Nuclear
spin hyperpolarization provides a promising route to overcome
the challenges imposed by the limited sensitivity of nuclear magnetic
resonance. Here we demonstrate that dissolution of spin-polarized
pentacene-doped naphthalene crystals enables transfer of polarization
to target molecules via intermolecular cross-relaxation at room temperature
and moderate magnetic fields (1.45 T). This makes it possible to exploit
the high spin polarization of optically polarized crystals, while
mitigating the challenges of its transfer to external nuclei. With
this method, we inject the highly polarized mixture into a benchtop
NMR spectrometer and observe the polarization dynamics for target 1H nuclei. Although the spectra are radiation damped due to
the high naphthalene magnetization, we describe a procedure to process
the data to obtain more conventional NMR spectra and extract the target
nuclei polarization. With the entire process occurring on a time scale
of 1 min, we observe NMR signals enhanced by factors between −200
and −1730 at 1.45 T for a range of small molecules.
Magnetic resonance imaging of 13 C-labeled metabolites enhanced by parahydrogen-induced polarization (PHIP) enables real-time monitoring of processes within the body. We introduce a robust, easily implementable technique for transferring parahydrogen-derived singlet order into 13 C magnetization using adiabatic radio frequency sweeps at microtesla fields. We experimentally demonstrate the applicability of this technique to several molecules, including some molecules relevant for metabolic imaging, where we show significant improvements in the achievable polarization, in some cases reaching above 60% nuclear spin polarization. Furthermore, we introduce a site-selective deuteration scheme, where deuterium is included in the coupling network of a pyruvate ester to enhance the efficiency of the polarization transfer. These improvements are enabled by the fact that the transfer protocol avoids relaxation induced by strongly coupled quadrupolar nuclei.
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