Role of biologically important zwitterionic buffer secondary ligands in the stability of the ternary complexes containing some metal ions and guanosine 5 '-monophosphate, inosine 5 '-monophosphate, and cytidine 5 '-monophosphate

Potentiometric equilibrium measurements have been pet-formed at (25.0 +/- 0 .1) degreesC and ionic strength I = 0.1 mol dm(-3) (KNO3) for the interacti on of guanosine 5'-monophosphate, inosine 5'-monophosphate, and cytidine 5' -monophosphate and Cu(II), Ni(II), Co(II), Mn(II), Zn(II), Pd(II), Ca(II), and Mg(II) with the biologically important secondary ligand zwitterionic bu ffers 3-[N-morpholinol]-2-hydroxypropanesulfonic acid, 3-[N-tris(hydroxymet hyl)methylamino]-2-hydroxypropanesulfonic acid, and N-2-acetamido-2-aminoet hanesulfonic acid in a 1:1:1 ratio. The experimental conditions were select ed such that self-association of the nucleotides and their complexes was ne gligibly small; that is, the monomeric complexes were studied. The formatio n of various 1:1:1 mixed ligand complexes was inferred from the potentiomet ric titration curves. Initial estimates of the formation constants of the r esulting species and the acid dissociation constants of guanosine 5'-monoph osphate, inosine 5'-monophosphate, cytidine 5'-monophosphate, and the secon dary ligands 3-[N-morpholinol] -2-hydroxypropanesulfonic acid, 3-[N-tris(hy droxymethyl)methylamino]-2-hydroxypropanesulfonic acid, and N-2-acetamido-2 -aminoethane sulfonic acid have been refined with the SUPERQUAD computer pr ogram.