Controlling with light the interaction between trans-tetrapyridyl ruthenium complexes and an oligonucleotide

Three new trans-ruthenium(ii) complexes coordinated to tetrapyridyl ligands, namely [Ru(bapbpy)(dmso)Cl]Cl ([2]Cl), [Ru(bapbpy)(Hmte)₂](PF₆)₂ ([3](PF₆)₂), and [Ru(biqbpy)(Hmte)₂](PF₆)₂ ([4](PF₆)₂), were prepared as analogues of [Ru(biqbpy)(dmso)Cl]Cl ([1]Cl), a recently described photoactivated chemotherapy agent. The new complexes were characterized, and their crystal structures showed the distorted coordination octahedron typical of this family of complexes. Their photoreactivity in solution was analyzed by spectrophotometry and mass spectrometry, which showed that the sulfur ligand was substituted upon blue light irradiation. The binding of the ruthenium complexes to a reference single-stranded oligonucleotide (s(^5'CTACGGTTTCAC^3')) was explored both in the dark and under light irradiation by gel electrophoresis and high-resolution mass spectrometry. While adduct formation in the dark was negligible for the four complexes, light irradiation led to the formation of adducts with one or two ruthenium centers per oligonucleotide. The absence of interactions in the dark and the presence of complex-oligonucleotide adducts demonstrate that visible light controls the interaction of these ruthenium complexes with nucleic acids.