Science, 19 July 2024, Volume 385，Issue 6706

《科学》2024年7月19日，第385卷，6706期

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化学Chemistry

Synthesis of a stable crystalline nitrene

一种稳定结晶亚硝烯的合成

▲ 作者：MARVIN JANSSEN, THOMAS FREDERICHS, MARIAN OLARU, ENNO LORK, EMANUEL HUPF, AND JENS BECKMANN

▲链接：

https://www.science.org/doi/10.1126/science.adp4963

▲摘要：

氮在其化合物中通常形成三个键。在某些情况下，它可以存在于只有一个键的基序中，但这些亚硝基分子往往具有极短的寿命，并且通过时间分辨光谱可以短暂地观察到。

最近，一类笨重的芳基框架稳定了氮的重同系物，锑和铋的亚硝基类似物。研究者发现，这样的框架也可以稳定亚硝基。该化合物被分离并进行了晶体学表征，电子顺磁共振波谱支持三重态基态。

▲ Abstract：

Nitrogen most commonly forms three bonds in its chemical compounds. In certain cases, it can persist in motifs with just one bond, but these nitrene molecules tend to have extremely short lifetimes and are seen transiently by time-resolved spectroscopy. Recently, a class of bulky aryl frameworks has stabilized nitrene analogs of nitrogen’s heavier congeners, antimony and bismuth. Janssen et al. now report that such a framework can stabilize a nitrene as well. The compound was isolated and characterized crystallographically, and electron paramagnetic resonance spectroscopy supported a triplet ground state.

Ph₃PCN₂: A stable reagent for carbon-atom transfer

Ph₃PCN₂: 稳定的碳原子转移试剂

▲ 作者：TAICHI KOIKE, JHEN-KUEI YU, AND MAX M. HANSMANN

▲链接：

https://www.science.org/doi/10.1126/science.ado4564

▲摘要：

在单原子水平上对分子中的化学位点进行精确修饰是化学中最优雅但又最困难的转化之一。为单原子碳的化学选择性引入而专门设计的试剂是一项特别艰巨的挑战。

研究者报告了一个直接的、无叠氮化物的结晶和可分离的化合物Ph₃PCN₂，这是一种稳定的化合物，其碳原子会连接到两个不稳定的化学基团，PPh₃和N₂。在不添加任何添加剂的情况下，重氮磷酰化作为包括Ph₃PCN在内的片段的高选择性转移试剂，传递端磷酰化的杂环烯和CN₂，生成多取代吡唑。

在与醛、无环酮和环酮（R₂C=0）的反应中，碳原子取代形成偏乙烯（R₂C=C），然后生成炔或丁腈。

▲ Abstract：

Precise modification of a chemical site in a molecule at the single-atom level is one of the most elegant yet difficult transformations in chemistry. A reagent specifically designed for chemoselective introduction of monoatomic carbon is a particularly formidable challenge. Here, we report a straightforward, azide-free synthesis of a crystalline and isolable diazophosphorus ylide, Ph₃PCN₂, a stable compound with a carbon atom bonded to two chemically labile groups, triphenylphosphine (PPh₃) and dinitrogen (N₂). Without any additives, the diazophosphorus ylide serves as a highly selective transfer reagent for fragments, including Ph₃PCN, to deliver phosphorus ylide–terminated heterocumulenes and CN₂ to produce multisubstituted pyrazoles. Ultimately, even exclusive carbon-atom transfer is possible. In reactions with aldehydes and acyclic and cyclic ketones (R₂C=O), the carbon-atom substitution forms a vinylidene (R₂C=C:) en route to alkynes or butatrienes.

Defective TiO_x overlayers catalyze propane dehydrogenation promoted by base metals

由非贵金属促进的有缺陷的TiO_x覆盖层催化丙烷脱氢

▲ 作者：SAI CHEN, YIYI XU, XIN CHANG, YUE PAN, GUODONG SUN, XIANHUI WANG, DONGLONG FU, CHUNLEI PEI, ZHI-JIAN ZHAO, AND JINLONG GONG

▲链接：

https://www.science.org/doi/10.1126/science.adp7379

▲摘要：

丙烷脱氢（PDH）制丙烯的工业催化剂是石油基裂化工艺的重要替代品，要么使用昂贵的金属，要么使用对环境不利的金属氧化物。钛纳米片通常是相对较差的丙烷脱氢催化剂，当它们完全包裹金属镍时变得非常活跃。

研究者报道了一种典型的活性较低的氧化物，氧化钛（TiO₂），可以与地球上丰富的金属镍（Ni）结合，形成一种非常规的Ni@TiO_x催化剂，用于高效的PDH。他们将镍离子装载到氧化铝支撑的氧化钛纳米片上，然后在600°C的氢气气氛中还原它们。

该工艺完全封装了金属镍，该催化剂在40%丙烷转化率下具有94%的丙烯选择性。氧空位周围的四配位钛是催化活性位点，地下金属镍是碳氢键活化的促进剂，促进了氢的脱附。

▲ Abstract：

Titanium nanosheets, which are normally relatively poor catalysts for propane dehydrogenation, become highly active when they completely encapsulate metallic nickel. Chen et al. loaded nickel ions onto titanium oxide nanosheets supported on alumina and then reduced them in a hydrogen atmosphere at 600°C. This process completely encapsulated the metallic nickel, and this catalyst displayed 94% propylene selectivity at 40% propane conversion. Tetra-coordinated titanium sites surrounding oxygen vacancies appeared to be the catalytically active site, and subsurface metallic nickel acted as a promoter for carbon-hydrogen bond activation and promoted hydrogen desorption.

物理学Physics

Dynamics of high-speed electrical tree growth in electron-irradiated polymethyl methacrylate

电子辐照聚甲基丙烯酸甲酯中高速电树生长动力学

▲ 作者：KATHRYN M. STURGE, NOAH HOPPIS, ARIANA M. BUSSIO, JONATHAN BARNEY, BRIAN BEAUDOIN, CAMERON BROWN, BRUCE CARLSTEN, CAROLYN CHUN, BRYSON C. CLIFFORD, AND TIMOTHY W. KOETH

▲链接：

https://www.science.org/doi/10.1126/science.ado5943

▲摘要：

介电材料是现代通信、国防和商业需求的基础。介质击穿是这些系统失效的主要原因，但这一过程并不是分清楚。研究者分析了两种不同类型的电树的介电击穿通道传播动力学。其中一种电树还没有被正式分类。

他们观察到这种电树的传播速度超过每秒1000万米。这些结果确定了对介电击穿理解的实质性空白，填补这些空白对于设计和工程中不易受静电放电故障影响的介电材料至关重要。

▲ Abstract：

Dielectric materials are foundational to our modern-day communications, defense, and commerce needs. Although dielectric breakdown is a primary cause of failure of these systems, we do not fully understand this process. We analyzed the dielectric breakdown channel propagation dynamics of two distinct types of electrical trees. One type of these electrical trees has not been formally classified. We observed the propagation speed of this electrical tree type to exceed 10 million meters per second. These results identify substantial gaps in the understanding of dielectric breakdown, and filling these gaps is paramount to the design and engineering of dielectric materials that are less susceptible to electrostatic discharge failure.

生物物理学Biophysics

Sculpting conducting nanopore size and shape through de novo protein design

通过从头开始的蛋白质设计雕刻导电纳米孔的大小和形状

▲ 作者：SAMUEL BERHANU, SAGARDIP MAJUMDER, THOMAS MüNTENER, JAMES WHITEHOUSE, CAROLIN BERNER, ASIM K. BERA, ALEX KANG, BINYONG LIANG, NASIR KHAN, AND ANASTASSIA A. VOROBIEVA

▲链接：

https://www.science.org/doi/10.1126/science.adn3796

▲摘要：

跨膜β—桶具有广泛的传感应用潜力。目前纳米孔传感器的工程方法仅限于自然发生的通道，这提供了次优的起点。相比之下，从头开始的蛋白质设计原则上可以创造无限数量的新纳米孔，具有任何所需的特性。

研究者描述了一种设计具有不同直径和孔隙几何形状的跨膜β—桶孔的一般方法。核磁共振和晶体学表征表明，这些设计是稳定折叠的，结构与设计模型相似。这些设计具有不同的电导，与它们的孔径相关，范围从110皮西门子（~0.5纳米孔径）到430皮西门子（~1.1纳米孔径）。该方法为传感和测序应用的跨膜纳米孔定制设计打开了大门。

▲ Abstract：

Transmembrane β-barrels have considerable potential for a broad range of sensing applications. Current engineering approaches for nanopore sensors are limited to naturally occurring channels, which provide suboptimal starting points. By contrast, de novo protein design can in principle create an unlimited number of new nanopores with any desired properties. Here we describe a general approach to designing transmembrane β-barrel pores with different diameters and pore geometries. Nuclear magnetic resonance and crystallographic characterization show that the designs are stably folded with structures resembling those of the design models. The designs have distinct conductances that correlate with their pore diameter, ranging from 110 picosiemens (~0.5 nanometer pore diameter) to 430 picosiemens (~1.1 nanometer pore diameter). Our approach opens the door to the custom design of transmembrane nanopores for sensing and sequencing applications.

生物化学Biochemistry

Multiscale photocatalytic proximity labeling reveals cell surface neighbors on and between cells

多尺度光催化接近标记揭示细胞表面和细胞之间的邻居

▲ 作者：ZHI LIN, KAITLIN SCHAEFER, IRENE LUI, ZI YAO, ANDREA FOSSATI, DANIELLE L. SWANEY, AJIKARUNIA PALAR, ANDREJ SALI, AND JAMES A. WELLS

▲链接：

https://www.science.org/doi/10.1126/science.adl5763

▲摘要：

细胞表面蛋白质可以与同一细胞上的其他蛋白质或与其他细胞中的蛋白质在空间和时间上发生相互作用。相关研究进展已经提高了这些相互作用的分辨率，可以通过接近标记来识别，但是整合来自不同长度尺度的信息是一个挑战。

研究者开发了一种使用有机光催化剂的方法，该方法可以激活几种具有不同自由基半衰期的常见反应探针，这些探针对应于不同的距离尺度。他们使用一种称为MultiMap的工作流程，确定了一种关键细胞表面受体的大量伴侣蛋白，并在T细胞免疫突触模型中描述了细胞—细胞相互作用。

▲ Abstract：

Cell surface proteins can have interactions with other proteins on the same cell or with proteins in other cells that vary in space and time. Recent advances have improved the resolution with which these interactions can be identified through proximity labeling, but it is a challenge to integrate information from different length scales. Lin et al. developed an approach that uses an organic photocatalyst that can activate several common reactive probes with different radical half-lives corresponding to different distance scales. Using a workflow called MultiMap, the authors identified a large number of partner proteins for a key cell surface receptor and profile cell-cell interactions in a T cell immune synapse model.