Di- and polynuclear silver(I) saccharinate complexes of tertiary diphosphane ligands: synthesis, structures, in vitro DNA binding, and antibacterial and anticancer properties

A series of new silver(I) saccharinate (sac) complexes, Ag₂(sac)₂(μ-dppm)H₂O]·H₂O (1), {Ag₂(μ-sac)₂(μ-dppe)]·3H₂O·CH₂Cl₂} _n (2), Ag₂(μ-sac)₂(μ-dppp)] _n (3), and Ag(sac)(μ-dppb)] _n (4) dppm is 1,1-bis(diphenylphosphino)methane, dppe is 1,2-bis(diphenylphosphino)ethane, dppp is 1,3-bis(diphenylphosphino)propane, and dppb is 1,4-bis(diphenylphosphino)butane], have been synthesized and characterized by C, H, N elemental analysis, IR spectroscopy, ¹H NMR, ¹³C NMR, and ³¹P NMR spectroscopy, electrospray ionization mass spectrometry, and thermogravimetry–differential thermal analysis. Single-crystal X-ray studies show that the diphosphanes act as bridging ligands to yield a dinuclear complex (1) and one-dimensional coordination polymers (2 and 4), whereas the sac ligand adopts a μ₂-N/O bridging mode in 2, and is N-coordinated in 1 and 4. The interaction of the silver(I) complexes with fish sperm DNA was investigated using UV–vis spectroscopy, fluorescence spectroscopy, and agarose gel electrophoresis. The binding studies indicate that the silver(I) complexes can interact with fish sperm DNA through intercalation, and complexes 1 and 3 have the highest binding affinity. The gel electrophoresis assay further confirms the binding of the complexes with the pBR322 plasmid DNA. The minimum inhibitory concentrations of the complexes indicate that complex 1 exhibits very high antibacterial activity against standard bacterial strains of Escherichia coli, Salmonella typhimurium, and Staphylococcus aureus, being much higher than those of AgNO₃, silver sulfadiazine, ciprofloxacin, and gentamicin. Moreover, complexes 1–3 exhibit very high cytotoxic activity against A549 and MCF-7 cancer cell lines, compared with AgNO₃ and cisplatin. The bacterial and cell growth inhibitions of the silver(I) complexes are closely related to their DNA binding affinities.