Thermodynamic of Interaction between Some Water-Soluble Porphyrins and DNA by Titration Microcalorimetry

In the present work, the interaction of three water soluble porphyrins, tetra (p-trimethyle) ammoniumphenyl porphyrin iodide (TAPP) as a cationic porphyrin, tetra sodium meso-tetrakis (p-sulphonatophenyle) porphyrin (TSPP) as an anionic porphyrin and manganese tetrakis (p-sulphonato phenyl)porphinato acetate (MnTSPP) as a metal porphyrin, with DNA have been studied by isothermaltitration microcalorimetry at 1 mM phosphate buffer, pH 7.0 and 25 °C. The values of bindingconstant, entropy, enthalpy and Gibbs free energy changes for binding of the first MnTSPP, and firstand second TSPP and TAPP molecules were estimated from microcalorimetric data analysis. Theresults represent that the process is both entropy and enthalpy driven and DNA induces selfaggregationof the porphyrins. The results indicate that both columbic and hydrophobic interactions actas self-aggregation driving forces for the formation of aggregates around DNA.