Metal ion interactions with nucleic acid base pairs in solution - A potentiometric study

The formation df bio-ligand chelates of some divalent transition metal ions, viz. Mn-II, Co-II, Ni-II, Cu-II, Zn-II and Cd-II with adenine as primary ligand (A) and 5-fluorouracil as the secondary ligand (L) has been carried out pH-metrically at 250 and at a constant ionic-strength, mu = 0.1 M (NaNO3). The stability constants of binary MA and ternary MAL complexes, where hi = Mn-II Co-II, Ni-II, Cu-II, Zn-II and Cd-II, A = adenine and L = 5-fluorouracil, have been determined using a modified Irving-Rossotti technique and found to follow the Irving-Williams trend. In all the cases, Co-II has minimum and Cu-II has maximum stability and all the mixed ligand complexes have been found to be less stable than the binary metal-5-fluorouracil complexes except Cu-II and Cd-II, while it is more stable than metal-adenine binary complexes.