Synthesis of bicyclo[3.1.1]heptanes, meta-substituted arene isosteres, from [3.1.1]propellane
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Non-enzymatic methylcyclization of alkenes
Methyltransferases are a broad class of enzymes that catalyse the transfer of methyl groups onto a wide variety of substrates and functionalities. In their most striking variant, bifunctional methyltransferase–cyclases both transfer a methyl group onto alkenes and induce cyclization (methylcyclization). Although recent years have seen substantial advances in the methylation of alkenes, especially hydromethylation, the reactivity demonstrated by bifunctional methyltransferase–cyclases in nature has yet to be developed into a synthetically viable method. Here we report a silver(I)-mediated electrophilic methylcyclization that rivals selectivities found in enzymes while not being limited by their inherent substrate specificity. Our method benefits from the use of commercial reagents, is applicable to a wide range of substrates, including heterocycles, and affords unique structures that are difficult to access via conventional synthetic methods. Furthermore, computational studies have been utilized to unravel the underlying mechanism and ultimately support a stepwise cationic reaction pathway with a rate-limiting methyltransfer.
Insights from a century of data reveal global trends in ex situ living plant collections
Ex situ living plant collections play a crucial role in providing nature-based solutions to twenty-first century global challenges. However, the complex dynamics of these artificial ecosystems are poorly quantified and understood, affecting biodiversity storage, conservation and utilization. To evaluate the management of ex situ plant diversity, we analysed a century of data comprising 2.2 million records, from a meta-collection currently holding ~500,000 accessions and 41% of global ex situ species diversity. Our study provides critical insights into the historical evolution, current state and future trajectory of global living collections. We reveal sigmoidal growth of a meta-collection that has reached capacity in both total accessions and total diversity, and identify intrinsic constraints on biodiversity management, including a median survival probability of 15 years. We explore the impact of external constraints and quantify the influence of the Convention on Biological Diversity, which we link to reduced acquisition of wild-origin and internationally sourced material by 44% and 38%, respectively. We further define the impact of these constraints on ex situ conservation but highlight targeted initiatives that successfully mitigate these challenges. Ultimately, our study underscores the urgent need for strategic prioritization and the re-evaluation of ex situ biodiversity management to achieve both scientific and conservation goals.
High-performance achromatic flat lens by multiplexing meta-atoms on a stepwise phase dispersion compensation layer
Flat optics have attracted interest for decades due to their flexibility in manipulating optical wave properties, which allows the miniaturization of bulky optical assemblies into integrated planar components. Recent advances in achromatic flat lenses have shown promising applications in various fields. However, it is a significant challenge for achromatic flat lenses with a high numerical aperture to simultaneously achieve broad bandwidth and expand the aperture sizes. Here, we present the zone division multiplex of the meta-atoms on a stepwise phase dispersion compensation (SPDC) layer to address the above challenge. In principle, the aperture size can be freely enlarged by increasing the optical thickness difference between the central and marginal zones of the SPDC layer, without the limit of the achromatic bandwidth. The SPDC layer also serves as the substrate, making the device thinner. Two achromatic flat lenses of 500 nm thickness with a bandwidth of 650–1000 nm are experimentally achieved: one with a numerical aperture of 0.9 and a radius of 20.1 µm, and another with a numerical aperture of 0.7 and a radius of 30.0 µm. To the best of our knowledge, they are the broadband achromatic flat lenses with highest numerical apertures, the largest aperture sizes and thinnest thickness reported so far. Microscopic imaging with a 1.10 µm resolution has also been demonstrated by white light illumination, surpassing any previously reported resolution attained by achromatic metalenses and multi-level diffractive lenses. These unprecedented performances mark a substantial step toward practical applications of flat lenses.
Fasting appetite-related gut hormone responses after weight loss induced by calorie restriction, exercise, or both in people with overweight or obesity: a meta‐analysis
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An umbrella review of health outcomes following traumatic brain injury
While numerous reviews have assessed the association between traumatic brain injury (TBI) and various mental and physical health outcomes, a comprehensive evaluation of the scope, validity, and quality of evidence is lacking. Here we present an umbrella review of a wide range of health outcomes following TBI and outline outcome risks across subpopulations. On 17 May 2023, we searched Embase, Medline, Global Health, PsycINFO, and Cochrane Database of Systematic Reviews for systematic reviews and meta-analyses. We compared risk ratios across different outcomes for risks compared with people without TBI and examined study quality, including heterogeneity, publication bias, and prediction intervals. The study was registered with PROSPERO (CRD42023432255). We identified 24 systematic reviews and meta-analyses covering 24 health outcomes in 31,397,958 participants. The current evidence base indicates an increased risk of multiple mental and physical health outcomes, including psychotic disorders, attention-deficit/hyperactivity disorder, suicide, and depression. Three outcomes—dementia, violence perpetration, and amyotrophic lateral sclerosis—had meta-analytical evidence of at least moderate quality, which suggest targets for more personalized assessment. Health-care services should review how to prevent adverse long-term outcomes in TBI.
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