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Abstract We report on the utility of Radiofrequency Amplification by Stimulated Emission Radiation (RASER) for background‐free proton detection of hyperpolarized biomolecules. We performed hyperpolarization of ≈0.3 M ethyl acetate via pairwise parahydrogen addition to vinyl acetate. A proton NMR signal with signal‐to‐noise ratio exceeding 100 000 was detected without radio‐frequency excitation at the clinically relevant magnetic field of 1.4 T using a standard (non‐cryogenic) inductive detector with quality factor ofQ=68. No proton background signal was observed from protonated solvent (methanol) or other added co‐solvents such as ethanol, water or bovine serum. Moreover, we demonstrate RASER detection without radio‐frequency excitation of a bolus of hyperpolarized contrast agent in biological fluid. Completely background‐free proton detection of hyperpolarized contrast agents in biological media paves the way to new applications in the areas of high‐resolution NMR spectroscopy and in vivo spectroscopy and imaging.
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This content will become publicly available on April 15, 2026
Front Cover: Proton Pachinko: Probing Excited‐State Intramolecular Proton Transfer of St. John's Wort‐Derived Fluorescent Photosensitizer Hypericin with Ultrafast Spectroscopy (Chem. Eur. J. 22/2025)
The Front Cover illustrates ultrafast spectroscopic insights into the photoexcited energy relaxation pathways of St. John's wort-derived fluorescent photosensitizer hypericin in solution. The bidirectional excited-state intramolecular proton transfer (ESIPT) gains prominence after UV excitation with enhanced photoprotection in a “proton pachinko”, whereas visible excitation results in more phototoxicity. More information can be found in the Research Article by C. Fang and co-workers (DOI: 10.1002/chem.202500639). Cover design by S. Johnson and C. Fang.
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- Award ID(s):
- 2003550
- PAR ID:
- 10587619
- Publisher / Repository:
- Wiley-VCH
- Date Published:
- Journal Name:
- Chemistry – A European Journal
- Volume:
- 31
- Issue:
- 22
- ISSN:
- 0947-6539
- Page Range / eLocation ID:
- FrontCover
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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