Solvent effects on the redox potential of the uranium(VI)?uranium(V) couple

Binary and ternary systems involving adenosine 5′-triphosphate (ATP), 2,2′-dipyridylamine (DPA) and magnesium, calcium, strontium, manganese, cobalt, copper, and zinc(II) metal ions have been investigated in aqueous media by potentiometric titrations. The analysis of the titration curves shows the existence of M(ATP)2−, M(ATP)(H)−, and M(ATP)2(H)24− species for alkaline-earth metal ions, while no ternary complex can be detected. For transition metal ions both binary and ternary species are found. Binary M(ATP)2(H)24− complexes are present in solutions containing manganese and cobalt(II) metal ions but these species cannot be revealed in the case of copper and zinc(II). Ternary complexes as M(ATP)(DPA)2− and M(ATP)(DPA)(H)− are common to all transition metals. Binuclear and hydroxo complexes as M2(ATP)(OH)− and M(ATP)(OH)3− are found only for copper and zinc(II). A hypothesis on the possible role of the species M-ATP in 1:2 ratio in the dephosphorylation mechanism is advanced on the basis of a comparison between the equilibrium data in the solution phase and the solid state structures of the magnesium, calcium, and manganese(II)- ATP-DPA systems.