Book of Abstracts: Albany 2009
June 16-20 2009
© Adenine Press (2008)
The Comparative Study of CuTAlPyP(4) and CoTAlPyP(4) Porphyrins with DNA
A comparative study of water-soluble Cu (II) and Co (II)-containing cationic tetrakis(N-Alyl-4-pyridiniumyl) porphyrin [CuTAlPyP(4) and CoTAlPyP(4)] and its metal free form H2TAlPyP(4) with calf thymus DNA (ct DNA) complexes have been studied by optical absorption, CD (circular dichroism) and melting methods. The studied porphyrins contain a long aliphatic strand with double bind in their peripheral radicals. The absorbance spectra at Soret band show a high hypochromic effect (65,2%) for interaction of H2TAlPyP(4) and CuTAlPyP(4) porphyrins with DNA and red shift, in the case of DNA-CoTAlPyP(4) complexes there are some blue shift and less hypochrom (31.4%). These effects are more appear at high ionic strength (μ=0.2). The binding parameters (Kb and n) were calculated using McGhee and von Hippel equation. The results indicated that the presence of Co(II) in porphyrin ring was decreasing binding parameters as against to H2TAlPyP(4) and CuTAlPyP(4) porphyrins. Binding mode with DNA was determined by sign of ICD spectra. It was shown, that the square planar complexes such as free bases and CuTAlPyP(4) intercalate between DNA base pairs (negative ICD band). For the porphyrin-metal complex, having axially bound ligands such as CoTAlPyP(4), intercalation is blocked and outside binding occurs (positive ICD band). Hence, determination of thermodynamic parameters governing DNA-porphyrin complex formation makes deeper insight into molecular basis of DNA-porphyrin interactions. Ionic strength of solution was changed by Mn2+ ions, small concentrations of which interacte with the phosphate groups of DNA leaving the grooves free and may generate or inhibit intercalation of porphyrin molecules. The measurements were done in 1 mM NaCl, pH 6.8, concentrations of Mn2+ ions are 0.001 M/P and 0.01M/P. It was shown, that both metalloporphyrins stabilized the double helix of DNA. According to the experimental results, it can be inferred that the interaction model of Cu(II)TAlPyP(4) with ctDNA is intercalative binding, while Co(II)TAlPyP(4) is the long-range assembly on the surface of ctDNA molecule.
Yerevan State University