Isotopological Fingerprinting Using ¹H/D Scrambling Identifies the Stereochemistry of Hyperpolarization Catalysts Transferring Spin Polarization from Parahydrogen to Substrates Using Signal Amplification by Reversible Exchange

Reversible Parahydrogen Induced Hyperpolarization of 15N in Unmodified Amino Acids Unraveled at High Magnetic Field

“…The chemical shift range from δ −23.45 to −24.00 ppm shows the hydride couple fingerprints of complexes with nitrogen functional groups in their axial positions (vide infra). [ 32,61 ] ln the present system, the hydride resonances occurring in this region are associated with complexes containing either ammonia or N‐bonded alanine in their axial position. The chemical shift range from δ −22.35 to −22.65 ppm in Figure 4a shows fingerprints of complexes with oxygen functional groups in their axial positions (vide infra).…”

“…1 H-labelling of a deuterated SABRE mixture allows structure elucidation of the activated SABRE complexes by discriminating the different binding sites of ammonia and/or amine-containing ligands based on their isotopic scrambling (Figure 2d). [61] In this study, 1 H-labelling was performed by adding hydrated ammonia (NH 4 OH) to a mixture containing: i) IrCl(COD)IMes, ii) p-H 2 , iii) alanine, and iv) deuterated methanol-d 4 . The resulting distribution of hydrides trans to the functional binding sites reveals the isotopic scrambling of the substrates and thus the structure of different mixed-ligand complexes formed upon activation of the IrCl(COD)IMes precursor.…”

“…Visualizing the isotopic scrambling using 2D zero-quantum NMR spectroscopy (2D-ZQ-NMR), structure elucidation of the complexes present in the hyperpolarization mixture however becomes straightforward. [54,61] In the octahedral SABRE complex, ZQ coherences created from the longitudinal triplet magnetization of a hydride couple evolve under their chemical shift difference. [61] Such chemical shift difference is generated when different ligands or different isotopologues of the same ligand occupy the equatorial positions (trans to the hydrides).…”

“…[54,61] In the octahedral SABRE complex, ZQ coherences created from the longitudinal triplet magnetization of a hydride couple evolve under their chemical shift difference. [61] Such chemical shift difference is generated when different ligands or different isotopologues of the same ligand occupy the equatorial positions (trans to the hydrides). Consequently, the rate of ZQ evolution becomes dependent on the chemical and isotopological composition of the complex (Figure 4b).…”

“…First, the catalyst stereochemistry was elucidated via hydride isotopological scrambling (Figure 1c). [61] Afterward, hyperpolarization of 15 N in ligated and free (co)-ligands was achieved via high-field SABRE (Figure 1d). [42,43,62,63] This approach offered careful oversight on the present conformations of the catalysts in solution, while specific RF pulsetrains experimentally controlled the distribution of spin order to either 15 N nuclei in alanine or ammonia.…”