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Tuning of pH enables carbon-13 hyperpolarization of oxalates by SABRE

Tuning of pH enables carbon-13 hyperpolarization of oxalates by SABRE
Tuning of pH enables carbon-13 hyperpolarization of oxalates by SABRE
Nuclear spin hyperpolarization transforms typically weak NMR responses into strong signals paving the way for low-gamma nuclei detection within practical time-frames. SABRE (Signal Amplification by Reversible Exchange) is a particularly popular hyperpolarization technique due to its simplicity but the pool of molecules it can polarize is limited. The recent advancement in the form of co-ligands has made SABRE applicable towards molecules with O-donor sites e.g. pyruvate, a key step towards its potential clinical application. Here we explore the SABRE hyperpolarization of another compound with an alpha-keto motif, namely oxalate. We show that hyperpolarization of oxalate may be achieved by adjusting the pH in the presence of sulfoxide co-ligands. The SABRE effect for oxalate in methanol solutions is most effective for the mono-protonated form, which is dominant in the solution around pH ∼2.8. The polarization levels become markedly lower at both higher and lower pH. Employing 50% enriched pH2 we achieve up to 0.33% net 13C polarization in mono-protonated oxalate. In an alternative procedure we show that the hyperpolarization effect in oxalates can also be realised by synthesizing an esterified version of it, without any substantive pH implications. Further, the procedures to create hyperpolarized singlet orders in such substrates are also investigated.
1359-7345
2291-2294
Singha roy, Soumya
fa8b7e87-8477-417a-932e-61e36581c720
Iali, Wissam
c5a0dd1d-92bd-4cc2-8ae6-dad6706acf20
Moustafa, Gamal
1a452cdc-4856-4243-9864-b391fb115f07
Levitt, Malcolm H.
bcc5a80a-e5c5-4e0e-9a9a-249d036747c3
Singha roy, Soumya
fa8b7e87-8477-417a-932e-61e36581c720
Iali, Wissam
c5a0dd1d-92bd-4cc2-8ae6-dad6706acf20
Moustafa, Gamal
1a452cdc-4856-4243-9864-b391fb115f07
Levitt, Malcolm H.
bcc5a80a-e5c5-4e0e-9a9a-249d036747c3

Singha roy, Soumya, Iali, Wissam, Moustafa, Gamal and Levitt, Malcolm H. (2022) Tuning of pH enables carbon-13 hyperpolarization of oxalates by SABRE. Chemical Communications, 58 (14), 2291-2294. (doi:10.1039/D1CC06973J).

Record type: Article

Abstract

Nuclear spin hyperpolarization transforms typically weak NMR responses into strong signals paving the way for low-gamma nuclei detection within practical time-frames. SABRE (Signal Amplification by Reversible Exchange) is a particularly popular hyperpolarization technique due to its simplicity but the pool of molecules it can polarize is limited. The recent advancement in the form of co-ligands has made SABRE applicable towards molecules with O-donor sites e.g. pyruvate, a key step towards its potential clinical application. Here we explore the SABRE hyperpolarization of another compound with an alpha-keto motif, namely oxalate. We show that hyperpolarization of oxalate may be achieved by adjusting the pH in the presence of sulfoxide co-ligands. The SABRE effect for oxalate in methanol solutions is most effective for the mono-protonated form, which is dominant in the solution around pH ∼2.8. The polarization levels become markedly lower at both higher and lower pH. Employing 50% enriched pH2 we achieve up to 0.33% net 13C polarization in mono-protonated oxalate. In an alternative procedure we show that the hyperpolarization effect in oxalates can also be realised by synthesizing an esterified version of it, without any substantive pH implications. Further, the procedures to create hyperpolarized singlet orders in such substrates are also investigated.

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Accepted/In Press date: 19 January 2022
e-pub ahead of print date: 20 January 2022
Published date: 20 January 2022
Additional Information: Funding Information: This work was supported by the EPSRC-UK (EP/P009980/1), the ERC (786707-FunMagResBeacons), and the University of Southampton. WI acknowledges support from the KFUMP-funded Grant-SR191019. We thank Weidong Gong for instrumental support. Publisher Copyright: © 2022 The Royal Society of Chemistry.

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Local EPrints ID: 454409
URI: http://eprints.soton.ac.uk/id/eprint/454409
ISSN: 1359-7345
PURE UUID: aca94f9e-0f9f-4f3a-b75c-ee1329ff9be6
ORCID for Gamal Moustafa: ORCID iD orcid.org/0000-0002-9940-0033
ORCID for Malcolm H. Levitt: ORCID iD orcid.org/0000-0001-9878-1180

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Date deposited: 09 Feb 2022 17:31
Last modified: 06 Jun 2024 04:11

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Contributors

Author: Soumya Singha roy
Author: Wissam Iali
Author: Gamal Moustafa ORCID iD

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