Abstract
Signal Amplification By Reversible Exchange in SHield Enabled Alignment Transfer (SABRE-SHEATH) is investigated to achieve rapid hyperpolarization of (13) C(1) spins of [1-(13) C]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 H(2) O. Order-unity (13) C (>50 %) polarization of catalyst-bound [1-(13) C]pyruvate is achieved in less than 30 s by restricting the chemical exchange of [1-(13) C]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 CD(3) OD. Efficient (13) C 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., ∼0.2 s(-1) versus ∼0.1 s(-1) , respectively, for a 6 mM catalyst-[1-(13) C]pyruvate sample). Finally, the catalyst-bound hyperpolarized [1-(13) C]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-(13) C]pyruvate produced via comparatively fast and simple SABRE-SHEATH-based approaches.