Inversion of Hyperpolarized 13 C NMR Signals through Cross-Correlated Cross-Relaxation in Dissolution DNP Experiments

Mattia Negroni (1) , David Guarin , Kateryna Che (1) , Ludovica M Epasto (1) , Ertan Turhan (1) , Albina Selimović (1) , Fanny Kozak (1) , Samuel Cousin (1) , Daniel Abergel (2) , Geoffrey Bodenhausen (2) , Dennis Kurzbach (1)

1 Universität Wien = University of Vienna
2 LBM UMR 7203 - Laboratoire des biomolécules

Dissolution dynamic nuclear polarization (DDNP) is a versatile tool to boost signal amplitudes in solution-state nuclear magnetic resonance (NMR) spectroscopy. For DDNP, nuclei are spin-hyperpolarized 'ex-situ' in a dedicated DNP device and then transferred to an NMR spectrometer for detection. Dramatic signal enhancements can be achieved, enabling shorter acquisition times, real-time monitoring of fast reactions, and reduced sample concentrations. Here we show how this transfer can affect NMR spectra through cross-correlated cross-relaxation (CCR), especially in the case of low-field passages. Such processes can selectively invert signals of 13 C spins in proton-carrying moieties. For their investigations, we use schemes for simultaneous or 'parallel' detection of hyperpolarized 1 H and 13 C nuclei. We find that 1 H 13 C CCR can invert signals of 13 C spins if the proton polarization is close to 100%. We deduce that low-field passage in a DDNP experiment, a common occurrence since the introduction of so-called 'ultra-shielded´ magnets, accelerates these effects due to field-dependent paramagnetic relaxation enhancements that can influence CCR, 13 C spins not coupled to nearby protons do not feature any inversion phenomena. The reported effects are demonstrated for various molecules, laboratory layouts, and DDNP systems. As coupled 13 C-1 H spin systems are ubiquitous, we expect these effects to be observed in various DDNP experiments. This might be exploited for selective spectroscopic labeling of hydrocarbons.

Domaines: Chimie théorique et/ou physique

Mattia Negroni, David Guarin, Kateryna Che, Ludovica M Epasto, Ertan Turhan, et al.. Inversion of Hyperpolarized 13 C NMR Signals through Cross-Correlated Cross-Relaxation in Dissolution DNP Experiments. Journal of Physical Chemistry B, 2022, 126 (24), pp.4599-4610. ⟨10.1021/acs.jpcb.2c03375⟩. ⟨hal-03874196⟩