Binding silver to chitooligosaccharides through N-heterocyclic carbenes: Synthesis and antimicrobial activity

Abstract

Silver containing products are widely used as antibacterial agents in wound dressings. The mechanism of action relies on the high reactivity of silver ions, which is also responsible of the lack of selectivity and stability of these products. Stabilization of silver by complexation and binding to a biocompatible material that selectively interacts with microorganisms will certainly lead to improved products. To prove this, chitooligosaccharides and one of its building blocks, D-glucosamine, were complexed with silver through the stable N-heterocyclic carbene (NHC) bond. Two amino moieties from each carbohydrate reacted to form a diimine, which was further converted into an imidazolium salt. This later precursor was complexed to silver to yield the NHCs complexes. The successively generated compounds were spectroscopically characterized by FT-IR, NMR, Inductively Coupled Plasma atomic emission spectroscopy and tested for activity against E. coli, Staphylococcus aureus, Bacillus subtilis, Pseudomonas aeruginosa and Candida albicans. The antimicrobial profiles of the silver complexes were similar or better than that of silver nitrate and generally more effective than the antiseptic of reference, PVP iodine. Complexation of silver to biocompatible and microbial selective materials through NHC bonds is a promising approach to develop more efficient silver carriers and wound care products.