Characterization of the sodium binding sites in microcrystalline ATP by 23Na-solid-state NMR and ab initio calculations

Stepwise conformational transition of disodium adenosine 5′-triphosphate (Na2ATP) crystals as a function of relative humidity (r.H.), was examined by means of high resolution 23Na, 31P solid state NMR spectroscopy and quantum mechanics calculations. 23Na-MQMAS solid state NMR spectra of hydrated disodium salts of adenosine 5,5′-triphosphate were measured to characterize the individual sodium sites. Quadrupolar coupling constants (CQ), and the asymmetry parameters of the electric field gradient tensors (η) of sodium-23 determined by quantum mechanical calculations (gaussian03) using larger clusters than in previous studies were compared to the experimental 23Na-MQMAS spectra.