Synthesis, structure, stability and antimicrobial activity of a ruthenium(II) helicate derived from a bis-bidentate "click" pyridyl-1,2,3-triazole ligand

Abstract

A [Ru2L3]4+ ruthenium(II) triply-stranded helicate was synthesized from a bis-bidentate "click" pyridyl-1,2,3-triazole ligand and RuCl3 in good yield (58%). The helicate was characterized by elemental analysis, IR, UV-Vis, 1H, 13C and 1H DOSY NMR spectroscopies and the molecular structure confirmed using X-ray crystallography. In contrast to similar, previously studied, [Fe2L3]4+ helicates the more kinetically inert [Ru2L3]4+ system proved stable (over a period of days) when exposed to either dimethyl sulfoxide (DMSO) or a DMSO solution of the common biological ligand histidine. The [Ru2L3]4+ helicate and the corresponding "free" ligand were tested for antimicrobial activity in vitro against both Gram positive (Staphylococcus aureus) and Gram negative (Escherichia coli) microorganisms. Agar-based disk diffusion assays indicated that the Ru(II) helicate displayed antimicrobial activity but the minimum inhibitory concentrations (MIC) proved to be extremely modest (MIC > 256 μg/mL).