DNA interactions of cobalt(III) mixed-polypyridyl complexes containing asymmetric ligands.

Three novel asymmetric ligands, 3-(pyridine-2-yl)-5,6-diphenyl-as-triazine (pdtb), 3-(pyridine-2-yl)-as-triazino[5,6-f]acenaphthylene (pdta) and 3-(pyridine-2-yl)-as-triazino[5,6-f]phenanthroline (pdtp) and their cobalt(III) complexes have been synthesized and characterized. Binding of the three complexes with calf thymus DNA (CT-DNA) has been investigated by spectroscopic methods, viscosity, cyclic voltammetry, and electrophoresis measurements. The experimental results indicate that the size and shape of the intercalated ligand have a marked effect on the binding affinity of complexes to CT-DNA. Complexes 2 and 3 have also been found to promote cleavage of plasmid pBR322 DNA from the supercoiled form I to the open circular form II upon irradiation.