The Antimicrobial Activity of Mononuclear Ruthenium(II) Complexes Containing the dppz Ligand

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 × 106m−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.