Order-Unity 13C Nuclear Polarization of [1-13C]Pyruvate in Seconds and the Interplay of Water and SABRE Enhancement

Signal Amplification By Reversible Exchange in SHield Enabled Alignment Transfer (SABRE-SHEATH) is investigated to achieve rapid hyperpolarization of C-13(1) spins of [1-C-13]pyruvate, using parahydrogen as the source of nuclear spin order. Pyruvate exchange with an iridium polarization transfer complex can be modulated via a sensitive interplay between temperature and co-ligation of DMSO and H2O. Order-unity C-13 (>50 %) polarization of catalyst-bound [1-C-13]pyruvate is achieved in less than 30 s by restricting the chemical exchange of [1-C-13]pyruvate at lower temperatures. On the catalyst bound pyruvate, 39 % polarization is measured using a 1.4 T NMR spectrometer, and extrapolated to >50 % at the end of build-up in situ. The highest measured polarization of a 30-mM pyruvate sample, including free and bound pyruvate is 13 % when using 20 mM DMSO and 0.5 M water in CD3OD. Efficient C-13 polarization is also enabled by favorable relaxation dynamics in sub-microtesla magnetic fields, as indicated by fast polarization buildup rates compared to the T-1 spin-relaxation rates (e. g., similar to 0.2 s(-1) versus similar to 0.1 s(-1), respectively, for a 6 mM catalyst-[1-C-13]pyruvate sample). Finally, the catalyst-bound hyperpolarized [1-C-13]pyruvate can be released rapidly by cycling the temperature and/or by optimizing the amount of water, paving the way to future biomedical applications of hyperpolarized [1-C-13]pyruvate produced via comparatively fast and simple SABRE-SHEATH-based approaches.

Automated summary

Signal Amplification By Reversible Exchange in SHield Enabled Alignment Transfer (SABRE-SHEATH) was investigated for rapid hyperpolarization of C-13(1) spins of [1-C-13]pyruvate using parahydrogen. The exchange of pyruvate with an iridium polarization transfer complex can be modulated by temperature and co-ligation conditions. Efficient C-13 polarization was achieved in less than 30 seconds by restricting the chemical exchange of [1-C-13]pyruvate at lower temperatures, with the possibility of fast release for future biomedical applications.