Abstract
Among hyperpolarization techniques, quantum-rotor-induced polarization (QRIP), also known as the Haupt effect, is a peculiar one. It is, on the one hand, rather simple to apply by cooling and heating a sample. On the other hand, only the methyl groups of a few substances seem to allow for the effect, which strongly limits the applicability of QRIP. While it is known that a high tunnel frequency is required, the structural conditions for the effect to occur have not been exhaustively studied yet. Here we report on our efforts to heuristically recognize structural motifs in molecular crystals able to allow to produce QRIP.
Highlights
NMR spectroscopy is a very versatile analytical method; as caused by the low Boltzmann ratio, it suffers from a lack of sensitivity
For the quantum-rotor-induced polarization (QRIP) experiments, the manual transfer was chosen, since the high viscosity of D2O hinders the liquid flow in the transfer system and results in air bubbles in the NMR tube inside the magnet, which will lead to a disturbed signal
The aim of this study was to gain further understanding of the structural requirements of methyl bearing substances allowing for QRIP signal enhancement in NMR spectroscopy
Summary
NMR spectroscopy is a very versatile analytical method; as caused by the low Boltzmann ratio, it suffers from a lack of sensitivity. Hyperpolarization methods are presently a hot topic (Halse, 2016; Köckenberger and Matysik, 2010; Kovtunov et al, 2018; Wang et al, 2019) Examples of these techniques are dynamic nuclear polarization (Ardenkjaer-Larsen, 2016; Kjeldsen et al, 2018; Lilly Thankamony et al, 2017; Milani et al, 2015; Ni et al, 2013), spin-exchange optical pumping (Hollenbach et al, 2016; Meersmann and Brunner, 2015; Norquay et al, 2018; Walker, 2011), photochemically induced dynamic nuclear polarization (Bode et al, 2012; Kiryutin et al, 2012; Sosnovsky et al, 2019), and para-hydrogen-induced polarization (Duckett and Mewis, 2012; Kiryutin et al, 2017; Korchak et al, 2009). With a custom-made setup, we were able to improve the safety and speed of the dissolution and transfer process, result-
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