Magnesium(II)‐ATP Complexes in 1‐Ethyl‐3‐Methylimidazolium Acetate Solutions Characterized by³¹Mg β‐Radiation‐Detected NMR Spectroscopy

Abstract

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-3methylimidazolium 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.

Near-surface dynamics of the ionic liquid EMIM-Ac above and below the glass transition

“…The exponent 0 ≤ β ≤ 1 produces a stretching of the exponential decay, which may result from an ensemble of probes with a broad distribution of T 1 's. 22 The case of β = 1 arises when each 8 Li has the same T 1 value. As in our earlier work, we shall interpret a β < 1 to be indicative of the dynamic heterogeneity characteristic of supercooled liquids and glasses.…”

“…The analysis was accomplished with the use of the bfit Python package. 23 The Fit: ax b + c a: 1 × 10 5 +5.9 × 10 7 5.2 × 10 6 (1/sK) b: 1.7 +0.12 0.0095 c: 0.077 +0.0069 0.0081 (1/s) Figure 3: The temperature dependence of the slow component of the biexponential relaxation of 8 Li in the empty Al sample holder, with a power law fit. The fast component was weakly linear with temperature, with a slope of 0.009 90(4) s −1 K and intercept of 0.33(1) s −1 .…”

“…19 The time-dependent polarization was determined by a measurement of the anisotropic β-decay of the 8 Li probe, which has a lifetime of 1.21 s. Measurements were taken using a static field of 6.55 T. With a gyromagnetic ratio of 6.3016 MHz T −1 , the nominal Larmor frequency of 8 Li was 41.27 MHz. With a nuclear spin of I = 2 and a nuclear quadrupole moment of +32.6 mb, the dominant mechanism for spin-lattice relaxation (SLR) of 8 Li in EMIM -Ac is likely through quadrupole coupling to fluctuations of the local electric field gradient. Thus, the polarization of the 8 Li ensemble is very sensitive to both translation and rotation of the host species on nanosecond timescales.…”

“…For example, 31 Mg β-NMR has been used to discriminate between magnesium coordination with oxygen and nitrogen, as well as to resolve different binding models with the biologically relevant molecule adenosine triphosphate. 7,8 Our previously published measurements of the RTIL 1-ethyl-3-methylimidazolium acetate (EMIM -Ac) show that 8 Li β-NMR is a good probe of both the dynamic rate and heterogeneity in the bulk (i.e., far from the surface when dynamics become depth-independent, about 50 nm in this case). 9 With respect to near-surface effects, precise control of the ion beam energy permits variation of the implantation depth with nanometer-scale resolution.…”

How Does Mg2+(aq) Interact with ATP(aq)? Biomolecular Structure through the Lens of Liquid-Jet Photoemission Spectroscopy

“…Due to the importance of ATP (aq) in biochemistry, the Mg 2+ −phosphate interactions have been previously explored by many techniques, e.g., using aqueous-phase X-ray emission, 61 infrared, 36 Raman, 62 and nuclear magnetic resonance (NMR) 63 spectroscopies. The Mg 2+ −ATP coordination chemistry has been recently investigated in the gas phase using mass spectrometry (in particular, phosphate− Mg 2+ −adenine interactions) 35 and in acetate solutions 64 using NMR spectroscopy. Previous LJ-PES work focused on the ribose or adenine units in ATP (aq) , 65−67 or on inorganic phosphate 6 aqueous solutions.…”