Stanbury, Emma, Richardson, Peter Michael orcid.org/0000-0002-6631-2459 and Duckett, Simon orcid.org/0000-0002-9788-6615 (2019) Understanding substrate substituent effects to improve catalytic efficiency in the SABRE hyperpolarisation process. Catalysis Science and Technology. CY-ART-02-2019-000396.R1. pp. 3914-3922. ISSN 2044-4761
Abstract
The use of parahydrogen based hyperpolarisation in NMR is becoming more widespread due to the rapidly expanding range of target molecules and low-cost of parahydrogen production. Hyperpolarisation via SABRE catalysis employs a metal complex to transfer polarisation from parahydrogen into a substrate whilst they are bound. In this paper we present a quantitative study of substrate–iridium ligation effects by reference to the substrates 4-chloropyridine (A), 4-pyridinecarboxaldehyde methyl hemiacetal (B), 4-methylpyridine (C) and 4-methoxypyridine (D), and evaluate the role they play in the SABRE catalysis. Substrates whose substituents enable stronger associations yield slower substrate dissociation rates (kd). A series of variable temperature studies link these exchange rates to optimal SABRE performance and reveal the critical impact of NMR relaxation times (T1). Longer catalyst residence times are shown to result in shorter substrate T1 values in solution as binding to iridium promotes relaxation thereby not only reducing SABRE efficiency but decreasing the overall level of achieved hyperpolarisation. Based on these data, a route to achieve more optimal SABRE performance is defined.
Metadata
Authors/Creators: |
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Copyright, Publisher and Additional Information: | © The Royal Society of Chemistry 2019 | ||||
Dates: |
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Institution: | The University of York | ||||
Academic Units: | The University of York > Faculty of Sciences (York) > Chemistry (York) | ||||
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Depositing User: | Pure (York) | ||||
Date Deposited: | 04 Jun 2019 11:20 | ||||
Last Modified: | 06 Dec 2023 13:08 | ||||
Published Version: | https://doi.org/10.1039/C9CY00396G | ||||
Status: | Published | ||||
Refereed: | Yes | ||||
Identification Number: | https://doi.org/10.1039/C9CY00396G |