<i>J</i> Coupling Constants of <1 Hz Enable <sup>13</sup>C Hyperpolarization of Pyruvate via Reversible Exchange of Parahydrogen
Charbel D. Assaf, Xin Gui, Alexander A. Auer, Simon B. Duckett, Jan‐Bernd Hövener, Andrey N. Pravdivtsev
Abstract
High Resolution Image Download MS PowerPoint Slide Observing pyruvate metabolism in vivo has become a focal point of molecular magnetic resonance imaging. Signal amplification by reversible exchange (SABRE) has recently emerged as a versatile hyperpolarization technique. Tuning of the spin order transfer (SOT) in SABRE is challenging as the small 1 H– 13 C J couplings, in the 13 C-pyruvate case, result in SOT being not readily discernible. We demonstrate an experimental method using frequency-selective excitation of parahydrogen-derived polarization SOT sequence (SEPP-SPINEPT); its application led to up to 5700-fold 13 C signal gain. In this way, we estimated the lifetime of two Ir–pyruvate SABRE complexes alongside the individual probing of eight small 1 H– 13 C J couplings that connect the hydride protons in these complexes to 1- and 2- 13 C pyruvate spins, affording values between 0 and 2.69 Hz. Using electronic structure calculations, we define the low-energy structure of the corresponding complexes. Hence, this study demonstrates a novel approach to analyzing the spin topology of short-lived organometallic complexes.