction. On the other hand, the durable coloration in the form of covalent bond on silk fabrics by aromatic primary amine dyes in Mannich reaction method demonstrated the tryptophan residue and tyrosine residues on silk fibroin were modified, as inferred from the simulation using peptides.