STUDIES ON STABILITY OF TERNARY MIXED-LIG AND COMPLEXES OF M(II)(ATP)(2-) AND NUCLEIC-ACID BASES (ADENINE AND CYTOSINE)

The stability constants of binary complexes ML(2+) (M(2+) = Cu2+, Co2, Ni2+, Zn2+, Cd2+; L=Adenine, Cytosine) and their ternary complexes w ith ATP(Adenosine 5'- triphosphate) were determined by potentiometric pH titration in aqueous solution(T=25 degrees C, I= 0.1 mol/L NaClO4), the stability of ternary complexes in relation to the stability of th eir binary parent complexes was characterized by the equilibrium const ants Delta lgK(M) (Delta lgK(M) = lgK(M(ATP)L)(M(ATP))-lgK(ML)(M)) cor responding to the equilibrium M(ATP)(2-)+ML(2+)=M(ATP)L(2-)+M(2+). The results obtained show that the Delta lgK(M) for L=Adenine and cytosin e is larger than that of the corresponding complexes of imidazole or a mmonia due to the intramolecular ligand-ligand stacking interaction an d hydrogen bond of the ternary complexes.