Alonso-Valdesueiro, Javier, Elliott, Stuart, Bengs, Christian, Meier, Benno and Levitt, Malcolm H. (2018) Testing signal enhancement mechanisms in the dissolution NMR of acetone. Journal of Magnetic Resonance, 286, 158-162. (doi:10.1016/j.jmr.2017.12.009).
Abstract
In cryogenic dissolution NMR experiments, a substance of interest is allowed to rest in a strong magnetic field at cryogenic temperature, before dissolving the substance in a warm solvent, transferring it to a high-resolution NMR spectrometer, and observing the solution-state NMR spectrum. In some cases, negative enhancements of the 13C NMR signals are observed, which have been attributed to quantum-rotor-induced polarization. We show that in the case of acetone (propan-2-one) the negative signal enhancements of the methyl 13C sites may be understood by invoking conventional cross-relaxation within the methyl groups. The 1H nuclei acquire a relative large net polarization through thermal equilibration in a magnetic field at low temperature, facilitated by the methyl rotation which acts as a relaxation sink; after dissolution, the 1H magnetization slowly returns to thermal equilibrium at high temperature, in part by cross-relaxation processes, which induce a transient negative polarization of nearby 13C nuclei. We provide evidence for this mechanism experimentally and theoretically by saturating the 1H magnetization using a radiofrequency field pulse sequence before dissolution and comparing the 13C magnetization evolution after dissolution with the results obtained from a conventional 1H-13C cross relaxation model of the CH3 moieties in acetone.
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- Faculties (pre 2018 reorg) > Faculty of Natural and Environmental Sciences (pre 2018 reorg) > Chemistry (pre 2018 reorg)
Current Faculties > Faculty of Engineering and Physical Sciences > School of Chemistry > Chemistry (pre 2018 reorg)
School of Chemistry > Chemistry (pre 2018 reorg) - Faculties (pre 2018 reorg) > Faculty of Natural and Environmental Sciences (pre 2018 reorg) > Chemistry (pre 2018 reorg) > Magnetic Resonance (pre 2018 reorg)
Current Faculties > Faculty of Engineering and Physical Sciences > School of Chemistry > Chemistry (pre 2018 reorg) > Magnetic Resonance (pre 2018 reorg)
School of Chemistry > Chemistry (pre 2018 reorg) > Magnetic Resonance (pre 2018 reorg) - Faculties (pre 2018 reorg) > Faculty of Natural and Environmental Sciences (pre 2018 reorg) > Institute for Life Sciences (pre 2018 reorg)
Current Faculties > Faculty of Environmental and Life Sciences > Institute for Life Sciences > Institute for Life Sciences (pre 2018 reorg)
Institute for Life Sciences > Institute for Life Sciences (pre 2018 reorg)
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