A role for low concentration reaction intermediates in the signal amplification by reversible exchange process revealed by theory and experiment

Fekete, M.; Roy, Soumya Singha; Duckett, Simon B.

doi:10.1039/c9cp06386b

Cited by 9 publications

(17 citation statements)

References 38 publications

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“…The temperature affects the polarization values by changing the exchange rate for binding to the SABRE catalyst . The temperature dependence of SABRE polarization for S1, S3 and S4 in the presence of coligands was measured (Figure ).…”

Section: Resultsmentioning

confidence: 99%

“…At the lower temperature of 310 K, the dissociation rate was 1.0 s −1 . This value can be compared to a value of 1.04 s −1 reported for pyridine or 2.37 s −1 for metroindazole in complexes of the type [Ir(IMes)(substrate) 2 (coligand)]Cl at 298 K, where maximum enhancement for 1 H was obtained …”

Section: Resultsmentioning

confidence: 99%

“…The temperature affects the polarization values by changing the exchange rate for binding to the SABRE catalyst. [18,30] The temperature dependence of SABRE polarization for S1, S3 and S4 in the presence of coligands was measured (Figure 3). The substrates S1 and S3 with the NH 2 substitutions show a maximum signal with the coligands at a temperature near 320 K. In contrast, the substrate S4 with CH substitution gives the highest polarization at the temperature of 288 K. Likewise, the substrate S2, as well as the model compound pyridine, without substitutions in the ortho-positions, require lower temperature compared to the NH 2 substituted molecules to show the maximum enhancements (Supporting Figure S7).…”

Section: Temperature Dependence Of Sabre Hyperpolarizationmentioning

confidence: 99%

“…[21,29] Acetonitrile has been used as an additive for the detection of low concentration species. [30] In this manuscript, we describe the hyperpolarization of biological compounds containing NH 2 and CH 3 ortho-substituted pyrimidines and pyridines with an Ir-IMes SABRE catalyst. Molecules with ortho-substitutions have previously been reported to yield no SABRE signal, which may be attributed to steric hindrance.…”

Section: Introductionmentioning

confidence: 99%

“…Deuterated ligands have been proposed as a means to direct the polarization to fewer protonated substrate molecules, thereby increasing the net spin polarization . Acetonitrile has been used as an additive for the detection of low concentration species …”

Section: Introductionmentioning

confidence: 99%

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Nuclear Spin Hyperpolarization of NH₂‐ and CH₃‐Substituted Pyridine and Pyrimidine Moieties by SABRE

2020

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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 bismesityl 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, the 1 H signal enhancement increased in several substrates with ortho NH 2 substitutions. For example, for a proton in 2,4-diaminopyrimidine, the enhancement factors increased from À 7 � 1 to À 210 � 20 with allylamine or to À 160 � 10 with acetonitrile. CH 3 substituted molecules yielded maximum signal enhancements of À 25 � 7 with acetonitrile addition, which is considerably less than the corresponding NH 2 substituted molecules, despite exhibiting similar steric size. With the more electron-donating NH 2 substitution resulting in greater enhancement, it is concluded that steric hindrance is not the only dominant factor in determining the polarizability of the CH 3 substituted 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 À 70.

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Section: Temperature Dependence Of Sabre Hyperpolarizationmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Nuclear Spin Hyperpolarization of NH₂‐ and CH₃‐Substituted Pyridine and Pyrimidine Moieties by SABRE

2020

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Long‐Term Generation of Longitudinal Spin Order Controlled by Ammonia Ligation Enables Rapid SABRE Hyperpolarized 2D NMR

et al. 2021

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Symmetry breaking of parahydrogen using iridium catalysts converts singlet spin order into observable hyperpolarization. In this contribution, iridium catalysts are designed to exhibit asymmetry in their hydrides, regulated by in situ generation of deuterated ammonia governed by ammonium buffers. The concentrations of ammonia (N) and pyridine (P) provide a handle to generate a variety of stereo‐chemically asymmetric N‐heterocyclic carbene iridium complexes, ligating either [3xP], [2xP;N], [P;2xN] or [3xN] in an octahedral SABRE type configuration. The non‐equivalent hydride positions, in correspondence with the ammonium buffer solutions, enables to extend singlet‐triplet or S⟩→|T0⟩ mixing at high magnetic field and experimentally induce prolonged generation of non‐equilibrium longitudinal two‐spin order. This long‐lasting magnetization can be exploited in hyperpolarized 2D‐OPSY‐COSY experiments providing direct structural information on the catalyst using a single contact with parahydrogen. Separately, field cycling revealed hyperpolarization properties in low‐field conditions. Controlling catalyst stereochemistry by introducing small and deuterated ligands, such as deuterated ammonia, simplifies the spin‐system. This is shown to unify experimental and theoretically derived field‐sweep experiments for four‐spin systems.

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Density Functional Theory Study of Reaction Equilibria in Signal Amplification by Reversible Exchange

et al. 2021

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An in-depth theoretical analysis of key chemical equilibria in Signal Amplification by Reversible Exchange (SABRE) is provided, employing density functional theory calculations to characterize the likely reaction network. For all reactions in the network, the potential energy surface is probed to identify minimum energy pathways. Energy barriers and transition states are calculated, and harmonic transition state theory is applied to calculate exchange rates that approximate experimental values. The reaction network energy surface can be modulated by chemical potentials that account for the depend-ence on concentration, temperature, and partial pressure of molecular constituents (hydrogen, methanol, pyridine) supplied to the experiment under equilibrium conditions. We show that, under typical experimental conditions, the Gibbs free energies of the two key states involved in pyridine-hydrogen exchange at the common Ir-IMes catalyst system in methanol are essentially the same, i. e., nearly optimal for SABRE. We also show that a methanol-containing intermediate is plausible as a transient species in the process.

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A role for low concentration reaction intermediates in the signal amplification by reversible exchange process revealed by theory and experiment

Abstract: A route to monitor the involvement of less abundant species during the catalytic transfer of hyperpolarisation from parahydrogen into a substrate is detailed.

Cited by 9 publications

References 38 publications

Nuclear Spin Hyperpolarization of NH₂‐ and CH₃‐Substituted Pyridine and Pyrimidine Moieties by SABRE

Nuclear Spin Hyperpolarization of NH₂‐ and CH₃‐Substituted Pyridine and Pyrimidine Moieties by SABRE

Long‐Term Generation of Longitudinal Spin Order Controlled by Ammonia Ligation Enables Rapid SABRE Hyperpolarized 2D NMR

Density Functional Theory Study of Reaction Equilibria in Signal Amplification by Reversible Exchange

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A role for low concentration reaction intermediates in the signal amplification by reversible exchange process revealed by theory and experiment

Abstract: A route to monitor the involvement of less abundant species during the catalytic transfer of hyperpolarisation from parahydrogen into a substrate is detailed.

Cited by 9 publications

References 38 publications

Nuclear Spin Hyperpolarization of NH2‐ and CH3‐Substituted Pyridine and Pyrimidine Moieties by SABRE

Nuclear Spin Hyperpolarization of NH2‐ and CH3‐Substituted Pyridine and Pyrimidine Moieties by SABRE

Long‐Term Generation of Longitudinal Spin Order Controlled by Ammonia Ligation Enables Rapid SABRE Hyperpolarized 2D NMR

Density Functional Theory Study of Reaction Equilibria in Signal Amplification by Reversible Exchange

Contact Info

Product

Resources

About

Nuclear Spin Hyperpolarization of NH₂‐ and CH₃‐Substituted Pyridine and Pyrimidine Moieties by SABRE

Nuclear Spin Hyperpolarization of NH₂‐ and CH₃‐Substituted Pyridine and Pyrimidine Moieties by SABRE