Synthesis and antimicrobial activity of new pyridine-based half-sandwich Ru(II) complexes

Abstract

Eight new ruthenium complexes (C1, C2 (Ru-benzene or Ru-toluene complexes with L1, 3-amino-2-chloropyridine); C3, C4 (Ru-benzene or Ru-toluene complexes with L2, 2-amino-5-chloropyridine); C5, C6 (Ru-benzene or Ru-toluene complexes with L3, 3-acetylpyridine); and C7, C8 (Ru-benzene or Ru-toluene complexes with L4, 4-acetylpyridine) were synthesized. The chemical structures and purity of the compounds were confirmed using standard analytical methods such as 1H,13C NMR and IR spectroscopy, mass spectrometry, and elemental analysis, and their electrochemical behavior was evaluated using cyclic voltammetry experiments. The stability of the compounds in dimethyl sulfoxide solution was confirmed using 1H NMR spectroscopy. Finally, the antimicrobial potential of two complex precursors (CP1, [Ru(η6-benzene)Cl(μ-Cl)]2 and CP2, [Ru(η6-toluene)Cl(μ-Cl)]2), four ligands (L1–L4), and eight corresponding complexes (C1–C8) was screened against nine pathogenic microorganisms and two reference bacterial strains using the micro-well dilution method. The highest antibacterial activity (0.63 mg/mL) was for C5 against Staphylococcus aureus, Bacillus cereus, Escherichia coli, and Salmonella enteritidis, while C8 displayed more pronounced antimicrobial activity against Candida albicans (MIC/MMC = 0.31 mg/mL). Subsequently, the studied complexes underwent a detailed examination utilizing the DFT methodology, acquiring important quantum-chemical descriptors. Notably, the HOMO-LUMO gap was established as a significant correlate with the antimicrobial activity of synthesized compounds.