Arnab Dey, Benoît Charrier, Karine Lemaitre, Victor Ribay, Dmitry Eshchenko, Marc Schnell, Roberto Melzi, Quentin Stern, Samuel F. Cousin, James G. Kempf, Sami Jannin, Jean-Nicolas Dumez, and Patrick Giraudeau
Nuclear magnetic resonance (NMR) is a great tool for analytical chemistry, but it is not the most sensitive one. This work aims to develop a sensitive and repeatable workflow for the analysis of complex samples by hyperpolarized 13C NMR. Through systematic and careful optimization of experimental parameters, we were able to achieve unprecedented sensitivity for the analysis of naturally abundant metabolite mixtures while maintaining the precision required for metabolomic studies.
Quantum-rotor-induced polarization, also called the Haupt effect, is a hyperpolarization technique in NMR relying on the coupling of nuclear spin states to rotational quantum states. The classic molecule showing this effect is γ-picoline. One might assume that many other molecules carrying a methyl group might also show this effect. Here we explore, using a heuristic approach, other molecules which appear to be promising candidates.
A straightforward line shape analysis of the 13C NMR spectra of [2-13C]sodium acetate can be used to indirectly evaluate the 13H polarization of the CH3 group and likely entire samples in the case of rapid and homogeneous 13H–1H spin diffusion. The results are potentially advantageous for polarizers that lack 1H radiofrequency hardware, measurements that are influenced by radiation damping or large background signals, or where acquisition of thermal equilibrium spectra is not feasible.
The use of hyperpolarized species, i.e., species whose nuclear polarization is transiently multiplied by several orders of magnitude, can perfectly be combined with the use of benchtop NMR spectrometers. In particular, laser-polarized 129Xe, due to its large chemical shift range and the proximity of its resonance frequency to 13C, can be observed on a non-dedicated low-field spectrometer. Detection of low amounts of molecules can be achieved using NMR techniques based on chemical exchange.
Methyl groups are rarely acidic. But in a lumazine derivative with biological significance the position-7 methyl group can be deprotonated. The existence of two protonation states is a prerequisite for a non-classical disproportionation reaction initiated by light. We provide evidence for such dismutation using a variant of nuclear magnetic resonance that is capable of detecting nuclear hyperpolarization. Our findings may shed new light on enzymatic riboflavin biosynthesis.
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Catalytic hydrogenation of unsaturated molecular precursors with parahydrogen provides a major signal enhancement in NMR, which is vital for many technical as well as biomedical applications. We show that dilution of catalytically active Pd with a less active metal in heterogeneous Pd-based catalysts provides significantly larger enhancements and that the judicious choice of the dilution metal can further improve the performance, as revealed by comparing Pd-Ag and Pd-In bimetallic catalysts.
Catalytic hydrogenation of unsaturated molecular precursors with parahydrogen provides a major...