化学Chemistry

▲ 作者：NICHOLAS R. BOYNTON, JOSEPH M. DENNIS, NEIL D. DOLINSKI, CHARLIE A. LINDBERG, ANTHONY P. KOTULA, GARRETT L. GROCKE, STEPHANIE L. VIVOD, JOSEPH L. LENHART, SHRAYESH N. PATEL, AND STUART J. ROWAN 

▲ 链接：

https://www.science.org/doi/10.1126/science.adi5009

▲ 摘要：

通过控制加热和冷却循环回火被用于调整一系列材料的微观结构，包括许多金属甚至巧克力。研究者将这一想法扩展到单一聚合物体系中机械性能的可逆转变。这种方法是通过包含相对较弱的thia-Michael键来实现的，与聚合物中的共价键相比，thia-Michael键能够在较低的温度下重组。

在较高的回火温度下，thia-Michael网络的交联密度降低，导致材料的刚度降低，而在较低的温度下回火会产生更硬的材料。由于结合和非结合交联的变化引起的动态反应诱导相分离，材料表现出形状记忆特性。

▲ Abstract：

Tempering through controlled heating and cooling cycles is used to adjust the microstructure of a range of materials, including many metals and even chocolate. Boynton et al. extended this idea to reversible transformations of the mechanical properties in a single polymer system. This method was achieved through the inclusion of thia-Michael bonds that are relatively weak and capable of reshuffling at lower temperatures compared with the covalent bonds in the polymer. At higher tempering temperatures, the cross-link density of the thia-Michael network decreases, resulting in a lower stiffness of the material, whereas tempering at lower temperatures creates a stiffer material. The material exhibits shape memory properties attributed to the dynamic reaction–induced phase separation caused by the change in bound and unbound cross-links. 

▲ 作者：MIAO WANG, YAHAO HUANG, AND PENG HU

▲ 链接：

https://www.science.org/doi/10.1126/science.adj9258

▲ 摘要：

在过去的二十年里，硼化反应作为一种替代许多原料化学品中大量不活泼的碳氢键的方法而出现。尽管如此，烷基链的位点选择性仍然是一个挑战。

研究者使用氯化铁光催化剂来促进可逆的氢原子转移过程，对链上的位点进行采样，并最终以高选择性将硼酯附加到末端碳上。流动系统实现了多图尺度下的高效反应。

▲ Abstract：

Borylation has emerged in the past two decades as a - means of substituting the otherwise unreactive carbon–hydrogen bonds abundant in many feedstock chemicals. Nonetheless, site selectivity in alkyl chains remains a challenge. Wang et al. used an iron chloride photocatalyst to prompt a reversible hydrogen atom transfer process that samples sites along the chain and ultimately appends boronic esters to the end carbon with high selectivity. A flow system enabled efficient reactivity at multigram scale. 

▲ 作者：FANG LI, W. FELIX ZHU, CLAIRE EMPEL, OLEKSANDR DATSENKO, ADARSH KUMAR, YAMENG XU, JOHANNA H. M. EHRLER, IULIANA ATODIRESEI, STEFAN KNAPP, AND RENE M. KOENIGS 

▲ 链接：

https://www.science.org/doi/10.1126/science.adm8095

▲ 摘要：

Pauson-Khand有机化学反应是近50年来化学中最常见的环加成反应之一。将两个不饱和键与一氧化碳偶联，转化仍然局限于一氧化碳作为C1构建块。研究者报告了类似的环加成反应与亚硝基烯作为N1单元。

非共轭二烯与亚硝基前体的反应产生常见饱和杂环的双环生物异构体，如哌啶、啉和哌嗪。实验和计算机制研究支持将三重态亚硝基的双自由基性质转化为π系。研究展示了该反应在药物化合物后期功能化和可溶性环氧化物水解酶抑制剂的发现中的效用。

▲ Abstract：

The Pauson-Khand reaction has in the past 50 years become one of the most common cycloaddition reactions in chemistry. Coupling two unsaturated bonds with carbon monoxide, the transformation remains limited to CO as a C1 building block. Herein we report analogous cycloaddition reactions with nitrenes as an N1 unit. The reaction of a nonconjugated diene with a nitrene precursor produces bicyclic bioisosteres of common saturated heterocycles such as piperidine, morpholine, and piperazine. Experimental and computational mechanistic studies support relaying of the diradical nature of triplet nitrene into the π-system. We showcase the reaction’s utility in late-stage functionalization of drug compounds and discovery of soluble epoxide hydrolase inhibitors.

▲ 作者：PEIDE ZHU, DENG WANG, YONG ZHANG , ZHENG LIANG, JINGBAI LI, JIE ZENG, JIYAO ZHANG, YINTAI XU, SIYING WU, AND BAOMIN XU

▲ 链接：

https://www.science.org/doi/10.1126/science.adj7081

▲ 摘要：

钙钛矿太阳能电池具有较高的缺陷容忍度，但薄膜前驱体中的杂质和非化学计量限制了电池的功率转换效率。研究者发现，水法制备甲脒碘化铅微晶为制备高纯度前体提供了一种低成本途径，且无需使用有机溶剂。

这条路线最大限度地减少杂质离子，如形成电荷载流子陷阱的钙。对于倒置太阳能电池，获得了25.3%的认证功率转换效率，并且在50℃下连续工作1000小时后仍保持该效率的94%。

▲ Abstract：

Perovskite solar cells have a high defect tolerance, but impurities and nonstoichiometries in the film precursor have limited power conversion efficiency. Zhu et al. report that the aqueous synthesis of microcrystals of formamidinium lead iodide provides a low-cost route to highly pure precursors without the use of organic solvents. This route minimizes impurity ions such as calcium that form charge carrier traps. For inverted solar cells, a certified power conversion efficiency of 25.3% was obtained, and 94% of this efficiency was retained after 1000 hours of continuous operation at 50℃. 

生态学Ecology

▲ 作者：ERICK J. LUNDGREN, JURAJ BERGMAN, JONAS TREPEL, SOPHIE MONSARRAT, JEPPE AAGAARD KRISTENSEN, RASMUS ?STERGAARD PEDERSEN, PATRICIO PEREYRA, MELANIE TIETJE, AND JENS-CHRISTIAN SVENNING 

▲ 链接：

https://www.science.org/doi/10.1126/science.adh2616

▲ 摘要：

史前以来，大型食草哺乳动物已经经历了灭绝和衰退。外地引进的巨型动物在一定程度上抵消了这些损失，但与本土巨型动物相比，它们被认为对植物有不同寻常的负面影响。

通过对来自221项研究的3995个样点尺度的植物丰度和多样性响应进行荟萃分析，研究者发现没有证据表明巨型动物的影响是由本土性、入侵性、野性、共同进化史或功能和系统发育新颖性决定的。也没有证据表明外来巨型动物比本土巨型动物更能促进外来植物的生长。

相反，研究者发现了强有力的证据表明，功能特征塑造了巨型动物的影响，体型更大、摄食量更大的巨型动物促进了植物的多样性。研究表明，基于性状的生态学比原生的概念更能洞察巨型动物和植物之间的相互作用。

▲ Abstract：

Large mammalian herbivores (megafauna) have experienced extinctions and declines since prehistory. Introduced megafauna have partly counteracted these losses yet are thought to have unusually negative effects on plants compared with native megafauna. Using a meta-analysis of 3995 plot-scale plant abundance and diversity responses from 221 studies, we found no evidence that megafauna impacts were shaped by nativeness,“invasiveness,” “feralness,” coevolutionary history, or functional and phylogenetic novelty. Nor was there evidence that introduced megafauna facilitate introduced plants more than native megafauna. Instead, we found strong evidence that functional traits shaped megafauna impacts, with larger-bodied and bulk-feeding megafauna promoting plant diversity. Our work suggests that trait-based ecology provides better insight into interactions between megafauna and plants than do concepts of nativeness.

机器学习Machine Learning