STRUCTURE AND DYNAMICS OF ADENOSINE TRIPHOSPHATE-AL(III) COMPLEXES AT PH 7.4

The interaction of Al(III) with adenosine 5'-triphosphate (ATP) was investigated at pH = 7.4 by P-31, C-13, H-1, and Al-27 NMR. Two complexes coexist in equilibrium: 2:1 and a 1:1 complexes, Al(III)(ATP)2 and Al(III)(ATP). Their phenomenological equilibrium constants of formation were calculated from the P-31 NMR data. They are in good agreement with independently determined thermodynamic equilibrium constants (Kiss, T.; Sovago, I.; Martin, R. B. Inorg. Chem. 1991, 30, 2130-2132). The exchange rate between free and Al(III)-bound ATP (in the 2:1 complex) was determined from a P-31-P-31 EXSY experiment to be 3.4 s-1 at 295 K, a value diagnostic of a dissociative mechanism from octahedral Al(III). The rate of exchange is probably governed by the rupture of the AI(III)-phosphate bonds, the Al(III)-ATP 1:1 complex being an intermediate in the exchange process. The P-31 NMR resonances of the complexes are broad. In the case of the 2:1 complex, since the line widths are linearly related to the square of the field of observation, while the longitudinal relaxation rates are independent of this field, the broadening could be ascribed to relatively fast exchange of two or more forms of this 2:1 complex. At 270 K, at least four signals could be observed for the complexed beta-P-31. The possible attribution of these signals to various diastereoisomers of the 2:1 complex is discussed.