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A Fluvio‐Lacustrine Environment Preserved in the Jezero Crater Inlet Channel, Neretva Vallis, Mars
No full textInternational audienceMartian fluvial valleys provide evidence for the surface flow of liquid water, making them a key target for rover-based investigations of ancient habitability. The Mars 2020 Perseverance rover spent ∼85 sols exploring the Bright Angel formation, exposed across the floor of Neretva Vallis: the western inlet channel of Jezero crater. This study documents the sedimentology and stratigraphy of the Bright Angel formation to reconstruct its depositional setting. The unit preserves a concave-up bedding structure consistent with a young channel-fill deposit, rather than an older unit exposed by incision of Neretva Vallis. The lower stratigraphy displays a fining-up sequence from coarse-grained sediments up to pebble-conglomerates (the Tuff Cliff member) into a ≥10-m-thick succession of laminated mudstone (the Walhalla Glades member), interpreted as a transgressive sequence recording the onset of lacustrine conditions in Neretva Vallis. Lenses of matrix-supported granule-conglomerate adjacent to the valley wall (the Fern Glen Rapids member) may preserve locally derived debris flows entering the lake. These are overlain by a polymict, matrix-supported, boulder-conglomerate (the Mount Spoonhead member), interpreted as a high-energy debrite derived from the watershed. The sequence is capped by cross-stratified sediments (the Serpentine Rapids member), preserving lake margin deposits. The Bright Angel lacustrine sequence occurs ∼10–50 m higher in elevation than the lake level anticipated for the Jezero western delta, requiring an additional period of lacustrine activity. The structure and spatial distribution of the unit leads us to propose that a late-stage blockage of Neretva Vallis may have facilitated the formation of a perched, valley-confined lake upstream
Sweet taste induced by miraculin from Sisrè pulp (Synsepalum dulcificum Schumach. & Thonn.) from Benin as affected by heat treatment
No full textInternational audienceThis work focused on the effect of heating treatments on the sweetening property of miraculin contained in Sisrè, the fruit of Synsepalum dulcificum, from Benin. The aim was to define suitable conditions for stabilizing the fruit pulp, at a lower cost while preserving its functional properties. The fruits, collected in the locality of Sèhouè in the Republic of Benin, were frozen whole, pulped and then stored at -20 • C before processing and analyzing. Heat treatments ranging from 40 to 70 • C were applied to the fresh pulp for 5 min. Sensory tests were performed on the heated pulp samples to test the functionality of miraculin and determine the remanence time of the induced sweet taste after treatment at different temperatures. Reverse-phase and steric-exclusion chromatography, in association with electrophoresis were performed to analyze the miraculin content of the pulps, and the generated data were compared with the sensory results. Sensory analysis showed that the sweetening effect of the native pulp before heat treatment lasted at least >1 h 30 min. A significant loss of functionality after exposure of the pulp to temperature values above 50 • C was observed. The results of analyses also showed that from 50 • C, the miraculin concentration decreased significantly. At temperature values above 50 • C, miraculin completely lost its functionality even if the pulp still contained miraculin, probably in its monomeric form that are not active. The intensity and remanence of the sweetening effect of miraculin depended on its concentration. These results demonstrated that the pulp of Sisrè cannot be stabilized by thermal pasteurization and that drying at low temperatures between 40 and 50 • C could be a good technological option for preserving its functionality
Modélisation hydrologique et changements climatiques. Méthodologie et applications
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Evaluation of a New Methylimidazole‐Containing Thiosemicarbazone as a Cu<sup>+</sup>/Cu<sup>2+</sup>‐Targeting Ligand in the Context of Alzheimer's Disease
No full textInternational audienceThe binding of copper ions to amyloid‐β (Aβ) peptide leads to reactive oxygen species (ROS) formation and toxic soluble oligomers, contributing to oxidative stress in Alzheimer's disease (AD). Thus, studying compounds with moderate copper affinity is a promising strategy to prevent its interaction with Aβ and reduce toxicity. Here, we evaluated a new tri‐coordinating thiosemicarbazone (HXE) with chelating properties to regulate cuprotoxicity in AD. The ligand was nontoxic against HT‐22 hippocampal neuronal cells and bound Cu+ and Cu2+ at pH 7.4, with affinity constants (log Kcond) of 8.7 and 12.3, respectively, showing high selectivity over Zn2+ (log Kapp = 5.0). In the presence of Aβ and Cu2+, HXE formed stable ternary complexes at physiological pH. Ascorbate consumption and coumarin‐3‐carboxylic acid fluorescence assays showed that the ligand significantly reduces Cu(Aβ16)‐mediated ROS production. It also prevented Cu2+ ‐induced modulation of Aβ40 self‐assembly and restored the typical fibrillar structure of apo‐Aβ40 aggregates. Overall, HXE effectively modulates metal‐associated Aβ toxicity and emerges as a promising candidate for AD bioinorganic management
Synchronous Miocene radiations and geographic-dependent diversification of pantropical Xylopia (Annonaceae).
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Asymmetric hydrogenation of ketones with planar chiral manganese(I) complexes
No full textInternational audienceTridentate P,N,N ferrocenyl ligands 4a-b with planar chirality only have been prepared and evaluated in the manganese-catalysed hydrogenation of aromatic ketones. The MnI complexes 5a-b, prepared in situ from ligands 4a-b and [MnBr(CO)5], showed a complex mixture of stereoisomers and cationic tricarbonyl/neutral dicarbonyl species. The catalytic activity of both complexes is excellent, with a total conversion of acetophenone in 4 h in the presence of 0.1 mol% catalyst and the mild K2CO3 base, under 30 bar of H2 at 50 °C. Ees of up to 69% were obtained with bulky pivalophenone in the presence of 1 mol% catalyst 5b. The results of a computational study, carried out on the Mn-catalysed hydrogenation mechanism, agree with the greater activity and lower enantioselectivity of 4a with respect to previously reported P,N,N ferrocenyl ligands bearing both planar and central chirality, highlighting the useful role of each chiral source
Dyadic Ru-based nanomaterials for visible light-driven photocatalytic hydrogen evolution
No full textInternational audienceVisible light-driven water splitting is an appealing strategy to store renewable energy in the chemical bonds of molecular hydrogen. In this regard, the development of photocatalytic architectures where charge transfer and recombination can be controlled represents a key challenge. The surface functionalization of Ru/RuO 2 nanoparticles (NPs) with the [Ru(2,2′-bpy) 2 (qpy)](PF 6 ) 2 photosensitizer (PS), yielding PS-NPs "dyadic" hybrid nanomaterials, represents a promising strategy. Four HER photocatalysts with different PS:NPs ratios are synthesized and thoroughly characterized by analytical and spectroscopic techniques. X-ray photoelectron spectroscopy (XPS) reveals the covalent binding of the PS to the NPs surface. Analysis of the photocatalytic performance in aqueous triethanolamine (TEOA) shows that the activation of the nanocatalyst (RuO 2 reduction) and the hydrogen evolution rate improves when the PS loading increases. Under visible-light irradiation, the nanomaterials with higher PS loading show sustained production of hydrogen for at least 80 h. The morphological and compositional evolution of the hybrid nanomaterials under photocatalytic conditions is studied and correlated with hydrogen production rates over time, pointing to a sequential leaching of PS from the nanomaterials surface. Additionally, photophysical experiments allow attaining an insight into the photochemical mechanism, which involves oxidative quenching with a fast electron injection, but also fast back electron transfer.</div
Root growth in Arabidopsis depends on the amount of glutathione and not the glutathione redox potential
No full textInternational audienceActivity of the root apical meristem and hence plant growth strictly depends on glutathione homeostasis. Despite compelling evidence for this dependency based on glutathione depletion, the cause for the growth arrest had remained unclear. Meristem control may depend on either the absolute amount of glutathione or on the glutathione redox potential (EGSH). To unambiguously distinguish those two options, we characterized an allelic series of six Arabidopsis mutants affected in glutamate-cysteine ligase, which catalyses the first step for the biosynthesis of reduced glutathione (GSH). When grown under the same conditions, even mutants with 20% and 50% of wild-type GSH amounts are slightly stunted. The most severely compromised mutants, zir1 and rml1, were crossed with either gr1, which lacks cyto-nuclear glutathione disulfide reductase and was used to induce a pronounced shift in EGSH, or with bir6, which has a diminished glutathione consumption and thus exhibits slightly increased levels of GSH. Based on theoretical considerations, these levels are not expected to shift the EGSH to any significant extent. Our study shows that deleting GR1 in the zir1 or rml1 background does not result in an obvious phenotypic change. By contrast, deleting BIR6 was sufficient to suppress the growth arrest in rml1 and to attenuate the growth restriction in zir1. These findings demonstrate that root growth is dependent on the availability of sufficient amounts of GSH, and not affected by pronounced changes in EGSH. This insight provides a decisive step towards understanding the mechanisms underpinning the proposed role of glutathione in growth control
Effectiveness and Implementation of Adapted Physical Activity Delivery Strategies for Older Adults Living With HIV in Ivory Coast: Protocol for a Type 2 Hybrid Randomized Controlled Trial
No full textInternational audienceBackground: With improved access to antiretroviral treatment, HIV infection has become a chronic disease, and the proportion of people living with HIV aged 50 years or older is increasing. However, the long-term evolution of this disease is associated with an increased risk of comorbidities and functional impairments, which negatively impact the social participation and quality of life of people living with HIV. In resource-limited countries, population aging is a new situation, and significant challenges remain unaddressed to respond to this demographic shift. Strong evidence supports the role of physical activity (PA) in improving health and decreasing functional limitations in many chronic conditions, including HIV. However, there is a lack of information on how to effectively implement this type of nondrug intervention in resource-limited contexts.Objective: This study aims to examine the effectiveness and implementation of 2 strategies to deliver an adapted PA program to older adults living with HIV.Methods: This is a prospective, randomized controlled trial following a type 2 hybrid design, with a dual focus on intervention effectiveness and implementation outcomes. It also includes prior formative research that provides information on the context and guides the implementation. Conducted in Ivory Coast, the study aims to randomize 180 people living with HIV aged 50 years or older, receiving antiretroviral treatment and presenting moderate functional limitations or disabilities into the following three arms: (1) a reference arm receiving a group-based PA program supervised by a coach, (2) an exploratory arm receiving a home-based PA program with remote supervision via phone calls and messaging apps, or (3) a control arm receiving health education sessions. The total follow-up period is planned for 12 months, with an initial 6-month active phase and then a 6-month maintenance phase. The primary effectiveness outcome is the increase in the number of steps in the 6-minute step-up test between baseline and 6 months. The secondary outcomes include changes in performance on other functional tests and improvements in cardiometabolic risk factors. The implementation outcomes include the acceptability, adoption, feasibility, and sustainability of the intervention.Results: This study is funded by ANRS Emerging Infectious Disease, which is also the study sponsor. It received ethical approval from the National Ethical Committee of Ivory Coast (00231 3124/MSHPCMU/CNESVS-km). As of manuscript submission, the baseline formative research has been completed, participants have been randomized, and they have started the PA activity program. Results dissemination will involve civil society and decision-makers through workshops and policy briefs.Conclusions: This study builds on previous research on healthy aging while living with HIV. Its hybrid design allows for a comprehensive evaluation of implementation processes and outcomes alongside effectiveness outcomes
Distinct contributions of suspended and sinking prokaryotes to mesopelagic carbon budget
No full textInternational audienceThe mesopelagic zone, between 100 and 1000 meters depth, is a crucial layer, in which carbon preliminary coming down from the surface is transformed before a portion makes it into the deep ocean. While eddies and their fronts influence surface productivity and carbon export, their effects deeper in the water column remain poorly understood. Here we show the importance and contribution of dark carbon fixation—the conversion of inorganic into organic carbon by prokaryotes—across five contrasting hydrological features in the North Atlantic, using isotopic tracers and quantification of chemoautotrophy genes. The approach allows simultaneous assessment of dark carbon fixation and heterotrophic activity of prokaryotes living suspended in seawater and attached to gravitationally settling particles. Our results highlight that heterotrophic prokaryotes attached to sinking particles contribute up to 21% of the total organic carbon required to sustain prokaryotic metabolism under the influence of eddy fronts. In contrast, dark carbon fixation by suspended prokaryotes can contribute up to half of the total carbon input to the mesopelagic zone in the cyclonic eddy. Our findings challenge the idea that carbon cycling in the mid-depth ocean is uniform, and highlight the need to integrate microbial fractions and physical heterogeneity into ocean carbon model