Microwave synthesis of mixed ligand diimine–thiosemicarbazone complexes of ruthenium(II): biophysical reactivity and cytotoxicity

A novel microwave-assisted synthetic method has been used to synthesise a series of mixed ligand ruthenium(II) compounds containing diimine as well as bidentate thiosemicarbazone ligands. The compounds contain the diimine 1,10-phenanthroline (phen) or 2,2′-bipyridine (bpy) and the thiosemicarbazone is derived from 9-anthraldehyde. Based on elemental analyses and spectroscopic data, the compounds are best formulated as [(phen)₂Ru(thiosemicarbazone)](PF₆)₂ and [(phen)₂Ru(thiosemicarbazone)](PF₆)₂ where thiosemicarbazone = 9-anthraldehydethiosemicarbazone, 9-anthraldehyde-N(4)-methylthiosemicarbazone, and 9-anthraldehyde-N(4)-ethylthiosemicarbazone. Fluorescence competition studies with ethidium bromide, along with viscometric measurements suggests that the complexes bind calf thymus DNA (CTDNA) relatively strongly via an intercalative mode possibly involving the aromatic rings of the diimine ligands. The complexes show good cytotoxic profiles against MCF-7 and MDA-MB-231 (breast adenocarcinoma) as well as HCT 116 and HT-29 (colorectal carcinoma) cell lines.