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 × 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