Magnesium(II)-ATP Complexes in 1-Ethyl-3-Methylimidazolium Acetate Solutions Characterized by Mg-31 beta-Radiation-Detected NMR Spectroscopy

The complexation of Mg-II with adenosine 5 '-triphosphate (ATP) is omnipresent in biochemical energy conversion, but is difficult to interrogate directly. Here we use the spin-1/2 beta-emitter Mg-31 to study Mg-II-ATP complexation in 1-ethyl-3-methylimidazolium acetate (EMIM-Ac) solutions using beta-radiation-detected nuclear magnetic resonance (beta-NMR). We demonstrate that (nuclear) spin-polarized Mg-31, following ion-implantation from an accelerator beamline into EMIM-Ac, binds to ATP within its radioactive lifetime before depolarizing. The evolution of the spectra with solute concentration indicates that the implanted Mg-31 initially bind to the solvent acetate anions, whereafter they undergo dynamic exchange and form either a mono- (Mg-31-ATP) or di-nuclear ((MgMg)-Mg-31-ATP) complex. The chemical shift of Mg-31-ATP is observed up-field of (MgMg)-Mg-31-ATP, in accord with quantum chemical calculations. These observations constitute a crucial advance towards using beta-NMR to probe chemistry and biochemistry in solution.