The antimicrobial activity of mononuclear ruthenium(II) complexes containing the dppz ligand

Abstract

The cis‐α isomer of [Ru(bb₇)(dppz)]²⁺ (dppz=dipyrido[3,2‐a:2′,3′‐c]phenazine; bb7=bis[4(4′‐methyl‐2,2′‐bipyridyl)]‐1,7‐alkane) has been synthesised. The minimum inhibitory concentrations and the minimum bactericidal concentrations of [Ru(bb₇)(dppz)]²⁺ and its parent complex [Ru(phen)₂(dppz)]²⁺ (phen=1,10‐phenanthroline) were determined against a range of bacteria. The results showed that both ruthenium complexes exhibited good activity against Gram‐positive bacteria, but [Ru(bb₇)(dppz)]²⁺ showed at least eightfold better activity against the Gram‐negative bacteria than [Ru(phen)₂(dppz)]²⁺. Luminescence assays demonstrated that [Ru(bb₇)(dppz)]²⁺ accumulated in a Gram‐negative bacterium to the same degree as in a Gram‐positive species, and assays with liposomes showed that [Ru(bb₇)(dppz)]²⁺ interacted more strongly with membranes than the parent [Ru(phen)₂(dppz)]²⁺ complex. The DNA binding affinity for [Ru(bb₇)(dppz)]²⁺ was determined to be 6.7 × 10⁶ m⁻¹. Although more toxic to eukaryotic cells than [Ru(phen)₂(dppz)]²⁺, [Ru(bb₇)(dppz)]²⁺ exhibited greater activity against bacteria than eukaryotic cells.