Synthesis and antibacterial properties of fully bio-based Schiff base and their cerium coordinated complexes

Bacterial infections caused by the surface of material are one of the world's major public health issues and the drug-resistance to the current antibiotics brings a serious concern to global healthcare. Although there have been significant efforts devoted to develop novel alternative antimicrobial materials, most of the developed organic antibacterial agents are derived from petrochemicals, which are suffered from long-term biosafety due to their non-degradability and potential long-term toxicity. In this study, amino acids (DL-Methionine, L-Tryptophan and L-Serine) and o-Vanillin were used as starting material to prepare fully bio-based Schiff bases and their Cerium coordinated metallic complexes. The structural characterization of ligands was performed by nuclear magnetic resonance spectrum (NMR), Fourier transform infrared spectroscopy (FT-IR), ultraviolet-visible spectrum (UV) and complexes were analyzed by X-ray electron diffraction (XPS) and FT-IR. The antibacterial performance of as prepared material was tested using minimum inhibitory concentration (MIC), growth curve, plate colony count, inhibition test (ZOI), staining of live/dead bacteria method. The results revealed that MIC of ligands was 0.5 mg/mL and 0.75 mg/mL against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) respectively. For plant colony count, compared to ligands, the bactericidal performance of complexes was increased by 20 times at 6 h, up to 32 mu g/mL. Noteworthily, the complex of DL-Methionine Schiff base ligand with cerium (MSL-Ce) exhibited the best antibacterial activities, showing broad-spectrum and long-lasting antibacterial behavior in the coating against Gram-positive bacterial and Gram-negative bacterial. The fully bio-based antibacterial agents indicate tremendous potential for antimicrobial coatings on different substrates for a variety of applications such as marine antifouling and biomedical fields.