ACS Earth and Space Chemistry最新文献

The search for the molecular origins of life likely must go through polyimines, and this quantum chemical work shows that the anti-(E,Z)-1,2-diiminoethane molecule would be the next natural step as a detection target. This conformer exhibits a 2.78 D dipole moment and is the second-lowest-energy conformer after the nonpolar anti-(E,E) form. Additionally, the previously assigned N–H antisymmetric stretch of the lowest-energy anti-(E,E) conformer should likely be decreased in frequency to closer to 2930 cm^–1. The full set of anharmonic, fundamental vibrational frequencies and spectroscopic constants of all six conformers are produced in this work and will aid in any possible, future characterization of 1,2-diiminoethane and its possible role in the buildup of prebiotic molecules where multiple C = N bonds are required.

Modeling atmospheric reactions that lead to the formation of secondary organic aerosol (SOA) is an important tool for understanding the current and future impacts of human activity on the environment. Vapor pressure is a key parameter in modeling these reactions, as it largely determines the gas-particle partitioning of atmospheric oxidation products. However, the vapor pressures of many atmospherically relevant molecules are still poorly constrained. To aid modeling efforts, several structure–activity relationships (SARs) based on group contribution methods have been developed for estimating compound vapor pressures. The current study evaluates how four of these SARs: SIMPOL, EVAPORATION, SPARC, and Nannoolal impact the modeled predictions of SOA yields for reactions of C₈–C₁₄ 1-alkenes and C₉–C₁₅ 2-methyl-1-alkenes with OH radicals in the presence of NO_x. The models include well-constrained, quantitative reaction mechanisms developed by our research group from several previous environmental chamber studies of product yields, gas-particle and gas-wall partitioning, and secondary reactions with OH radicals. Based on our previous product studies and the results of this study, there was no need to account for particle-phase oligomer formation. Comparison of modeled and measured SOA yields provide insight into the major products responsible for SOA formation over the large range of carbon numbers, and the sources of discrepancies between model predictions and measurements. The generally moderate to poor model-measurement agreement exemplifies the need for further development of vapor pressure estimation methods, which have a major impact on atmospheric SOA modeling. The systems studied here could be useful to others interested in developing and evaluating models for simulating SOA formation.

Efflux of carbon dioxide from soil is a central component of the carbon cycle and climate models, but one potentially large source is rarely indicated, namely, photochemical decomposition of soil organic matter. A survey from diverse environments around the world shows that this process is almost ubiquitous and comparable in magnitude to respiration. Moreover, it can persist when respiration subsides, such as in dry and cold soils.

Laboratory experiments extend our possibility to understand the behavior of organic molecules under extraterrestrial conditions. In the scope of such simulation experiments, organic molecules are often prepared as thin films, embedded in ice matrices, or adsorbed onto mineral surfaces. Albeit a single-species approach often adequately mimics the conditions to be studied, there are scenarios where the interactions between different organic molecules should be considered. In this work, we investigate the interaction of the two simplest α-amino acids, glycine and alanine, while codeposited as homogeneous nanolayers. Our results demonstrate that their interaction leads to deposition patterns, infrared signatures, and electronic properties that cannot be predicted by studying each molecular species in isolation. We conclude that organic interactions influence the photochemistry and spectroscopic signatures of biomolecules potentially present in planetary environments of interest such as Titan’s surface.

The phase state of secondary organic aerosols (SOA) can range from liquid through amorphous semisolid to glassy solid, which is important to consider as it influences various multiphase processes including SOA formation and partitioning, multiphase chemistry, and cloud activation. In this study, we simulate the glass transition temperature and viscosity of SOA over the globe using the global chemical transport model, GEOS-Chem. The simulated spatial distributions show that SOA at the surface exist as liquid over equatorial regions and oceans, semisolid in the midlatitude continental regions, and glassy solid over lands with low relative humidity. The predicted SOA viscosities are mostly consistent with the available measurements. In the free troposphere, SOA particles are mostly predicted to be semisolid at 850 hPa and glassy solid at 500 hPa, except over tropical regions including Amazonia, where SOA are predicted to be low viscous. Phase state also exhibits seasonal variation with a higher frequency of semisolid and solid particles in winter compared to warmer seasons. We calculate equilibration time scales of SOA partitioning (τ_eq) and effective mass accommodation coefficient (α_eff), indicating that τ_eq is shorter than the chemical time step of GEOS-Chem of 20 min and α_eff is close to unity for most locations at the surface level, supporting the application of equilibrium SOA partitioning. However, τ_eq is prolonged and α_eff is lowered over drylands and most regions in the upper troposphere, suggesting that kinetically limited growth would need to be considered for these regions in future large-scale model studies.

Advancements in off-world food and fiber production should seek to utilize regolith as a source of nutrients and prepare it for use as a solid plant growth substrate. Towards this goal, aeroponic biowaste streams containing both inorganic nutrients and root system efflux from plants provide an opportunity for accelerated weathering and enhancement of extraterrestrial soils. To test this hypothesis, an aeroponic system was built that contained Martian simulant (Mars Mojave Simulant-2; MMS-2), inert sand, and a no-filter control to evaluate the in-line filters for simultaneous mineral weathering and recycling of biowastes from wheat. The growth performance of wheat in aeroponics was highly productive across all treatments. After inundation with biowastes from the aeroponic system growing wheat for 40 days, MMS-2 sorbed P and K and released Al, B, Ca, Fe, Mn, Na, and S into the nutrient solution. Generated plant biowaste was mixed into MMS-2 and sand treatments, which increased the extractable Fe, K, Mg, P, and S in MMS-2. Substrate chemical properties were quantified (e.g., total C and N, total and extractable elements, pH, EC, particle size, and P species). Augmentation of MMS-2 with aeroponic biowastes followed by amendment with plant residue greatly improved wheat growth compared with the unmodified MMS-2, which resulted in plant death. This technology expands lunar/Martian base agriculture by offering a means to acquire nutrients from weathered regolith while simultaneously improving the fertility of extraterrestrial soils.

Fe(III)-reducing bacteria, consisting of different species with varying cell numbers in the environment, are present, together with redox-active electron shuttles and both dissolved and solid Fe(III) species. However, the effect of electron shuttles and Fe(III)-organic-matter(Fe(III)-OM) complexes on microbial Fe(III) reduction is mainly based on a few early isolated model strains. Due to variations in experimental methods among different researchers, it remains unclear whether these two types of compounds influence different Fe(III)-reducing bacteria differently at varying cell numbers. To address this question, we conducted cell suspension experiments with Shewanella oneidensis MR-1, Aeromonas sp. CD and Aeromonas sp. XH, and evaluated reduction rates of Fe(III)-citrate and ferrihydrite with or without AQDS at three different inoculum concentrations. Our results showed that electron shuttles promoted Fe(III) reduction to different extents among these bacteria, along with varying ratios of the rates of Fe(III)-OM reduction and ferrihydrite reduction. Furthermore, cell numbers also influenced the impact of electron shuttle on Fe(III) reduction; ferrihydrite reduction rates were not increasing proportionally with increasing inoculum concentrations when electron shuttles were present. Comparative genomics suggested that differences in the identity of the Fe(III) reductase and the type of Fe(III)-chelators potentially synthesized probably led to these varied promotional effects. These results highlight the significant differences between model and nonmodel Fe(III)-reducing bacteria, suggesting that the presence of Fe(III)-OM complexes and electron shuttles may determine the presence and abundances of certain Fe(III)-reducing bacteria in different environments.

Modern euxinic environments are useful proxies for early Earth. We investigated the morphological and chemical properties preserved in sediments impacted by a modern euxinic spring, an early Earth proxy, as compared to adjacent unimpacted sediments. We used X-ray diffraction (XRD) to analyze the mineralogy of bulk sediment and isolated clay fractions. We further examined the morphology and chemistry of smectite clay nanoparticles using scanning/transmission electron microscopy (S/TEM) and energy-dispersive X-ray spectroscopy (EDX). XRD results show that pyrite and barite are present in all of the impacted sediments but absent in the unimpacted sediments. Although grain size analysis shows the impacted samples have more clay-sized particles, the mineralogy of impacted and unimpacted clay fractions is composed of smectite, chlorite, kaolinite, and illite clays. We further focused on smectite clay nanoparticles, as they are known to be sensitive proxies for redox conditions. Smectites with a platy and cornflake texture were prevalent in all samples. However, EDX results reveal differences between the smectites in the impacted and unimpacted samples: impacted smectites additionally incorporate S, Ba, and Sr. Furthermore, STEM–EDX shows evidence of nanoscale barite and pyrite precipitation on the impacted smectites. Ultimately, this study demonstrates that (1) XRD-detectable sulfur bearing minerals in a soil profile exposed to euxinic groundwater are present outside the zone with visible sediment iron reduction and (2) Al-smectite nanoparticles primarily respond to euxinic conditions by immobilizing cations via adsorption or interlayer cation exchange rather than significantly changing their octahedral sheet cation composition.

Infrared (IR) cooling of polycyclic aromatic hydrocarbon (PAH) molecules is a major radiative stabilization mechanism of PAHs present in space and is the origin of the aromatic infrared bands (AIBs). Here, we report an anharmonic cascade model in a master equation framework to model IR emission rates and emission spectra of energized PAHs as a function of internal energy. The underlying (simple harmonic cascade) framework for fundamental vibrations has been developed through the modeling of cooling rates of PAH cations and other carboneaous ions measured in electrostatic ion storage ring experiments performed under “molecular cloud in a box” conditions. The anharmonic extension is necessitated because cyano-PAHs, recently identified in Taurus Molecular Cloud-1 (TMC-1), exhibit strong anharmonic couplings, which make substantial contributions to the IR emission dynamics. We report an experimental mid-IR (650–3200 cm^–1) absorption spectrum of 2-cyanoindene (2CNI), which is the smallest cyano-PAH that has been identified in TMC-1 and model its IR cooling rates and emission properties. The mid-IR absorption spectrum is reasonably described by anharmonic calculations at the B3LYP/N07D level of theory that include resonance polyad matrices, although the CN-stretch mode frequency continues to be difficult to describe. The anharmonic cascade framework can be readily applied to other neutral or charged PAHs and is also readily extended to include competing processes, such as recurrent fluorescence and isomerization.

Among the numerous molecular systems found in the interstellar medium (ISM), vinyl cyanide is the first identified olephinic nitrile. While it has been observed in various sources, its detection in Sgr B2 is notable as the 2₁₁–2₁₂ rotational transition exhibits maser features. This indicates that local thermodynamic equilibrium conditions are not fulfilled, and an accurate estimation of the molecular abundance in such conditions involves solving the statistical equilibrium equations, taking into account the competition between the radiative and collisional processes. This, in turn, requires the knowledge of rotational excitation data for collisions with the most abundant species, He or H₂. In this paper, the first three-dimensional CH₂CHCN–He potential energy surface is computed using the explicitly correlated coupled-cluster theory [(CCSD(T)-F12] with a combination of two basis sets. Scattering calculations of the rotational (de-)excitation of CH₂CHCN induced by He atoms are performed with the quantum mechanical close-coupling method in the low-energy regime. Rotational state-to-state cross sections derived from these calculations are used to compute the corresponding rate coefficients. The interaction potential exhibits a high anisotropy, with a global minimum of −53.5 cm^–1 and multiple local minima. Collisional cross sections are calculated for total energies up to 100 cm^–1. When the cross sections are thermally averaged, collisional rate coefficients are determined for temperatures up to 20 K. A propensity favoring the transitions with Δk_a = 0 is observed.