Inhibition and Promotion of the Oxidation Processes of Water-Soluble Cationic Co(II)-Porphyrin Under Its Interaction with Nucleic Acids

Abstract

Using the methods of absorption spectroscopy and resonance Raman scattering, we have made a comparative study of water-soluble cationic Co(II)- and Co(III)-5,10,15,20-tetrakis(4-N-methyl-pyridiniumyl)porphyrins(CoII(TMpy-P4) and CoIII(TMpy-P4) with DNA and synthetic single- and double-stranded polynucleotides. It has been found that CoII(TMpy-P4), which in aqueous solutions containing no nucleic acids is readily oxidized to CoIII(TMpy-P4) by the molecular oxygen dissolved there, markedly changes its oxidation ability when bound to nucleic acid. Under interaction with guanine-containing polynucleotides, the rate of change in the oxidation state of cobalt from Co(II) to Co(III) increases as compared to such for the solution of porphyrin in a buffer. But in complexes with DNA and adenine- and thymine-containing polynucleotides, CoII(TMpy-P4), on the contrary, becomes stable. The observed effects of inhibition/promotion of CoII(TMpy-P4) oxidation when it is bound to nucleic acids are assumed to be due to the weakening/strengthening of the electron-donor properties of the extraligand on cobalt, which leads to a change in cobalt affinity to molecular oxygen. The role of immobilized water molecules in the change in the properties of cobalt extraligands has been considered. On the basis of the analysis of the spectral data obtained, modes for incorporating CoII(TMpy-P4) into DNA and model polynucleotides are proposed.