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  Geminal parahydrogen-induced polarization: accumulating long-lived singlet order on methylene proton pairs

Dagys, L., Ripka, B., Leutzsch, M., Moustafa, G. A. I., Eills, J., Colell, J. F. P., et al. (2020). Geminal parahydrogen-induced polarization: accumulating long-lived singlet order on methylene proton pairs. Magnetic Resonance, 1, 175-186. doi:10.5194/mr-1-175-2020.

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 Creators:
Dagys, Laurynas1, Author
Ripka, Barbara1, Author
Leutzsch, Markus2, Author              
Moustafa, Gamal A. I.1, Author
Eills, James3, Author
Colell, Johannes F. P.1, Author
Levitt, Malcolm H.1, Author
Affiliations:
1School of Chemistry, University of Southampton, Southampton SO17 1BJ, UK, ou_persistent22              
2Service Department Farès (NMR), Max-Planck-Institut für Kohlenforschung, Max Planck Society, ou_1445623              
3Helmholtz Institute Mainz, Johannes Gutenberg University, 55099 Mainz, Germany, ou_persistent22              

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 Abstract: In the majority of hydrogenative parahydrogen-induced polarization (PHIP) experiments, the hydrogen molecule undergoes pairwise cis addition to an unsaturated precursor to occupy vicinal positions on the product molecule. However, some ruthenium-based hydrogenation catalysts induce geminal hydrogenation, leading to a reaction product in which the two hydrogen atoms are transferred to the same carbon centre, forming a methylene (CH2) group. The singlet order of parahydrogen is substantially retained over the geminal hydrogenation reaction, giving rise to a singlet-hyperpolarized CH2 group. Although the T1 relaxation times of the methylene protons are often short, the singlet order has a long lifetime, provided that singlet–triplet mixing is suppressed, either by chemical equivalence of the protons or by applying a resonant radiofrequency field. The long lifetime of the singlet order enables the accumulation of hyperpolarization during the slow hydrogenation reaction. We introduce a kinetic model for the behaviour of the observed hyperpolarized signals, including both the chemical kinetics and the spin dynamics of the reacting molecules. Our work demonstrates the feasibility of producing singlet-hyperpolarized methylene moieties by parahydrogen-induced polarization. This potentially extends the range of molecular agents which may be generated in a hyperpolarized state by chemical reactions of parahydrogen.

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Language(s): eng - English
 Dates: 2020-06-192020-07-272020-08-07
 Publication Status: Published online
 Pages: 12
 Publishing info: -
 Table of Contents: -
 Rev. Type: Peer
 Identifiers: DOI: 10.5194/mr-1-175-2020
 Degree: -

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Title: Magnetic Resonance
  Abbreviation : Magn. Reson.
Source Genre: Journal
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Publ. Info: Göttingen : Copernicus Publications
Pages: - Volume / Issue: 1 Sequence Number: - Start / End Page: 175 - 186 Identifier: Other: 2699-0016
CoNE: https://pure.mpg.de/cone/journals/resource/2699-0016