Design, Synthesis, and Antimicrobial Profiling of Novel Schiff Base Metal (II) Complexes: Structural Characterization and Structure

This study aimed to design, synthesize, and characterize novel ruthenium (II) Schiff base complexes as potential antimicrobial agents to address the growing crisis of multidrug-resistant bacterial infections. Despite advances in antibiotic development, resistance to existing drugs, particularly in Staphylococcus aureus and Escherichia coli-demands new compounds with alternative mechanisms of action. A key research gap lies in the limited exploration of pyridine-imine Schiff base ruthenium complexes with systematic substitution (-Br, -OH) and a comparison between simple Ru (II) and Ru(II)-p-cymene architectures. Ligands and their Ru (II) complexes were synthesized and characterized by FT-IR, UV-Vis, <sup>1</sup>H NMR, and melting point. Antimicrobial activity was evaluated using agar disc diffusion against both bacterial strains at concentrations ranging from 125 to 1000 µg/mL, with data analyzed using two-way ANOVA and Fisher’s LSD test (α = 0.05). Results showed Ru (II) complexes exhibited significantly higher inhibition than free ligands (p ≤ 0.05), with bromo- and hydroxy-substituted cymene complexes (e.g., L-C2, L1-C2) displaying the strongest activity (up to 14 -15 mm zones). Although all compounds were less potent than gentamycin, the enhanced bioactivity upon metal coordination supports Tweedy’s chelation theory. These findings validate Ru (II)-Schiff base complexes as promising scaffolds for future antimicrobial development, warranting further studies on MIC, toxicity, and antifungal activity.