Synthesis, characterization and DNA interactions of 5,15-(4-pyridyl)-10,20-(pentafluorophenyl)porphyrin coordinated to two [Ru(bipy)2Cl]+ groups

A new porphyrin 5,15-(4-pyridyl)-10,20-(pentafluorophenyl)porphyrin (H2DPDPFPP) and its diruthenium(II) analog ([trans-H2(DPDPFPP)Ru2(bipy)4Cl2(PF6)2]) have been synthesized and characterized. Electronic transitions associated with the porphyrin consist of an intense Soret band near 400 nm and four Q-bands from 500 nm to 650 nm. Coordination of two [Ru(bipy)2Cl]+ groups, where bipy = 2,2′-bipyridine, to the pyridyl nitrogens of the porphyrin give additional electronic transitions associated with the bipy orbitals and metal to ligand charge transfer (MLCT) transitions associated with the Ru(II) and bipy orbitals. Reversible redox couples in the cathodic region occur at E1/2 = −0.74 V and −1.21 V versus Ag/AgCl reference which are shifted to more positive potentials when the porphyrin is coordinated to the Ru(II) groups. Gel electrophoresis studies with linearized pUC18 indicate an interaction between the metallated porphyrin and DNA which is confirmed by UV/Vis titrations with calf thymus (CT) DNA giving a binding constant of ca. 105 M−1. When buffered, pH 7, solutions of circular plasmid DNA containing the ruthenium porphyrin are irradiated with a 50 W tungsten lamp cleavage of the DNA is observed.