Experimental and theoretical analysis of Al3+ complexation with ADP and ATP

Abstract Al 3+ ion is known to interact significantly with a number of biochemical systems, and has been linked to a number of human diseases. Owing to the affinity of Al 3+ for phosphate oxygens, much recent interest has focused on complexes that Al 3+ can form with nucleoside di- and tri-phosphates. ATP, for example, may serve as a major intracellular chelator of Al 3+ . While potentiometric titrations have provided a wealth of information on the nature of various nucleoside phosphate-Al 3+ species which can exist in solution under a given set of conditions, this approach alone cannot distinguish between all possible complexes that may exist, especially where dimers or high multimeric forms are present. In this paper, 500 MHz 1 H NMR data collected on samples that vary in the nature of the nucleoside phosphate (i.e., either ADP or ATP), the concentration of nucleoside phosphate (from 0.5 to 10 mM), the pH (from 5.0 to 7.0), and the ratio of total Al 3+ to total nucleoside phosphate (from 0.455 to 1.0) were simultaneously analyzed by a nonlinear least squares procedure, providing evidence for several Al 3+ -nucleoside phosphate complexes along with the associated formation constants (all fits being characterized by apparent σ values 3+ and nucleotide are HOM 2 L 2 and ML, while with excess ligand ML 2 complexes predominate. Bases in the ML 2 complexes are about 87% stacked.