Abstract
Hyperpolarization methods, which increase the sensitivity of nuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI), have the potential to expand the range of applications of these powerful analytical techniques and to enable the use of smaller and cheaper devices. The signal amplification by reversible exchange (SABRE) method is of particular interest because it is relatively low-cost, straight-forward to implement, produces high-levels of renewable signal enhancement, and can be interfaced with low-cost and portable NMR detectors. In this work, we demonstrate an in situ approach to SABRE hyperpolarization that can be achieved using a simple, commercially-available Earth’s field NMR detector to provide 1H polarization levels of up to 3.3%. This corresponds to a signal enhancement over the Earth’s magnetic field by a factor of ε > 2 × 108. The key benefit of our approach is that it can be used to directly probe the polarization transfer process at the heart of the SABRE technique. In particular, we demonstrate the use of in situ hyperpolarization to observe the activation of the SABRE catalyst, the build-up of signal in the polarization transfer field (PTF), the dependence of the hyperpolarization level on the strength of the PTF, and the rate of decay of the hyperpolarization in the ultra-low-field regime.
Highlights
Magnetic resonance is a powerful analytical technique with a wide range of applications from the use of nuclear magnetic resonance (NMR) spectroscopy for reaction monitoring in solutions to the use of magnetic resonance imaging (MRI) for clinical diagnosis
The hydrides and substrate molecules bound trans to the hydrides are in rapid reversible exchange with an excess of parahydrogen and substrate in free solution
The polarization transfer between the p-H2 -derived hydrides and the NMR-active nuclei of the bound substrates is mediated by the scalar (J) coupling network of the iridium di-hydride complex
Summary
Magnetic resonance is a powerful analytical technique with a wide range of applications from the use of nuclear magnetic resonance (NMR) spectroscopy for reaction monitoring in solutions to the use of magnetic resonance imaging (MRI) for clinical diagnosis. In a standard NMR or MRI experiment, only a small fraction (typically a few ppm) of the nuclei in the sample are observed. This fraction of observed nuclei is called the polarization. Hyperpolarization is a general name for a range of techniques that aim to increase the sensitivity of magnetic resonance by temporarily increasing the fraction of observable nuclei [1,2,3,4,5,6,7]
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