Medium effect and thermodynamic studies for the proton-ligand and metal-ligand formation constants of the ternary systems M-II + adenosine-5 '-triphosphate (ATP) plus asparagine

Proton-ligand and metal-ligand stability constants formed in the ternary sy stem Ni-II + adenosine-5 ' -triphosphate (ATP) + asparagine are determined pi-I-metrically in different aqueous-organic solvent mixtures at 25 degrees C and at a constant ionic strength I = 0.10 mol dm(-3) (KNO3), and are disc ussed in terms of both the proportion and solvent characteristics. The orga nic solvents used are ethanol, DMF, dioxane, and acetonitrile (AN). It was concluded that solvent effects such as stabilization of the proton by ion-s olvent interaction as well as the basicity of the medium, in addition to th e electrostatic effect,have a profound influence on the proton-ligand forma tion constants for ATP and asparagine. On the other hand, the electrostatic effect of the medium and the hydrogen-bonding interaction seem to play the major role in the formation of the binary and ternary metal complexes. Mor eover, the thermodynamic functions DeltaH, DeltaG degrees, and DeltaS degre es associated with the formation of proton-ligand and the 1:1 binary as wel l as the 1:1:1 ternary metal complexes in the system M-II + (ATP) + asparag ine (where M-II = Cu-II, Ni-II, and Co-II) in pure aqueous media were also determined and discussed.