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Abstract Hyperpolarized orthohydrogen (o‐H₂) is a frequent product of parahydrogen‐based hyperpolarization approaches like signal amplification by reversible exchange (SABRE), where the hyperpolarizedo‐H₂signal is usually absorptive. We describe a novel manifestation of this effect wherein large antiphaseo‐H₂signals are observed, with¹H enhancements up to ≈500‐fold (effective polarizationP_H≈1.6 %). This anomalous effect is attained only when using an intact heterogeneous catalyst constructed using a metal–organic framework (MOF) and is qualitatively independent of substrate nature. This seemingly paradoxical observation is analogous to the “partial negative line” (PNL) effect recently explained in the context of Parahydrogen Induced Polarization (PHIP) by Ivanov and co‐workers. The two‐spin order of theo‐H₂resonance is manifested by a two‐fold higher Rabi frequency, and the lifetime of the antiphase HPo‐H₂resonance is extended by several‐fold. 

Thioredoxin reductases (TrxR) activate thioredoxins (Trx) that regulate the activity of diverse target proteins essential to prokaryotic and eukaryotic life. However, very little is understood of TrxR/Trx systems and redox control in methanogenic microbes from the domain Archaea (methanogens), for which genomes are abundant with annotations for ferredoxin:thioredoxin reductases [Fdx/thioredoxin reductase (FTR)] from group 4 of the widespread FTR-like family. Only two from the FTR-like family are characterized: the plant-type FTR from group 1 and FDR from group 6. Herein, the group 4 archetype (AFTR) from Methanosarcina acetivorans was characterized to advance understanding of the family and TrxR/Trx systems in methanogens. The modeled structure of AFTR, together with EPR and Mössbauer spectroscopies, supports a catalytic mechanism similar to plant-type FTR and FDR, albeit with important exceptions. EPR spectroscopy of reduced AFTR identified a transient [4Fe−4S]1+ cluster exhibiting a mixture of S = 7/2 and typical S = 1/2 signals, although rare for proteins containing [4Fe−4S] clusters, it is most likely the on-pathway intermediate in the disulfide reduction. Furthermore, an active site histidine equivalent to residues essential for the activity of plant-type FTR and FDR was found dispensable for AFTR. Finally, a unique thioredoxin system was reconstituted from AFTR, ferredoxin, and Trx2 from M. acetivorans, for which specialized target proteins were identified that are essential for growth and other diverse metabolisms. 

Using methane as a reagent to synthesize high-value chemicals and high-energy density fuels through C−C coupling has attracted intense attention in recent decades, as it avoids completely breaking all C−H bonds in CH4. In the present study, we demonstrated that the coupling of HCHO with the CH3 species from CH4 activation to produce ethanol can be accomplished on the single Pd atom−In2O3 catalyst based on the results of density functional theory (DFT) calculations. The results show that the supported single Pd atom stabilizes the CH3 species following the activation of one C−H bond of CH4, while HCHO adsorbs on the neighboring In site. Facile C−C coupling of HCHO with the methyl species is achieved with an activation barrier of 0.56 eV. We further examined the C−C coupling on other single metal atoms, including Ni, Rh, Pt, and Ag, supported on In2O3 by following a similar pathway and found that a balance of the three key steps for ethanol formation, i.e., CH4 activation, C−C coupling, and ethoxy hydrogenation, was achieved on Pd/In2O3. Taking the production of acetaldehyde and ethylene on the Pd/In2O3 catalyst into consideration, the DFT-based microkinetic analysis indicates that ethanol is the dominant product on the Pd/In2O3 catalyst. The facile C−C coupling between HCHO and dissociated CH4 makes formaldehyde a potential C1 source in the conversion and utilization of methane through an energy- and atom-efficient process. 

The present work investigates the potential for enhancing the NMR signals of DNA nucleobases by parahydrogen-based hyperpolarization. Signal amplification by reversible exchange (SABRE) and SABRE in Shield Enables Alignment Transfer to Heteronuclei (SABRE-SHEATH) of selected DNA nucleobases is demonstrated with the enhancement (ε) of 1H, 15N, and/or 13C spins in 3-methyladenine, cytosine, and 6-O-guanine. Solutions of the standard SABRE homogenous catalyst Ir(1,5-cyclooctadeine)(1,3-bis(2,4,6-trimethylphenyl)imidazolium)Cl (“IrIMes”) and a given nucleobase in deuterated ethanol/water solutions yielded low 1H ε values (≤10), likely reflecting weak catalyst binding. However, we achieved natural-abundance enhancement of 15N signals for 3-methyladenine of ~3300 and ~1900 for the imidazole ring nitrogen atoms. 1H and 15N 3-methyladenine studies revealed that methylation of adenine affords preferential binding of the imidazole ring over the pyrimidine ring. Interestingly, signal enhancements (ε~240) of both 15N atoms for doubly labelled cytosine reveal the preferential binding of specific tautomer(s), thus giving insight into the matching of polarization-transfer and tautomerization time scales. 13C enhancements of up to nearly 50-fold were also obtained for this cytosine isotopomer. These efforts may enable the future investigation of processes underlying cellular function and/or dysfunction, including how DNA nucleobase tautomerization influences mismatching in base-pairing.