Low-field thermal mixing in [1-13C] pyruvic acid for brute-force hyperpolarization
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...
| Main Authors: | , , , , , |
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| Format: | Article |
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Royal Society of Chemistry
2016
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| Online Access: | https://eprints.nottingham.ac.uk/35166/ |
| _version_ | 1848795018495524864 |
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| author | Peat, David T. Hirsch, Matthew L. Gadian, David G. Horsewill, Anthony J. Owers-Bradley, John R. Kempf, James G. |
| author_facet | Peat, David T. Hirsch, Matthew L. Gadian, David G. Horsewill, Anthony J. Owers-Bradley, John R. Kempf, James G. |
| author_sort | Peat, David T. |
| building | Nottingham Research Data Repository |
| collection | Online Access |
| description | 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. |
| first_indexed | 2025-11-14T19:25:25Z |
| format | Article |
| id | nottingham-35166 |
| institution | University of Nottingham Malaysia Campus |
| institution_category | Local University |
| last_indexed | 2025-11-14T19:25:25Z |
| publishDate | 2016 |
| publisher | Royal Society of Chemistry |
| recordtype | eprints |
| repository_type | Digital Repository |
| spelling | nottingham-351662020-05-04T17:55:24Z https://eprints.nottingham.ac.uk/35166/ 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. 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. Royal Society of Chemistry 2016-06-24 Article PeerReviewed Peat, David T., Hirsch, Matthew L., Gadian, David G., Horsewill, Anthony J., Owers-Bradley, John R. and Kempf, James G. (2016) Low-field thermal mixing in [1-13C] pyruvic acid for brute-force hyperpolarization. Physical Chemistry Chemical Physics, 18 (28). pp. 19173-19182. ISSN 1463-9076 http://dx.doi.org/10.1039/C6CP02853E 10.1039/C6CP02853E 10.1039/C6CP02853E 10.1039/C6CP02853E |
| spellingShingle | 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 |
| title | Low-field thermal mixing in [1-13C] pyruvic acid for brute-force hyperpolarization |
| title_full | Low-field thermal mixing in [1-13C] pyruvic acid for brute-force hyperpolarization |
| title_fullStr | Low-field thermal mixing in [1-13C] pyruvic acid for brute-force hyperpolarization |
| title_full_unstemmed | Low-field thermal mixing in [1-13C] pyruvic acid for brute-force hyperpolarization |
| title_short | Low-field thermal mixing in [1-13C] pyruvic acid for brute-force hyperpolarization |
| title_sort | low-field thermal mixing in [1-13c] pyruvic acid for brute-force hyperpolarization |
| url | https://eprints.nottingham.ac.uk/35166/ https://eprints.nottingham.ac.uk/35166/ https://eprints.nottingham.ac.uk/35166/ |