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.

Keywords:

• Ruthenium-arene complex
• pyridine derivative
• antimicrobial activity
• electrochemical behavior
• DFT calculations

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported by the Ministry of Science, Technological Development and Innovation of Republic of Serbia, grant numbers 451-03-47/2023-01/200168, 451-03-47/2023-01/200288, 451-03-47/2023-01/200113, and 451-03-47/2023-01/200124.