Magnesium(II)-ATP Complexes in 1-Ethyl-3-Methylimidazolium Acetate Solutions Characterized by 31 Mg β-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 β-emitter ³¹ Mg to study Mg ^II -ATP complexation in 1-ethyl-3-methylimidazolium acetate (EMIM-Ac) solutions using β-radiation-detected nuclear magnetic resonance (β-NMR). We demonstrate that (nuclear) spin-polarized ³¹ Mg, 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 ³¹ Mg initially bind to the solvent acetate anions, whereafter they undergo dynamic exchange and form either a mono- ( ³¹ Mg-ATP) or di-nuclear ( ³¹ MgMg-ATP) complex. The chemical shift of ³¹ Mg-ATP is observed up-field of ³¹ MgMg-ATP, in accord with quantum chemical calculations. These observations constitute a crucial advance towards using β-NMR to probe chemistry and biochemistry in solution.
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