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

The cis ‐α isomer of [Ru(bb 7 )(dppz)] 2+ (dppz=dipyrido[3,2‐ a :2′,3′‐ c ]phenazine; bb 7 =bis[4(4′‐methyl‐2,2′‐bipyridyl)]‐1,7‐alkane) has been synthesised. The minimum inhibitory concentrations and the minimum bactericidal concentrations of [Ru(bb 7 )(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(bb 7 )(dppz)] 2+ showed at least eightfold better activity against the Gram‐negative bacteria than [Ru(phen) 2 (dppz)] 2+ . Luminescence assays demonstrated that [Ru(bb 7 )(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(bb 7 )(dppz)] 2+ interacted more strongly with membranes than the parent [Ru(phen) 2 (dppz)] 2+ complex. The DNA binding affinity for [Ru(bb 7 )(dppz)] 2+ was determined to be 6.7 × 10 6   m −1 . Although more toxic to eukaryotic cells than [Ru(phen) 2 (dppz)] 2+ , [Ru(bb 7 )(dppz)] 2+ exhibited greater activity against bacteria than eukaryotic cells.