The present study provides antibacterial and thermal improvements of chitosan-based systems through chemical modification with different quaternary ammonium salts using 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC) as mediator. Three different ammonium salts with a carboxylic acid end group are synthesized through a quaternization reaction between bromohexanoic acid and the respective tertiary amines (quinoline, N,N-dimethylbenzylamine and pyridine). They are then chemically grafted along the chitosan backbone using EDC as a carboxyl activating agent for the coupling with the primary amine groups. This allows three different chitosan derivatives to be obtained: Quinolinium-Chitosan (QA-Cs), Benzalkonium-Chitosan (BK-Cs), and Pyridinium-Chitosan (PA-Cs), respectively. The chemical structures are characterized by 1H NMR analysis. The thermal stability is analyzed by thermogravimetric analysis. Antibacterial efficiencies of chitosan derivatives against Pseudomonas aeruginosa and Staphylococcus aureus strains are determined.
All the chitosan derivatives show negligible antibacterial activity against Gram-positive S. aureus strain. However, the antibacterial activity against Gram-negative P. aeruginosa strain is significantly improved.