The structural features of poly(dG-dC).poly(dG-dC) at complexation with some porphyrins

Abstract

The binding peculiarities of the water-soluble meso-tetra-(4N-hydroxyethylpyridyl) porphyrin (H₂TOEtPyP4) and its Cu- and Co-derivatives (CuTOEtPyP4 and CoTOEtPyP4) with synthetic double-stranded alternating polynucleotide poly(dG-dC).poly(dG-dC) were investigated by UV/Vis absorption and circular dichroism (CD) methods. It was shown that the porphyrins with planar structure such as H₂TOEtPyP4 and CuTOEtPyP4 interact with poly(dG-dC).poly(dG-dC) via intercalation at low relative concentrations (r = [porphyrin]/[polynucleotide]), while at high r - via intercalation and external binding modes. In the case of no planar porphyrin CoTOEtPyP4 complexation occurs only by external binding mode. The binding constant K_b and the exclusion parameter n calculated for H₂TOEtPyP4, CuTOEtPyP4 and CoTOEtPyP4 porphyrins with poly(dG-dC).poly(dG-dC) complexes was 1.50 x10⁷, M^-1 (n = 1.76); 9.29 x10⁷, M^-1 (n = 1.18); and 0.28 x10⁷, M^-1 (n = 2.65) correspondingly. The values of binding parameters for each porphyrin-poly(dG-dC).poly(dG-dC) complexes demonstrated good agreement with the proposed binding models. Communicated by Ramaswamy H. Sarma.

Keywords: Stacking; Circular Dichroism; Intercalation; Polynucleotide; Porphyrin; UV/Vis Absorption.