Light induced photoreactions with plasmidDNA by Cu/Ru and Cu/Ru/Pt multi-metallic porphyrins

Abstract

Coordination of two [Ru(bipy)₂Cl]⁺ moieties (where bipy = 2,2′-bipyridine) to the pyridyl nitrogens in the 5,10-positions of meso-5,10,15-(4-Pyridyl)-20-(pentafluorophenyl)porphyrin gives the diruthenium porphyrin complex II. Insertion of copper(II) into the porphyrin center allows for the third pyridyl nitrogen to coordinate to Pt(dmso)Cl₂. Electronic transitions associated with the ruthenium porphyrin include an intense Soret band and four less intense Q-bands in the visible region of the spectrum. An intense π–π* transition in the UV region associated with the bipyridyl groups and a metal to ligand charge transfer (MLCT) band appearing as a shoulder to the Soret band are also observed. A slight blue shift of the Soret band and collapse of the Q-bands into one band is observed upon insertion of Cu(II) into the porphyrin center. No change in the electronic spectrum is observed upon coordination of the Pt(dmso)Cl₂ moiety. Electrochemical properties associated with the complexes include a redox couple in the cathodic region attributed to the porphyrin and a redox couple in the anodic region due to the Ru^III/II couple. DNA titrations of the Cu/Ru and Cu/Ru/Pt porphyrins indicate that both complexes interact strongly with DNA potentially through a partial intercalation mechanism. Gel electrophoresis studies indicate that the Cu/Ru/Pt porphyrin has a greater effect on DNA migration through the gel than the well known DNA binding agent cis-platin. Irradiation of aqueous solutions of the Cu/Ru porphyrin and supercoiled DNA at a 5 : 1 base pair to complex ratio (in the absence of oxygen) with visible light above 400 nm shows a nicking of the DNA. Repeat experiments in the presence of oxygen show that the Cu/Ru porphyrin photocleaves the DNA, giving the linear form, as evidenced by gel electrophoresis.