Synthesis, characterization, and biological activity assessment of quaternary ammonium-functionalized cellulose: enhanced antimicrobial features, free radical scavenging and thermal stability

The incorporation of antimicrobial functionalities into cellulose represents a significant advancement in biopolymer modification, enhancing its potential applications in biomedical and food sectors. In this study, we synthesized and characterized quaternary ammonium-functionalized cellulose (Q-Cell) and its intermediates, employing a three-step modification strategy (tosylation, amination, and quaternization). Structural and functional attributes of the derivatives were elucidated using SEM, TGA, FT-IR, and NMR ( 1 H and 13 C) spectroscopy. The optimized synthesis under an aqueous alkaline medium (H₂O/NaOH/triethylamine) at 5 °C for 5 h enabled selective functionalization while preserving the cellulose backbone integrity. A thorough assessment of the structural characterization and stability of the components revealed that the modified cellulose demonstrated superior antibacterial and antioxidant properties accompanied with enhanced thermal properties. The antimicrobial assessment revealed 100% inhibition of E. coli and S. aureus at 250 µg/L with MIC values of 4 and 8 µg/mL, respectively. Additionally, Q-Cell exhibited superior free radical-scavenging ability in superoxide, hydroxyl, and DPPH assays, attributed to electrostatic stabilization of radicals and charge-assisted hydrogen transfer mechanisms. These findings suggest that Q-Cell is a promising candidate for antimicrobial and antioxidant applications in biomedical, pharmaceutical, and food packaging industries.