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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]

The beta-detected nuclear magnetic resonance ( β-NMR) in liquid HO has been observed for the first time using a short-lived β-ray emitter N ( I = 1, T =11 ms). A nuclear spin polarized N beam with an energy of about 20 MeV/nucleon was implanted into an enclosed water sample. About 50 % of implanted N ions maintained nuclear polarization and exhibited a β-NMR spectrum. The chemical shift of N in HO relative to N in Pt was deduced to be −(3.6±0.5) × 10 ppm. [ABSTRACT FROM AUTHOR]

The ground-state energy of polarized and unpolarized liquid He is calculated using the variational theory. A variational wave function is constrained to be normalized appropriately by including the three-body terms in the cluster expansion of the two-body radial distribution function. The higher-order terms have been found to be important to obtain an equation of state which is in agreement with experimental data. The saturation density of unpolarized liquid He was found to be 0.267σ, which decreases by enhancing the polarization. For all relevant densities, the ground-state energy of the spin-polarized system is higher than that in the unpolarized case. [ABSTRACT FROM AUTHOR]

Full one-loop electroweak corrections for an e-e+→tt¯ process associated with sequential t→bμνμ decay are discussed. At the one-loop level, the spin-polarization effects of the initial electron and positron beams are included in the total and differential cross sections. A narrow-width approximation is used to treat the top-quark production and decay while including full spin correlations between them. We observed that the radiative corrections due to the weak interaction have a large polarization dependence on both the total and the differential cross sections. Therefore, experimental observables that depend on angular distributions such as the forward-backward asymmetry of the top-production angle must be treated carefully including radiative corrections. We also observed that the energy distribution of bottom quarks is largely affected by the radiative corrections. [ABSTRACT FROM AUTHOR]