PMC

Setup for the SABRE-SHEATH experiment. (A) shows the sample in an NMR tube held inside the μ-metal shield, where para-H₂ is bubbled through the solution. After hyperpolarization the sample is transferred into NMR spectrometer for detection. (B) para-H₂ and ¹⁵N-pyridine (¹⁵N-Py) in exchange with [IrH₂(¹⁵N-Py)₃(IMes)]⁺. On the catalyst para-H₂ transfers its hyperpolarization to ¹⁵N-Py through the J-coupling network. The equatorial ¹⁵N-Py (blue) is in fast exchange and responsible for the hyperpolarization of the free ¹⁵N-Py (green).

(A) ¹⁵N SABRE-SHEATH of a 48 mM sample of ¹⁵N-nicotinamide (¹⁵N enrichment of ∼66%) in methanol-d₄ using 2 mM of activated IMes catalyst. An enhancement ε of ∼20,000-fold (corresponding to %P_15N ∼ 7%) was achieved in comparison to (B) a spectrum of thermally polarized sample of 12.5 M ¹⁵N-Py (note the vertical axis is scaled by 50 fold). The spectrum of HP ¹⁵N-nicotinamide shows the expected three resonances of free and bound species. See for details.

Single-shot ¹⁵N NMR SABRE spectra. (A) SABRE-SHEATH experiment with Ir catalyst and ¹⁵N-Py concentrations of 0.24 and 4 mM respectively result in 30,000-fold signal enhancement corresponding to P ∼10% with ¹⁵N T₁ ∼ 42 s at 9.4 T. (B) Shows that increase of Ir catalyst and ¹⁵N-Py concentrations results in further increased NMR signals, but relative enhancement and P levels decrease. An in-phase triplet split by 11 Hz is observed in both A and B. SABRE-SHEATH experiments (A, B) also reveal both bound ¹⁵N-Py ligand site of the activated Ir catalyst. (C) NMR spectrum of neat 12.5 M ¹⁵N-Py used for calibration. (D) ¹⁵N-SABRE at conditions optimized for ¹H hyperpolarization (6 ± 4 mT) results in antiphase triplets and lower enhancements.