Comparison of the effectiveness of various metal ions on the formation of the ternary complexes containing adenosine 5′-mono-, 5′-di-, and 5′-triphosphate and some zwitterionic buffers for biochemical and physiological research

Potentiometric equilibrium measurements have been performed at (25.0 +/- 0.1) degrees C and ionic strength I = 0.1 mol dm(-3) KNO3 for the interaction of adenosine 5'-mono-, 5'-di-, and 5'-triphosphate and Cu(II), Co(II), Ni(II), Mn(II), Zn(II), Ca(II), and Mg(II) with the biologically important secondary ligand zwitterionic buffers 3-[N-bis(hydroxyethyl)amino]-2-hydroxypropanesulfonic acid, 3-[N-tris(hydroxymethyl)methylamino]-2-hydroxypropanesulfonic acid, (3-[N-morpholinol)-2-hydroxy propanesulfonic acid, N-(2-acetamido)-2-aminoethanesulfonic acid, and 2-(cyclohexylamino)ethanesulfonic acid in a 1:1:1 ratio, and the formation of various 1:1:1 normal and protonated mixed ligand complex species was inferred from the potentiometric pH titration curves. The experimental conditions were selected such that self-association of the nucleotides and their complexes was negligibly small; i.e., the monomeric normal and protonated ternary complexes were studied. Initial estimates of the formation constants of the resulting species and the acid dissociation constants of adenosine 5'-monophosphate, adenosine 5'-diphosphate, and adenosine 5'-triphosphate and the zwitterionic buffers secondary ligands have been refined with the SUPERQUAD computer program. In some M(II) ternary systems the interligand interactions or some cooperativity between the coordinate ligands, possibly H bond formation, have been found to be most effective in deciding the stability of the ternary complexes formed in solutions.