cis-[Rh2(μ-O2CCH3)2(CH3CN)6]2+ as a photoactivated cisplatin analog

The complex cis-[Rh2(μ-O2CCH3)2(CH3CN)6]2+ (1) exchanges the two axial CH3CN ligands for solvent molecules in water to yield cis-[Rh2(μ-O2CCH3)2(CH3CN)4(H2O)2]2+ (2). Photolysis of 2 in H2O results in the photoaquation of two equatorial acetonitrile ligands to yield [Rh2(μ-O2CCH3)2(CH3CN)2(H2O)4]2+ (3), which is able to covalently bind to free 2,2′-bipyridine (bpy) and 9-ethylguanine in solution, as well as double-stranded DNA (λirr ≥ 455 nm). Complex 2 exhibits 20-fold lower cytotoxicity towards human skin cells than hematoporphyrin in the dark, and its toxicity increases by a factor of 34 when irradiated with visible light (400-700 nm, 30 min). This increase in cytotoxicity by 2 upon irradiation is ∼7 times greater than that measured for hematoporphyrin. These properties make 2 a promising photo-cisplatin analog and a potential agent for photodynamic therapy. To our knowledge, 2 is the first metal-metal bonded complex to bind to DNA upon irradiation with visible light. Copyright © 2006 American Chemical Society.