Abstract: Signal Amplification By Reversible Exchange (SABRE) utilizes non-equilibrium spin order of parahydrogen as a source of strong NMR signal enhancement aimed to increase NMR sensitivity. In SABRE, parahydrogen and to-be-polarized substrate form a transient polarization transfer complex. Performed inside high magnetic field of an NMR-spectrometer, SABRE allows to hyperpolarize nuclear spins without additional polarizers, however, requires thorough pulse sequence design. The high-field polarization transfer strategy strongly depends on the type of the spin system formed by the parahydrogen-nascent protons in the SABRE-complex: chemically equivalent or non-equivalent. SABRE hyperpolarization in chemically equivalent spin systems has drawn much attention, while targeting on a limited pool of substrates. Efficient hyperpolarization in chemically non-equivalent complexes remained a missing piece of the puzzle for completeness of high-field SABRE and possibility to polarize an arbitrary SABRE substrate. Thus, this work reports multinuclear 1H-15N pulse sequences for efficient 15N hyperpolarization in chemically non-equivalent SABRE-complexes. The first pulse sequence relies on simultaneous 1H and 15N radiofrequency (RF) excitation of complex-bound nuclei with weak continuous wave (CW) magnetic fields. The proposed pulse-sequence allowed us not only to hyperpolarize 15N nuclei in a mixture of antimicrobial drugs containing a 5-nitroimidazol moiety at their natural 15N isotopic abundance (0.76 % of 15N polarization), but also to precisely assign from which SABRE-complexes this polarization emanates. The second approach is based on INEPT pulse sequence and leads to 15N hyperpolarization (0.4-0.7 % of 15N polarization) in a robust manner with the minimal experimental optimization. Figure 1. Schematic representation of CW-irradiation used for the high-field SABRE polarization transfer. Weak CW fields selectively excite HA hydride proton (on-resonant field) and 15N nuclei (with slightly off-resonant field) in the SABRE-complex. Acknowledgements This work was supported by the Russian Science Foundation (№ 23-73-10103).

Cite: Markelov D.A. , Kozinenko V.P. , Kiryutin A.S. , Yurkovskaya A.V.
Efficient in-magnet 15N hyperpolarization of antimicrobial drugs induced by reversible exchange of parahydrogen with Ir-based catalyst
The international conference «Chemistry of Organoelement Compounds and Polymers – 2024» 18-22 Nov 2024