title: The stability of DNA-porphyrin complexes in the presence of Mn(II) ions.
abstract: The complex formation of porphyrins with DNA leads to changes of stability of DNA. In the present study we investigated binding properties and the thermodynamic parameters of a water-soluble, cationic planar Cu(II)-containing meso-tetrakis(4-N-butyl-pyridiniumyl)porphyrin [CuTButPyP4] and nonplanar Co(II)-containing meso-tetrakis(4-N-butyl-pyridiniumyl)porphyrin [CoButPyP4] with calf thymus DNA in the presence of divalent manganese ions. For displaying the changes of thermodynamic parameters (T(m) and ΔT) the melting curves of DNA-porphyrin complexes in the presence of Mn(2+) ions have been obtained. The enthalpy (ΔH) of helix-coil transition has been also evaluated. It was shown that the binding of ions to DNA proceeds in two stages depending on the manganese/DNA phosphates molar ratio [Mn]/[P]. At the first stage (0.001<[Mn]/[P]<1), the interaction of manganese ions with DNA phosphates occurs, causing an additional screening of their negative charge and the stabilization of the double helix. As a result, the best conditions for intercalation of CuTButPyP4 or of peripheral rings of CoButPyP4 occur. The significant increase of T(m), but less changes of ΔT were observed. At the second stage (1<[Mn]/[P]<4), the ions interact with both the phosphates and the nitrogen bases of DNA. At this stage, it is possible for the manganese ion to coordinate simultaneously to the oxygen atom of the phosphate and the neighboring base of DNA. At a higher [Mn]/[P] ratio, the destabilization of the double helix begins, and partial breakage of the hydrogen bonds between the nitrogen bases occurs. Respectively the destabilization of DNA in the presence of both porphyrins takes place.
authors: Department of Molecular Physics, Faculty of Physics, Yerevan State University, Armenia. ananyan.gayane@gmail.com
authors: G
authors: G
authors: Ananyan
authors: A
authors: A
authors: Avetisyan
authors: L
authors: L
authors: Aloyan
authors: Y
authors: Y
authors: Dalyan
mesh_terms: D000818:Animals; D002417:Cattle; D002942:Circular Dichroism; D004247:DNA / Q000737:chemistry / Q000378:metabolism*; D007477:Ions / Q000737:chemistry / Q000378:metabolism; D008345:Manganese / Q000737:chemistry / Q000378:metabolism*; D008958:Models, Molecular; D009691:Nucleic Acid Denaturation; D011166:Porphyrins / Q000737:chemistry / Q000378:metabolism*; D013816:Thermodynamics
chemical_list: D007477:Ions; D011166:Porphyrins; D008345:Manganese; D004247:DNA; C427203:calf thymus DNA