Synthesis and characterization of new quaternized galactomannan derivatives with antibacterial activity

The continuous increase in bacterial resistance requires the study and development of new biocompatible antibacterial materials. Galactomannan gum was extracted from endosperms of Dimorphandra gardneriana seeds, modified through quaternization reactions (with NaOH/CHPTAC), and evaluated for antimicrobial activity. Four quaternized derivatives were obtained (QG1-QG4). The derivatives were characterized by FTIR, NMR, and rheology, which confirmed the cationization. The galactomannan structure was theoretically studied, and Zeta potential exhibited positive increase in the charge of quaternized derivatives, changing from -3.2 mV (unmodified galactomannan) to +59.35 mV (QG4). Elemental analysis revealed an increase in degree of substitution (DS) between the derivatives, of which QG4 exhibited the highest DS (0.51). QG4 exhibited a bactericidal effect in the antimicrobial test for determination of minimal inhibitory and bactericidal concentrations, against Gram-positive bacteria. Atomic force microscopy showed an increase in bacterial cell surface roughness and decrease in cell height after treatment with QG4. QG3 and QG4 demonstrated antibiofilm potential, showing 50 % and 40 % of inhibition, respectively. After MTT assay, cell viability was maintained approximately 100 % for all derivatives at concentrations of 20 mg/mL on RAW 264.7 macrophages and 86 % with 250 μg/mL on L929 cells. Galactomannan was successfully modified, demonstrating strong antibacterial activity, concomitant to the increase in DS, Zeta potential and reduction of molar mass, with good biocompatibility. Therefore, this study presents a new material with potential for development of formulations for biomedical applications, from industrial waste, strengthening of the D. gardneriana production chain.