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Binding Of Meso-Tetra Kis (4-N-Methyl-Pyridinium) Porphyrin And Its Mn (III) And Co (III) Complexes With Calf Thymus DNA: A Thermodynamic Approach

Abdol-Khalegh Bordbar, Morteza Keshavarz

The binding of meso-tetra kis (4-N-methy-pyridinium) porphyrin, TMPyP and its Mn (III) (MnTMPyP) and Co(III) (CoTMPyP) derivatives to calf thymus DNA have been studied in thermodynamic viewpoint using Uv/Vis spectroscopy. The measurements were done in 1mM phosphate buffer, pH 7.0 and various temperatures. The optical absorption spectra of porphyrins were analyzed in order to obtain binding constants and stoichiometries using SQUAD soft ware .The results show that the best fitting corresponds to a 1:1 complex model between base pair of DNA and porphyrins. The estimation of binding constant at various temperatures enabled us to calculate all of the thermodynamic parameters of binding using Vant Hoff equation. The following order has been obtained for binding affinity and exothermicity of binding process, MnTMPyP > CoTMPyP > TMPyP.This results and the trend of variation of spectral features of porphyrin in titration experiments with DNA indicate the groove binding mode and special feature of central metal ion of porphyrin in the strength of binding.