Probing signal amplification by reversible exchange using an NMR flow system

Ryan E. Mewis, Kevin D. Atkinson, Michael J. Cowley, Simon B. Duckett*, Gary G. R. Green, Richard A. Green, Louise A. R. Highton, David Kilgour, Lyrelle S. Lloyd, Joost A. B. Lohman, David C. Williamson

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

Abstract

Hyperpolarization methods are used in NMR to overcome its inherent sensitivity problem. Herein, the biologically relevant target nicotinamide is polarized by the hyperpolarization technique signal amplification by reversible exchange. We illustrate how the polarization transfer field, and the concentrations of parahydrogen, the polarization-transfer-catalyst and substrate can be used to maximize signal amplification by reversible exchange effectiveness by reference to the first-order spin system of this target. The catalyst is shown to be crucial in this process, first by facilitating the transfer of hyperpolarization from parahydrogen to nicotinamide and then by depleting the resulting polarized states through further interaction. The 15 longitudinal one, two, three and four spin order terms produced are rigorously identified and quantified using an automated flow apparatus in conjunction with NMR pulse sequences based on the only parahydrogen spectroscopy protocol. The rates of build-up of these terms were shown to follow the order four similar to three>two>single spin; this order parallels their rates of relaxation. The result of these competing effects is that the less-efficiently formed single-spin order terms dominate at the point of measurement with the two-spin terms having amplitudes that are an order of magnitude lower. We also complete further measurements to demonstrate that C-13 NMR spectra can be readily collected where the long-lived quaternary C-13 signals appear with significant intensity. These are improved upon by using INEPT. In summary, we dissect the complexity of this method, highlighting its benefits to the NMR community and its applicability for high-sensitivity magnetic resonance imaging detection in the future. (c) 2014 The Authors. Magnetic Resonance in Chemistry by John Wiley & Sons, Ltd.

Original languageEnglish
Pages (from-to)358-369
Number of pages12
JournalMagnetic Resonance in Chemistry
Volume52
Issue number7
DOIs
Publication statusPublished - Jul 2014

Keywords

  • NMR
  • parahydrogen
  • SABRE
  • hyperpolarization
  • HYDROGEN INDUCED POLARIZATION
  • PARAHYDROGEN-INDUCED POLARIZATION
  • HETEROCYCLIC CARBENE COMPLEXES
  • ZERO-QUANTUM COHERENCE
  • MRI CONTRAST AGENTS
  • MAGNETIC-RESONANCE
  • SPECTROSCOPY OPSY
  • SPIN SYSTEMS
  • HYPERPOLARIZATION
  • NICOTINAMIDE

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