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 sec ondary ligand zwitterionic buffers 3-[N-bis(hydroxyethyl)amino]-2-hydroxypr opanesulfonic acid, 3-[N-tris(hydroxymethyl)methylamino]-2-hydroxypropanesu lfonic acid, (3-[N-morpholinol)-2-hydroxy propanesulfonic acid, N-(2-acetam ido)-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 titra tion curves. The experimental conditions were selected such that self-assoc iation of the nucleotides and their complexes was negligibly small; i.e., t he 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'-diphosph ate, and adenosine 5'-triphosphate and the zwitterionic buffers secondary l igands 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 m ost effective in deciding the stability of the ternary complexes formed in solutions.