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

Document Type : Research Paper




In order to shed more light on the effect of peripheral groups of porphyrin core into
physicochemical properties and DNA binding behavior of porphyrins, we have chosen to
investigate 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) complexes
derivatives have been studied in thermodynamic viewpoint using Uv/Vis spectroscopy. They have
been chosen because of their good solubility in physiological solution as well as moderately
hydrophobic property, so that we may consider them as promising compounds for clinical
applications. 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 software. 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 as to calculate all of the
thermodynamic parameters of binding using vant Hoff equation. All of the studied porphyrins
showed strong electrolyte effect and increasing of NaCl concentration induces self-aggregation of
porphyrins. We also made a comparison between the properties of above-mentioned porphyrins
and 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 monomer
at low ionic strength medium. While TBzPyP and CuTBzPyP formed ill-defined self-aggregates
at high strength medium. The hypochromicity among with small red shift has been observed in
Soret band of porphyrins due to increasing of DNA.