Development of viscometric methods for studying the interaction of various porphyrins with DNA. Part I: meso-tetra-(4N-hydroxyethylpyridyl) porphyrin and its Ni-, Cu-, Co- and Zn- containing derivatives

Abstract

The influence of water soluble cationic meso-tetra(4N-hydroxyethyl)pyridyl porphyrin ( H 2 THOEtPyP 4) and it's metal complexes with Ni ( II ), Cu ( II ), Co ( II ) and Zn ( II ) on hydrodynamic and spectral behavior of DNA solutions has been studied by viscometry and UV-vis absorption methods. It was shown that the presence of planar porphyrins, such as H 2 THOEtPyP 4, NiTHOEtPyP 4 and CuTHOEtPyP 4 leads to an increase in viscosity at relatively small concentrations, and then decreases to stable values. Such behavior corresponds to intercalation of these porphyrins in DNA structure, which results in a decrease of helical twist and lengthening of the DNA molecule. In the case of porphyrins with axial ligands, such as ZnTHOEtPyP 4 and CoTHOEtPyP 4, the relative viscosity decreases, which is explained by self-stacking of these porphyrins on DNA surface. Calculation and interpretation of binding parameters (Kb and n) demonstrated good agreement of viscometric and spectrophotometric measurements.