Palladium(II) 4,5-Diphenylimidazole Cyclometalated Complexes: DNA Interaction

Abstract

In this paper, we show the synthesis of palladium(II) 4,5-phenylimidazole cyclometalated complexes. They have been characterized by IR, 1 H- and 13 C-NMR spectroscopy. The cyclometalated dimer compound 2 [Pd(C 15 H 11 N 2 1)(μ-OAc)] 2 and the cyclometalated monomer compound 5 [PdBr(SEt 2 )(C 15 H 11 N 2 )], having OAc and Br as leaving groups, interact with DNA, modifying its secondary structure (as measured by T m and CD), without modifying its tertiary structure (as determined by measurement of the electrophoretic mobility in agarose gels). The monomeric compound 5 seems to be the one that induces the highest alterations in DNA secondary structure since it strongly modifies the CD spectrum of the DNA. Melting data of drug-DNA complexes suggest that, at low drug concentration, the 4,5-Imd ligand intercalates between the base pairs in the DNA molecule, increasing the T m , while at high drug concentrations the palladium(II) centers destabilize the double helix, producing a lowering in T m values. These results indicate that complexes containing planar structures might selectively bind to DNA that is not supercoiled, and that therefore it only has a secondary structure.