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

The cis-alpha 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(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(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 x 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.