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Geminal parahydrogen-induced polarization: accumulating long-lived singlet order on Methylene Proton pairs

Geminal parahydrogen-induced polarization: accumulating long-lived singlet order on Methylene Proton pairs
Geminal parahydrogen-induced polarization: accumulating long-lived singlet order on Methylene Proton pairs
In the majority of hydrogenative PHIP (Parahydrogen Induced Polarization) 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 twohydrogen atoms are transferred to the same carbon center, 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, providing 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 maybe generated in a hyperpolarized state by chemical reactions of parahydrogen.
1-21
Dagys, Laurynas
0de61597-b152-4bee-a934-123a9d2de883
Ripka, Barbara H
4eaf858c-09a2-4072-97d0-912585c371cd
Leutzsch, Markus
facee439-cca3-43f4-8996-c35d3454dea8
Moustafa, Gamal
1a452cdc-4856-4243-9864-b391fb115f07
Eills, James
23130b21-68fa-4c8b-9399-e55f2e71ef36
Colell, Johannes FP
22725cf4-eec8-455f-a5ad-0d120b961af4
Levitt, Malcolm H.
bcc5a80a-e5c5-4e0e-9a9a-249d036747c3
Dagys, Laurynas
0de61597-b152-4bee-a934-123a9d2de883
Ripka, Barbara H
4eaf858c-09a2-4072-97d0-912585c371cd
Leutzsch, Markus
facee439-cca3-43f4-8996-c35d3454dea8
Moustafa, Gamal
1a452cdc-4856-4243-9864-b391fb115f07
Eills, James
23130b21-68fa-4c8b-9399-e55f2e71ef36
Colell, Johannes FP
22725cf4-eec8-455f-a5ad-0d120b961af4
Levitt, Malcolm H.
bcc5a80a-e5c5-4e0e-9a9a-249d036747c3

Dagys, Laurynas, Ripka, Barbara H, Leutzsch, Markus, Moustafa, Gamal, Eills, James, Colell, Johannes FP and Levitt, Malcolm H. (2020) Geminal parahydrogen-induced polarization: accumulating long-lived singlet order on Methylene Proton pairs. Magnetic Resonance, 1-21. (doi:10.5194/mr-2020-16). (In Press)

Record type: Article

Abstract

In the majority of hydrogenative PHIP (Parahydrogen Induced Polarization) 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 twohydrogen atoms are transferred to the same carbon center, 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, providing 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 maybe generated in a hyperpolarized state by chemical reactions of parahydrogen.

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Accepted/In Press date: 27 July 2020

Identifiers

Local EPrints ID: 442949
URI: http://eprints.soton.ac.uk/id/eprint/442949
PURE UUID: 8454d83a-2cdf-4aad-a2e7-24940562ecc9
ORCID for Malcolm H. Levitt: ORCID iD orcid.org/0000-0001-9878-1180

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Date deposited: 04 Aug 2020 16:30
Last modified: 07 Oct 2020 01:45

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