Ternary complexes in solution. XIV. The stability increasing effect of the pyridyl and imidazole groups on the formation of mixed amine-copper(II)-adenosine 5'-monophosphate complexes.

The stability constants of the ternary Cu2+ complexes containing adenosine 5′-monophosphate (AMP) and as a second ligand, 2,2′-bipyridyl, 4- (2′-pyridyl) imidazole, 2-picolylamine, 4-aminomethylimidazole, and ethylenediamine were determined by potentiometric titration in water containing 10% dioxane (I=0.1; 25°C). For the equilibrium, Cu (amine) 2++Cu (AMP) ⇄Cu (amine) (AMP) +Cu2+, the corresponding constants are (in the order of the above amine ligands), Δ log K =log =0.53, 0.20, 0.04, —0.35, and—0.45; hence, inthefirst cases the equilibrium is considerably on the side of the mixed-ligand complex. The importance of the π-system of the amine for the stability of the mixed-ligand Cu2+ complexes is obvious from the given series. The imidazole group, an important binding site for metal ions in biological systems, has clearly qualities similar to the pyridyl group (Inorg. Chem. 9, 1238 [1970]), i. e. the stability of ternary Cu2+ complexes containing these groups is increased.