Hyperpolarizing Small Molecules using Parahydrogen and Solid‐State Spin Diffusion

Abstract

Parahydrogen‐induced polarization (PHIP) is an inexpensive way to produce hyperpolarized molecules with polarization levels of >10% in the solution‐state, but is strongly limited in generality since it requires chemical reactions/interactions with H2. Here we report a new method to widen the scope of PHIP hyperpolarization: a source molecule is produced via PHIP with high 13C polarization, and precipitated out of solution together with a target species. Spin diffusion within the solid carries the polarization onto 13C spins of the target, which can then be dissolved for solution‐state applications. We name this method PHIP‐SSD (PHIP with solid‐state spin diffusion) and demonstrate it using PHIP‐polarized [1‐13C]‐fumarate as the source molecule, to polarize different 13C‐labelled target molecules. 13C polarizations of between 0.01 and 3% were measured on [1‐13C]‐benzoic acid, depending on the molar ratio of fumarate:benzoate in the solid state. We also show that PHIP‐SSD does not require specific co‐crystallization conditions by grinding dry powders of target molecules together with solid fumarate crystals, and obtain 13C signal enhancements of between 100 and 200 on [13C,15N2]‐urea, [1‐13C]‐pyruvate, and [1‐13C]‐benzoic acid. This approach appears to be a promising new strategy for facile hyperpolarization based on PHIP.