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

The influence of water soluble cationic meso-tetra(4N-hydroxyethyl)pyridyl porphyrin (H(2)THOEtPyP4) 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)THOEtPyP4, NiTHOEtPyP4 and CuTHOEtPyP4 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 ZnTHOEtPyP4 and CoTHOEtPyP4, the relative viscosity decreases, which is explained by self-stacking of these porphyrins on DNA surface. Calculation and interpretation of binding parameters (K-b and n) demonstrated good agreement of viscometric and spectrophotometric measurements.