THERMODYNAMIC ANALYSIS OF ETHIDIUM-BROMIDE INTERACTION WITH DEOXYTETRARIBONUCLEOTIDE 5'-D(CPGPCPG) IN AQUEOUS-SOLUTIONS BASED ON THE H-1-NMR DATA

Temperature dependences of chemical shifts of protons of ethidium brom ide mixed with aqueous solution of self-complementary deoxytetraribonu cleosidetriphosphate 5'-d(CpGpCpG) are measured using a pulse NMR spec trometer (500 MHz). The applied procedures for calculating thermodynam ic parameters enabled us to separate the contributions of different re actions to the overall heat of complexation at equilibrium between var ious species formed in aqueous solutions. Mole fractions of aggregates are calculated as functions of temperature. Free Gibbs energies, enth alpies, and entropies of formation of 1:1, 2:1, 1:2, and 2:2 complexes between ethidium bromide and tetranucleotide are estimated. A compara tive thermodynamic analysis of complexation of acridine dye (proflavin e) and ethidium bromide with 5'-d(CpGpCpG) under identical experimenta l conditions is accomplished.