编译 | 未玖

Nature, 2 May 2024 , VOL 629, ISSUE 8010
《自然》2024年5月2日，第629卷，8010期

天文学Astronomy

A magnetar giant flare in the nearby starburst galaxy M82

星暴星系M82附近的一颗磁星巨大耀斑

▲ 作者：Sandro Mereghetti, Michela Rigoselli, Ruben Salvaterra, Dominik Patryk Pacholski, James Craig Rodi, Diego Gotz, et al.

▲ 链接：

https://www.nature.com/articles/s41586-024-07285-4

▲ 摘要：

磁星巨大耀斑是一种罕见的爆发事件，在不到1秒钟的时间里，从年轻的中子星释放出高达10⁴⁷尔格的伽马射线，磁场高达10^15?16  G。大约50年来，在银河系和大麦哲伦星云的磁星上只观测到三次这样的耀斑。

这个小样本可通过系外事件的发现而扩大，因为几分之一秒巨大耀斑的亮度可达到10⁴⁶尔格/s以上，这使其在几十兆秒差距内可见。然而，在这些距离上，很难将它们与短伽马射线暴（GRBs）区分开来；远得多、能量大得多（10^50?53尔格）的事件通常源于紧凑的双星合并。

人们已提出一些具有不同置信区间的短GRBs，这是附近星系中的候选磁星巨大耀斑。研究组报道了GRB 231115A的观测结果，其与星暴星系M82的位置一致。GRB 231115A的光谱特性，加上爆发长度，在几小时内获得的X射线和光学对应物的限制，以及缺乏引力波信号，毫无疑问地证明了这次爆发是来自M82磁星的巨大耀斑。

▲ Abstract：

Magnetar giant flares are rare explosive events releasing up to  10⁴⁷?erg in gamma rays in less than 1?second from young neutron stars with magnetic fields up to 10^15?16?G. Only three such flares have been seen from magnetars in our Galaxy and in the Large Magellanic Cloud in roughly 50?years. This small sample can be enlarged by the discovery of extragalactic events, as for a fraction of a second giant flares reach luminosities above 10⁴⁶ergs^?1, which makes them visible up to a few tens of megaparsecs. However, at these distances they are difficult to distinguish from short gamma-ray bursts (GRBs); much more distant and energetic (10^50?53erg) events, originating in compact binary mergers. A few short GRBs have been proposed, with different amounts of confidence, as candidate giant magnetar flares in nearby galaxies. Here we report observations of GRB 231115A, positionally coincident with the starburst galaxy M82. Its spectral properties, along with the length of the burst, the limits on its X-ray and optical counterparts obtained within a few hours, and the lack of a gravitational wave signal, unambiguously qualify this burst as a giant flare from a magnetar in M82.

材料科学Materials Science

Bevel-edge epitaxy of ferroelectric rhombohedral boron nitride single crystal

铁电斜方六面体氮化硼单晶的斜边外延

▲ 作者：Li Wang, Jiajie Qi, Wenya Wei, Mengqi Wu, Zhibin Zhang, Xiaomin Li, et al.

▲ 链接：

https://www.nature.com/articles/s41586-024-07286-3

▲ 摘要：

在二维电介质家族中，斜方六面体氮化硼（rBN）不仅具有六方氮化硼的优越性能（包括低介电常数和耗散、强电绝缘性、良好的化学稳定性、高导热性和无悬空键的原子平坦性），而且还具有源于面内和面外中心对称破缺的有用光学非线性和界面铁电性。然而，由于需要前所未有的生长控制来协调每层的晶格取向和每个界面的滑动矢量，制备大尺寸单晶rBN层仍颇具挑战。

研究组报道了一种使用斜边外延来制备厘米尺寸单晶rBN层的简单方法，在相邻镍表面上具有精确的层间ABC堆叠。结果在斜面（110）处成功地精确制造了阶地面（100）聚束台阶边缘的单晶镍基底，同时引导每个BN层中一致的硼-氮键取向，并通过每个斜面附近的成核来引导BN层的斜方六面体堆叠。

研究组验证了原生BN层的纯斜方六面体相，并在高居里温度下表现出稳健、均匀和可切换的铁电性。该工作为单晶二维层的精确堆叠控制生长提供了有效途径，并为基于堆叠二维材料的适用多功能器件奠定了基础。

▲ Abstract：

Within the family of two-dimensional dielectrics, rhombohedral boron nitride (rBN) is considerably promising owing to having not only the superior properties of hexagonal boron nitride—including low permittivity and dissipation, strong electrical insulation, good chemical stability, high thermal conductivity and atomic flatness without dangling bonds—but also useful optical nonlinearity and interfacial ferroelectricity originating from the broken in-plane and out-of-plane centrosymmetry. However, the preparation of large-sized single-crystal rBN layers remains a challenge, owing to the requisite unprecedented growth controls to coordinate the lattice orientation of each layer and the sliding vector of every interface. Here we report a facile methodology using bevel-edge epitaxy to prepare centimetre-sized single-crystal rBN layers with exact interlayer ABC stacking on a vicinal nickel surface. We realized successful accurate fabrication over a single-crystal nickel substrate with bunched step edges of the terrace facet (100) at the bevel facet (110), which simultaneously guided the consistent boron–nitrogen bond orientation in each BN layer and the rhombohedral stacking of BN layers via nucleation near each bevel facet. The pure rhombohedral phase of the as-grown BN layers was verified, and consequently showed robust, homogeneous and switchable ferroelectricity with a high Curie temperature. Our work provides an effective route for accurate stacking-controlled growth of single-crystal two-dimensional layers and presents a foundation for applicable multifunctional devices based on stacked two-dimensional materials.

High-performance fibre battery with polymer gel electrolyte

聚合物凝胶电解质的高性能纤维电池

▲ 作者：Chenhao Lu, Haibo Jiang, Xiangran Cheng, Jiqing He, Yao Long, Yingfan Chang, et al.

▲ 链接：

https://www.nature.com/articles/s41586-024-07343-x

▲ 摘要：

聚合物凝胶电解质替代液体电解质是公认的解决可穿戴电池安全性问题和实现高柔性的通用有效途径。然而，由于润湿不足，聚合物凝胶电解质与电极之间的界面较差，产生了更差的电化学性能，特别是在电池变形时。

研究组报道了一种设计电极通道结构的策略，以整合聚合物凝胶电解质，并形成紧密稳定的界面，以实现高性能可穿戴电池。作为演示，多个电极纤维一起旋转形成排列通道，同时每个电极纤维的表面设计有网络通道。

单体溶液首先沿着排列通道有效渗透，然后进入网络通道。然后，这些单体被聚合成凝胶电解质，并与电极形成紧密稳定的界面。所得纤维锂离子电池（FLB）表现出较高的电化学性能（例如，能量密度约为128 Wh kg^?1）。

该策略还实现了FLB的生产，速率高达每绕组单元3600 mh^?1。连续的FLB被编织成50 cm×30 cm的纺织品，提供2975 mAh的输出容量。FLB纺织品在极端条件下安全工作，例如- 40℃和80℃的温度和- 0.08 MPa的真空。FLB有望应用于消防和太空探索。

▲ Abstract：

Replacement of liquid electrolytes with polymer gel electrolytes is recognized as a general and effective way of solving safety problems and achieving high flexibility in wearable batteries. However, the poor interface between polymer gel electrolyte and electrode, caused by insufficient wetting, produces much poorer electrochemical properties, especially during the deformation of the battery. Here we report a strategy for designing channel structures in electrodes to incorporate polymer gel electrolytes and to form intimate and stable interfaces for high-performance wearable batteries. As a demonstration, multiple electrode fibres were rotated together to form aligned channels, while the surface of each electrode fibre was designed with networked channels. The monomer solution was effectively infiltrated first along the aligned channels and then into the networked channels. The monomers were then polymerized to produce a gel electrolyte and form intimate and stable interfaces with the electrodes. The resulting fibre lithium-ion battery (FLB) showed high electrochemical performances (for example, an energy density of about 128?Wh?kg^?1. This strategy also enabled the production of FLBs with a high rate of 3,600?mh^?1per winding unit. The continuous FLBs were woven into a 50?cm?×?30?cm textile to provide an output capacity of 2,975?mAh. The FLB textiles worked safely under extreme conditions, such as temperatures of ?40?°C and 80?°C and a vacuum of ?0.08?MPa. The FLBs show promise for applications in firefighting and space exploration.

化学Chemistry

Long-term continuous ammonia electrosynthesis

长期连续氨电合成

▲ 作者：Shaofeng Li, Yuanyuan Zhou, Xianbiao Fu, Jakob B. Pedersen, Mattia Saccoccio, Suzanne Z. Andersen, et al.

▲ 链接：

https://www.nature.com/articles/s41586-024-07276-5

▲ 摘要：

氨在化肥和化学工业中至关重要，被认为是一种无碳燃料。在环境条件下，氮电合成氨为哈伯-博世工艺提供了一个有吸引力的替代方案，锂介导的氮还原代表了一种有前途的连续流氨电合成方法，将氮还原与氢氧化相结合。然而，由于聚合和挥发性问题，通常用作溶剂的四氢呋喃阻碍了长期氨生产。

研究组展示了链醚基电解质可实现长期连续氨合成。他们发现链醚基溶剂表现出非聚合特性和高沸点（162℃），并在气体扩散电极上形成致密的固体-电解质界面层，促进氨在气相中的释放，确保电解质的稳定性。

研究组演示了在1 bar压力和室温下，该溶剂在25 cm²电极的流动电解槽中连续运行300小时，实现了电流到氨的效率为64±1%，气相氨含量高达约98%。该研究结果突出了溶剂在长期连续氨合成中的关键作用。

▲ Abstract：

Ammonia is crucial as a fertilizer and in the chemical industry and is considered to be a carbon-free fuel. Ammonia electrosynthesis from nitrogen under ambient conditions offers an attractive alternative to the Haber–Bosch process, and lithium-mediated nitrogen reduction represents a promising approach to continuous-flow ammonia electrosynthesis, coupling nitrogen reduction with hydrogen oxidation. However, tetrahydrofuran, which is commonly used as a solvent, impedes long-term ammonia production owing to polymerization and volatility problems. Here we show that a chain-ether-based electrolyte enables long-term continuous ammonia synthesis. We find that a chain-ether-based solvent exhibits non-polymerization properties and a high boiling point (162?°C) and forms a compact solid-electrolyte interphase layer on the gas diffusion electrode, facilitating ammonia release in the gas phase and ensuring electrolyte stability. We demonstrate 300?h of continuous operation in a flow electrolyser with a 25?cm2 electrode at 1?bar pressure and room temperature, and achieve a current-to-ammonia efficiency of 64?±?1% with a gas-phase ammonia content of approximately 98%. Our results highlight the crucial role of the solvent in long-term continuous ammonia synthesis.

Stereoselective amino acid synthesis by photobiocatalytic oxidative coupling

光生物催化氧化偶联合成立体选择性氨基酸

▲ 作者：Tian-Ci Wang, Binh Khanh Mai, Zheng Zhang, Zhiyu Bo, Jiedong Li, Peng Liu, et al.

▲ 链接：

https://www.nature.com/articles/s41586-024-07284-5

▲ 摘要：

利用光来扩大酶反应性的光生物催化最近已成为开发自然界新化学物质的一种强大策略。这些体系在小分子催化剂长期无法催化的不对称自由基反应中显示出潜力。到目前为止，非天然光生物催化反应仅限于整体还原和氧化还原中性过程。

研究组报道了光生物催化有机硼试剂和氨基酸之间的不对称sp³–sp³氧化交叉偶联反应。该反应需要工程吡哆醛生物催化剂、光氧化还原催化剂和氧化剂的协同使用。通过自由基机制重新改良吡哆醛-5′-磷酸依赖酶家族（即苏氨酸醛缩酶），对甘氨酸和α-支链氨基酸底物进行α-C–H功能化，产生一系列具有最多两个连续立体中心的α-三取代和四取代的非经典氨基酸。

吡哆醛自由基酶的定向进化实现了一级和二级自由基前体（包括苄基、烯丙基和烷基硼试剂）以对映体控制和非对映体控制的方式偶联。协同光氧化还原-吡哆醛生物催化为sp³–sp³氧化偶联提供了一个平台，实现了化学或生物学未知的立体选择性分子间自由基转化。

▲ Abstract：

Photobiocatalysis—where light is used to expand the reactivity of an enzyme—has recently emerged as a powerful strategy to develop chemistries that are new to nature. These systems have shown potential in asymmetric radical reactions that have long eluded small-molecule catalysts. So far, unnatural photobiocatalytic reactions are limited to overall reductive and redox-neutral processes. Here we report photobiocatalytic asymmetric sp³–sp³oxidative cross-coupling between organoboron reagents and amino acids. This reaction requires the cooperative use of engineered pyridoxal biocatalysts, photoredox catalysts and an oxidizing agent. We repurpose a family of pyridoxal-5′-phosphate-dependent enzymes, threonine aldolases, for the α-C–H functionalization of glycine and α-branched amino acid substrates by a radical mechanism, giving rise to a range of α-tri- and tetrasubstituted non-canonical amino acids  possessing up to two contiguous stereocentres. Directed evolution of pyridoxal radical enzymes allowed primary and secondary radical precursors, including benzyl, allyl and alkylboron reagents, to be coupled in an enantio- and diastereocontrolled fashion. Cooperative photoredox–pyridoxal biocatalysis provides a platform for sp³–sp³ oxidative coupling, permitting the stereoselective, intermolecular free-radical transformations that are unknown to chemistry or biology.

地球科学One Earth

Environmental drivers of increased ecosystem respiration in a warming tundra

变暖苔原生态系统呼吸增加的环境驱动因素

▲ 作者：S. L. Maes, J. Dietrich, G. Midolo, S. Schwieger, M. Kummu, V. Vandvik, et al.

▲ 链接：

https://www.nature.com/articles/s41586-024-07274-7

▲ 摘要：

北极和高山苔原生态系统是有机碳的巨大储存库。气候变暖可能刺激生态系统的呼吸作用，并将碳释放到大气中。这种刺激的幅度和持续性以及驱动其变化的环境机制仍不明确。这阻碍了全球陆地碳-气候反馈预测的准确性。

研究组综合了在28个北极和高山苔原站点进行的56个开放顶室原位变暖实验的136个数据集，这些实验的运行时间从不到1年至25年不等。结果发现，空气温度平均升高1.4℃[置信区间（CI）0.9-2.0℃]和土壤温度平均升高0.4℃[置信区间（CI）0.2-0.7℃]会导致生长季生态系统呼吸增加30%[CI 22-38%]（n = 136）。

研究结果表明，生态系统呼吸的刺激是由于植物相关呼吸和微生物呼吸的增加（n = 9），并且持续至少25年（n = 136）。气候变暖对呼吸作用的影响程度主要受气候变暖引起的局部土壤条件变化（即总氮浓度和pH值的变化），以及这些条件下与环境相关的空间变化（特别是总氮浓度和碳氮比）所驱动。

氮限制较强的苔原地区和气候变暖刺激了植物和微生物养分周转的地区似乎对变暖的呼吸反应特别敏感。这些结果强调了局部土壤条件及其变暖引起的变化，对未来气候影响生态系统呼吸的重要性。

▲ Abstract：

Arctic and alpine tundra ecosystems are large reservoirs of organic carbon. Climate warming may stimulate ecosystem respiration and release carbon into the atmosphere. The magnitude and persistency of this stimulation and the environmental mechanisms that drive its variation remain uncertain. This hampers the accuracy of global land carbon–climate feedback projections. Here we synthesize 136 datasets from 56 open-top chamber in situ warming experiments located at 28 arctic and alpine tundra sites which have been running for less than 1?year up to 25?years. We show that a mean rise of 1.4?°C [confidence interval (CI) 0.9–2.0?°C] in air and 0.4?°C [CI 0.2–0.7?°C] in soil temperature results in an increase in growing season ecosystem respiration by 30% [CI 22–38%] (n?=?136). Our findings indicate that the stimulation of ecosystem respiration was due to increases in both plant-related and microbial respiration (n?=?9) and continued for at least 25?years (n?=?136). The magnitude of the warming effects on respiration was driven by variation in warming-induced changes in local soil conditions, that is, changes in total nitrogen concentration and pH and by context-dependent spatial variation in these conditions, in particular total nitrogen concentration and the carbon:nitrogen ratio. Tundra sites with stronger nitrogen limitations and sites in which warming had stimulated plant and microbial nutrient turnover seemed particularly sensitive in their respiration response to warming. The results highlight the importance of local soil conditions and warming-induced changes therein for future climatic impacts on respiration.