RESUMO
The binding of water-soluble meso-tetra-(4N-oxyethylpyridyl) porphyrin (H2TOEtPyP4) and its manganese (III) derivative (MnTOEtPyP4) with calf thymus DNA have been quantitatively studied using UV/Vis spectrophotometry, Circular Dichroism (CD), thermal melting curves and viscometry. The results show, that porphyrins interact with DNA via one binding mode at low relative concentrations (r) and two binding modes at high values of r. The binding constant (Kb) and stoichiometry (n) were determined from binding isotherms for both porphyrin-DNA complexes. The thermal melting analysis indicates that the double-helical structure of DNA molecules is stabilizing in presence of studied porphyrins. At certain concentrations of porphyrin, two-stage melting curves were observed, which indicates the existence of two different binding modes. Obtained results show that MnTOEtPyP4 associates with DNA duplex via outside binding mode.Communicated by Ramaswamy H. Sarma.
RESUMO
The present paper is an overview of studying of DNA-porphyrin interactions using viscometry in combination with the spectroscopic methods. It was shown, that when porphyrins interact with DNA as an outside binder, the interaction mode and intensity does not depend on metal center, peripheral substituent's and their positions on pyridylic ring. In case of planar porphyrins, the binding type is mainly determined by type of peripheral substituent's and their position on the pyridylic ring. Currently, viscometry is widely used to study the interaction of porphyrins with DNA as an adjunct to other methods. Due to high accuracy and maximum sensitivity to changes in the size and shape of macromolecules, it is recommended to use viscometry as the cogent method for studying the interaction of small molecules with DNA, especially if intercalation is expected using other methods if necessary to confirm the results obtained. AbbreviationsDNAdeoxyribonucleic acidH2TAllPyP4meso-tetra-(4N-allylpyridyl) porphyrinH2TAllPyP3meso-tetra-(3N-allylpyridyl) porphyrinH2THOEtPyP4meso-tetra-(4N-hydroxyethylpyridyl) porphyrinH2THOEtPyP3meso-tetra-(3N-hydroxyethylpyridyl) porphyrinUV/VIS spectrophotometryultraviolet-visible spectrophotometryCD spectroscopycircular dichroism spectroscopyCommunicated by Ramaswamy H. Sarma.