Polarization transfer via field sweeping in parahydrogen-enhanced nuclear magnetic resonance

Abstract

We show that in a spin system of two magnetically inequivalent protons coupled to a heteronucleus such as 13 C, an adiabatic magnetic field sweep, passing through zero field, transfers proton singlet order into magnetization of the coupled heteronucleus. This effect is potentially useful in parahydrogen-enhanced nuclear magnetic resonance, and is demonstrated on singlet-hyperpolarized [1-13 C]maleic acid, which is prepared via the reaction between [1-13 C]acetylene dicarboxylic acid and para-enriched hydrogen gas. The magnetic field sweeps are of microtesla amplitudes, and have durations on the order of seconds. We show a polarization enhancement by a factor of 10 4 in the 13 C spectra of [1-13 C]maleic acid in a 1.4 T magnetic field.

Representation of population exchange at level anti-crossings

“…This method has been successfully implemented (Eills et al, 2019) to polarize 13 C nuclei in a system of two protons prepared in the singlet spin state and a carbon nucleus. In this case, two protons (spins and ) coupled to a 13 C nucleus (spin ), the spin Hamiltonian takes the form:…”

“…Hereafter, we follow the results of Eills et al (Eills et al, 2019) For Ĥ 0 the eigen-basis of states is the "singlet-triplet-Zeeman" basis. In ref.…”

“…In ref. (Eills et al, 2019) such a basis is introduced in two ways. The obvious one is to use the basis ℤ = {| 〉, | + 〉, | 0 〉, | − 〉} 12 ⊗ {| 〉, | 〉} .…”

“…In this work, we introduce 25 the main concept and formalism and provide a number of NMR-relevant examples, showing how the approach works. These examples include consideration of spin order transfer upon adiabatic inversion (Lukzen and Steiner, 1995;Eills et al, 2019) of the external magnetic field and, more generally, NMR experiments with field jumps (Miesel et al, 2006;Pravdivtsev et al, 2013a), as well as some pulsed NMR experiments, such as cross-polarization (Hartmann and Hahn, 1962;Pines et al, 1972). Last but not least, 30…”

Generalised magnetisation-to-singlet-order transfer in nuclear magnetic resonance

“…[15][16][17][25][26][27][28][31][32][33][34] Further extensions to the case of heteronuclear spin systems are feasible, for example in the context of parahydrogenenhanced NMR. [63][64][65]…”