Skip to main content

Research Repository

Advanced Search

Low-field thermal mixing in [1-13C] pyruvic acid for brute-force hyperpolarization

Peat, David T.; Hirsch, Matthew L.; Gadian, David G.; Horsewill, Anthony J.; Owers-Bradley, John R.; Kempf, James G.

Low-field thermal mixing in [1-13C] pyruvic acid for brute-force hyperpolarization Thumbnail


Authors

David T. Peat

Matthew L. Hirsch

David G. Gadian

Anthony J. Horsewill

John R. Owers-Bradley

James G. Kempf



Abstract

We detail the process of low-field thermal mixing (LFTM) between 1H and 13C nuclei in neat [1-13C] pyruvic acid at cryogenic temperatures (4–15 K). Using fast-field-cycling NMR, 1H nuclei in the molecule were polarized at modest high field (2 T) and then equilibrated with 13C nuclei by fast cycling (∼300–400 ms) to a low field (0–300 G) that activates thermal mixing. The 13C NMR spectrum was recorded after fast cycling back to 2 T. The 13C signal derives from 1H polarization via LFTM, in which the polarized (‘cold’) proton bath contacts the unpolarised (‘hot’) 13C bath at a field so low that Zeeman and dipolar interactions are similar-sized and fluctuations in the latter drive 1H–13C equilibration. By varying mixing time (tmix) and field (Bmix), we determined field-dependent rates of polarization transfer (1/τ) and decay (1/T1m) during mixing. This defines conditions for effective mixing, as utilized in ‘brute-force’ hyperpolarization of low-γ nuclei like 13C using Boltzmann polarization from nearby protons. For neat pyruvic acid, near-optimum mixing occurs for tmix ∼ 100–300 ms and Bmix ∼ 30–60 G. Three forms of frozen neat pyruvic acid were tested: two glassy samples, (one well-deoxygenated, the other O2-exposed) and one sample pre-treated by annealing (also well-deoxygenated). Both annealing and the presence of O2 are known to dramatically alter high-field longitudinal relaxation (T1) of 1H and 13C (up to 102–103-fold effects). Here, we found smaller, but still critical factors of ∼(2–5)× on both τ and T1m. Annealed, well-deoxygenated samples exhibit the longest time constants, e.g., τ ∼ 30–70 ms and T1m ∼ 1–20 s, each growing vs. Bmix. Mixing ‘turns off’ for Bmix > ∼100 G. That T1m ≫ τ is consistent with earlier success with polarization transfer from 1H to 13C by LFTM.

Citation

Peat, D. T., Hirsch, M. L., Gadian, D. G., Horsewill, A. J., Owers-Bradley, J. R., & Kempf, J. G. (2016). Low-field thermal mixing in [1-13C] pyruvic acid for brute-force hyperpolarization. Physical Chemistry Chemical Physics, 18(28), 19173-19182. https://doi.org/10.1039/C6CP02853E

Journal Article Type Article
Acceptance Date Jun 23, 2016
Online Publication Date Jun 24, 2016
Publication Date Jun 24, 2016
Deposit Date Jul 19, 2016
Publicly Available Date Mar 29, 2024
Journal Physical Chemistry Chemical Physics
Print ISSN 1463-9076
Electronic ISSN 1463-9084
Publisher Royal Society of Chemistry
Peer Reviewed Peer Reviewed
Volume 18
Issue 28
Pages 19173-19182
DOI https://doi.org/10.1039/C6CP02853E
Public URL https://nottingham-repository.worktribe.com/output/793704
Publisher URL http://dx.doi.org/10.1039/C6CP02853E

Files





You might also like



Downloadable Citations