Optimisation of dynamic nuclear polarisation using “off-the-shelf” Gd(iii)-based polarising agents

Cheney, Daniel J.; Cerreia Vioglio, Paolo; Brookfield, Adam; Blanc, Frédéric

Abstract

Complexes of paramagnetic metal ions, in particular Gd3+, have been demonstrated as efficient polarising agents for magic-angle spinning (MAS) dynamic nuclear polarisation (DNP). We recently demonstrated that commercially available and inexpensive Gd(NO3)3 is suitable for use as an “off-the-shelf” MAS DNP polarising agent, providing promising sensitivity enhancements to 1H, 13C, and 15N NMR signals. Here we expand upon this approach by investigating the impact of the Gd(NO3)3 concentration and by exploring a larger range of readily available Gd3+ sources. We found that a Gd(NO3)3 concentration of 20 mM in the case of 1H and 13C, and 40 mM in the case of 15N, offers optimum signal enhancements and is rationalised as a trade-off between DNP enhancements, polarisation build-up times, and electron paramagnetic resonance (EPR) spin-spin relaxation times. We determined that a range of different gadolinium compounds (GdCl3, Gd2(SO4)3, GdBr3, and Gd(OAc)3) are also suitable for use as polarising agents and yield 1H, 13C, and 15N signal enhancements of variable values. Gd(OAc)3 yields lower signal enhancements, which is proposed to be the result of greater local asymmetry at the Gd3+ centre leading to EPR line broadening, and the methyl group in the acetate ion acting as a relaxation sink and limiting the nuclear polarisation available.

Citation

Cheney, D. J., Cerreia Vioglio, P., Brookfield, A., & Blanc, F. (2024). Optimisation of dynamic nuclear polarisation using “off-the-shelf” Gd(iii)-based polarising agents. Physical Chemistry Chemical Physics, 26(37), 24395-24406. https://doi.org/10.1039/d4cp02924k

• Journal Article Type: Article
• Acceptance Date: Aug 23, 2024
• Online Publication Date: Sep 11, 2024
• Publication Date: Sep 11, 2024
• Deposit Date: Nov 14, 2024
• Publicly Available Date: Nov 18, 2024
• Journal: Physical Chemistry Chemical Physics
• Print ISSN: 1463-9076
• Electronic ISSN: 1463-9084
• Publisher: Royal Society of Chemistry
• Peer Reviewed: Peer Reviewed
• Volume: 26
• Issue: 37
• Pages: 24395-24406
• DOI: https://doi.org/10.1039/d4cp02924k
• Public URL: https://nottingham-repository.worktribe.com/output/39711994
• Publisher URL: https://pubs.rsc.org/en/content/articlelanding/2024/cp/d4cp02924k