Parahydrogen Based Hyperpolarization for Multinuclear NMR Spectroscopy in Ultra-Low Magnetic Fields

We used a superconducting quantum interference device (SQUID) as broadband detector and signal amplification by reversible exchange (SABRE) to measure hyperpolarized NMR spectra of 1H and 19F simultaneously, highlighting the complexity of the underlying coupling mechanisms.
.Ultra-low field 19F and 1H MR spectra of hyperpolarized
3-fluoropyridine (upper row), ethyl-5-fluoronicotinic acid (middle row), and
3,5-bis(trifluoromethyl)pyridine (lower row). Substances and catalysts were dissolved in methanol and measured at
144 μT. Signals around 5770 Hz can be assigned to the 19F nuclei showing the 1H- 19F coupling. Signals around 6134 Hz can be assigned to the 1H signal. The blue, red and violet lines represent the measured spectra whereas the green lines represent simulated spectra based on high-field determined coupling constants

Ultra-low field (ULF) nuclear magnetic resonance (NMR) is a promising spectroscopy method allowing for, e.g., the simultaneous detection of multiple nuclei. To overcome the low signal-to-noise ratio that usually hampers a wider application, we used an alternative approach to ULF NMR, which makes use of the hyperpolarizing technique signal amplification by reversible exchange (SABRE). In contrast to standard parahydrogen hyperpolarization, SABRE can continuously hyperpolarize 1H as well as other MR-active nuclei. For simultaneous measurements of 1H and 19F under SABRE conditions a superconducting quantum interference device (SQUID)-based NMR detection unit was adapted. We successfully hyperpolarized fluorinated pyridine derivatives with an up to 2000-fold signal enhancement in 19F. SABRE combined with simultaneous SQUID-based broadband multinuclear detection enable the quantitative analysis of multinuclear processes.

1.
Buckenmaier, K., M. Rudolph, C. Back, T. Misztal, U. Bommerich, P. Fehling, D. Koelle, R. Kleiner, H. A. Mayer, K. Scheffler, J. Bernarding, and M. Plaumann:
Squid-based detection of ultra-low-field multinuclear NMR of substances hyperpolarized using signal amplification by reversible exchange.
Scientific Reports 2017: 7:13431.
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