Potentiometric equilibrium measurements have been performed at (25.0 ( 0.1) °C and ionic strength I ) 0.1 mol dm -3 KNO 3 for the interaction of adenosine 5′-monophosphate, guanosine 5′-monophosphate, cytidine 5′-monophosphate, and La(III), Ce(III), Pr(III), and Eu(III) with the biologically important secondary ligand zwitterionic buffers (3-[N-morpholinol])-2-hydroxypropanesulfonic acid, 2-(N-morpholino)ethanesulfonic acid, N-2-acetamido-2-aminoethanesulfonic acid, and N-2-hydroxyethylpiperazine-N-2ethanesulfonic acid. Measurements were made in a 1:1:1 ratio. Formation constants for the monohydroxy, dihydroxy, and dimeric ligand complexes for the binary systems Ln(III) + adenosine 5′-monophosphate, Ln(III) + guanosine 5′-monophosphate, Ln(III) + cytidine 5′-monophosphate, and Ln(III) + zwitterionic buffers have been evaluated. 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 due to stacking interaction was negligibly small; that is, the monomeric normal and protonated ternary complexes were studied.

Potentiometric equilibrium measurements have been performed at (25.0 ± 0.1) °C and ionic strength I = 0.1 mol dm-3 (KNO3) for the interaction 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 buffers 3-[N-morpholinol]-2-hydroxypropanesulfonic acid, 3-[N-tris(hydroxymethyl)methylamino]-2-hydroxypropanesulfonic acid, and N-2-acetamido-2-aminoethanesulfonic acid in a 1:1:1 ratio. The experimental conditions were selected such that self-association of the nucleotides and their complexes was negligibly small; that is, the monomeric complexes were studied. The formation of various 1:1:1 mixed ligand complexes was inferred from the potentiometric titration curves. Initial estimates of the formation constants of the resulting species and the acid dissociation constants of guanosine 5‘-monophosphate, inosine 5‘-monophosphate, cytidine 5‘-monophosphate, and the secondary ligands 3-[N-morpholinol]-2-hydroxypropanesulfonic acid, 3-[N-tris(hydroxymethyl)methylamino]-2-hydroxypropanesulfonic acid, and N-2-acetamido-2-aminoethane sulfonic acid have been refined with the SUPERQUAD computer program.