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 (1)H 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.