Synthesis and antimicrobial properties of new chitosan derivatives containing guanidinium groups

[Display omitted] •New chitosan derivatives bearing guanidinium functions were prepared and characterized.•The four derivatives displayed improved antimicrobial activity in comparison with neat chitosan.•Biosourced and renewable chitosan derivatives could be applied as antimicrobial surfaces. New chitosan derivatives bearing guanidinium functions were synthesized following different synthesis strategies. N-guanidinium chitosan acetate and N-guanidinium chitosan chloride were synthesized by direct reaction between chitosan and cyanamide in the presence of scandium(III) triflate. The synthesis of N-guanidinium chitosan (N,N′-dicyclohexyl) chloride and N-guanidinium chitosan (N-(3-dimethylaminopropyl)-N'-ethyl hydrochloride) chloride involved the reaction of chitosan with carbodiimides in ionic liquid. The chitosan derivatives were characterized by analytical techniques including 13C solid state NMR, FT-IR spectroscopies, thermogravimetry and elemental analysis. The antimicrobial properties of chitosan and the new derivatives were investigated using the minimal inhibitory concentration (MIC) technique. All new guanylated chitosan derivatives displayed high antimicrobial activity in comparison with neat chitosan. The N-guanidinium chitosan acetate reduced the time required for killing to half in comparison with chitosan and recorded MIC values less than 3.125 mg/mL against all assayed microorganisms. This work opens new perspectives for using chitosan derivatives as antimicrobial surfaces.