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 eight-times better activity across 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, while assays with liposomes showed that [Ru(bb7)(dppz)]2+ interacted more strongly with membranes compared to 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