Abstract
<jats:p>Determining the thermodynamic parameters of the DNA transition from a highly ordered double-helical conformation to a disordered coiled state in the presence of ligands is key to understanding the structural features of complex formation. Calorimetry is commonly used to determine the enthalpy ΔH and entropy ΔS of the helix-coil transition. In this study, these parameters were determined using an alternative method: UV spectrophotometric melting. The melting temperature and melting range (Tm and ΔT) of DNA complexes with water-soluble cationic Co(II)-meso-tetra(4-N-allylpyridyl)porphyrin (CoTAllPyP4) were obtained. The enthalpy of the helix-coil transition during complex formation with CoTAllPyP4 was shown to be endothermic, which is caused by both the rupture of hydrogen bonds between nucleotide pairs and the release of porphyrin molecules from the surface of the DNA double helix. The entropic contribution is positive because the system becomes more disordered.</jats:p>