Physicochemical Study of the Interaction of some Water Soluble Porphyrins with Calf Thymus DNA

In order to shed more light on the effect of peripheral groups of porphyrin core intophysicochemical properties and DNA binding behavior of porphyrins, we have chosen toinvestigate solution properties and calf thymus DNA binding behavior of meso-tetrakis (4-Nbenzyl-pyridyl) porphyrin (TBZPyP) and its Mn (III), Co (III), Ni (II) and Cu (II) complexesderivatives have been studied in thermodynamic viewpoint using Uv/Vis spectroscopy. They havebeen chosen because of their good solubility in physiological solution as well as moderatelyhydrophobic property, so that we may consider them as promising compounds for clinicalapplications. The measurements were done in 1mM phosphate buffer, pH 7.0 and varioustemperatures. The optical absorption spectra of porphyrins were analyzed in order to obtainbinding constants and stoichiometries using SQUAD software. The results show that the bestfitting corresponds to a 1:1 complex model between base pair of DNA and porphyrins. Theestimation of binding constant at various temperatures enabled as to calculate all of thethermodynamic parameters of binding using vant Hoff equation. All of the studied porphyrinsshowed strong electrolyte effect and increasing of NaCl concentration induces self-aggregation ofporphyrins. We also made a comparison between the properties of above-mentioned porphyrinsand that of a less-hydrophobic water-soluble porphyrin [meso Tetrakis (4-N-Methyl-pyridyl)porphyrin (TMPyP). The results showed that the above-mentioned porphyrins exist as monomerat low ionic strength medium. While TBzPyP and CuTBzPyP formed ill-defined self-aggregatesat high strength medium. The hypochromicity among with small red shift has been observed inSoret band of porphyrins due to increasing of DNA.