轴手性羰基化合物不仅广泛存在于天然产物、生物活性分子、药物和材料中，也是一类具有优势结构的手性配体或有机催化剂，在不对称催化中具有广阔的应用前景。但是这类结构的合成往往需要繁琐的步骤，一定程度上限制了它们的进一步发展。尽管近年来不对称催化合成轴手性化合物的方法得到了空前发展，但通过不对称羰基化反应直接合成轴手性羰基化合物仍有待发展。催化羰基化反应是合成羰基化合物最高效的方法，自19世纪30年代首次实现以来，羰基化已经成为均相催化领域工业应用规模最大的反应，通过该技术每年生产超过千万吨大宗和精细化学品。相比之下，不对称羰基化反应的发展则相对滞后，主要存在以下挑战：（1）高压CO与手性配体竞争配位，削弱了配体的手性控制能力；（2）酰基金属物种的转化能垒高，且往往是反应的决速步，需要较高的温度；（3）产生的手性羰基化合物在反应体系中易消旋化。尽管如此，在过去的几十年里仍有许多不对称羰基化反应被开发出来，但底物范围大多局限于降冰片烯、苯乙烯、环丙烯等活化的烯烃，且反应主要构筑具有中心手性的羰基化合物，利用不对称羰基化反应合成轴手性羰基化合物的方法仍有待开发。近日，上海交通大学变革性分子前沿科学中心刘家旺课题组，利用手性钯催化剂，通过底物动态动力学不对称转化的策略，发展了外消旋联杂芳基三氟甲磺酸酯与CO以及胺类亲核试剂的不对称胺羰化反应，实现了轴手性酰胺的高效、高对映选择性合成。详细的机理研究表明：酰胺产物的杂环氮原子与NH结构之间的分子内氢键作用会加速产物的轴旋转，从而导致产物的对映选择性显著下降，而碳酸铯的使用破坏了这种分子内氢键，是反应取得高对映选择性的关键。此外，合成的部分酰胺产物可以直接作为手性三齿配体应用到铜催化的不对称自由基反应中，展示了其作为手性配体的应用潜力。 查看详细>>

While amosquito bite is often no more than atemporary bother,in many parts of the world it can be scary.One mosquito species,Aedes aegypti,spreads the viruses that cause over 100,000,000 cases of dengue,yellow fever,Zika and other diseases every year.Another,Anopheles gambiae,spreads the parasite that causes malaria.The World Health Organization estimates that malaria alone causes more than 400,000 deaths every year.Indeed,their capacity to transmit disease has earned mosquitoes the title of deadliest animal.Male mosquitoes are harmless,but females need blood for egg development.It’s no surprise that there’s over 100 years of rigorous research on how they find their hosts.Over that time,scientists have discovered there is no one single cue that these insects rely on.Instead,they integrate information from many different senses across various distances.A team led by researchers at UC Santa Barbara has added another sense to the mosquito’s documented repertoire:infrared detection.Infrared radiation from asource roughly the temperature of human skin doubled the insects’overall host-seeking behavior when combined with CO2 and human odor.The mosquitoes overwhelmingly navigated toward this infrared source while host seeking.The researchers also discovered where this infrared detector is located and how it works on amorphological and biochemical level.The results are detailed in the journal Nature.“The mosquito we study,Aedes aegypti,is exceptionally skilled at finding human hosts,”said co-lead author Nicolas DeBeaubien,a former graduate student and postdoctoral researcher at UCSB in Professor Craig Montell’s laboratory.“This work sheds new light on how they achieve this.” 查看详细>>

氮元素是地球上所有生物合成蛋白质、核酸和各种生物大分子的基本单元。尽管大气中N2丰度高达78%，但自然界的生物固氮过程远不能满足人类生产粮食过程中指数性增长的肥料需求。哈伯工艺实现了人工固定氮气合成氨（N2+3H2?2NH3），在可持续农业生产过程中扮演着关键角色。此外，NH3具有载氢容量高（17.7 wt%）、能量密度大（3 kWh/kg）和燃烧过程零碳排放等优点，在能量存储领域具有重要价值。据估计，全球每年氨产量在2050年将超过3.5亿吨。N2分子中N≡N键的键能极高（940 kJ mol-1），哈伯工艺需要在极为苛刻条件下（350–450℃、150–250大气压）才能实现规模化合成氨。该过程每年大约消耗全球能量供应的1-2%并贡献了超1.4%的CO2排放。与此同时，哈伯工艺消耗的H2主要来源于能源密集的甲烷蒸汽重整过程，这使得每生产1吨NH3的同时释放了1.9吨CO2。因此，亟需发展能够在温和条件下以环境友好且非集中方式合成氨的新技术。研究表明，以太阳能和电能等绿色能源为驱动力，通过光/电化学催化还原氮气或硝酸根来合成氨，有望在能源危机与碳排放双重压力下替代传统哈伯工艺。鉴于全球可再生能源的布局具有便捷性、规模化、分散性和季节性，光催化、光热催化和电催化还原过程可以通过紧凑的小规模装置在温和条件下实现原位合成氨，从而达到工业合成氨工厂难以满足的定制化需求。在光/电催化合成氨工艺中，反应效率、产物选择性与多相催化剂活性位点的精细几何结构、电子结构密切相关。从几何结构角度而言，催化剂的形貌、尺寸和暴露晶面不仅决定了其与反应物分子相互作用，还可以通过改变活化能来影响反应速率；从电子结构角度而言，催化位点的分布和态密度制约了其与反应物的电子间相互作用，进而影响反应路径及产物选择性。此外，多相催化剂的稳定性决定了其在实际反应中长期运行的可行性，而这与其表面原子结构密切相关。针对以上问题，团队近年来以太阳能或电能为驱动力，催化还原环境中无毒的N2分子或有害的NO3-合成NH3（图1），证实了调控催化剂活性位点能够显著提高合成氨反应的活性和产物选择性；通过设计的透过式耦合装置，在无需调节溶液pH下实现了高效氨分离与回收；针对绿色能源驱动的氮循环过程，探讨了其当前在基础研究和工业应用中面临的挑战。 查看详细>>

National University of Singapore(NUS)nutritionists have found that 5-Hydroxytryptophan(5-HTP)supplementation can improve sleep quality in Singaporean older adults,particularly in individuals with poor sleep patterns,and manage their gut microbiome composition.Ensuring good sleep quality is an integral part of achieving good health.However,a mental health study published in 2022 reported that close to 17 per cent of older adults aged 65 and above in Singapore are suffering from poor sleep quality,which has been linked to worse health outcomes,such as agreater risk of chronic diseases and cognitive impairment.There is growing evidence on the association between gut microbiota composition and sleep quality.Additionally,there are pharmaceutical sleep aids available to help poor sleepers achieve agood night’s sleep.However,such aids may induce adverse side effects,including digestive problems and headaches.Dietary supplements,such as anaturally occurring amino acid,5-HTP,are available,but its efficacy on sleep quality in older adults is unclear.Through a12-week clinical trial on 30 older adults,aged 65 and over,NUS researchers set out to evaluate the impact of 5-HTP supplementation on sleep quality and gut microbiota composition on older adults.The research team was led by Assistant Professor Kim Jung Eun from the Department of Food Science and Technology(NUS FST)under the NUS Faculty of Science,and the study was conducted in collaboration with Adjunct Associate Professor Johnson Fam from the Department of Psychological Medicine at the NUS Yong Loo Lin School of Medicine.Based on the results of the clinical trial,the NUS team discovered that supplementation of 5-HTP can improve sleep quality in Singaporean older adults and this improvement was predominantly observed in poor sleepers which could be linked to the modulation of their gut microbiome composition.The team’s findings were published in the journal Clinical Nutrition on 17 January 2024. 查看详细>>

本工作利用表面原生氧化层缺陷锚定策略将Ni单原子锚定在泡沫钛表面，制备了具有孤立非对称性Ni–O–Ti位点的Ni单原子整体钛电极，彻底规避了桥连对称性Ni–O–Ni位点的形成。其中，强亲氧Ti位点与尿素C=O基团作用，以氧端构型吸附尿素，增加了尿素分子C?N键的共振电子云密度，从而避免C?N键过早断裂，促进分子内N–N偶联选择性生成N2。在1.40 VRHE电位下，实现了99%的N2选择性和22.0 mL h–1阴极产氢速率。进一步以商业太阳能单晶硅为电源，构建了可再生能源驱动的高效电解尿液制氢原型装置。本研究实现了尿素的选择性氧化，并阐明了尿素选择性氧化机制，为电解富尿素污水制氢技术奠定了理论基础。球差校正透射电镜和同步辐射证明，Ni以单原子形式分散在泡沫钛表面，通过O桥键与次外层的Ti原子配位，形成孤立的非对称性Ni–O–Ti位点，规避了对称桥连的Ni–O–Ni位点。非对称性Ni–O–Ti位点在1.30 VRHE电位下即可实现10 mA cm–2尿素氧化电流密度。更重要的是，该电极尿素氧化的N2选择性高达99%，几乎不产生氰酸盐和（亚）硝酸盐有害产物，在长达10天的运行过程中始终保持出色的尿素氧化活性和N2选择性。含15N同位素的尿素氧化实验表明，生成的N2来自单个尿素分子内的N–N偶联。原位电化学拉曼光谱和傅里叶变换红外光谱证明，与传统的氮端尿素吸附构型不同，非对称Ni–O–Ti中的强亲氧Ti位点以氧端构型吸附尿素、向尿素分子的C?N键注入电子，导致C?N键红外振动蓝移，从而强化、稳定了C?N键，提高了尿素氧化至N2的选择性。DFT模拟验证了尿素分子以氧端构型吸附在Ni–O–Ti位点，并进一步定量化了不同构型尿素分子C?N键的共振电子云密度和键强；尿素氧化吉布斯自由能计算发现，氧端吸附构型的尿素倾向于发生分子内N–N偶联形成N2，而氮端吸附构型的尿素倾向于发生C?N键断裂，最终形成氰酸盐和（亚）硝酸盐，阐明了吸附构型依赖的尿素选择性氧化机制。基于非对称Ni–O–Ti位点尿素选择性氧化，该团队构建了太阳能驱动的电解尿液耦合阴极制氢原型装置。该装置将制氢的太阳能理论能量利用率提升到9.6%，具有良好的尿液脱氮效率和稳定的制氢活性，为实际尿液处理和资源化提供了一种有前景的方案。 查看详细>>

Unlike traditional printed circuit boards,which are flat,3D circuitry enables components to be stacked and integrated vertically—dramatically reducing the footprint required for devices.Advancing the frontiers of 3D printed circuits,a team of researchers from the National University of Singapore(NUS)has developed astate-of-the-art technique-known as tension-driven CHARM3D-to fabricate three-dimensional(3D),self-healing electronic circuits.This new technique enables the 3D printing of free-standing metallic structures without requiring support materials and external pressure.The research team led by Associate Professor Benjamin Tee from the Department of Materials Science and Engineering in the NUS College of Design and Engineering used Field’s metal to demonstrate how CHARM3D can fabricate awide range of electronics,allowing for more compact designs in devices such as wearable sensors,wireless communication systems and electromagnetic metamaterials.In healthcare,for instance,CHARM3D facilitates the development of contactless vital sign monitoring devices—enhancing patient comfort while enabling continuous monitoring.In signal sensing,it optimises the performance of 3D antennas,leading to improved communication systems,more accurate medical imaging and robust security applications.The team’s findings were published in the journal Nature Electronics on 25 July 2024.Assoc Prof Tee is the corresponding author of the research paper. 查看详细>>

近日，中国科学院近代物理研究所的科研人员与来自法国、芬兰、南非和英国等国家的合作者首次成功测量了β缓发质子核镧-120的激发态结构，在质子滴线原子核的质子中子相互作用和形状演化的研究中取得重要进展，相关成果于近期发表在Physics Letters B上。理论预言，当位于中重质量区的原子核靠近N="Z线时，质子-中子相互作用会增强，并对激发态的结构产生重要影响。同时，原子核可能伴随形状的演化，呈现出“橄榄球”（长椭球），甚至是稀有的“南瓜形”（扁椭球）、“梨形”（八极形变）和“猕猴桃形”（三轴形变）。因此，通过实验测量奇特核的激发态性质对于检验相关理论模型至关重要。为了探索极端丰质子镧原子核的结构演化及其背后的物理机制，近代物理所和法国巴黎萨克雷大学的研究人员主导开展了寻找镧-120激发态的实验。镧-120是一种稀有的β缓发质子核，于1984年首次发现。由于熔合蒸发反应生成镧-120的截面极小，反应产物十分复杂，因此分离及鉴别镧-120极其困难。在过去的40年中，实验物理学家一直未能成功测量到镧-120的激发态。研究团队利用芬兰于韦斯屈莱大学重离子加速器上的质量分析谱仪和伽马探测器阵列，结合多种时间空间关联测量技术，首次在实验上建立了镧-120的激发态能级结构，发现镧-120的奇偶能级劈裂符合系统性，但是它的电磁跃迁比显著不同。结合理论模型，研究团队发现镧-120展现出一种稀有的三轴形变，并且质子-中子相互作用在描述质子滴线奇奇核的结构中扮演着重要角色。该研究得到了国家自然科学基金、中法科研伙伴交流计划项目和中国科学院未来伙伴网络专项的支持。 查看详细>>

A team of astrophysicists led by Caltech has managed for the first time to simulate the journey of primordial gas dating from the early universe to the stage at which it becomes swept up in adisk of material fueling asingle supermassive black hole.The new computer simulation upends ideas about such disks that astronomers have held since the 1970s and paves the way for new discoveries about how black holes and galaxies grow and evolve."Our new simulation marks the culmination of several years of work from two large collaborations started here at Caltech,"says Phil Hopkins,the Ira S.Bowen Professor of Theoretical Astrophysics.The first collaboration,nicknamed FIRE(Feedback in Realistic Environments),has focused on the larger scales in the universe,studying questions such as how galaxies form and what happens when galaxies collide.The other,dubbed STARFORGE,was designed to examine much smaller scales,including how stars form in individual clouds of gas."But there was this big gap between the two,"Hopkins explains."Now,for the first time,we have bridged that gap."To do that,the researchers had to build asimulation with aresolution that is more than 1,000 times greater than the previous best in the field.To the team‘s surprise,as reported in The Open Journal of Astrophysics,the simulation revealed that magnetic fields play amuch larger role than previously believed in forming and shaping the huge disks of material that swirl around and feed the supermassive black holes."Our theories told us the disks should be flat like crepes,"Hopkins says."But we knew this wasn‘t right because astronomical observations reveal that the disks are actually fluffy—more like an angel cake.Our simulation helped us understand that magnetic fields are propping up the disk material,making it fluffier." 查看详细>>

If there’s one thing we humans are good at,it’s producing heat.Significant amounts,and in many cases most of the energy we generate and put into our systems we lose as heat,whether it be our appliances,our transportation,our factories,even our electrical grid.“Waste heat is everywhere,”said UC Santa Barbara mechanical engineering professor Bolin Liao,who specializes in thermal science and renewable energy.“Our power plants,our car exhaust pipes—there are so many places where we create excess heat waste.”For the moment,we’re fairly limited as to how we can make the most out of this dissipating heat.But Liao and UCSB colleagues,alongside collaborators from Ohio State University and University of Hong Kong are making headway toward putting that heat to use,with afirst-time comprehensive characterization of the thermoelectric properties of high-quality cadmium arsenide thin films.“If we could harvest that waste heat then that would be fantastic,”he said.“That would really increase our energy efficiency and it’s also areally sustainable energy source.”The team’s research is published in the journal Advanced Materials.A better thermoelectric material“To obtain high efficiency,we need the material to conduct electricity well,conduct heat poorly and generate ahigh voltage for agiven temperature difference,”Liao said.Poor heat conduction minimizes heat dissipation while maintaining atemperature difference across the material,resulting in an electric current enhanced by the material’s high-performing electric conductivity.The voltage resulting from atemperature gradient is known as the Seebeck effect.This combination of electrical and thermal transport properties is ideal but,according to Liao,“very hard to achieve in practice.”Enter cadmium arsenide(Cd3As2),a Dirac semimetal with promising transport properties,in particular,a low thermal conductivity and high electron mobility.“We were pretty excited about this material,and we thought‘okay,this is really acombination of these two great properties,”Liao said.“But there is only one problem.“This problem was that in addition to good electric conduction and poor thermal conduction,you also need this material to be able to generate enough voltage under atemperature gradient.”As asemimetal,cadmium arsenide is excellent at conducting electricity very rapidly,but it only generates avery small Seebeck voltage.To create auseful voltage,Liao explained,one would need to open up aband gap.“You want this material to have acertain energy range where the electrons cannot conduct.That’s called aband gap,”he said.Because of the gap,which essentially blocks the free flow of electrons,enough electrical“pressure”(a.k.a.voltage)can build up as aresponse to atemperature difference across the material.In bulk cadmium arsenide crystals,there is no band gap. 查看详细>>

近日，上海交通大学电子信息与电气工程学院感知科学与工程学院黄震宇团队在基于变换声学的降噪且通流应用方向取得重要进展，相关成果以“Meta-barriers for ventilated sound reduction via transformation acoustics”（通过变换声学实现通风隔音的超屏障）为题，以上海交通大学电子信息与电气工程学院为第一单位发表在International Journal of Mechanical Sciences上。研究背景大型动力装备的噪声控制不仅需要采用各种措施来降低声音，还需要确保噪声控制措施的实施对装备通流散热的影响尽可能小。在保持介质有效流动的同时阻断声波的传播是一个违反直觉的物理过程。根据经典波动力学，介质充当声波传播的载体，阻断声波会限制介质流动，从而影响通流散热性能。作为一个具体实用性的研究课题，学者们在解决降噪与通流散热之间的矛盾方面付出了巨大的努力。然而，现有的方案无法兼顾低频宽带声波抑制与高通量介质流动，无法满足大型动力装备的噪声控制需求。创新成果针对以上问题，黄震宇团队提出了一种基于变换声学的超屏障（Meta-barrier），用于实现低频宽带降噪，同时保持高通量介质流动。所提出的超屏障由内部空气核心和由具有高阻尼耗散的双负声学超材料制成的涂层组成。与传统屏障不同，超屏障具有远超过其实际尺寸的散射截面，使其能够在增强的阻挡效应之外提供相干干涉效应。而相干干涉效应则可直接降低由开孔辐射的声波辐射效率。此外，涂层中固有的材料阻尼在宽频范围内对超屏障的降噪性能具有积极影响。论文详细推导了超屏障的构成参数，并给出了超屏障与开孔之间的多重散射现象的理论描述。基于有限元数值模型，演示了在大放置距离和宽入射角的情况下超屏障的稳健降噪性能。制备的元屏障样件，具备75%的风速比，可以在500–1000Hz的频率范围内实现卓越的透射声衰减。这项工作对基于变换声学的无源声学装置的设计和开发具有极大的启发和推动作用。变换声学的基本原理是通过数学变换，通常为坐标变换，来设计声学材料或结构，从而实现对声波传播的控制。变换声学是一个跨学科的研究领域，它结合了数学、物理和工程学的知识，为声波的控制和应用提供了新的可能性。随着声学超材料技术的发展，变换声学有望在未来的声学研究和应用中发挥更大的作用。这项工作可视为基于变换声学的超屏障实现低频宽带降噪和高效通流应用的前奏。后续研究工作包括使用更多的单元组成层来构建双负声学超材料涂层以接近连续梯度阻抗，制造三维超屏障并在真实房间尺度进行试验验证，平面结构形式设计的超屏障以减少空间占用，并寻求更容易生产和更具成本效益的制造超屏障的技术以促进其实际应用。 查看详细>>