Synthesis, characterization and DNA-binding characteristics of Ru(II) molecular light switch complexes

A series of four polypyridyl Ru(II) complexes such as [Ru(L)(4)(PIP)](2+) and [Ru(L)(4)PPIP](2+) where L is 4-amino pyridine and Pyridine (PIP = 2-phenylimidazo[4,5-f] [1, 10] phenanthroline), (PPIP = 2-(4'-phenoxy-phenyl) imidazo[4,5-][1, 10]phenanthroline) have been synthesized and characterized by elemental analysis, physicochemical methods such as UV-vis, IR and NMR spectroscopic techniques. The DNA-binding behavior of these complexes was investigated by electronic absorption titrations, fluorescence spectroscopy, viscosity measurements and salt-dependent studies. The experimental results indicate that all these complexes can bind to DNA through an intercalation mode, the DNA-binding affinities of these complexes follow the order [Ru(4-APy)(4)(PPIP)](2+)(1) > [Ru(Py)(4)PPIP](2+)(2) > [Ru(4-APy)(4)(PIP)](2+)(3) > [Ru(Py)(4)PIP](2+)(4). Noticeably, these complexes have been found to be efficient photosensitisers for strand scissions in plasmid DNA. Further, all four complexes screened for their antimicrobial activity indicate that the complexes show appreciable activity against Escherichia coli and Neurospora Crassa. In addition, in the presence of Co2+, the emission of DNA-[Ru(L-4)PPIP/PIP](2+) can be quenched and recovered by the addition of EDTA, which exhibited the DNA "light switch" properties.