编译 | 未玖

Nature, 6 July 2023, VOL 619, ISSUE 7968

《自然》2023年7月6日，第619卷，7968期

天文学Astronomy

X-ray polarization evidence for a 200-year-old flare of Sgr A*

Sgr A* 200年耀斑的X射线偏振证据

▲ 作者：Frédéric Marin, Eugene Churazov, Ildar Khabibullin, Riccardo Ferrazzoli, Laura Di Gesu, Thibault Barnouin, et al.

▲ 链接：

https://www.nature.com/articles/s41586-023-06064-x

▲ 摘要：

银河系中心有一个质量约为太阳400万倍的黑洞（人马座A* ，Sgr A），目前非常沉寂，其亮度比活跃星系核低几个数量级。星系中心区域致密气体对SgrA* X射线的反射为研究其过去数百年和数千年的耀斑活动提供了一种方法。

从Sgr A*附近巨大分子云观测到的X射线连续体的形状和强荧光铁线与反射情景一致。如果这种解释正确，反射的连续辐射应该是极化的。

研究组报道了使用成像X射线偏振探测器在银河系中心分子云方向上的偏振X射线发射的观测结果。经测量偏振度为31%±11%，偏振角为- 48°±11°。

所测偏振角与Sgr A*为主要发射源的偏振角相一致，偏振度表明大约200年前，Sgr A*的X射线光度与塞弗特星系的光度曾短暂相当。

▲ Abstract：

The centre of the Milky Way Galaxy hosts a black hole with a solar mass of about 4 million (Sagittarius A* (Sgr A)) that is very quiescent at present with a luminosity many orders of magnitude below those of active galactic nuclei. Reflection of X-rays from Sgr A* by dense gas in the Galactic Centre region offers a means to study its past flaring activity on timescales of hundreds and thousands of years. The shape of the X-ray continuum and the strong fluorescent iron line observed from giant molecular clouds in the vicinity of Sgr A* are consistent with the reflection scenario. If this interpretation is correct, the reflected continuum emission should be polarized. Here we report observations of polarized X-ray emission in the direction of the molecular clouds in the Galactic Centre using the Imaging X-ray Polarimetry Explorer. We measure a polarization degree of 31%±11%, and a polarization angle of 48°±11°. The polarization angle is consistent with Sgr?A* being the primary source of the emission, and the polarization degree implies that some 200 years ago, the X-ray luminosity of Sgr?A* was briefly comparable to that of a Seyfert galaxy.

材料科学Materials Science

Liquid metal for high-entropy alloy nanoparticles synthesis

液态金属用于高熵合金纳米颗粒的合成

▲ 作者：Guanghui Cao, Jingjing Liang, Zenglong Guo, Kena Yang, Gang Wang, Huiliu Wang, et al.

▲ 链接：

https://www.nature.com/articles/s41586-023-06082-9

▲ 摘要：

高熵合金纳米颗粒（HEA-NPs）作为功能材料具有广阔的应用前景。然而，到目前为止，已实现的高熵合金仅限于相似元素的调色板，这极大地阻碍了不同应用的材料设计、性能优化和机理探索。

研究组发现，赋予其他元素负混合焓的液态金属可提供稳定的热力学条件，并作为理想的动态混合储层，从而在温和反应条件下合成多种金属元素的HEA-NPs。所涉及的元素具有广泛的原子半径（1.24-1.97 Å）和熔点（303-3683 K）。

研究组通过混合焓调谐实现了纳米颗粒的精确制造结构，此外还原位捕获了实时转换过程（即从液态金属到结晶HEA-NPs），证实了合金化过程中的动态裂变-聚变行为。

▲ Abstract：

High-entropy alloy nanoparticles (HEA-NPs) show great potential as functional materials. However, thus far, the realized high-entropy alloys have been restricted to palettes of similar elements, which greatly hinders the material design, property optimization and mechanistic exploration for different lications. Herein, we discovered that liquid metal endowing negative mixing enthalpy with other elements could provide a stable thermodynamic condition and act as a desirable dynamic mixing reservoir, thus realizing the synthesis of HEA-NPs with a diverse range of metal elements in mild reaction conditions. The involved elements have a wide range of atomic radii (1.24–1.97 ) and melting points (303–3,683 K). We also realized the precisely fabricated structures of nanoparticles via mixing enthalpy tuning. Moreover, the real-time conversion process (that is, from liquid metal to crystalline HEA-NPs) is captured in situ, which confirmed a dynamic fission–fusion behaviour during the alloying process.

机械工程Mechanical Engineering

Harnessing a paper-folding mechanism for reconfigurable DNA origami

利用折纸机构进行可重构DNA折纸

▲ 作者：Myoungseok Kim, Chanseok Lee, Kyounghwa Jeon, Jae Young Lee, Young-Joo Kim, Jae Gyung Lee, et al.

▲ 链接：

https://www.nature.com/articles/s41586-023-06181-7

▲ 摘要：

折纸机构因其在将可变形状和刚度编程到结构中的独特能力和优势，已被广泛用于可重构宏观系统的构建。然而，尽管基于DNA自组装的各种动态结构已被开发出来，但由于缺乏合适的设计原则，很少被用于构建分子水平系统。

研究组提出了一种利用折纸机构来创建可重构DNA折纸结构的方法。其主要思想是建立一个参考平面线框结构，边缘遵循折纸中的折痕图案，以便折叠成各种目标形状。

研究组利用DNA链位移以高产率实现了几种类似纸张的折叠和展开模式，并展示了正交折叠、可重复折叠和展开、基于折叠的microRNA检测和荧光信号控制。由pH值或光源变化触发的刺激响应性折叠和展开也可以实现。

此外，通过采用分层组装，研究组以高度可编程的方式扩展了折纸机构的设计空间和复杂性。因其高可编程性和可扩展性，研究组希冀所提出的基于折纸的重构方法将推动复杂分子系统的发展。

▲ Abstract：

The paper-folding mechanism has been widely adopted in building of reconfigurable macroscale systems because of its unique capabilities and advantages in programming variable shapes and stiffness into a structure. However, it has barely been exploited in the construction of molecular-level systems owing to the lack of a suitable design principle, even though various dynamic structures based on DNA self-assembly have been developed. Here we propose a method to harness the paper-folding mechanism to create reconfigurable DNA origami structures. The main idea is to build a reference, planar wireframe structure whose edges follow a crease pattern in paper folding so that it can be folded into various target shapes. We realized several paper-like folding and unfolding patterns using DNA strand displacement with high yield. Orthogonal folding, repeatable folding and unfolding, folding-based microRNA detection and fluorescence signal control were demonstrated. Stimuli-responsive folding and unfolding triggered by pH or light-source change were also possible. Moreover, by employing hierarchical assembly we could expand the design space and complexity of the paper-folding mechanism in a highly programmable manner. Because of its high programmability and scalability, we expect that the proposed paper-folding-based reconfiguration method will advance the development of complex molecular systems.

化学Chemistry

General cross-coupling reactions with adaptive dynamic homogeneous catalysis

具有自适应动态均相催化的通用交叉偶联反应

▲ 作者：Indrajit Ghosh, Nikita Shlapakov, Tobias A. Karl, Jonas Düker, Maksim Nikitin, Julia V. Burykina, et al.

▲ 链接：

https://www.nature.com/articles/s41586-023-06087-4

▲ 摘要：

交叉偶联反应是现代有机合成中最重要的转化之一。虽然考虑到各种方案，目前已报道的（杂）芳基卤化物和亲核试剂偶联配体的范围非常大，但不同化合物类别的反应条件差异很大，需要重新逐个优化反应条件。

研究组介绍了在可见光驱动的氧化还原反应条件下，镍自适应动态均相催化（AD-HoC）对通用C（sp2）-（杂）原子偶联反应的催化作用。催化体系的自调节性质实现了交叉偶联反应中数十种不同类型亲核试剂的简单分类。

在可预测的反应条件下，九种不同成键反应（即C（sp2）–S、Se、N、P、B、O、C（sp3、sp2、sp）、Si、Cl）数以百计的合成实例综合证明了这一点。催化反应中心和条件因加入的亲核试剂或（如果需要）商业廉价胺碱而有所不同。

▲ Abstract：

Cross-coupling reactions are among the most important transformations in modern organic synthesis. Although the range of reported (het)aryl halides and nucleophile coupling partners is very large considering various protocols, the reaction conditions vary considerably between compound classes, necessitating renewed case-by-case optimization of the reaction conditions. Here we introduce adaptive dynamic homogeneous catalysis (AD-HoC) with nickel under visible-light-driven redox reaction conditions for general C(sp2)–(hetero)atom coupling reactions. The self-adjustive nature of the catalytic system allowed the simple classification of dozens of various classes of nucleophiles in cross-coupling reactions. This is synthetically demonstrated in nine different bond-forming reactions (in this case, C(sp2)–S, Se, N, P, B, O, C(sp3, sp2, sp), Si, Cl) with hundreds of synthetic examples under predictable reaction conditions. The catalytic reaction centre(s) and conditions differ from one another by the added nucleophile, or if required, a commercially available inexpensive amine base.

地球科学Earth Science

Medieval demise of a Himalayan giant summit induced by mega-landslide

巨型滑坡导致了中世纪时喜马拉雅巨型山峰的消亡

▲ 作者：Jérôme Lavé, Cyrielle Guérin, Pierre G. Valla, Valery Guillou, Thomas Rigaudier, Lucilla Benedetti, et al.

▲ 链接：

https://www.nature.com/articles/s41586-023-06040-5

▲ 摘要：

尽管人们对喜马拉雅山脉的侵蚀进行了大量研究，但尚不清楚喜马拉雅山脉的高峰是如何被侵蚀的。

虽然谷底被冰川有效侵蚀，但侵蚀从冰斗延伸到冰峰线前壁的冰缘过程强度似乎随着海拔升高而急剧下降。这种对比表明，喜马拉雅最高峰侵蚀程度较低，且远低于区域岩石抬升率，这引发了人们对其长期演化的质疑。

研究组报道了公元1190年左右安纳普尔纳地块（尼泊尔中部）发生的一次巨大岩石滑坡的地质证据，涉及岩石总体积约为23 km3。这一事件使一座古山顶坍塌，其高峰可能在海拔8000米以上。

研究数据表明，高海拔侵蚀的一种模式可能是巨型岩石滑坡，导致山脊高程突然降低数百米，并最终阻止喜马拉雅山峰不成比例的增长。这种与陡坡和高起伏有关的侵蚀模式源自峰值基底更大的机械强度，或因高海拔永久冻土层的存在。

巨型岩石滑坡也对景观演变和自然灾害有影响：大量的细碎沉积物可以填满下游150多千米的山谷，在一个世纪或更长的时间里超过了喜马拉雅河流的沉积物负荷。

▲ Abstract：

Despite numerous studies on Himalayan erosion, it is not known how the very high Himalayan peaks erode. Although valley floors are efficiently eroded by glaciers, the intensity of periglacial processes, which erode the headwalls extending from glacial cirques to crest lines, seems to decrease sharply with altitude. This contrast suggests that erosion is muted and much lower than regional rock uplift rates for the highest Himalayan peaks, raising questions about their long-term evolution. Here we report geological evidence for a giant rockslide that occurred around 1190 AD in the Annapurna massif (central Nepal), involving a total rock volume of about 23 km3. This event collapsed a palaeo-summit, probably culminating above 8,000?m in altitude. Our data suggest that a mode of high-altitude erosion could be mega-rockslides, leading to the sudden reduction of ridge-crest elevation by several hundred metres and ultimately preventing the disproportionate growth of the Himalayan peaks. This erosion mode, associated with steep slopes and high relief, arises from a greater mechanical strength of the peak substratum, probably because of the presence of permafrost at high altitude. Giant rockslides also have implications for landscape evolution and natural hazards: the massive supply of finely crushed sediments can fill valleys more than 150 km farther downstream and overwhelm the sediment load in Himalayan rivers for a century or more.

Safe and just Earth system boundaries

安全公正的地球系统边界

▲ 作者：Johan Rockström, Joyeeta Gupta, Dahe Qin, Steven J. Lade, Jesse F. Abrams, Lauren S. Andersen, et al.

▲ 链接：

https://www.nature.com/articles/s41586-023-06083-8

▲ 摘要：

地球系统的稳定性和复原力与人类福祉不可分割地联系在一起，但人们普遍认识不到两者间的相互依存性；因此，其往往被独立对待。

研究组使用建模和文献评估来量化全球和亚全球尺度上气候、生物圈、水和营养循环以及气溶胶的安全和公正的地球系统边界（ESBs）。他们提出ESBs以维持地球系统的复原力和稳定性（安全ESBs），并最大限度地减少地球系统变化对人类造成的重大伤害（对于正义而言必要但非充分的条件）。更严格的安全或公正边界设置了综合安全和公正ESB。

该研究结果表明，对于气候和大气气溶胶负荷，公正考虑比安全考虑更能约束综合ESBs。8个全球量化的安全和公正ESB中有7个已越界，在全球超过一半的陆地面积内至少有两个区域安全和公正ESB也已越界。

研究组认为，该评估为今后针对所有人保护全球公域提供了一个定量基础。

▲ Abstract：

The stability and resilience of the Earth system and human well-being are inseparably linked, yet their interdependencies are generally under-recognized; consequently, they are often treated independently. Here, we use modelling and literature assessment to quantify safe and just Earth system boundaries (ESBs) for climate, the biosphere, water and nutrient cycles, and aerosols at global and subglobal scales. We propose ESBs for maintaining the resilience and stability of the Earth system (safe ESBs) and minimizing exposure to significant harm to humans from Earth system change (a necessary but not sufficient condition for justice). The stricter of the safe or just boundaries sets the integrated safe and just ESB. Our findings show that justice considerations constrain the integrated ESBs more than safety considerations for climate and atmospheric aerosol loading. Seven of eight globally quantified safe and just ESBs and at least two regional safe and just ESBs in over half of global land area are already exceeded. We propose that our assessment provides a quantitative foundation for safeguarding the global commons for all people now and into the future.