Interaction of 5, 10, 15, 20-Tetrakis (N-Benzylpyridilium-4-yl) Porphyrin (H2TBzPyP) and Its Metal Derivatives with Calf Thymus DNA

Interactions of 5, 10, 15, 20-tetrakis (N-benzylpyridilium-4-yl) porphyrin (TBzPyP) and its metal complexes (Cu(II), Ni(II), Co(II) and Mn(III)) with calf thymus DNA were investigated in view of thermodynamics; using UV-vis spectroscopy. The measurements were done in 5 mM phosphate buffer, pH 7.0. The optical absorption spectra of porphyrins were analyzed in order to obtain binding constants and stoichiometries using SQUAD software. The results show that the best fitting corresponds to 1:1 complex model between base pair of DNA and porphyrins. Running the measurements at various temperatures provided the completed thermodynamic analysis on basis of van't Hoff equation. The results represents the enthalpy driven of the process and the predominate role of electrostatic interaction. The following order has been obtained for binding affinity and exothermicity: MnTBzPyP > CoTBzPyP > NiTBzPyP > CuTBzPyP > TBzPyP This result has been interpreted on basis of the chemical structure of porphyrins and electronegativity of their central metal. The values of calculated binding constants represent the less affinity of TBzPyP and its metal derivatives to DNA in comparison with meso-tetrakis(N-methylpyridnium-4-yl)porphyrin (TMPyP). This can be related to the larger peripheral benzyl groups of TBzPyP that probably inhibits stronger intercalation binding and favors outside self-stacking and non-specific binding.