Parahydrogen-induced polarization of13C nuclei by side-arm hydrogenation (PHIP-SAH) for [1-13C]acetate and [1-13C]pyruvate esters with application of PH-INEPT-type pulse sequences for1H to13C polarization transfer is reported, and its efficiency is compared with that of polarization transfer based on magnetic field cycling (MFC). The pulse-sequence transfer approach may have its merits in some applications because the entire hyperpolarization procedure is implemented directly in an NMR or MRI instrument, whereas MFC requires a controlled field variation at low magnetic fields. Optimization of the PH-INEPT-type transfer sequences resulted in13C polarization values of 0.66 ± 0.04% and 0.19 ± 0.02% for allyl [1-13C]pyruvate and ethyl [1-13C]acetate, respectively, which is lower than the corresponding polarization levels obtained with MFC for1H to13C polarization transfer (3.95 ± 0.05% and 0.65 ± 0.05% for allyl [1-13C]pyruvate and ethyl [1-13C]acetate, respectively). Nevertheless, a significant13C NMR signal enhancement with respect to thermal polarization allowed us to perform13C MR imaging of both biologically relevant hyperpolarized molecules which can be used to produce useful contrast agents for the in vivo imaging applications.
Magnetic resonance imaging of [1‐13C]hyperpolarized carboxylates (most notably, [1‐13C]pyruvate) allows one to visualize abnormal metabolism in tumors and other pathologies. Herein, we investigate the efficiency of1H and13C hyperpolarization of acetate and pyruvate esters with ethyl, propyl and allyl alcoholic moieties using heterogeneous hydrogenation of corresponding vinyl, allyl and propargyl precursors in isotopically unlabeled and 1‐13C‐enriched forms with parahydrogen over Rh/TiO2catalysts in methanol‐d4and in D2O. The maximum obtained1H polarization was 0.6±0.2 % (for propyl acetate in CD3OD), while the highest13C polarization was 0.10±0.03 % (for ethyl acetate in CD3OD). Hyperpolarization of acetate esters surpassed that of pyruvates, while esters with a triple carbon‐carbon bond in unsaturated alcoholic moiety were less efficient as parahydrogen‐induced polarization precursors than esters with a double bond. Among the compounds studied, the maximum1H and13C NMR signal intensities were observed for propyl acetate. Ethyl acetate yielded slightly less intense NMR signals which were dramatically greater than those of other esters under study.
more » « less- Award ID(s):
- 1904780
- NSF-PAR ID:
- 10232008
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- ChemPhysChem
- Volume:
- 22
- Issue:
- 13
- ISSN:
- 1439-4235
- Page Range / eLocation ID:
- p. 1389-1396
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Q ) of 32 without any modifications. C‐13 RASER signals were observed for several minutes on a single bolus of hyperpolarized substrate to achieve 21 mHz NMR linewidths. The feasibility of creating long‐lasting C‐13 RASER on biomolecular carriers opens a wide range of new opportunities for the rapidly expanding field of C‐13 magnetic resonance hyperpolarization. -
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