Abstract: The stability constants of binary complexes ML²⁺(M²⁺=Cu²⁺, Co²⁺, Ni²⁺,Zn²⁺, Cd²⁺; L=Adenine, Cytosine) and their ternary complexes with ATP (Adenosine 5'-triphosphate) were determined by potentiometric pHtitration in aqueous solution (T=25℃,I=0.1mol/L NaClO₄), the stability of ternary complexes in relation to the stability of their binary parent complexes was characterized by the equilibrium constants △lgK_m(△lgK_M=lgK_M(ATP)L^M(ATP)-lgK_ML^M) corresponding to the equilibrium M(ATP)^2-+ML²⁺=M (ATP)L^2-+M²⁺. The results obtained show that the △lgK_mfor L=Adenine and cytosine is larger than that of the corresponding complexes of imidazole or ammonia due to the intramolecular ligand-ligand stacking interaction and hydrogen bond of the ternary complexes.

Key words: Ternary mixed-ligand complexes, ATP, Nucleic acid bases, Stability constants, Stacking interaction