Antioxidant Activity of Silk Peptide and Co-initiation Behavior in Free Radical Photopolymerization of Acrylamide

Abstract

A water-soluble silk peptide (SP) was fractioned to a series of SP fractions with different molecular weight. The antioxidant activity of these fractions was investigated by the ABTS and DPPH assays, and the co-initiating ability of each fraction in type II photoinitiator was evaluated in photopolymerization of acrylamide, using camphorquinone as the sensitizer. Gel permeation chromatograph was used to investigate molecular weight distributions of SP fractions. The results showed that with the increase of the proportion of the component with molecular weight of about 200 in SP fractions, antioxidant activity and co-initiation ability became poor. Four essential amino acids, Ala, Gly, Ser and Tyr of SP and their respective pentapeptides were also assessed for these two functions. Among them, pentatyrosine exhibited the most excellent performance in two functions, which might be ascribed to its excellent electron/hydrogen donation capability. And pentaglycine had good behavior in these two functions, suggesting that the polypeptide chain was responsible for electron/hydrogen donation. By 1H NMR analysis, it was speculated that the photoinitiation active center was located on the methylene group of pentaglycine. The electron/hydrogen donor of SP is the inherent reason for antioxidant function and photoinitiation performance of SP.