Non‐Pairwise Interactions in Parahydrogen Experiments: Nuclear Exchange of Single Protons Enables Bulk Water Hyperpolarization

Hyperpolarization with parahydrogen (p‐H2) is a fast developing field in NMR, which enables overcoming the inherent low sensitivity of this important technique. The hyperpolarization of solvents, particularly of water, offers a wide range of applications for structural investigations of macromolecul...

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Bibliographic Details
Published in:Chemphyschem 2018-10, Vol.19 (20), p.2614-2620
Main Authors: Emondts, Meike, Schikowski, Daniel, Klankermayer, Jürgen, Schleker, P. Philipp M.
Format: Article
Language:English
Subjects:
Atomic properties
Boundary conditions
Exchanging
Hydrogen atoms
Hydrogen storage
Hyperpolarization
Macromolecules
Medical imaging
NEPTUN
NMR
Nuclear magnetic resonance
Nuclei (nuclear physics)
Organic chemistry
parahydrogen
Polarization
Solvents
water
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Summary:Hyperpolarization with parahydrogen (p‐H2) is a fast developing field in NMR, which enables overcoming the inherent low sensitivity of this important technique. The hyperpolarization of solvents, particularly of water, offers a wide range of applications for structural investigations of macromolecules and biomedical imaging. Until lately, only organic solvents could be polarized by means of parahydrogen via coherent redistribution of polarization (SABRE mechanism). In this study, we investigate in detail the mechanism of the recently reported bulk water hyperpolarization with a combination of theoretical and experimental methods, finally showing a chemical exchange pathway of single protons as basis for the enhancement. The prerequisites for preserving hyperpolarization upon separation of the two hydrogen atoms of p−H2 are demonstrated by theoretical examinations of the boundary conditions for the hyperpolarization experiments in accordance with the OneH−PHIP theory. These findings yielded the proposal of the novel NEPTUN mechanism (Nuclear Exchange Polarization by Transposing Unattached Nuclei) as the non‐hydrogenative equivalent to the established OneH−PHIP and thus the missing link in parahydrogen hyperpolarization theory. The mechanism of the recently reported bulk water hyperpolarization is investigated. The authors find that polarization is transferred by the exchange of single protons between p‐H2 and water and call their new observation NEPTUN (Nuclear Exchange Polarization by Transposing Unattached Nuclei).
ISSN:1439-4235
1439-7641
DOI:10.1002/cphc.201800521