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Chemical activation of the nuclear singlet state of dihydrogen, para‐hydrogen, can dramatically increase the sensitivity of magnetic resonance spectroscopy and imaging. Here, we show that the highly reversible activation of para‐hydrogen by an iridium pyridylpyrrolide complex is capable of producing this hyperpolarisation effect. Bound alkene ligands exhibit signal enhancement without reduction to alkanes, which is in contrast to the most widely used hyperpolarisation catalysts. The complex is recoverable due to the highly reversible binding and release of H2, and result in enhanced hydride signals in a wide range of coordinating and non‐coordinating deuterated solvents. Synthetic modification of the ligand substituents and the addition of co‐ligands show a strong dependence of chemical structure on reactivity, which reveals an untapped potential to exploit pyridylpyrrolides as ligands in the development of tunable para‐hydrogen induced hyperpolarisation catalysts or molecular probes. [ABSTRACT FROM AUTHOR]

Hydrogen is a widely considered energy storage option. Hydrogen liquefaction allows for a substantial increase in volumetric energy density; the required conversion of ortho-hydrogen (o-H 2) to para-hydrogen (p-H 2) is however one of several challenges. This conversion requires a catalyst for sufficiently rapid kinetics, however available conversion data is sparse. To this end, a high throughput ortho-hydrogen (o-H 2) to para-hydrogen (p-H 2) conversion apparatus is detailed. This enables measurements at a controlled temperature of 77 K via the use of in-situ Raman Spectroscopy for quantitative determination of the ortho-para composition. Conversion kinetic data were acquired for a hydrous ferric oxide catalyst. These data were in reasonable agreement with limited existing literature, thus providing some validation for the use of conversion kinetic models, derived from such data, in hydrogen liquefaction design. Kinetic data was acquired using hydrogen provided via electrolysis; the effect of impurity (H 2 O) carry-over on conversion kinetics is considered. • Apparatus constructed for quantitative ortho-para conversion measurements. • Ortho-para hydrogen conversion kinetics measured for hydrous ferric oxide at 77K. • Data broadly consistent with current kinetic models used in liquefaction design. • Effect of moisture carry-over from electrolysis on reaction kinetics quantified. [ABSTRACT FROM AUTHOR]

Enhancing magnetic resonance signal via hyperpolarization techniques enables the real‐time detection of metabolic transformations even in vivo. The use of para‐hydrogen to enhance 13C‐enriched metabolites has opened a rapid pathway for the production of hyperpolarized metabolites, which usually requires specialized equipment. Metabolite precursors that can be hyperpolarized and converted into metabolites at any given field would open up opportunities for many labs to make use of this technology because already existing hardware could be used. We report here on the complete synthesis and hyperpolarization of suitable precursor molecules of the side‐arm hydrogenation approach. The better accessibility to such side‐arms promises that the para‐hydrogen approach can be implemented in every lab with existing two channel NMR spectrometers for 1H and 13C independent of the magnetic field. [ABSTRACT FROM AUTHOR]

Hyperpolarization methods in magnetic resonance enhance the signals by several orders of magnitude, opening new windows for real‐time investigations of dynamic processes in vitro and in vivo. Here, we propose a field‐independent para‐hydrogen‐based pulsed method to produce rapidly hyperpolarized 13C‐labeled substrates. We demonstrate the method by polarizing the carboxylic carbon of the pyruvate moiety in a purposely designed precursor to 24 % at ≈22 mT. Following a fast purification procedure, we measure 8 % polarization on free [1‐13C]pyruvate in clean water solutions at physiological conditions at 7 T. The enhanced signals allow real‐time monitoring of the pyruvate‐lactate conversion in cancer cells, demonstrating the potential of the method for biomedical applications in combination with existing or developing magnetic resonance technologies. [ABSTRACT FROM AUTHOR]

H‐atom tunneling reactions play important roles in astrochemistry, but an understanding of these reactions is still in its infancy. The unique properties associated with quantum solid para‐hydrogen provide an effective environment for the generation and reactions in situ of H atoms at low temperature. Several techniques have been employed to generate H atoms to study astrochemically relevant systems that provide significant insight into the formation of complex organic molecules (COM) and help to explain the relations between the abundance of some pairs of stable species. These results introduce new concepts in astrochemistry, including H‐induced H abstraction, H‐induced fragmentation, and H‐induced uphill isomerization in darkness that have been overlooked previously. This mini‐review summarizes the state of the art in this field, discussing fundamental understanding and techniques concerning H‐atom generation, H‐tunneling reactions, and their applications; the perspectives and open questions that await further exploration are discussed. [ABSTRACT FROM AUTHOR]

Nuclear magnetic resonance (NMR) is widely applied from analytics to biomedicine although it is an inherently insensitive phenomenon. Overcoming sensitivity challenges is key to further broaden the applicability of NMR and, for example, improve medical diagnostics. Here, we present a rapid strategy to enhance the signals of 13C‐labelled metabolites with para‐hydrogen and, in particular, 13C‐pyruvate, an important molecule for the energy metabolism. We succeeded to obtain an average of 27 % 13C polarization of 1‐13C‐pyruvate in water which allowed us to introduce two applications for studying cellular metabolism. Firstly, we demonstrate that the metabolism of 1‐13C‐pyruvate can serve as a biomarker in cellular models of Parkinson's disease and, secondly, we introduce the opportunity to combine real‐time metabolic analysis with protein structure determination in the same cells. Based on the here presented results, we envision the use of our approach for future biomedical studies to detect diseases. [ABSTRACT FROM AUTHOR]

Recent developments in para‐hydrogen‐induced polarization (PHIP) methods allow the nuclear magnetic resonance (NMR) detection of specific classes of compounds, down to sub‐micromolar concentration in solution. However, when dealing with complex mixtures, signal resolution requires the acquisition of 2D PHIP‐NMR spectra, which often results in long experimental times. This strongly limits the applicability of these 2D PHIP‐NMR techniques in areas in which high‐throughput analysis is required. Here, we present a combination of fast acquisition and nonuniform sampling that can afford a 10‐fold reduction in measuring time without compromising the spectral quality. This approach was tested on a mixture of substrates at micromolar concentration, for which a resolved 2D PHIP spectrum was acquired in less than 3 min. [ABSTRACT FROM AUTHOR]

ParaHydrogen induced polarization (PHIP) is an efficient and cost-effective hyperpolarization method, but its application to biological investigations has been hampered, so far, due to chemical challenges. PHIP is obtained by means of the addition of hydrogen, enriched in the para-spin isomer, to an unsaturated substrate. Both hydrogen atoms must be transferred to the same substrate, in a pairwise manner, by a suitable hydrogenation catalyst; therefore, a de-hydrogenated precursor of the target molecule is necessary. This has strongly limited the number of parahydrogen polarized substrates. The non-hydrogenative approach brilliantly circumvents this central issue, but has not been translated to in-vivo yet. Recent advancements in hydrogenative PHIP (h-PHIP) considerably widened the possibility to hyperpolarize metabolites and, in this review, we will focus on substrates that have been obtained by means of this method and used in vivo. Attention will also be paid to the requirements that must be met and on the issues that have still to be tackled to obtain further improvements and to push PHIP substrates in biological applications. [ABSTRACT FROM AUTHOR]

Nuclear Magnetic Resonance allows the non-invasive detection and quantitation of metabolites to be carried out in cells and tissues. This means that that metabolic changes can be revealed without the need for sample processing and the destruction of the biological matrix. The main limitation to the application of this method to biological studies is its intrinsic low sensitivity. The introduction of hyperpolarization techniques and, in particular, of dissolution-Dynamic Nuclear Polarization (d-DNP) and ParaHydrogen Induced Polarization (PHIP) is a significant breakthrough for the field as the MR signals of molecules and, most importantly, metabolites, can be increased by some orders of magnitude. Hyperpolarized pyruvate is the metabolite that has been most widely used for the investigation of metabolic alterations in cancer and other diseases. Although d-DNP is currently the gold-standard hyperpolarization method, its high costs and intrinsically slow hyperpolarization procedure are a hurdle to the application of this tool. However, PHIP is cost effective and fast and hyperpolarized pyruvate can be obtained using the so-called Side Arm Hydrogenation approach (PHIP-SAH). The potential toxicity of a solution of the hyperpolarized metabolite that is obtained in this way is presented herein. HP pyruvate has then been used for metabolic studies on different prostate cancer cells lines (DU145, PC3, and LnCap). The results obtained using the HP metabolite have been compared with those from conventional biochemical assays.

Nuclear Magnetic Resonance allows the non-invasive detection and quantitation of metabolites to be carried out in cells and tissues. This means that that metabolic changes can be revealed without the need for sample processing and the destruction of the biological matrix. The main limitation to the application of this method to biological studies is its intrinsic low sensitivity. The introduction of hyperpolarization techniques and, in particular, of dissolution-Dynamic Nuclear Polarization (d-DNP) and ParaHydrogen Induced Polarization (PHIP) is a significant breakthrough for the field as the MR signals of molecules and, most importantly, metabolites, can be increased by some orders of magnitude. Hyperpolarized pyruvate is the metabolite that has been most widely used for the investigation of metabolic alterations in cancer and other diseases. Although d-DNP is currently the gold-standard hyperpolarization method, its high costs and intrinsically slow hyperpolarization procedure are a hurdle to the application of this tool. However, PHIP is cost effective and fast and hyperpolarized pyruvate can be obtained using the so-called Side Arm Hydrogenation approach (PHIP-SAH). The potential toxicity of a solution of the hyperpolarized metabolite that is obtained in this way is presented herein. HP pyruvate has then been used for metabolic studies on different prostate cancer cells lines (DU145, PC3, and LnCap). The results obtained using the HP metabolite have been compared with those from conventional biochemical assays. [ABSTRACT FROM AUTHOR]

Graphical abstract Review of performance of eight multiplet polarization (PASADENA) observation pulse schemes with a single scan suppression of background signal. In-phase and anti-phase spectra can be obtained on choice. Practical recommendations are given. Highlights: • OPSY sequences for anti-phase or in-phase PHIP spectra observation. • Strong suppression of thermally polarized signals. • OPSY with refocused chemical shift evolution. Abstract The hyperpolarization of nuclear spins using para hydrogen is an interesting effect that allows to increase the magnetic resonance signal by several orders of magnitude. Known as ParaHydrogen And Synthesis Allow Dramatically Enhanced Nuclear Alignment (PASADENA) and ParaHydrogen Induced Polarization (PHIP), the method was successfully used for in vitro analysis and in vivo imaging. In this contribution, we investigated four known and four new variants of Only Parahydrogen SpectroscopY (OPSY) sequences (Aguilar et al., 2007) with respect to the selective preparation of hyperpolarized NMR signal and background suppression. Depending on the method chosen, either anti-phase, in-phase or a mixture of both signals are obtained: anti-phase signals are beneficial to identify hyperpolarized signals and the structure or J-coupling constants; in-phase signals are useful for imaging applications or when the lines are broad. This comprehensive overview of sequences new and old facilitates selecting the right sequence for the task at hand. [ABSTRACT FROM AUTHOR]

Nuclear magnetic resonance (NMR) studies of complex mixtures are often limited by the low sensitivity of the technique and by spectral overlap. We have recently reported on an NMR chemosensor on the basis of para‐Hydrogen Induced Polarization that potentially addresses both these issues, albeit for specific classes of compounds. This approach makes use of Signal Amplification By Reversible Exchange (SABRE) catalysts in methanol and allows selective detection and quantification of dilute analytes in complex mixtures. Herein, we demonstrate that, despite a large decrease in attained hyperpolarization, this method can be extended to water–alcohol mixtures. Our approach was tested on whisky, where nitrogenous heterocyclic flavor components at low‐micromolar concentration could be detected and quantified. [ABSTRACT FROM AUTHOR]

A novel conceptual approach is described that is based on the transfer of hyperpolarization from para-hydrogen in view of generating a population imbalance between the two spin isomers of H 2 O. The approach is analogous to SABRE (Signal Amplification By Reversible Exchange) and makes use of the transfer of spin order from para-hydrogen to H 2 O in a hypothetical organometallic complex. The spin order transfer is expected to be most efficient at avoided level crossings. The highest achievable enrichment levels of para- and ortho-water are discussed. [ABSTRACT FROM AUTHOR]

Hyperpolarized NMR is a promising approach to address the sensitivity limits of conventional NMR metabolomics approaches, which currently fails to detect minute metabolite concentrations in biological samples. This review describes how tremendous signal enhancement offered by dissolution-dynamic nuclear polarization and parahydrogen-based techniques can be fully exploited for molecular omics sciences. Recent developments, including the combination of hyperpolarization techniques with fast multi-dimensional NMR implementation and quantitative workflows are described, and a comprehensive comparison of existing hyperpolarization techniques is proposed. High-throughput, sensitivity, resolution and other relevant challenges that should be tackled for a general application of hyperpolarized NMR in metabolomics are discussed. [Display omitted] • Hyperpolarized techniques can break the sensitivity barrier of NMR metabolomics. • Dissolution-DNP and parahydrogen-based methods are particularly promising. • Recent applications include metabolic fingerprint and targeted quantification. [ABSTRACT FROM AUTHOR]

Nuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI) suffer from low sensitivity and limited nuclear spin memory lifetimes. Although hyperpolarization techniques increase sensitivity, there is also a desire to increase relaxation times to expand the range of applications addressable by these methods. Here, we demonstrate a route to create hyperpolarized magnetization in 13C nuclear spin pairs that last much longer than normal lifetimes by storage in a singlet state. By combining molecular design and low-field storage with para-hydrogen derived hyperpolarization, we achieve more than three orders of signal amplification relative to equilibrium Zeeman polarization and an order of magnitude extension in state lifetime. These studies use a range of specifically synthesized pyridazine derivatives and dimethyl p-tolyl phenyl pyridazine is the most successful, achieving a lifetime of about 190 s in low-field, which leads to a 13C-signal that is visible for 10 minutes. [ABSTRACT FROM AUTHOR]

Signal amplification by reversible exchange (SABRE) is shown to allow access to strongly enhanced 1H NMR signals in a range of substrates in aqueous media. To achieve this outcome, phase-transfer catalysis is exploited, which leads to less than 1.5×10−6 mol dm−3 of the iridium catalyst in the aqueous phase. These observations reflect a compelling route to produce a saline-based hyperpolarized bolus in just a few seconds for subsequent in vivo MRI monitoring. The new process has been called catalyst separated hyperpolarization through signal amplification by reversible exchange or CASH-SABRE. We illustrate this method for the substrates pyrazine, 5-methylpyrimidine, 4,6- d2-methyl nicotinate, 4,6- d2-nicotinamide and pyridazine achieving 1H signal gains of approximately 790-, 340-, 3000-, 260- and 380-fold per proton at 9.4 T at the time point at which phase separation is complete. [ABSTRACT FROM AUTHOR]

A strong limitation of nuclear magnetic resonance is its low inherent sensitivity that can be overcome by using an appropriate hyperpolarization technique. Presently, dynamic nuclear polarization and spin-exchange optical pumping are the only hyperpolarization techniques that are used in applied medicine. However, both are relatively complex in use and expensive. Here we present a modification of the signal amplification by reversible exchange (SABRE) hyperpolarization method - SABRE on stabilized Ir-complexes. A stabilized Ir-complex (here we used bipyridine for stabilization) can be hyperpolarized in a wide range of magnetic fields from a few μT upto 10 T with 15N polarization of about 1-3%. Moreover, the investigated complex can be incorporated into biomolecules or other bulky molecules; in this situation exchange with para-hydrogen will allow one to continuously generate hyperpolarization. [ABSTRACT FROM AUTHOR]

Nuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI) are two extremely important techniques with applications ranging from molecular structure determination to human imaging. However, in many cases the applicability of NMR and MRI are limited by inherently poor sensitivity and insufficient nuclear spin lifetime. Here we demonstrate a cost-efficient and fast technique that tackles both issues simultaneously. We use the signal amplification by reversible exchange (SABRE) technique to hyperpolarize the target 1H nuclei and store this polarization in long-lived singlet (LLS) form after suitable radiofrequency (rf) pulses. Compared to the normal scenario, we achieve three orders of signal enhancement and one order of lifetime extension, leading to 1H NMR signal detection 15 minutes after the creation of the detected states. The creation of such hyperpolarized long-lived polarization reflects an important step forward in the pipeline to see such agents used as clinical probes of disease. [ABSTRACT FROM AUTHOR]

The carbon-hydrogen composite systems of para-hydrogen ( p -H 2 ) sandwiched by a couple of graphene sheets have been investigated by means of path integral centroid molecular dynamics simulations at 17 K. It has been shown that sandwiched hydrogen is liquid-like but p -H 2 molecules are preferably adsorbed onto the graphene sheets because of attractive graphene-hydrogen interaction. The diffusion coefficient of p -H 2 molecules in the direction parallel to the graphene sheets is comparable to that in pure liquid p -H 2 . There exists a characteristic mode of 140 cm −1 of the p -H 2 molecules, attributed to adsorption-binding motion perpendicular to the graphene sheets. [ABSTRACT FROM AUTHOR]

By sampling gaseous hydrogen from a circulating liquid hydrogen loop for Laser Raman spectroscopy, we measured the para-/ortho-hydrogen fractions in liquid hydrogen under neutron irradiation for the first time to identify whether irradiated hydrogen has an elevated ortho-hydrogen fraction. This measurement indicates that para-hydrogen equilibrium persists at 300 kW proton power in the presence of an iron(III) oxide hydroxide [Fe(OH) 3 ] catalyst. The measurements will be repeated as the power at the Japan Proton Accelerator Research Complex (J-PARC) increases to the MW level. [ABSTRACT FROM AUTHOR]

High-resolution infrared (IR) spectra of R-(+)-3-methylcyclopentanone (R3MCP) in para-hydrogen (pH2) crystal were recorded and compared with the corresponding IR spectra of R3MCP in Argon (Ar) isolation matrix as well as the IR spectra of the neat crystalline R3MCP at low deposition temperature of 4 ± 0.05 K. Moreover, IR spectra of R3MCP, hosted in pH2 crystal, were recorded using a high-resolution Fourier transform IR spectrometer as a function of sample concentration and over the range 10-300 ppm. Furthermore, density functional theory calculations of simulated IR spectra for the optimized geometries of R3MCP equatorial-methyl and axial-methyl conformers are compared with experimental spectra for the purpose of investigating molecular conformation. Upon comparison between theoretical and experimental IR spectra, vibrational modes arising from equatorial and axial conformers have been successfully assigned and related to the individual conformer's structure. [ABSTRACT FROM AUTHOR]

Fe-modified zeolite was prepared by ion-exchange of zeolite with ferric chloride and calcination, for effective spin conversion of ortho- to-para-hydrogen. Studies carried out using BET, SEM, EDS, and VSM techniques. Results indicated that spin conversion rate showed great dependence on magnetic properties of the composite according to calcination temperature change. For lower sintering temperatures, the samples showed more paramagnetic behavior. As sintering temperature increased, ferromagnetic state increase, while paramagnetic states decreased. The highest spin conversion was observed at paramagnetic state, comparing with ferromagnetic, at lower calcination temperature. Moreover, Fe-modified zeolite showed a superior hydrodynamic property such as the pressure drop ratio of composite to a commercial iron oxide. These composites can be applied in more efficient hydrogen liquefaction processes. [ABSTRACT FROM AUTHOR]

At the Japan Proton Accelerator Research Complex (J-PARC), a pulsed spallation neutron source provides neutrons with high intensity and narrow pulse width pulse to promote researches on a variety of science in the Materials and Life Science Experimental Facility (MLF). It was designed to be driven by a proton beam with an energy of 3 GeV, a power of 1 MW at a repetition rate of 25 Hz, that is world’s highest power level. It is still on the way towards the goal to accomplish the operation with a 1 MW proton beam. In this review, distinctive features of the target-moderator-reflector system of the pulsed spallation neutron source are presented.

Nuclear magnetic resonance is often the technique of choice in chemical analysis because of its sensitivity to molecular structure, quantitative character, and straightforward sample preparation. However, determination of trace analytes in complex mixtures is generally limited by low sensitivity and extensive signal overlap. Here, we present an approach for continuous hyperpolarization at high magnetic field that is based on signal amplification by reversible exchange (SABRE) and can be straightforwardly incorporated in multidimensional NMR experiments. This method was implemented in a 2D correlation experiment that allows detection and quantification of analytes at nanomolar concentration in complex solutions. [ABSTRACT FROM AUTHOR]

We recently reported an experiment which focused on demonstrating the macro-coherent amplification mechanism. This mechanism, which was proposed for neutrino mass measurements, indicates that a multi-particle emission rate should be amplified by coherence in a suitable medium. Using a para-hydrogen molecule gas target and the adiabatic Raman excitation method, we observed that the two photon emission rate was amplified by a factor of more than 10 from the spontaneous emission rate. This paper briefly summarizes the previous experimental result and presents the current status and the future prospect. [ABSTRACT FROM AUTHOR]

We present Fourier-transform infrared (FTIR) spectroscopic studies of the IR-induced Cl + H 2 ( v = 1) → HCl + H reaction in a parahydrogen (pH 2 ) matrix aimed at distinguishing between two proposed reactions mechanisms; direct-IR and vibron-mediated. The Cl atom reactants are produced via 355 nm in situ photolysis of a Cl 2 doped pH 2 matrix. After photolysis is complete, a long-pass IR filter in the FTIR beam is removed and we measure the ensuing IR-induced reaction kinetics using rapid scan FTIR spectroscopy. We follow both the decay of the Cl atom reactant and growth of the HCl product using the Cl spin–orbit (SO) + Q 1 (0) and HCl R 1 (0) transitions, respectively. We show the IR-induced reaction mechanism depends on the spectral profile of the IR radiation; for IR spectral profiles that have significant IR intensities between 4000 and 5000 cm −1 we observe first-order kinetics that are assigned to a vibron-mediated mechanism and for spectral profiles that have significant IR intensities that include the Cl SO + Q 1 (0) transition near 5094 cm −1 we observe bi-exponential kinetics that are dominated by the direct-IR mechanism at early reaction times. We can distinguish between the two mechanisms using the observed kinetics. We investigate the reaction kinetics for different FTIR optical setups, for a range of sample conditions, and start and stop the IR-induced reaction to investigate the importance of secondary H atom reactions. We also study the IR-induced reaction in Br/Cl co-doped pH 2 samples and show the presence of the Br atom quenches the vibron-mediated reaction kinetics presumably because the Br-atoms serve as efficient vibron traps. This paper indicates that in a highly enriched pH 2 matrix the H atoms that are produced by the IR-induced Cl atom reaction likely do not play a significant role in the measured reaction kinetics which implies these secondary H atom reactions are highly selective. [ABSTRACT FROM AUTHOR]

Para-hydrogen-induced polarization (PHIP) is a technique capable of producing spin polarization at a magnitude far greater than state-of-the-art magnets. A significant application of PHIP is to generate contrast agents for biomedical imaging. Clinically viable and effective contrast agents not only require high levels of polarization but heterogeneous catalysts that can be used in water to eliminate the toxicity impact. Herein, we demonstrate the use of Pt nanoparticles capped with glutathione to induce heterogeneous PHIP in water. The ligand-inhibited surface diffusion on the nanoparticles resulted in a 1H polarization of P=0.25 % for hydroxyethyl propionate, a known contrast agent for magnetic resonance angiography. Transferring the 1H polarization to a 13C nucleus using a para-hydrogen polarizer yielded a polarization of 0.013 %. The nuclear-spin polarizations achieved in these experiments are the first reported to date involving heterogeneous reactions in water. [ABSTRACT FROM AUTHOR]

Analytical expressions for the signal enhancement in solid-state PHIP NMR spectroscopy mediated by homonuclear dipolar interactions and single pulse or spin-echo excitation are developed and simulated numerically. It is shown that an efficient enhancement of the proton NMR signal in solid-state NMR studies of chemisorbed hydrogen on surfaces is possible. Employing typical reaction efficacy, enhancement-factors of ca. 30–40 can be expected both under ALTADENA and under PASADENA conditions. This result has important consequences for the practical application of the method, since it potentially allows the design of an in-situ flow setup, where the para-hydrogen is adsorbed and desorbed from catalyst surfaces inside the NMR magnet. [ABSTRACT FROM AUTHOR]

In a recent numerical optimization study we have found that liquid para-hydrogen coupled cold neutron moderators deliver 3-5 times higher cold neutron brightness at a spallation neutron source if they take the form of a flat, quasi 2-dimensional disc, in contrast to the conventional more voluminous shapes used by now. In the present paper we describe a simple theoretical explanation of this unexpected behavior, which is based on the large difference in para-hydrogen between the values of the scattering mean free path for thermal neutrons (in the range of 1 cm) and its much larger equivalent for cold neutrons. This model leads to the conclusions that the optimal shape for high brightness para-hydrogen neutron moderators is the quasi 1-dimensional tube and these low dimensional moderators can also deliver much enhanced cold neutron brightness in fission reactor neutron sources, compared to the much more voluminous liquid D2 or H2 moderators currently used. Neutronic simulation calculations confirm both of these theoretical conclusions. [ABSTRACT FROM AUTHOR]

Object: To determine the storability of para-hydrogen before reestablishment of the room temperature thermal equilibrium mixture. Materials and methods: Para-hydrogen was produced at near 100 % purity and mixed with different oxygen quantities to determine the rate of conversion to the thermal equilibrium mixture of 75: 25 % ( ortho: para) by detecting the ortho-hydrogen H nuclear magnetic resonance using a 9.4 T imager. Results: The para-hydrogen to ortho-hydrogen velocity constant, k, near room temperature (292 K) was determined to be 8.27 ± 1.30 L/mol·min. This value was calculated utilizing four different oxygen fractions. Conclusions: Para-hydrogen conversion to ortho-hydrogen by oxygen can be minimized for long term storage with judicious removal of oxygen contamination. Prior calculated velocity rates were confirmed demonstrating a dependence on only the oxygen concentration. [ABSTRACT FROM AUTHOR]

Improved adsorbent types and compositions have been developed for the challenging separation of the ortho- and para-hydrogen spin isomers at 77 K. From a systematic study of commercially available adsorbent types, it has been found that zeolites of type X offer the largest capacity and selectivity towards ortho-hydrogen and that performance is significantly impacted by the cation type and the number of cations present in the zeolite. For the present separation improved performance was obtained with larger Group I cations, especially K and Cs. Another key property of the adsorbents addressed in the present work is the need to control the adsorbent composition to avoid unwanted catalytic conversion of the para- to ortho-hydrogen. A common source of unwanted catalytic activity in many adsorbent compositions was identified as the presence of unwanted transition metal impurities, especially iron associated with the natural clays, commonly employed as binding agents in the commercial agglomerated zeolite products. To avoid this, equivalent adsorbent compositions were agglomerated instead using colloidal silica binding agents which successfully minimize back conversion of the para- to ortho-hydrogen and produced adsorbents with higher capacities and selectivities for the ortho component at the test temperature of 77 K. These advanced adsorbents can be applied in more efficient hydrogen liquefaction processes. [ABSTRACT FROM AUTHOR]

The reaction of unsaturated substrates with hydrogen gas enriched in the para spin isomer leads to products with a high degree of nuclear singlet spin order. This leads to greatly enhanced NMR signals, with important potential applications such as magnetic resonance imaging (MRI) of metabolic processes. Although parahydrogen-induced polarization has the advantage of being cheap, compact, and mobile, especially when performed in ultralow magnetic fields, efficiency is lost when more than a few protons are involved. This strongly restricts the range of compatible substances. We show that these difficulties may be overcome by a combination of deuteration with the application of a sinusoidally modulated longitudinal field as a well as a transverse rotating magnetic field. We demonstrate a six-fold enhancement in the 13 C hyperpolarization of [1- 13 C, 2,3-d 2 ]-succinic acid, as compared with standard hyperpolarization methods, applied in the same ultralow field regime., (© 2022 The Authors. ChemPhysChem published by Wiley-VCH GmbH.)

Abstract: The unperturbed neutron brightness of a moderator can be defined from the number of neutrons leaving the surface of a moderator completely surrounded by a reflector. Without openings for beam extraction, it is the maximum brightness that can be theoretically achieved in a moderator. The unperturbed brightness of a cylindrical cold moderator filled with pure para-H2 was calculated using MCNPX; the moderator dimensions were optimised, for a fixed target and reflector geometry corresponding to the present concept for the ESS spallation source. This quantity does not depend on openings for beam extraction and therefore can be used for a first-round optimisation of a moderator, before effects due to beam openings are considered. We find that such an optimisation yields to a factor of 2 increase with respect to a conventional volume moderator, large enough to accommodate a viewed surface of 12×12cm2: the unperturbed neutron brightness is maximum for a disc-shaped moderator of 15cm diameter, 1.4cm height. The reasons for this increase can be related to the properties of the scattering cross-section of para-H2, to the added reflector around the exit surface in the case of a compact moderator, and to a directionality effect. This large optimisation gain in the unperturbed brightness hints towards similar potentials for the perturbed neutron brightness, in particular in conjunction with advancing the optical quality of neutron delivery from the moderator to the sample, where by Liouville theorem the brightness is conserved over the beam trajectory, except for absorption and similar type losses. [Copyright &y& Elsevier]

Abstract: We apply non-equilibrium thermodynamics to describe the adsorption and desorption of molecular hydrogen on graphene. Lateral interactions, precursor states in both adsorption and desorption, and limited dimer conversion are important to explain semi-quantitatively the main features of temperature-programmed desorption spectra. All energy and vibrational parameters are taken from density functional calculations. Deficiencies in previous attempts are discussed. We also point out the need for a multi-dimensional dynamic theory. [Copyright &y& Elsevier]

Highlights: [•] Application of para-hydrogen polarized samples as molecular imaging agents and future challenges. [•] Detection of minute substance amounts for reactor monitoring and trace analysis. [•] Use of PHIP in inhomogeneous fields and in time domain experiments. [•] Recent developments of PHIP phenomena in ultra-low field and zero-field NMR. [ABSTRACT FROM AUTHOR]

Hyperpolarization methods in magnetic resonance enhance the signals by several orders of magnitude, opening new windows for real-time investigations of dynamic processes in vitro and in vivo. Here, we propose a field-independent para-hydrogen-based pulsed method to produce rapidly hyperpolarized 13 C-labeled substrates. We demonstrate the method by polarizing the carboxylic carbon of the pyruvate moiety in a purposely designed precursor to 24 % at ≈22 mT. Following a fast purification procedure, we measure 8 % polarization on free [1- 13 C]pyruvate in clean water solutions at physiological conditions at 7 T. The enhanced signals allow real-time monitoring of the pyruvate-lactate conversion in cancer cells, demonstrating the potential of the method for biomedical applications in combination with existing or developing magnetic resonance technologies., (© 2022 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

Para-hydrogen-induced polarization effects have been observed in the 29Si NMR spectra of trimethylsilyl para-hydrogenated molecules. The high signal enhancements and the long T1 values observed for the 29Si hyperpolarized resonances point toward the possibility of using 29Si for hyperpolarization applications. A method for the discrimination of multiple compounds and/or complex mixtures of hydroxylic compounds (such as steroids), consisting of the silylization of alcoholic functionalities with an unsaturated silylalkyl moiety and subsequent reaction with para-H2, is proposed. Copyright © 2012 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Abstract: We have been performing research on the Totalized Hydrogen Energy Utilization System (THEUS) which has applications to commercial buildings and a planned added function of supplying energy to stations for hydrogen and electric vehicles. In that case we will utilize liquid hydrogen transported from a hydrogen station and all Boil-Off Gas (BOG) will be recovered in THEUS’s metal hydride tanks. It is known that BOG is chiefly composed of para-hydrogen, which has different thermo-physical properties from normal hydrogen. It has been reported that some metal hydride alloys work as a catalyst to accelerate the para-ortho conversion and the conversion proceeds relatively fast in the case of La–Ni5. The conversion is considered to be an endothermic reaction. A misch metal (Mm)-Ni5 metal hydride alloy, which contained La and Ni, was used in our THEUS metal hydride tank. To examine the effect of the para-ortho conversion on the THEUS operation, we investigated the absorption/desorption characteristics of the metal hydride tank with BOG. We confirmed that the effect of the heat of conversion was very small and BOG could be treated as normal hydrogen for practical application. [Copyright &y& Elsevier]

Abstract: We have developed a large, thin solid hydrogen target (SHT) that is 30mm in diameter and 1mm thick for elastic scattering of protons from unstable nuclei. By using para-H2 that has a high thermal conductivity at low temperatures, we could prevent sublimation at the target center due to radiation from the higher temperature surroundings. The uniform SHT was used during long-term scattering experiments and it maintained its shape and thickness. [Copyright &y& Elsevier]