"Direct" 13 C Hyperpolarization of 13 C-Acetate by MicroTesla NMR Signal Amplification by Reversible Exchange (SABRE)

• Published in: Angewandte Chemie International Edition 2020-01, Vol.59 (1), p.418-423
• Main Authors: Gemeinhardt, Max E, Limbach, Miranda N, Gebhardt, Thomas R, Eriksson, Clark W, Eriksson, Shannon L, Lindale, Jacob R, Goodson, Elysia A, Warren, Warren S, Chekmenev, Eduard Y, Goodson, Boyd M
• Format: Article
• Language: English
• ISSN: 1433-7851; 1521-3773
• DOI: 10.1002/anie.201910506

Herein, we demonstrate "direct" C hyperpolarization of C-acetate via signal amplification by reversible exchange (SABRE). The standard SABRE homogeneous catalyst [Ir-IMes; [IrCl(COD)(IMes)], (IMes=1,3-bis(2,4,6-trimethylphenyl), imidazole-2-ylidene; COD=cyclooctadiene)] was first activated in the presence of an auxiliary substrate (pyridine) in alcohol. Following addition of sodium 1- C-acetate, parahydrogen bubbling within a microtesla magnetic field (i.e. under conditions of SABRE in shield enables alignment transfer to heteronuclei, SABRE-SHEATH) resulted in positive enhancements of up to ≈100-fold in the C NMR signal compared to thermal equilibrium at 9.4 T. The present results are consistent with a mechanism of "direct" transfer of spin order from parahydrogen to C spins of acetate weakly bound to the catalyst, under conditions of fast exchange with respect to the C acetate resonance, but we find that relaxation dynamics at microtesla fields alter the optimal matching from the traditional SABRE-SHEATH picture. Further development of this approach could lead to new ways to rapidly, cheaply, and simply hyperpolarize a broad range of substrates (e.g. metabolites with carboxyl groups) for various applications, including biomedical NMR and MRI of cellular and in vivo metabolism.