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Testing signal enhancement mechanisms in the dissolution NMR of acetone

Testing signal enhancement mechanisms in the dissolution NMR of acetone
Testing signal enhancement mechanisms in the dissolution NMR of acetone
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.
1090-7807
158-162
Alonso-Valdesueiro, Javier
8d37c9c4-02e9-472e-be0d-965afd1678d0
Elliott, Stuart
6cc724de-f75f-4c0f-a00a-e712b4e73b12
Bengs, Christian
6d086f95-d3e8-4adc-86a5-6b255aee4dd1
Meier, Benno
ed19bfd6-3347-43f1-9e1a-06e6586ee4d1
Levitt, Malcolm H.
bcc5a80a-e5c5-4e0e-9a9a-249d036747c3
Alonso-Valdesueiro, Javier
8d37c9c4-02e9-472e-be0d-965afd1678d0
Elliott, Stuart
6cc724de-f75f-4c0f-a00a-e712b4e73b12
Bengs, Christian
6d086f95-d3e8-4adc-86a5-6b255aee4dd1
Meier, Benno
ed19bfd6-3347-43f1-9e1a-06e6586ee4d1
Levitt, Malcolm H.
bcc5a80a-e5c5-4e0e-9a9a-249d036747c3

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).

Record type: Article

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.

Text JMR_17_301R1_accepted - Accepted Manuscript
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Text JMR-17-301R1-accepted
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More information

Accepted/In Press date: 12 December 2017
e-pub ahead of print date: 13 December 2017
Published date: 1 January 2018

Identifiers

Local EPrints ID: 417031
URI: https://eprints.soton.ac.uk/id/eprint/417031
ISSN: 1090-7807
PURE UUID: 522bdf12-5031-45ac-bf5c-286ce0bef76a
ORCID for Benno Meier: ORCID iD orcid.org/0000-0003-2258-1507
ORCID for Malcolm H. Levitt: ORCID iD orcid.org/0000-0001-9878-1180

Catalogue record

Date deposited: 17 Jan 2018 17:30
Last modified: 14 Jul 2018 00:34

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Contributors

Author: Javier Alonso-Valdesueiro
Author: Stuart Elliott
Author: Christian Bengs
Author: Benno Meier ORCID iD

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