Medium Effect and Thermodynamic Studies for the Proton−Ligand and Metal−Ligand Formation Constants of the Ternary Systems MII + Adenosine-5‘-triphosphate (ATP) + Asparagine

Proton−ligand and metal−ligand stability constants formed in the ternary system NiII + adenosine-5‘-triphosphate (ATP) + asparagine are determined pH-metrically in different aqueous−organic solvent mixtures at 25 °C and at a constant ionic strength I = 0.10 mol dm-3 (KNO3), and are discussed in terms of both the proportion and solvent characteristics. The organic solvents used are ethanol, DMF, dioxane, and acetonitrile (AN). It was concluded that solvent effects such as stabilization of the proton by ion−solvent interaction as well as the basicity of the medium, in addition to the electrostatic effect, have a profound influence on the proton−ligand formation 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. Moreover, the thermodynamic functions ΔH, ΔG°, and ΔS° associated with the formation of proton−ligand and the 1:1 binary as well as the...