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1. Spin Transitions and Compressibility of ε‐Fe ₇ N ₃ and γ′‐Fe ₄ N: Implications for Iron Alloys in Terrestrial Planet Cores

   https://doi.org/10.1029/2020JB020660  

   Lv, Mingda; Liu, Jiachao; Zhu, Feng; Li, Jie; Zhang, Dongzhou; Xiao, Yuming; Dorfman, Susannah M. (November 2020, Journal of Geophysical Research: Solid Earth)

   Abstract Iron nitrides are possible constituents of the cores of Earth and other terrestrial planets. Pressure‐induced magnetic changes in iron nitrides and effects on compressibility remain poorly understood. Here we report synchrotron X‐ray emission spectroscopy (XES) and X‐ray diffraction (XRD) results for ε‐Fe₇N₃and γ′‐Fe₄N up to 60 GPa at 300 K. The XES spectra reveal completion of high‐ to low‐spin transition in ε‐Fe₇N₃and γ′‐Fe₄N at 43 and 34 GPa, respectively. The completion of the spin transition induces stiffening in bulk modulus of ε‐Fe₇N₃by 22% at ~40 GPa, but has no resolvable effect on the compression behavior of γ′‐Fe₄N. Fitting pressure‐volume data to the Birch‐Murnaghan equation of state yieldsV₀ = 83.29 ± 0.03 (ų),K₀ = 232 ± 9 GPa,K₀′ = 4.1 ± 0.5 for nonmagnetic ε‐Fe₇N₃above the spin transition completion pressure, andV₀ = 54.82 ± 0.02 (ų),K₀ = 152 ± 2 GPa,K₀′ = 4.0 ± 0.1 for γ′‐Fe₄N over the studied pressure range. By reexamining evidence for spin transition and effects on compressibility of other candidate components of terrestrial planet cores, Fe₃S, Fe₃P, Fe₇C₃, and Fe₃C based on previous XES and XRD measurements, we located the completion of high‐ to low‐spin transition at ~67, 38, 50, and 30 GPa at 300 K, respectively. The completion of spin transitions of Fe₃S, Fe₃P, and Fe₃C induces elastic stiffening, whereas that of Fe₇C₃induces elastic softening. Changes in compressibility at completion of spin transitions in iron‐light element alloys may influence the properties of Earth's and planetary cores. 

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2. Carbon substrate re‐orders relative growth of a bacterium using Mo‐, V‐, or Fe‐nitrogenase for nitrogen fixation

   https://doi.org/10.1111/1462-2920.14955  

   Luxem, Katja_E; Kraepiel, Anne_M_L; Zhang, Lichun; Waldbauer, Jacob_R; Zhang, Xinning (February 2020, Environmental Microbiology)

   Summary Biological nitrogen fixation is catalyzed by the molybdenum (Mo), vanadium (V) and iron (Fe)‐only nitrogenase metalloenzymes. Studies with purified enzymes have found that the ‘alternative’ V‐ and Fe‐nitrogenases generally reduce N₂more slowly and produce more byproduct H₂than the Mo‐nitrogenase, leading to an assumption that their usage results in slower growth. Here we show that, in the metabolically versatile photoheterotrophRhodopseudomonas palustris, the type of carbon substrate influences the relative rates of diazotrophic growth based on different nitrogenase isoforms. The V‐nitrogenase supports growth as fast as the Mo‐nitrogenase on acetate but not on the more oxidized substrate succinate. Our data suggest that this is due to insufficient electron flux to the V‐nitrogenase isoform on succinate compared with acetate. Despite slightly faster growth based on the V‐nitrogenase on acetate, the wild‐type strain uses exclusively the Mo‐nitrogenase on both carbon substrates. Notably, the differences in H₂:N₂stoichiometry by alternative nitrogenases (~1.5 for V‐nitrogenase, ~4–7 for Fe‐nitrogenase) and Mo‐nitrogenase (~1) measured here are lower than priorin vitroestimates. These results indicate that the metabolic costs of V‐based nitrogen fixation could be less significant for growth than previously assumed, helping explain why alternative nitrogenase genes persist in diverse diazotroph lineages and are broadly distributed in the environment. 

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3. Constraining the H ₂ column densities in the diffuse interstellar medium using dust extinction and H I data

   https://doi.org/10.1051/0004-6361/202347968  

   Skalidis, R; Goldsmith, P F; Hopkins, P F; Ponnada, S B (February 2024, Astronomy & Astrophysics)

   Context. Carbon monoxide (CO) is a poor tracer of H₂in the diffuse interstellar medium (ISM), where most of the carbon is not incorporated into CO molecules, unlike the situation at higher extinctions. Aims. We present a novel, indirect method for constraining H₂column densities (N_H2) without employing CO observations. We show that previously recognized nonlinearities in the relation between the extinction,A_V(H₂), derived from dust emission and the H Icolumn density (N_H I) are due to the presence of molecular gas. Methods. We employed archival (N_H2) data, obtained from the UV spectra of stars, and calculatedA_V(H₂) toward these sight lines using 3D extinction maps. The following relation fits the data: logN_H2= 1.38742 (logA_V(H₂)⁾³− 0.05359 (logA_V(H₂)⁾²+ 0.25722 logA_V(H₂) + 20.67191. This relation is useful for constrainingN_H2in the diffuse ISM as it requires onlyN_H Iand dust extinction data, which are both easily accessible. In 95% of the cases, the estimates produced by the fitted equation have deviations of less than a factor of 3.5. We constructed aN_H2map of our Galaxy and compared it to the CO integrated intensity (W_CO) distribution. Results. We find that the average ratio (X_CO) betweenN_H2andW_COis approximately equal to 2 × 10²⁰cm⁻²(K km s⁻¹)⁻¹, consistent with previous estimates. However, we find that theX_COfactor varies by orders of magnitude on arcminute scales between the outer and the central portions of molecular clouds. For regions withN_H2≳ 10²⁰cm⁻², we estimate that the average H₂fractional abundance,f_H2= 2N_H2/(2N_H2+N_H I), is 0.25. Multiple (distinct) largely atomic clouds are likely found along high-extinction sightlines (A_V≥ 1 mag), hence limitingf_H2in these directions. Conclusions. More than 50% of the lines of sight withN_H2≥ 10²⁰cm⁻²are untraceable by CO with aJ= 1−0 sensitivity limitW_CO= 1 K km s⁻¹. 

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4. Synthesis of Tris[2‐(dimethylamino)ethyl]amine with Regiospecific Deuterium Labels

   https://doi.org/10.1002/slct.202300053  

   Sobieski, Julian; Ruzhylo, Illia; Szczepaniak, Grzegorz; Gorczyński, Adam; Matyjaszewski, Krzysztof; Manoury, Eric; Poli, Rinaldo (February 2023, ChemistrySelect)

   Abstract Simple synthetic routes to regioselectively deuterated tris[2‐(dimethylamino)ethyl]amine (Me₆TREN) variants are described. Imine formation with formaldehyde‐d₂from tris(2‐aminoethyl)amine (TREN) and subsequent reductions with NaBD₄afforded N[CH₂CH₂N(CD₃)₂]₃ord₁₈‐Me₆TREN in 79 % yield. A trisubstitution protocol from 2‐bromo‐N,N‐dimethylacetamide and ammonium carbonate and subsequent reduction of the N(CH₂CONMe₂)₃intermediate by lithium aluminum deuteride has afforded N[CH₂CD₂N(CH₃)₂]₃or (d₆‐arm)‐Me₆TREN in three steps and 52 % overall yield. A similar protocol from 2‐bromo‐N,N‐dimethyl‐d₂‐acetamide, obtained in two steps fromd₄‐acetic acid, with reduction of the N(CD₂CONMe₂)₃intermediate by lithium aluminum hydride has afforded N[CD₂CH₂N(CH₃)₂]₃or (d₆‐cap)‐Me₆TREN in four steps and 13 % overall yield from CD₃COOD. 

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5. Sustained bacterial N2O reduction at acidic pH

   https://doi.org/10.1038/s41467-024-48236-x  

   He, Guang; Chen, Gao; Xie, Yongchao; Swift, Cynthia M.; Ramirez, Diana; Cha, Gyuhyon; Konstantinidis, Konstantinos T.; Radosevich, Mark; Löffler, Frank E. (May 2024, Nature Communications)

   Abstract Nitrous oxide (N₂O) is a climate-active gas with emissions predicted to increase due to agricultural intensification. Microbial reduction of N₂O to dinitrogen (N₂) is the major consumption process but microbial N₂O reduction under acidic conditions is considered negligible, albeit strongly acidic soils harbornosZgenes encoding N₂O reductase. Here, we study a co-culture derived from acidic tropical forest soil that reduces N₂O at pH 4.5. The co-culture exhibits bimodal growth with aSerratiasp. fermenting pyruvate followed by hydrogenotrophic N₂O reduction by aDesulfosporosinussp. Integrated omics and physiological characterization revealed interspecies nutritional interactions, with the pyruvate fermentingSerratiasp. supplying amino acids as essential growth factors to the N₂O-reducingDesulfosporosinussp. Thus, we demonstrate growth-linked N₂O reduction between pH 4.5 and 6, highlighting microbial N₂O reduction potential in acidic soils. 

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