Hyperpolarized orthohydrogen (
The role of ligands in rhodium‐ and iridium‐catalyzed
- Award ID(s):
- 1905341
- NSF-PAR ID:
- 10250466
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- ChemPhysChem
- Volume:
- 22
- Issue:
- 14
- ISSN:
- 1439-4235
- Page Range / eLocation ID:
- p. 1518-1526
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract o ‐H2) is a frequent product of parahydrogen‐based hyperpolarization approaches like signal amplification by reversible exchange (SABRE), where the hyperpolarizedo ‐H2signal is usually absorptive. We describe a novel manifestation of this effect wherein large antiphaseo ‐H2signals are observed, with1H enhancements up to ≈500‐fold (effective polarizationP H≈1.6 %). This anomalous effect is attained only when using an intact heterogeneous catalyst constructed using a metal–organic framework (MOF) and is qualitatively independent of substrate nature. This seemingly paradoxical observation is analogous to the “partial negative line” (PNL) effect recently explained in the context of Parahydrogen Induced Polarization (PHIP) by Ivanov and co‐workers. The two‐spin order of theo ‐H2resonance is manifested by a two‐fold higher Rabi frequency, and the lifetime of the antiphase HPo ‐H2resonance is extended by several‐fold. -
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Abstract Hyperpolarized orthohydrogen (
o ‐H2) is a frequent product of parahydrogen‐based hyperpolarization approaches like signal amplification by reversible exchange (SABRE), where the hyperpolarizedo ‐H2signal is usually absorptive. We describe a novel manifestation of this effect wherein large antiphaseo ‐H2signals are observed, with1H enhancements up to ≈500‐fold (effective polarizationP H≈1.6 %). This anomalous effect is attained only when using an intact heterogeneous catalyst constructed using a metal–organic framework (MOF) and is qualitatively independent of substrate nature. This seemingly paradoxical observation is analogous to the “partial negative line” (PNL) effect recently explained in the context of Parahydrogen Induced Polarization (PHIP) by Ivanov and co‐workers. The two‐spin order of theo ‐H2resonance is manifested by a two‐fold higher Rabi frequency, and the lifetime of the antiphase HPo ‐H2resonance is extended by several‐fold. -
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Abstract Hyperpolarization of N‐heterocycles with signal amplification by reversible exchange (SABRE) induces NMR sensitivity gains for biological molecules. Substitutions with functional groups, in particular in the
ortho ‐position of the heterocycle, however, result in low polarization using a typical Ir catalyst with a bis‐mesityl N‐heterocyclic carbene ligand for SABRE, presumably due to steric hindrance. With the addition of allylamine or acetonitrile as coligands to the precatalyst chloro(1,5‐cyclooctadiene)[4,5‐dimethyl‐1,3‐bis(2,4,6‐trimethylphenyl)imidazol‐2‐ylidene] iridium, the1H signal enhancement increased in several substrates withortho NH2substitutions. For example, for a proton in 2,4‐diaminopyrimidine, the enhancement factors increased from −7±1 to −210±20 with allylamine or to −160±10 with acetonitrile. CH3substituted molecules yielded maximum signal enhancements of −25±7 with acetonitrile addition, which is considerably less than the corresponding NH2substituted molecules, despite exhibiting similar steric size. With the more electron‐donating NH2substitution resulting in greater enhancement, it is concluded that steric hindrance is not the only dominant factor in determining the polarizability of the CH3substituted compounds. The addition of allylamine increased the signal enhancement for the 290 Da trimethoprim, a molecule with a 2,4‐diaminopyrimidine moiety serving as an antibacterial agent, to −70. -
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Abstract Hyperpolarization techniques are key to extending the capabilities of MRI for the investigation of structural, functional and metabolic processes in vivo. Recent heterogeneous catalyst development has produced high polarization in water using parahydrogen with biologically relevant contrast agents. A heterogeneous ligand‐stabilized Rh catalyst is introduced that is capable of achieving15N polarization of 12.2±2.7 % by hydrogenation of neurine into a choline derivative. This is the highest15N polarization of any parahydrogen method in water to date. Notably, this was performed using a deuterated quaternary amine with an exceptionally long spin‐lattice relaxation time (
T 1) of 21.0±0.4 min. These results open the door to the possibility of15N in vivo imaging using nontoxic similar model systems because of the biocompatibility of the production media and the stability of the heterogeneous catalyst using parahydrogen‐induced polarization (PHIP) as the hyperpolarization method. -
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Abstract Hyperpolarization techniques are key to extending the capabilities of MRI for the investigation of structural, functional and metabolic processes in vivo. Recent heterogeneous catalyst development has produced high polarization in water using parahydrogen with biologically relevant contrast agents. A heterogeneous ligand‐stabilized Rh catalyst is introduced that is capable of achieving15N polarization of 12.2±2.7 % by hydrogenation of neurine into a choline derivative. This is the highest15N polarization of any parahydrogen method in water to date. Notably, this was performed using a deuterated quaternary amine with an exceptionally long spin‐lattice relaxation time (
T 1) of 21.0±0.4 min. These results open the door to the possibility of15N in vivo imaging using nontoxic similar model systems because of the biocompatibility of the production media and the stability of the heterogeneous catalyst using parahydrogen‐induced polarization (PHIP) as the hyperpolarization method.
