Study of Al interaction with AMP, ADP and ATP in aqueous solution.

The interaction of Al and nucleotide ligands, namely adenosine-5'-monophosphate, (AMP), adenosine-5'-diphosphate, (ADP), adenosine-5'-triphosphate, (ATP), has been studied in aqueous solution at T = 298.15 K and I = 0.15 mol L in NaCl (only for Al-ATP system at I = 0.1 mol L). Formation constants and speciation models for the species formed are discussed on the basis of potentiometric results. The speciation models found for the three systems include ML and ML species in all the cases, and for Al-ADP and ATP systems, MLH, MLOH and MLOH species as well. The formation constant value for ML species shows the trend, AMP < ADP < ATP. H NMR spectroscopy was also employed for the study of Al-ATP system. The H NMR results are in agreement with the speciation model obtained from analysis of potentiometric titration data, confirming the stabilities of the main species. Enthalpy change values were obtained by titration calorimetry; for the main Al-ATP species (at T = 298.15 K and I = 0.1 mol L in NaCl), they resulted always higher than zero, as typical for hard-hard interactions. The dependence of formation constants on ionic strength over the range I = 0.1 to 1 mol L in NaCl is also reported for Al-ATP system. The sequestering ability of the nucleotides under study towards Al was also evaluated by the empirical parameter pL.