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(CC BY-NC 4.0).
The peculiarities of binding the water-soluble meso-tetra-(4N-oxyethylpyridyl) porphyrin (TOEPyP4) with B-DNA and A-DNA have been studied by means of UV-VIS spectrophotometry and circular dichroism method. The binding constant (Kb) and stoichiometry (n) were determined based on the absorbance spectra for each DNA–porphyrin complex. The free energy, enthalpy and entropy of binding also were calculated using the values of Kb. A comparative analysis with TOEPyP4–B-DNA complex was performed. The obtained results show that the porphyrin interacts with B-DNA by way of intercalation at low relative concentrations (r = Cporf./CDNA) and external binding at large values of r, whereas the interaction of TOEPyP4 with A-DNA occurs via the outside binding mode only.