Synthesis, Characterisation and Antimicrobial Studies of some 2,6-bis(1,2,3-Triazol-4-yl)Pyridine Ruthenium(II) “Click” Complexes

A family of homo- and hetero-leptic ruthenium(II) bis-tridentate complexes generated from 2,6-bis(1-R-1,2,3-triazol-4-yl)pyridine “click” ligands (R-tripy) with either aliphatic or aromatic substituents were synthesized (35–97%). The family of compounds were tested for antimicrobial activity in vitro against both Staphylococcus aureus (S. aureus, ATCC 25923) and Escherichia coli (E. coli, ATCC 25922) bacteria. The antibacterial activity showed dependence on the alkyl chain length of the [Ru(R-tripy) ₂ ] ²⁺ (Cl ⁻ ) ₂ complexes, with the best activity occurring for the three complexes featuring either hexyl or heptyl substituents on the ligands. The minimum inhibitory concentrations (MICs) for the most active mononuclear complex [Ru(hexyltripy)(heptyltripy)] ²⁺ (Cl ⁻ ) ₂ were 2 μg/mL and 8 μg/mL respectively against S. aureus and E. coli. The three most active complexes were screened against other pathogenic bacteria, including two strains of Methicillin resistant S. aureus (MRSA). The compounds showed good activity against the Gram positive strains (MIC=4–8 μg/mL) but were less effective against Gram negative bacteria (MIC=8–16 μg/mL). Cytotoxicity experiments with eukaryotic cells lines (cancer and skin) suggested that the R-tripy ligands and complexes were reasonably cytotoxic (IC ₅₀ =2–25 μM) and displayed little to no selectivity for bacteria over eukaryotic cells lines.