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1. Nitrous oxide from chemodenitrification: A possible missing link in the Proterozoic greenhouse and the evolution of aerobic respiration

   https://doi.org/10.1111/gbi.12311  

   Stanton, Chloe L. ; Reinhard, Christopher T. ; Kasting, James F. ; Ostrom, Nathaniel E. ; Haslun, Joshua A. ; Lyons, Timothy W. ; Glass, Jennifer B. ( August 2018 , Geobiology)

   The potent greenhouse gas nitrous oxide (N₂O) may have been an important constituent of Earth's atmosphere during Proterozoic (~2.5–0.5 Ga). Here, we tested the hypothesis that chemodenitrification, the rapid reduction of nitric oxide by ferrous iron, would have enhanced the flux of N₂O from ferruginous Proterozoic seas. We empirically derived a rate law,, and measured an isotopic site preference of +16‰ for the reaction. Using this empirical rate law, and integrating across an oceanwide oxycline, we found that lownM NOand μM‐lowmMFe²⁺concentrations could have sustained a sea‐air flux of 100–200 Tg N₂O–N year⁻¹, if N₂fixation rates were near‐modern and all fixed N₂was emitted as N₂O. A 1D photochemical model was used to obtain steady‐state atmospheric N₂O concentrations as a function of sea‐air N₂O flux across the wide range of possiblepO₂values (0.001–1PAL). At 100–200 Tg N₂O–N year⁻¹and >0.1PALO₂, this model yielded low‐ppmv N₂O, which would produce several degrees of greenhouse warming at 1.6 ppmvCH₄and 320 ppmvCO₂. These results suggest that enhanced N₂O production in ferruginous seawater via a previously unconsidered chemodenitrification pathway may have helped to fill a Proterozoic “greenhouse gap,” reconciling an ice‐free Mesoproterozoic Earth with a less luminous early Sun. A particularly notable result was that high N₂O fluxes at intermediate O₂concentrations (0.01–0.1PAL) would have enhanced ozone screening of solarUVradiation. Due to rapid photolysis in the absence of an ozone shield, N₂O is unlikely to have been an important greenhouse gas if Mesoproterozoic O₂was 0.001PAL. At low O₂, N₂O might have played a more important role as life's primary terminal electron acceptor during the transition from an anoxic to oxic surface Earth, and correspondingly, from anaerobic to aerobic metabolisms.

    

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2. High‐resolution microstructural and compositional analyses of shock deformed apatite from the peak ring of the Chicxulub impact crater

   https://doi.org/10.1111/maps.13541  

   Cox, Morgan A. ; Erickson, Timmons M. ; Schmieder, Martin ; Christoffersen, Roy ; Ross, Daniel K. ; Cavosie, Aaron J. ; Bland, Phil A. ; Kring, David A. ; IODP–ICDP Expedition 364 Scientists ( August 2020 , Meteoritics & Planetary Science)

   The mineral apatite, Ca₅(PO₄)₃(F,Cl,OH), is a ubiquitous accessory mineral, with its volatile content and isotopic compositions used to interpret the evolution of H₂O on planetary bodies. During hypervelocity impact, extreme pressures shock target rocks resulting in deformation of minerals; however, relatively few microstructural studies of apatite have been undertaken. Given its widespread distribution in the solar system, it is important to understand how apatite responds to progressive shock metamorphism. Here, we present detailed microstructural analyses of shock deformation in ~560 apatite grains throughout ~550 m of shocked granitoid rock from the peak ring of the Chicxulub impact structure, Mexico. A combination of high‐resolution backscattered electron (BSE) imaging, electron backscatter diffraction mapping, transmission Kikuchi diffraction mapping, and transmission electron microscopy is used to characterize deformation within apatite grains. Systematic, crystallographically controlled deformation bands are present within apatite, consistent with tilt boundaries that contain the <c> (axis) and result from slip in <> (direction) on(plane) during shock deformation. Deformation bands contain complex subgrain domains, isolated dislocations, and low‐angle boundaries of ~1° to 2°. Planar fractures within apatite form conjugate sets that are oriented within either {, {, {, or. Complementary electron microprobe analyses (EPMA) of a subset of recrystallized and partially recrystallized apatite grains show that there is an apparent change in MgO content in shock‐recrystallized apatite compositions. This study shows that the response of apatite to shock deformation can be highly variable, and that application of a combined microstructural and chemical analysis workflow can reveal complex deformation histories in apatite grains, some of which result in changes to crystal structure and composition, which are important for understanding the genesis of apatite in both terrestrial and extraterrestrial environments.

    

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3. A SUBLIME 3D Model for Cometary Coma Emission: The Hypervolatile-rich Comet C/2016 R2 (PanSTARRS)

   https://doi.org/10.3847/1538-4357/ac5893  

   Cordiner, M. A. ; Coulson, I. M. ; Garcia-Berrios, E. ; Qi, C. ; Lique, F. ; Zołtowski, M. ; de Val-Borro, M. ; Kuan, Y. -J. ; Ip, W. -H. ; Mairs, S. ; et al ( April 2022 , The Astrophysical Journal)

   The coma of comet C/2016 R2 (PanSTARRS) is one of the most chemically peculiar ever observed, in particular due to its extremely high CO/H₂O and${\mathrm{N}}_2^{+}$/H₂O ratios, and unusual trace volatile abundances. However, the complex shape of its CO emission lines, as well as uncertainties in the coma structure and excitation, has lead to ambiguities in the total CO production rate. We performed high-resolution, spatially, spectrally, and temporally resolved CO observations using the James Clerk Maxwell Telescope and Submillimeter Array to elucidate the outgassing behavior of C/2016 R2. Results are analyzed using a new, time-dependent, three-dimensional radiative transfer code (SUBlimating gases in LIME; SUBLIME, based on the open-source version of the LIne Modeling Engine), incorporating for the first time, accurate state-to-state collisional rate coefficients for the CO–CO system. The total CO production rate was found to be in the range of (3.8 − 7.6) × 10²⁸s⁻¹between 2018 January 13 and February 1 (atr_H= 2.8–2.9 au), with a mean value of (5.3 ± 0.6) × 10²⁸s⁻¹. The emission is concentrated in a near-sunward jet, with a half-opening angle of ∼62° and an outflow velocity of 0.51 ± 0.01 km s⁻¹, compared to 0.25 ± 0.01 km s⁻¹in the ambient (and nightside) coma. Evidence was also found for an extended source of CO emission, possibly due to icy grain sublimation around 1.2 × 10⁵km from the nucleus. Based on the coma molecular abundances, we propose that the nucleus ices of C/2016 R2 can be divided into a rapidly sublimating apolar phase, rich in CO, CO₂, N₂, and CH₃OH, and a predominantly frozen (or less abundant), polar phase containing more H₂O, CH₄, H₂CO, and HCN.

    

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4. Weyl Fermions and broken symmetry phases of laterally confined 3 He films

   https://doi.org/10.1088/1361-648X/acf42b  

   Wu, Hao ; Sauls, J. A. ( September 2023 , Journal of Physics: Condensed Matter)

   Broken symmetries in topological condensed matter systems have implications for the spectrum of Fermionic excitations confined on surfaces or topological defects. The Fermionic spectrum of confined (quasi-2D)³He-A consists of branches of chiral edge states. The negative energy states are related to the ground-state angular momentum,$L_z=(N/2)\hslash$, for$N/2$Cooper pairs. The power law suppression of the angular momentum,$L_z(T)\simeq (N/2)\hslash [1-\frac{2}{3}(\pi T/\mathrm{\Delta }{)}^2]$for$0⩽T\ll T_c$, in the fully gapped 2D chiral A-phase reflects the thermal excitation of the chiral edge Fermions. We discuss the effects of wave function overlap, and hybridization between edge states confined near opposing edge boundaries on the edge currents, ground-state angular momentum and ground-state order parameter of superfluid³He thin films. Under strong lateral confinement, the chiral A phase undergoes a sequence of phase transitions, first to a pair density wave (PDW) phase with broken translational symmetry at$D_{c2}\sim 16{\xi }_0$. The PDW phase is described by a periodic array of chiral domains with alternating chirality, separated by domain walls. The period of PDW phase diverges as the confinement length$D\to D_{c_2}$. The PDW phase breaks time-reversal symmetry, translation invariance, but is invariant under the combination of time-reversal and translation by a one-half period of the PDW. The mass current distribution of the PDW phase reflects this combined symmetry, and originates from the spectra of edge Fermions and the chiral branches bound to the domain walls. Under sufficiently strong confinement a second-order transition occurs to the non-chiral ‘polar phase’ at$D_{c1}\sim 9{\xi }_0$, in which a single p-wave orbital state of Cooper pairs is aligned along the channel.

    

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5. NMR Study of CO 2 Capture by Butylamine and Oligopeptide KDDE in Aqueous Solution: Capture Efficiency and Gibbs Free Energy of the Capture Reaction as a Function of pH**

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

   Yang, Kaidi ; Schell, Joseph ; Gallazzi, Fabio ; Wycoff, Wei ; Glaser, Rainer ( April 2023 , ChemPhysChem)

   We have been interested in the development of rubisco‐based biomimetic systems for reversible CO₂capture from air. Our design of the chemical CO₂capture and release (CCR) system is informed by the understanding of the binding of the activator CO₂(^ACO₂) in rubisco (ribulose‐1,5‐bisphosphate carboxylase/oxygenase). The active site consists of the tetrapeptide sequence Lys‐Asp‐Asp‐Glu (or KDDE) and the Lys sidechain amine is responsible for the CO₂capture reaction. We are studying the structural chemistry and the thermodynamics of CO₂capture based on the tetrapeptide CH₃CO−KDDE−NH₂(“KDDE”) in aqueous solution to develop rubisco mimetic CCR systems. Here, we report the results of¹H NMR and¹³C NMR analyses of CO₂capture by butylamine and by KDDE. The carbamylation of butylamine was studied to develop the NMR method and with the protocol established, we were able to quantify the oligopeptide carbamylation at much lower concentration. We performed a pH profile in the multi equilibrium system and measured amine species and carbamic acid/carbamate species by the integration of¹H NMR signals as a function of pH in the range 8≤pH≤11. The determination of ΔG₁(R) for the reaction R−NH₂+CO₂R−NH−COOH requires the solution of a multi‐equilibrium equation system, which accounts for the dissociation constantsK₂andK₃controlling carbonate and bicarbonate concentrations, the acid dissociation constantK₄of the conjugated acid of the amine, and the acid dissociation constantK₅of the alkylcarbamic acid. We show how the multi‐equilibrium equation system can be solved with the measurements of the daughter/parent ratioX, the knowledge of the pH values, and the initial concentrations [HCO₃⁻]₀and [R‐NH₂]₀. For the reaction energies of the carbamylations of butylamine and KDDE, our best values are ΔG₁(Bu)=−1.57 kcal/mol and ΔG₁(KDDE)=−1.17 kcal/mol. Both CO₂capture reactions are modestly exergonic and thereby ensure reversibility in an energy‐efficient manner. These results validate the hypothesis that KDDE‐type oligopeptides may serve as reversible CCR systems in aqueous solution and guide designs for their improvement.

    

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