Ternary complexes of 5′-cytidine monophosphate and cytosine with some biologically important secondary ligands

Potentiometric equilibrium measurements have been made at 35°C for the interaction of 5′-cytidine monophosphate and Cu(II), Ni(II), Zn(II), Co(II), Mn(II), Mg(II) and Ca(II) with biologically important secondary ligands (glycine, oxalic cid, histidine and histamine) in a 1:1:1 ratio. Similar studies with cytosine were carried out for comparison. For the above systems, the ternary complexes are found to be more stable than the corresponding binary complexes. The Δ log K values for 1 : 1 : 1 complexes of metal-5′-cytidine monophosphate (or cytosine) with aromatic ligands are more positive compared to the corresponding complexes with aliphatic ligands. This is explained in terms of “stacking phenomenon” that occur between the two aromatic moieties of the primary and secondary ligands in solution.