Antibacterial potential of mono- Ru(II) and bi-metallic Ru(II)-Mn(II) inorganic compounds with phosphino-fluoroquinolone conjugates

Herein, we present two novel heterobimetallic complexes Ru(II)-Mn(II) (Ru(η 6 - p -cymene)Cl 2 PCpMnCl 2 (H 2 O) 2 (RuPCpMn) and Ru(η 6 - p -cymene)Cl 2 PNrMnCl 2 (H 2 O) 2 (RuPNrMn)) with phosphines (PCp, PNr) derived from fluoroquinolones antibiotics (HCp–ciprofloxacin and HNr–norfloxacin). Compounds were characterized using elemental analysis, Fourier-transform infrared spectroscopy (FT-IR), electron paramagnetic resonance (EPR), electronic absorption spectroscopy (UV-Vis), and electrospray ionization mass spectrometry (ESI-MS). The antibacterial activity in vitro of heterobimetallic complexes together with literature monometallic Cu I and Ru II complexes possessing the same and different phosphine ligands was evaluated. The results indicate that structural modifications of metal-fluoroquinolone complexes affect their antibacterial properties. The mononuclear ruthenium(II) complexes exhibited broad-spectrum activity, particularly against Gram-negative bacteria, whereas the incorporation of manganese(II) ions did not lead to substantial improvement of antibacterial activity in vitro . However, complexes containing phosphine ligands without fluoroquinolone motifs but with, e.g. , alkaloid, exhibited significantly reduced activity, emphasizing the importance of maintaining the pharmacophoric integrity of the fluoroquinolone core.