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Hyperpolarization has become a powerful tool to enhance the sensitivity of magnetic resonance. A universal tool to hyperpolarize small molecules in solution, however, has not yet emerged. Transferring hyperpolarized, labile protons between molecules is a promising approach towards this end. Therefore, hydrogenative parahydrogen-induced polarization (PHIP) was recently proposed as a source to polarize exchanging protons (PHIP-X). Here, we identified four key components that govern PHIP-X: adding the spin order, polarizing the labile proton, proton exchange, and polarization of the target nucleus. We investigated the last two steps experimentally and using simulations. We found optimal exchange rates and field cycling methods to polarize the target molecules. We also investigated the influence of spin relaxation of exchanging protons on the target polarization. It was found experimentally that transferring the polarization from protons directly bound to the target X-nucleus (here 13C) of lactate and methanol using a pulse sequence was more efficient than applying a corresponding sequence to the labile proton. Furthermore, varying the concentrations of the transfer and target molecules yielded a distinct maximum 13C polarization. We believe this work will further help to understand and optimize PHIP-X towards a broadly applicable hyperpolarization method. Hyperpolarization has become a powerful tool to enhance the sensitivity of NMR analyses, whereby hydrogenative parahydrogen-induced polarization with exchanging protons could broaden its applicability. Here, the authors identify four key components that govern the polarization of exchanging protons, and propose optimal exchange rates and field cycling methods to polarize target molecules. [ABSTRACT FROM AUTHOR]

Metabolism is a fundamental process that underlies human health and diseases. Nuclear magnetic resonance (NMR) techniques offer a powerful approach to identify metabolic processes and track the flux of metabolites at the molecular level in living systems. An in vitro study through in-cell NMR tracks metabolites in real time and investigates protein structures and dynamics in a state close to their most natural environment. This technique characterizes metabolites and proteins involved in metabolic pathways in prokaryotic and eukaryotic cells. In vivo magnetic resonance spectroscopy (MRS) enables whole-organism metabolic monitoring by visualizing the spatial distribution of metabolites and targeted proteins. One limitation of these NMR techniques is the sensitivity, for which a possible improved approach is through isotopic enrichment or hyperpolarization methods, including dynamic nuclear polarization (DNP) and parahydrogen-induced polarization (PHIP). DNP involves the transfer of high polarization from electronic spins of radicals to surrounding nuclear spins for signal enhancements, allowing the detection of low-abundance metabolites and real-time monitoring of metabolic activities. PHIP enables the transfer of nuclear spin polarization from parahydrogen to other nuclei for signal enhancements, particularly in proton NMR, and has been applied in studies of enzymatic reactions and cell signaling. This review provides an overview of in-cell NMR, in vivo MRS, and hyperpolarization techniques, highlighting their applications in metabolic studies and discussing challenges and future perspectives. [ABSTRACT FROM AUTHOR]

The parahydrogen-induced polarization technique allows one to significantly enhance the NMR signal. Novel results on the parahydrogen-induced polarization of C2—C3 hydrocarbons using metal complexes are presented. Gaseous propane with the nuclear spin polarization level of at least 0.8% can be produced by bubbling parahydrogen through a solution of propylene and a homogeneous hydrogenation catalyst. Hydrogenation of acetylene with parahydrogen over Wilkinson's catalyst can result in the formation of hyperpolarized ethylene. The shape of the NMR lines indicates that this reaction proceeds as a syn-addition of molecular hydrogen. The reactions of several ethylene complexes of rhodium and platinum with parahydrogen were studied. The [Rh(η2-C2H4)2Cl]2 complex reacts with parahydrogen to form hyperpolarized ethane, whereas [Pt(η2-C2H4)(PPh3)2] converts to the hyperpolarized dihydride complex cis-[Pt(H)2(PPh3)2]. [ABSTRACT FROM AUTHOR]