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

Abstract

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