Primordial Cells Research Articles

Vacuum-ultraviolet irradiation of pyridine:acetylene ices relevant to Titan astrochemistry.

Nitrogen-containing polycyclic aromatic hydrocarbons (NPAHs) are important molecules for astrochemistry and prebiotic chemistry, as their occurrence spans from interstellar molecular clouds to planetary systems. Their formation has been previously explored in gas phase experiments, but the role of solid-state chemical reactions in their formation under cryogenic conditions remains elusive. Here, we explore the formation of NPAHs through vacuum ultraviolet (VUV) irradiation of pyridine:acetylene ices in amorphous and co-crystalline phases, with the aim to simulate conditions relevant to the interstellar medium and Titan's atmosphere. Our results show that the synthesis of ethynylpyridines from VUV-irradiated pyridine:acetylene amorphous ices is achievable at 18 K. In the co-crystal phase, photolysis at 110 K leads to the formation of NPAHs such as quinolizinium+ and precursors, reflecting a dynamical system under our conditions. In contrast, irradiation at 90 K under stable conditions did not produce volatile photoproducts. These results suggest that such chemical processes can occur in Titan's atmosphere and potentially in its stratosphere, where the co-condensation of these molecules can form composite ices. Concurrently, the formation of stable co-crystals can influence the depletion rates of pyridine, which suggests that these structures can be preserved and potentially delivered to Titan's surface. Our findings provide insights into the molecular diversity and chemical evolution of organic matter on Titan, crucial for future space exploration missions, such as the Dragonfly mission, which may uncover higher-order organics derived from pyridine precursors on Titan's surface.

Induction of Primordial Germ Cell-Like Cells from Rat Pluripotent Stem Cells.

In vitro induction of primordial germ cell like-cells (PGCLCs) from pluripotent stem cells (PSCs) is a robust method that will contribute to understanding the fundamentals of cell fate decisions, animal breeding, and future reproductive medicine. Here, we introduce this system established in the rat model. We describe a stepwise protocol to induce epiblast-like cells and subsequent PGCLCs by forming spherical aggregates from rat PSCs. We also describe a protocol to mature these PGCLCs from specified/migratory to the gonadal stage by aggregation with female gonadal somatic cells.

DNA methylation restricts coordinated germline and neural fates in embryonic stem cell differentiation.

As embryonic stem cells (ESCs) transition from naive to primed pluripotency during early mammalian development, they acquire high DNA methylation levels. During this transition, the germline is specified and undergoes genome-wide DNA demethylation, while emergence of the three somatic germ layers is preceded by acquisition of somatic DNA methylation levels in the primed epiblast. DNA methylation is essential for embryogenesis, but the point at which it becomes critical during differentiation and whether all lineages equally depend on it is unclear. Here, using culture modeling of cellular transitions, we found that DNA methylation-free mouse ESCs with triple DNA methyltransferase knockout (TKO) progressed through the continuum of pluripotency states but demonstrated skewed differentiation abilities toward neural versus other somatic lineages. More saliently, TKO ESCs were fully competent for establishing primordial germ cell-like cells, even showing temporally extended and self-sustained capacity for the germline fate. By mapping chromatin states, we found that neural and germline lineages are linked by a similar enhancer dynamic upon exit from the naive state, defined by common sets of transcription factors, including methyl-sensitive ones, that fail to be decommissioned in the absence of DNA methylation. We propose that DNA methylation controls the temporality of a coordinated neural-germline axis of the preferred differentiation route during early development.

Enhanced condensation kinetics in aqueous microdroplets driven by coupled surface reactions and gas-phase partitioning.

Although aqueous microdroplets have been shown to exhibit enhanced chemical reactivity compared to bulk solutions, mechanisms for these enhancements are not completely understood. Here we combine experimental measurements and kinetic modeling to show the strong coupling of interfacial reactions and gas/droplet partitioning in the condensation reaction of pyruvic acid (PA) to yield zymonic acid (ZA) in acidic aqueous microdroplets. Experimental analysis of single microdroplets reveals the substantial influence of evaporation of PA and partitioning of water on the size-, relative humidity (RH)- and temperature-dependent sigmoidal reaction kinetics for the condensation reaction. A newly developed diffusion-reaction-partitioning model is used to simulate the complex kinetics observed in the microdroplets. The model can quantitatively predict the size and compositional changes as the reaction proceeds under different environmental conditions, and provides insights into how microdroplet reactivity is controlled by coupled interfacial reactions and the gas-phase partitioning of PA and water. Importantly, the kinetic model best fits the data when an autocatalytic step is included in the mechanism, i.e. a reaction step where the product, ZA, catalyzes the interfacial condensation reaction. Overall, the dynamic nature of aqueous microdroplet chemistry and the coupling of interfacial chemistry with gas-phase partitioning are demonstrated. Furthermore, autocatalysis of small organic molecules at the air-water interface for aqueous microdroplets, shown here for the first time, has implications for several fields including prebiotic chemistry, atmospheric chemistry and chemical synthesis.

Protein desulfurization and deselenization.

Methods enabling the dechalcogenation of thiols or selenols have been investigated and developed for a long time in fields of research as diverse as the study of prebiotic chemistry, the engineering of fuel processing techniques, the study of biomolecule structures and function or the chemical synthesis of biomolecules. The dechalcogenation of thiol or selenol amino acids is nowadays a particularly flourishing area of research for being a pillar of modern chemical protein synthesis, when used in combination with thiol or selenol-based chemoselective peptide ligation chemistries. This review offers a comprehensive and scholarly overview of the field, emphasizing emerging trends and providing a detailed and critical mechanistic discussion of the dechalcogenation methods developed so far. Taking advantage of recently published reports, it also clarifies some unexpected desulfurization reactions that were observed in the past and for which no explanation was provided at the time. Additionally, the review includes a discussion on principal desulfurization methods within the framework of newly introduced green chemistry metrics and toolkits, providing a well-rounded exploration of the subject.

Impact‐Generated Permeability and Hydrothermal Circulation at the Vredefort Impact Structure, South Africa

AbstractThe 2.02 billion year old Vredefort impact structure in South Africa offers a unique opportunity to study large‐scale impact processes on Earth. Vredefort's large size (∼250 km in diameter) and eroded topography provides the opportunity to study the effects of shock physics at depth and post‐formation hydrothermal alteration. In this work, we simulate the formation of the Vredefort structure building upon recent shock physics (iSALE) simulations. We expand those simulations to cover a wider range of input conditions, and compute impact‐driven porosity and permeability. The latter quantities are used to perform fluid mobility simulations (HYDROTHERM). We find that the Vredefort event produced significant impact‐generated porosity (up to 30%) in an annulus from about 50 to 100 km from the center and up to several kilometers in depth. The corresponding estimated permeability (up to 10−12 m2) would have allowed for large scale subsurface fluid flows. Our hydrothermal calculations show that the Vredefort impact event could have generated a complex crustal fluid pattern within the crater rim that lasted for hundreds of thousand years, with localized flow concentration regions, opening a new interpretation for the mobilization and location of the ore deposits in the Witwatersrand basin. The combined approach utilizing impact and hydrothermal simulations constitute a powerful tool to understand geochemical processes at Vredefort, as well as to assess the ability of large impacts to drive crustal chemistry with far‐reaching consequences for the prebiotic evolution of the early Earth.

Proposal of a Process for selection solar cells Nanosatellite

By the PEDAGOSAT project we aim to democratize all educational activities related to CubeSat-class: nanosatellite, from physics through engineering, technical achievements, integration, to testing and operations to the greatest number of students. The key idea is to eventually have our academic nanosatellite training platform offering an open source opportunity to Algerians universities, and having the capacity to cover all engineer training areas relating to "small satellites". As part of this project, some satellite subsystems, test and emulation facilities will be realized, processes and procedures for testing and integration related to space technology will be addressed, implemented and even mastered. The presented work is part of the development of the on-board power system, and covers the selection of solar cells for the manufacture of solar panels of this satellite. The main source of energy present in space is solar energy, it a continuous and inexhaustible source that a satellite can. In satellite we use a solar panel to ensure its operation. In the dimensioning of a satellite, it is essential to identify these electrical power requirements named “power budget analysis”. Indeed, this makes it possible to determine the number of cells and/solar panels to be installed to guarantee the power continuity of the satellite in sunlight phase of its orbit by recharging its batteries and feeding equipment’s. During all the mission duration; from the beginning of life (BOL) after the launch to it deorbits (EOL) to disintegrate in the atmosphere. For the PEDAGO-SAT as for other satellites, it will be necessary to verify the parameters and physical characteristics of the solar cells/panels according to certified procedures and methodologies in order to be able to pronounce on their qualification for aerospace use. In this context, we propose a low-cost process revision to be able to carry out qualification tests with an accessible facility in the university labs. This revision will also concern the development of homemade means and software that fit the investments that may be made by the Algerian research and academic facilities. As illustrated in this paper a performance evaluation of low-cost solar cells was done using the developed solution and the selected cells will be integrated in the solar panels of PEDAGOSAT.

Olivine-catalyzed glycolaldehyde and sugar synthesis under aqueous conditions: Application to prebiotic chemistry

The presence of minerals in the prebiotic environment likely shaped the evolution of organic matter, thereby contributing to the emergence of prebiotic systems. Records of such systems are lacking and the interactions between abiotic organic matter and primary minerals remain poorly understood. Here, we demonstrate the ability of olivine silicates, in simulated early Earth or planetary aqueous environments, to catalyse glycolaldehyde formation from only formaldehyde, and help producing sugars that are essential components for life, through the formose reaction. By combining comprehensive gas chromatography analyses on experimental samples with quantum chemical simulations, we provide a mechanism for an olivine-catalyzed glycolaldehyde formation. Our findings suggest that olivine plays a triple role in the formose chemical network: maintaining an alkaline pH, enabling the initiation step towards the formation of glycoladehyde (which is typically the most challenging step) and promoting the autocatalytic cycle. These results open-up new scenarios on the impact of primary minerals on the evolution of chemical pathways in aqueous environments that were probably essential for the emergence of the first biomolecules.

Principles of cognitive biology and the concept of biocivilisations

A range of studies published in the last few decades promotes the cognitive aspects of life: all organisms, from bacteria to mammals, are capable of sensing/perception, decision-making, problem-solving, learning, and other cognitive functions, including sentience and consciousness. In this paper I present a scientific and philosophical synthesis of these studies, leading to an integrated view of cognitive biology. This view is expressed through the four principles applicable to all living systems: (1) sentience and consciousness, (2) autopoiesis, (3) free energy principle and relational biology, and (4) cognitive repertoire. The principles are circular, and they reinforce themselves. The circularity is not rigid, meaning that hierarchical and heterarchical shifts are widespread in the biosphere. The above principles emerged at the dawn of life, with the first cells, bacteria and archaea. All biogenic forms and functions that emerged since then can be traced to the first cells – indivisible units of biological agency. Following these principles, I developed the concept of biocivilisations to explain various forms of social intelligence in different kingdoms of life. The term biociviloisations draws on the human interpretation of the concept of civilisation, which searches for non-human equivalents of communication, engineering, science, medicine, art, and agriculture, in all kingdoms of life by applying the principles of cognitive biology. Potential avenues for testing the concept of biocivilisations are highlighted.

Metabolic memory of Δ9-tetrahydrocannabinol exposure in pluripotent stem cells and primordial germ cells-like cells

Cannabis, the most consumed illicit psychoactive drug in the world, is increasingly used by pregnant women. However, while cannabinoid receptors are expressed in the early embryo, the impact of phytocannabinoids exposure on early embryonic processes is lacking. Here, we leverage a stepwise in vitro differentiation system that captures the early embryonic developmental cascade to investigate the impact of exposure to the most abundant phytocannabinoid, Δ9-tetrahydrocannabinol (Δ9-THC). We demonstrate that Δ9-THC increases the proliferation of naive mouse embryonic stem cells (ESCs) but not of their primed counterpart. Surprisingly, this increased proliferation, dependent on the CB1 receptor binding, is only associated with moderate transcriptomic changes. Instead, Δ9-THC capitalizes on ESCs’ metabolic bivalence by increasing their glycolytic rates and anabolic capabilities. A memory of this metabolic rewiring is retained throughout differentiation to Primordial Germ Cell-Like Cells in the absence of direct exposure and is associated with an alteration of their transcriptional profile. These results represent the first in-depth molecular characterization of the impact of Δ9-THC exposure on early stages of germline development.

Metabolic memory of Δ9-tetrahydrocannabinol exposure in pluripotent stem cells and primordial germ cells-like cells.

Cannabis, the most consumed illicit psychoactive drug in the world, is increasingly used by pregnant women. However, while cannabinoid receptors are expressed in the early embryo, the impact of phytocannabinoids exposure on early embryonic processes is lacking. Here, we leverage a stepwise in vitro differentiation system that captures the early embryonic developmental cascade to investigate the impact of exposure to the most abundant phytocannabinoid, Δ9-tetrahydrocannabinol (Δ9-THC). We demonstrate that Δ9-THC increases the proliferation of naive mouse embryonic stem cells (ESCs) but not of their primed counterpart. Surprisingly, this increased proliferation, dependent on the CB1 receptor binding, is only associated with moderate transcriptomic changes. Instead, Δ9-THC capitalizes on ESCs' metabolic bivalence by increasing their glycolytic rates and anabolic capabilities. A memory of this metabolic rewiring is retained throughout differentiation to Primordial Germ Cell-Like Cells in the absence of direct exposure and is associated with an alteration of their transcriptional profile. These results represent the first in-depth molecular characterization of the impact of Δ9-THC exposure on early stages of germline development.

Mesoporous Carbon Supported Catalyst for Heavy Duty Fuel Cells

The interaction between the catalyst and the carbon support is crucial to both the performance and durability of the membrane electrode assembly (MEA) in a polymer electrolyte membrane fuel cell. Local oxygen transport resistance (RO2) has shown to be a significant contributor to the overpotential loss in the catalyst layer.1 Utilizing mesoporous carbon supports has shown to reduce RO2 compared to high surface area carbon and prevent ionomer poisoning of Pt inside the pores.2 Engineered catalyst supports (ECS) synthesized through templated organic precursor provides improved control of resulting carbon morphology.3 This work presents a detailed study of the performance and durability of the ECS supported catalyst. Effect of Pt weight percentage on the carbon support, ionomer loading, and the ionomer type on the catalyst performance and durability is presented. Figure 1 shows the performance at beginning of life (BOL) and end of life (EOL) after 90000 cycles, using US DOE’s electrocatalyst protocol, for MEAs with different ionomer loadings. Polarization curve, Pt accessibility through CO stripping, and RO2 from limiting current will be presented are measured at different intervals between BOL and EOL. Characterization of the Pt particle and catalyst layer structure performed at BOL and EOL will also be presented. This study highlights the value of the morphological and electrochemical evaluation to provide detailed insights into the catalyst and mesoporous carbon support interaction. Acknowledgement This research is supported by Technology Readiness Gross Receipts Tax Credit through New Mexico Legislature. This research is supported by U.S. Department of Energy (DOE) Hydrogen and Fuel Cell Technologies Office, through the Million Mile Fuel Cell Truck Consortium (M2FCT). References 1 Kongkanand, A. et al. Journal of Physical Chemistry Letters, 7, (7), 1127-1137, 2016.2 Ramaswamy, N. et al. Journal of The Electrochemical Society, 167, (6), 064515, 2020.3 Ramaswamy, N. US DOE Hydrogen and Fuel Cells Program: 2020 Annual Merit Review and Peer Evaluation Report, 2020. Figure 1

Comparison of MEA Degradation through FCV Actual Driving Test and Load-Cycle Durability Test

Introduction In research and development of high-durability polymer electrolyte fuel cells (PEFCs) for fuel cell vehicles (FCVs), accelerated stress tests (ASTs) are employed to evaluate durability of materials with a short time [1-3]. In order to validate an AST, it is necessary to confirm that the degradation mechanisms in the AST and in actual FCV operation are consistent, and to elucidate quantitative correspondence of their degradation rates. In this study, we analyzed degradation of a membrane electrode assembly (MEA) after FCV real-world driving and compared the degradation factor with that of a load-cycle durability test in a laboratory. Experiments MEA samples were extracted from an FC stack of a Toyota MIRAI 2014 model which was operated in real-world driving of 200,000 km, about 6000 h. MEA performance and electrochemical properties of them were investigated using a small differential cell with a straight flow field. As a comparison, another MEA at beginning of life (BOL) was subjected to a load-cycle durability test following a protocol encouraged by New Energy and Industrial Technology Development Organization (NEDO), Japan. Cell temperature and relative humidity were controlled at 80°C and 100%, respectively. A square-wave potential cycle shown in Figure 1 was adopted. MEA performance was investigated after cycles of 500, 1000, 3000, 10,000, and 30,000. Structures of catalyst layers and catalyst particles were analyzed for the MEAs after driving test and 30,000 cycles of the load-cycle test using scanning electron microscope (SEM), transmission electron microscope (TEM), and X-ray absorption fine structure (XAFS). Results and discussion The performance of the MEA after 200,000 km driving is close to that of the MEA after 30,000 cycles of the load-cycle test as shown in Figure 2. The performance degradation is mainly attributed to degradation of the catalyst layer, and properties of a gas diffusion layer and a proton exchange membrane are unchanged from those of the BOL sample. Degradation mechanisms of the catalyst layers in the driving test and the load cycle test are well corresponding. First, mass activities of PtCo catalyst decay to about a half of the BOL value mainly due to the decrease in electrochemically effective surface areas (ECSAs) as represented in Figure 3. Decrease rates of the ECSAs are consistent with the increase in average particle sizes of the catalyst. The catalyst size distributions of the two samples are also comparable. Then, oxygen transport resistance in the catalyst layers is increased. The resistance of the samples after the driving test and 30,000 cycles of the load-cycle test are twice as large as the BOL value. As shown in Figure 4, the transport resistance obviously exhibits inverse proportion to the catalyst surface area. This relationship represents that the primary factor of the resistance is one at vicinity of catalyst particles including ionomer permeation [4], and increase in it is attributed to decrease in the catalyst surface area. A performance simulation based on a simple 1-dimensioal MEA model supports that the decrease in the ECSA causes most of the MEA performance degradation through the deterioration in the catalyst activity and the oxygen transport resistance. Conclusions The MEA performance degradation after the 200,000 km real-world driving with the system of MIRAI 2014 model is primarily caused by catalyst metal coarsening and is well simulated by NEDO load-cycle durability test of 30,000 cycles. This result has validated the test protocol and should contribute to a target-setting of durability of future MEAs.

Microscale Simulation of Carbon Support Structure Degradation in Polymer Electrolyte Fuel Cell

Understanding the mechanism of Polymer electrolyte fuel cell (PEFC) degradation plays an important role in improving fuel cell performance and durability. For the PEFC system, the structure of catalyst layers (CLs) is the critical component that determines cell performance. The PEFC degradation due to the reduction of carbon on the CLs has been investigated in previous studies [1]. In our past studies, we focused on the actual heterogeneous porous structure of catalyst layer. From these results, it was found that mass transport performance of oxygen and proton in heterogeneous porous catalyst layer, which consists of carbon support, ionomer and void space, is much lower than that of theoretical prediction in homogeneous porous media [2-5]. In addition, it depends on the structure of carbon black, the coating structure of ionomer and the local distribution of these materials. Thus, it is important to understand and to predict the carbon support structure change by degradation because this structural degradation strongly affect the mass transport performance. In this work, the effect of CLs porous carbon support degradation on cell performance is investigated by microscale simulation.The CLs structures, consisting of porous carbon, ionomer, and Pt, are created by our previous study multi-block method [2,6]. In our simulation, we focus on studying the effect of CLs' beginning-of-life (BOL) and end-of-life (EOL) structure in the degradation process. The CLs creation procedure is illustrated in Fig. 1. Firstly, CLs structure are created by packing CB and covered ionomer and Pt. The amount of ionomer and Pt are assumed as constant during the degradation process. Therefore, the amount of carbon is reduced in EOL structure. In this study, various CLs structures with decreasing of carbon volume are constructed. Furthermore, the mechanical stress distribution under compression condition was simulated in each structure to understand the effect of framework of carbon on local porosity in catalyst layer. The effect of carbon corrosion in CLs is investigated by calculating the cell performance of PEFC of each CLs structure by ORR mass transport and electrochemical reaction calculation with our previous method [6].The cell performance is significantly decreased by reducing carbon. The degradation mechanism of PFEC is explained by degradation of not only effective surface area but also the porous structure change which affect oxygen diffusion performance. Moreover, compared with BOL structure the apparant thickness of covered ionomer layer is higher in EOL structures because of carbon corrosion and constancy of ionomer. Hence, the higher oxygen diffusion resistance in secondary pore and ionomer layer occur in CLs degradation structures. The effect of this dynamic structure change on cell output performance will be reported in this presentation.Acknowledgements:This research was supported by the New Energy and Industrial Technology Development Organization (NEDO), Japan, grant number P20003-20001327-0.

Carbon Corrosion Behavior of Carbon Support Materials for PGM-Based Catalysts in PEM Fuel Cells

The proton exchange membrane fuel cell (PEMFC) is a promising device for the transportation sector of a fossil free society, using green hydrogen from water electrolysis as a clean and sustainable option. However, sluggish kinetics as well as durability issues limit the implementation until this day. Therefore, modifications to the platinum catalysts [1] and the carbon supports [2] are made to improve the overall performance and durability of the cathode catalyst system.Herein, we present the investigation of the carbon corrosion behavior of different carbon support materials in PEMFCs using online nondispersive infrared (NDIR).The different carbon supports used for this study are commercial materials such as Vulcan, Ketjenblack EC-300J and Ketjenblack EC-600JD as well as self-synthesized mesoporous carbon nanodendrites (MCND). [3] The MCND support material is a highly porous high surface area carbon, which makes it a suitable candidate for fuel cell applications. Onto the support materials, Pt nanoparticles were deposited using a customized fluidized bed reduction reactor [4], resulting in similar Pt particle size and distribution onto the support material, thus making a comparison between different supports possible. Beginning of life (BOL) measurements in a single cell setup, as shown in Figure 1, show promising performance of the platinum catalyst supported on MCND (Pt/CMCND) compared to the platinum catalysts on commercial supports. Furthermore, we will present the investigated carbon corrosion behavior of the different support materials conducted by accelerated stress tests (AST) based on the DOE support degradation protocol. The online quantification of the evolved CO and CO2 from the cathode catalyst layer is measured using our online NDIR giving insight in the carbon corrosion resistivity of the different support materials. Together with the performance measurements, we develop a better understanding of the impact of the carbon support material on the performance and durability of the cathode catalyst layer.Literature:[1] Strasser, P; Kühl, S. Nano Energy 2016, 29, 166.[2] Ott, S. et. al., Nat. Mater. 2020, 19 (1), 77-85.[3] Numao, S. et al., Carbon 2009, 47, 306-312.[4] Hornberger, E. et. Al. J. Electrochem. Soc. 2020, 167, 114509. Figure 1: Air polarization curves of the four different catalysts under the following conditions: 80° C, 100% RH, 150 kPaabs backpressure, stoich.: 1.5 (H2) and 2 (air), min. flow: 50 ml/min (H2) and 800 ml/min (air). Figure 1

Chemo-Mechanical Durability of Reinforced Fuel Cell Membranes in the Presence of Metallic Foreign Particles

High-throughput production is vital to achieve cost-effective proton exchange membrane fuel cells (PEMFCs) at scale1. The high-volume mass production of PEMFCs using industrial manufacturing machinery may however introduce unwanted material in the final product due to the wear and tear of the machinery. As an example, roll-to-roll processes applied to the manufacture of catalyst coated membrane (CCM) generally use Fe alloys such as stainless steel2 components that could release fine metallic particles or related debris that may affect the product quality3,4. Therefore, it is important to understand the fundamental impact of such non-uniformities on PEMFC performance and durability.This work focusses on the impact of slightly oxidized iron (Fe) and stainless steel 316L (SS316L) micro-particles entrapped between the cathode catalyst layer (CCL) and a GORE-SELECT® Membrane A. Fe cations are considered as Fenton’s catalyst/reagent which enhance harmful radical generation and ionomer attack, known to weaken its mechanical strength and ionic conductivity5. Therefore, membrane electrode assemblies (MEAs) containing solid Fe and SS316L particles were prepared to conduct in-situ PEMFC experiments and identify their impact on membrane degradation and durability. The chosen particles were placed carefully on the bare membrane at selected locations based on the flow field design of the graphite bipolar plates. Later, the assembled MEAs were tested using a small-scale fixture (SSF) fuel cell in a combined chemical and mechanical AST after beginning-of-life (BOL) conditioning and diagnostics6.X-ray computed tomography (XCT) has been shown to be a powerful and non-invasive 3D characterization tool for analyzing membrane degradation7,8. Thus, periodic same-location XCT visualization of the CCL-membrane interface was performed after every 10 AST cycles. According to the Fe Pourbaix diagram9, Fe oxidizes to Fe2+ at 0.77 V and indeed, in this work, complete dissolution of the Fe-50µm particles was observed leaving cavities at the CCL-membrane interface. This dissolution manifested as a distinct black spot in CT imaging, as highlighted by the enclosed red circle in Figure 1. In contrast, corrosion of SS316L particles is usually prevented by a native oxide layer formation during fuel cell operational conditions10. The Fe particle laden AST reached membrane failure within 30 cycles and indicates an escalation of degradation by global membrane thinning. This is substantially lower than the baseline AST without particles. The XCT images for Fe-50µm AST seen in Figure 1 show that severe global membrane thinning occurred in the Fe-50µm MEA, which contributed to a high electrochemical leak detection (ELDT) signal exceeding test failure criteria. In contrast, the SS316L MEA did not reach the threshold failure criteria for the AST duration, however, the average OCV remained lower as compared to the baseline MEA AST. XCT imaging showed that the SS316L- 50µm particles did not dissolve throughout the AST duration and the membrane thinning was more pronounced near the particle rather than globally. Additionally, we have evaluated whether chemically and mechanically mitigated GORE-SELECT Membrane® B could enable more robustness and minimize impact of multiple metallic particles. Analysis of combined chemo-mechanical AST with a larger dimension SS316L-500µm present on mitigated GORE-SELECT® Membrane B suggest that chemical and mechanical mitigation can reduce impact of large particles and enable lifetime response at the level close to baseline. In conclusion, the membrane lifetime and failure mode were found to be strongly dependent on the particle chemical composition and membrane degradation mitigation strategies, which are therefore should be considered at PEM design stages to reduce risks and improve CCM and MEA production quality. Keywords: PEM durability, quality control, cost reduction, XCT Acknowledgments This research was supported by the Natural Sciences and Engineering Research Council of Canada, Canada Foundation for Innovation, British Columbia Knowledge Development Fund, Western Economic Diversification Canada, Ballard Power Systems, and W.L. Gore & Associates. This research was undertaken, in part, thanks to funding from the Canada Research Chairs program. References H. Tsuchiya and O. Kobayashi, Int. J. Hydrogen Energy, 29, 985–990 (2004).J. Chen, H. Liu, Y. A. Huang, and Z. Yin, J. Manuf. Process., 23, 175–182 (2016).A. Phillips et al., Fuel Cells, 20, 60–69 (2020).A. Phillips, M. Ulsh, K. C. Neyerlin, J. Porter, and G. Bender, Int. J. Hydrogen Energy, 43, 6390–6399.J. G. Goodwin, K. Hongsirikarn, S. Greenway, and S. Creager, J. Power Sources, 195, 7213–7220 (2010).Y. Chen et al., J. Power Sources, 520, 230673 (2022).Y. Chen et al., J. Power Sources, 520, 230674 (2022).Y. Singh et al., J. Power Sources, 412, 224–237 (2019).R. Tolouei et al., Phys. Chem. Chem. Phys., 18, 19637–19646 (2016).N. Kumar et al., Int. J. Energy Res., 44, 6804–6818 (2020). Figure 1

MicroRNA171a regulates plant development and enhances drought stress tolerance

MicroRNAs (miRNAs) play an important role in plant development, and are involved in biotic and abiotic stress resistance. Previously, we identified the miR171a being as a drought-responsive miRNA in rice by small RNA sequencing. However, the mechanisms underlying the involvement of miR171a in drought stress response remains unknown. Therefore, in this study, we aimed to elucidate the molecular mechanisms miR171a in drought stress response. miR171a-overexpression (OX-miR171a) and miR171a-blocking (STTM171, a short tandem target mimic) lines were generated and characterized. The results indicated that overexpression of miR171a affected rice yield related traits, including primary panicles, 1000–grain weight, and root development trait by regulating primordial differentiation and cell size in the meristematic zone. Furthermore, miR171a overexpression significantly enhanced drought tolerance. In addition miR171a gene knockout significantly reduced this trait in both rice and Arabidopsis. We confirmed that miR171a overexpression confers plant abscisic acid-dependent drought stress resistance. In conclusion, we found that miR171a plays a key role in modulating plant growth development and drought response. Therefore, miR171a serves as a potential target for engineering improved plant drought resistance and yield.

The tautomer-specific excited state dynamics of 2,6-diaminopurine using resonance-enhanced multiphoton ionization and quantum chemical calculations.

2,6-Diaminopurine (2,6-dAP) is an alternative nucleobase that potentially played a role in prebiotic chemistry. We studied its excited state dynamics in the gas phase by REMPI, IR-UV hole burning, and ps pump-probe spectroscopy and performed quantum chemical calculations at the SCS-ADC(2) level of theory to interpret the experimental results. We found the 9H tautomer to have a small barrier to ultrafast relaxation via puckering of its 6-membered ring. The 7H tautomer has a larger barrier to reach a conical intersection and also has a sizable triplet yield. These results are discussed relative to other purines, for which 9H tautomerization appears to be more photostable than 7H and homosubstituted purines appear to be less photostable than heterosubstituted or singly substituted purines.

Replication elongates short DNA, reduces sequence bias and develops trimer structure.

The origin of molecular evolution required the replication of short oligonucleotides to form longer polymers. Prebiotically plausible oligonucleotide pools tend to contain more of some nucleobases than others. It has been unclear whether this initial bias persists and how it affects replication. To investigate this, we examined the evolution of 12-mer biased short DNA pools using an enzymatic model system. This allowed us to study the long timescales involved in evolution, since it is not yet possible with currently investigated prebiotic replication chemistries. Our analysis using next-generation sequencing from different time points revealed that the initial nucleotide bias of the pool disappeared in the elongated pool after isothermal replication. In contrast, the nucleotide composition at each position in the elongated sequences remained biased and varied with both position and initial bias. Furthermore, we observed the emergence of highly periodic dimer and trimer motifs in the rapidly elongated sequences. This shift in nucleotide composition and the emergence of structure through templated replication could help explain how biased prebiotic pools could undergo molecular evolution and lead to complex functional nucleic acids.

CRISPR loss of function screening to identify genes involved in human primordial germ cell-like cell development.

Despite our increasing knowledge of molecular mechanisms guiding various aspects of human reproduction, those underlying human primordial germ cell (PGC) development remain largely unknown. Here, we conducted custom CRISPR screening in an in vitro system of human PGC-like cells (hPGCLCs) to identify genes required for acquisition and maintenance of PGC fate. Amongst our candidates, we identified TCL1A, an AKT coactivator. Functional assessment in our in vitro hPGCLCs system revealed that TCL1A played a critical role in later stages of hPGCLC development. Moreover, we found that TCL1A loss reduced AKT-mTOR signaling, downregulated expression of genes related to translational control, and subsequently led to a reduction in global protein synthesis and proliferation. Together, our study highlights the utility of CRISPR screening for human in vitro-derived germ cells and identifies novel translational regulators critical for hPGCLC development.