Synthesis and in vitro antimicrobial and antioxidant activities of quaternary ammonium chitosan modified with nisin

Nisin had been grafted onto quaternary ammonium chitosan (QCS) through an enzyme-catalyzed reaction to enhance its limited antimicrobial activity. QCS was synthesized by incorporating N-(3-chloro-2-hydroxypropyl) trimethyl ammonium chloride (CHPTAC) onto chitosan’s primary amine group. The modification had been confirmed by FT-IR and 1H NMR spectroscopy. Degree of substitution (DS) of QCS–nisin could be controlled by adjusting the reaction conditions. The synthesized compounds were screened in vitro to evaluate their antimicrobial and antioxidant activities. The results suggested that QCS–nisin significantly suppressed the growth of both gram-positive bacteria and gram-negative bacteria; The antioxidant effects on 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical, hydroxyl radical and hydrogen peroxide (H2O2) proved to be enhanced with increasing DS and concentration. In addition, QCS–nisin showed excellent moisture absorption and retention properties; MTT assay exhibited that QCS–nisin revealed low cytotoxicity effects on cultured NIH-3T3 fibroblasts. These results suggest that QCS–nisin would appear to be a promising candidate for wound dressing application.