Binding, electrochemical activation, and cleavage of DNA by cobalt(II) tetrakis-N-methylpyridyl porphyrin and its β-pyrrole brominated derivative

The binding of nucleic acids by water-soluble cobalt( II) tetrakis-N-methylpyridyl porphyrin, ( TMPyP) Co, and its highly electron-deficient derivative cobalt( II) tetrakis-N-methyl pyridyl-beta-octabromoporphyrin, ( Br8TMPyP) Co, was investigated by UV-visible absorption, circular dichroism ( CD), and electrochemical and gel electrophoresis methods. The changes of the absorption spectra during the titration of these complexes with polynucleotides revealed a shift in the absorption maxima and a hypochromicity of the porphyrin Soret bands. The intrinsic binding constants were found to be in the range of 10(5)-10(6) M-1. These values were higher for the more electron-deficient ( Br8TMPyP) Co. Induced CD bands were noticed in the Soret region of the complexes due to the interaction of these complexes with different polynucleotides, and an analysis of the CD spectra supported a mainly external mode of binding. Electrochemical studies revealed the cleavage of polynucleotides by ( TMPyP) Co and ( Br8TMPyP) Co in the presence of oxygen preferentially at the A-T base pair region. Gel electrophoresis experiments further supported the cleavage of nucleic acids. The results indicate that the beta-pyrrole brominated porphyrin, ( Br8TMPyP) Co, binds strongly and cleaves nucleic acids efficiently as compared with ( TMPyP) Co. This electrolytic procedure offers a unique tool in biotechnology for cleaving double-stranded DNA with specificity at the A-T regions.