Solid-state 1H spin polarimetry by 13CH3 nuclear magnetic resonance.

Stuart J Elliott,Quentin Stern,Sami Jannin

doi:10.5194/mr-2-643-2021

Abstract

Dissolution dynamic nuclear polarization is used to prepare nuclear spin polarizations approaching unity. At present, H polarization quantification in the solid state remains fastidious due to the requirement of measuring thermal equilibrium signals. Line shape polarimetry of solid-state nuclear magnetic resonance spectra is used to determine several useful properties regarding the spin system under investigation. In the case of highly polarized nuclear spins, such as those prepared under the conditions of dissolution dynamic nuclear polarization experiments, the absolute polarization of a particular isotopic species within the sample may be directly inferred from the characteristics of the corresponding resonance line shape. In situations where direct measurements of polarization are complicated by deleterious phenomena, indirect estimates of polarization using coupled heteronuclear spins prove informative. We present a simple analysis of the C spectral line shape of [2-C]sodium acetate based on the normalized deviation of the centre of gravity of the C peaks, which can be used to indirectly evaluate the proton polarization of the methyl group moiety and very likely the entire sample in the case of rapid and homogeneous H-H spin diffusion. For the case of positive microwave irradiation, H polarization was found to increase with an increasing normalized centre of gravity deviation. These results suggest that, as a dopant, [2-C]sodium acetate could be used to indirectly gauge H polarizations in standard sample formulations, which is potentially advantageous for (i)samples polarized in commercial dissolution dynamic nuclear polarization devices that lack H radiofrequency hardware, (ii)measurements that are deleteriously influenced by radiation damping or complicated by the presence of large background signals and (iii)situations where the acquisition of a thermal equilibrium spectrum is not feasible.

Highlights

Classical nuclear magnetic resonance (NMR) experiments produce inherently weak signals
The significantly boosted NMR signal intensities from metabolites hyperpolarized by implementing a dissolution dynamic nuclear polarization approach have been used in the characterization of cancer in human patients (Nelson et al, 2013; Chen et al, 2020; Gallagher et al, 2020)
The achieved levels of 13C polarization PC are lower than those previously reported in the literature (Bornet et al, 2016) but were not further optimized since only the 13C NMR line shape was of interest in this study as a probe for absolute 1H polarization

Summary

Introduction

Classical nuclear magnetic resonance (NMR) experiments produce inherently weak signals. The significantly boosted NMR signal intensities from metabolites hyperpolarized by implementing a dissolution dynamic nuclear polarization (dDNP) approach have been used in the characterization of cancer in human patients (Nelson et al, 2013; Chen et al, 2020; Gallagher et al, 2020). To hyperpolarize nuclear spins via the dDNP approach, the spin system of interest is co-frozen in a mixture of aqueous solvents and glassing agents with a carefully chosen paramagnetic radical species (Abragam and Goldman, 1978). The dDNP-compatible solution is subsequently frozen at liquid-helium temperatures (where the solvent matrix forms a glass) inside a magnetic field and is irradiated with slightly off-resonant (with respect to the centre of electron spin transition) microwaves, which transfer the high electron spin polarization to the nuclear spins of interest (Kundu et al, 2019)

Methods

Results

Discussion

Conclusion