[Calorimetric study of the helix-coil transition in DNA during interaction with Cu2+ ions]

Using the method of differential scanning calorimetry, the DNA helix-coil transition was studied in solutions (10(-3) M Na+, 10(-3) M tris HCl, pH 7.0) containing divalent copper ions at relative metal ion concentrations (Mt2+/PDNA) ranging from 0.2 to 20. Dependences of the melting temperature and enthalpy on relative ion concentration were determined. An aggregation of Cu(2+) + DNA complexes in the range of average ion concentration was established. It is shown that the melting enthalpy of "units" increases with copper ion concentration. The data obtained were compared with values determined by UV-spectroscopy. Association constants for Cu2+ binding to DNA were defined by the ligand theory.