Synthesis, characterization and investigation of the antibacterial activity of cationic complexes of Ru(II)-p-cymene phosphine with weakly-coordinating acetonitrile ligands

The synthesis and characterization of ruthenium(II)-arene triarylphosphine complexes, Ru(η 6 - p -cymene)(PAr 3 )(NCCH 3 )ClPF 6 , where Ar = (3,5- t Bu 2 C 6 H 3 -) ( L1 ), (3,5-Me 2 C 6 H 3 -) ( L2 ), (4-MeO-3,5-Me 2 C 6 H 2 -) ( L3) and (4-MeOC 6 H 4 -) ( L4 ), are described. The structures have been confirmed by IR and 31 P NMR spectroscopy and by single crystal X ray diffraction studies. The redox behavior of the complexes has been investigated by voltammetry in CH 3 CN, with stability over a wide potential window ΔE ≅ 2.7 V. The antibacterial properties of the complexes have been studied against a Gram-positive and a Gram-negative strain. Complex 2 exhibits strong activity against S. aureus (MIC 25 µmol L -1 , IC 50 13.5 µmol L -1 ) and notably potent activity against MRSA (MIC 12.5 µmol L -1 , IC 50 8.52 µmol L -1 ). Complex 3 also demonstrates activity against S. aureus (MIC 25 µmol L -1 , IC 50 15.9 µmol L -1 ) and MRSA (IC 50 11.04 µmol L -1 ), though its MIC against MRSA is >100 µmol L -1 . By contrast, complex 4 is inactive. The interactions of 2 and 4 with phospholipid monolayers were investigated by the Langmuir monolayer method, in a system that simulates the Staphylococcus aureus cell membrane. Complex 2 interacts with and disrupts the organization of these monolayers, and this result possibly indicates that cell membrane rupture causes the antibacterial effect.