《自然》（20240502出版）一周論文導讀

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

天文學Astronomy

A magnetar giant flare in the nearby starburst galaxy M82

星暴星系M82附近的一顆磁星巨大耀斑

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

▲ 鏈接：

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

▲ 摘要：

磁星巨大耀斑是一種罕見的爆發事件，在不到1秒鐘的時間里，從年輕的中子星釋放出高達10⁴⁷爾格的伽馬射線，磁場高達10^15?16  G。大約50年來，在銀河系和大麥哲倫星云的磁星上只觀測到三次這樣的耀斑。

這個小樣本可通過系外事件的發現而擴大，因為幾分之一秒巨大耀斑的亮度可達到10⁴⁶爾格/s以上，這使其在幾十兆秒差距內可見。然而，在這些距離上，很難將它們與短伽馬射線暴（GRBs）區分開來；遠得多、能量大得多（10^50?53爾格）的事件通常源于緊湊的雙星合并。

人們已提出一些具有不同置信區間的短GRBs，這是附近星系中的候選磁星巨大耀斑。研究組報道了GRB 231115A的觀測結果，其與星暴星系M82的位置一致。GRB 231115A的光譜特性，加上爆發長度，在幾小時內獲得的X射線和光學對應物的限制，以及缺乏引力波信號，毫無疑問地證明了這次爆發是來自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.

材料科學Materials Science

Bevel-edge epitaxy of ferroelectric rhombohedral boron nitride single crystal

鐵電斜方六面體氮化硼單晶的斜邊外延

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

▲ 鏈接：

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

▲ 摘要：

在二維電介質家族中，斜方六面體氮化硼（rBN）不僅具有六方氮化硼的優越性能（包括低介電常數和耗散、強電絕緣性、良好的化學穩定性、高導熱性和無懸空鍵的原子平坦性），而且還具有源于面內和面外中心對稱破缺的有用光學非線性和界面鐵電性。然而，由于需要前所未有的生長控制來協調每層的晶格取向和每個界面的滑動矢量，制備大尺寸單晶rBN層仍頗具挑戰。

研究組報道了一種使用斜邊外延來制備厘米尺寸單晶rBN層的簡單方法，在相鄰鎳表面上具有精確的層間ABC堆疊。結果在斜面（110）處成功地精確制造了階地面（100）聚束臺階邊緣的單晶鎳基底，同時引導每個BN層中一致的硼-氮鍵取向，并通過每個斜面附近的成核來引導BN層的斜方六面體堆疊。

研究組驗證了原生BN層的純斜方六面體相，并在高居里溫度下表現出穩健、均勻和可切換的鐵電性。該工作為單晶二維層的精確堆疊控制生長提供了有效途徑，并為基于堆疊二維材料的適用多功能器件奠定了基礎。

▲ 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

聚合物凝膠電解質的高性能纖維電池

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

▲ 鏈接：

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

▲ 摘要：

聚合物凝膠電解質替代液體電解質是公認的解決可穿戴電池安全性問題和實現高柔性的通用有效途徑。然而，由于潤濕不足，聚合物凝膠電解質與電極之間的界面較差，產生了更差的電化學性能，特別是在電池變形時。

研究組報道了一種設計電極通道結構的策略，以整合聚合物凝膠電解質，并形成緊密穩定的界面，以實現高性能可穿戴電池。作為演示，多個電極纖維一起旋轉形成排列通道，同時每個電極纖維的表面設計有網絡通道。

單體溶液首先沿著排列通道有效滲透，然后進入網絡通道。然后，這些單體被聚合成凝膠電解質，并與電極形成緊密穩定的界面。所得纖維鋰離子電池（FLB）表現出較高的電化學性能（例如，能量密度約為128 Wh kg^?1）。

該策略還實現了FLB的生產，速率高達每繞組單元3600 mh^?1。連續的FLB被編織成50 cm×30 cm的紡織品，提供2975 mAh的輸出容量。FLB紡織品在極端條件下安全工作，例如- 40℃和80℃的溫度和- 0.08 MPa的真空。FLB有望應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.

化學Chemistry

Long-term continuous ammonia electrosynthesis

長期連續氨電合成

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

▲ 鏈接：

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

▲ 摘要：

氨在化肥和化學工業中至關重要，被認為是一種無碳燃料。在環境條件下，氮電合成氨為哈伯-博世工藝提供了一個有吸引力的替代方案，鋰介導的氮還原代表了一種有前途的連續流氨電合成方法，將氮還原與氫氧化相結合。然而，由于聚合和揮發性問題，通常用作溶劑的四氫呋喃阻礙了長期氨生產。

研究組展示了鏈醚基電解質可實現長期連續氨合成。他們發現鏈醚基溶劑表現出非聚合特性和高沸點（162℃），并在氣體擴散電極上形成致密的固體-電解質界面層，促進氨在氣相中的釋放，確保電解質的穩定性。

研究組演示了在1 bar壓力和室溫下，該溶劑在25 cm²電極的流動電解槽中連續運行300小時，實現了電流到氨的效率為64±1%，氣相氨含量高達約98%。該研究結果突出了溶劑在長期連續氨合成中的關鍵作用。

▲ 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

光生物催化氧化偶聯合成立體選擇性氨基酸

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

▲ 鏈接：

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

▲ 摘要：

利用光來擴大酶反應性的光生物催化最近已成為開發自然界新化學物質的一種強大策略。這些體系在小分子催化劑長期無法催化的不對稱自由基反應中顯示出潛力。到目前為止，非天然光生物催化反應僅限于整體還原和氧化還原中性過程。

研究組報道了光生物催化有機硼試劑和氨基酸之間的不對稱sp³–sp³氧化交叉偶聯反應。該反應需要工程吡哆醛生物催化劑、光氧化還原催化劑和氧化劑的協同使用。通過自由基機制重新改良吡哆醛-5′-磷酸依賴酶家族（即蘇氨酸醛縮酶），對甘氨酸和α-支鏈氨基酸底物進行α-C–H功能化，產生一系列具有最多兩個連續立體中心的α-三取代和四取代的非經典氨基酸。

吡哆醛自由基酶的定向進化實現了一級和二級自由基前體（包括芐基、烯丙基和烷基硼試劑）以對映體控制和非對映體控制的方式偶聯。協同光氧化還原-吡哆醛生物催化為sp³–sp³氧化偶聯提供了一個平臺，實現了化學或生物學未知的立體選擇性分子間自由基轉化。

▲ 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.

地球科學One Earth

Environmental drivers of increased ecosystem respiration in a warming tundra

變暖苔原生態系統呼吸增加的環境驅動因素

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

▲ 鏈接：

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

▲ 摘要：

北極和高山苔原生態系統是有機碳的巨大儲存庫。氣候變暖可能刺激生態系統的呼吸作用，并將碳釋放到大氣中。這種刺激的幅度和持續性以及驅動其變化的環境機制仍不明確。這阻礙了全球陸地碳-氣候反饋預測的準確性。

研究組綜合了在28個北極和高山苔原站點進行的56個開放頂室原位變暖實驗的136個數據集，這些實驗的運行時間從不到1年至25年不等。結果發現，空氣溫度平均升高1.4℃[置信區間（CI）0.9-2.0℃]和土壤溫度平均升高0.4℃[置信區間（CI）0.2-0.7℃]會導致生長季生態系統呼吸增加30%[CI 22-38%]（n = 136）。

研究結果表明，生態系統呼吸的刺激是由于植物相關呼吸和微生物呼吸的增加（n = 9），并且持續至少25年（n = 136）。氣候變暖對呼吸作用的影響程度主要受氣候變暖引起的局部土壤條件變化（即總氮濃度和pH值的變化），以及這些條件下與環境相關的空間變化（特別是總氮濃度和碳氮比）所驅動。

氮限制較強的苔原地區和氣候變暖刺激了植物和微生物養分周轉的地區似乎對變暖的呼吸反應特別敏感。這些結果強調了局部土壤條件及其變暖引起的變化，對未來氣候影響生態系統呼吸的重要性。

▲ 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.