编译｜冯维维
Science, 5 November 2021, VOLUME 374 ISSUE 6568
《科学》2021年11月5日，第374卷，6568期
分子化学
Molecular chemistry
Mapping the catalytic conformations of an assembly-line polyketide synthase module
绘制装配线聚酮合酶模块的催化构象
作者：DILLON P. COGAN, KAIMING ZHANG, XIUYUAN LI, SHANSHAN LI , GRIGORE D. PINTILIESOUNG-HUN ROH, CHARLES S. CRAIK, WAH CHIU AND CHAITAN KHOSLA
链接：
https://www.science.org/doi/10.1126/science.abi8358
摘要
放线菌是生物活性小分子如聚酮类抗生素的高产者。这些分子通过在一个不断增长的蛋白质链上添加短碳单元来构建，或像脂肪酸合成那样迭代，或通过从一个不同的酶复合物传递到下一个酶复合物的模块化方式。
作者报道了作用中的聚酮合酶模块的结构，利用其中一个结构域的抗体稳定性。两组研究人员都可视化了多种构象状态和结构域的不对称排列，提供了这些分子组装机如何将底物从一个活性位点转移到另一个活性位点的见解。
Abstract
Actinomycete bacteria are prolific producers of bioactive small molecules such as polyketide antibiotics. These molecules are built by the addition of short carbon units to a growing, protein-tethered chain, either iteratively as in fatty acid synthesis or in a modular fashion by a hand-off from one distinct enzyme complex to the next. Bagde et al. and Cogan et al. report structures of polyketide synthase modules in action, taking advantage of antibody stabilization of one of the domains. Both groups visualized multiple conformational states and an asymmetric arrangement of domains, providing insight into how these molecular assembly machines transfer substrates from one active site to another.
Carbonyl 1,2-transposition through triflate-mediated α-amination
通过三磷酸盐介导的羰基转位
作者：ZHAO WU, XIAOLONG XU, JIANCHUN WANG, AND GUANGBIN DONG
链接：
https://www.science.org/doi/10.1126/science.abl7854
摘要
化学家花费了巨大的精力来精确定位氧原子在分子框架中的位置。作者报道了一种方便的方法，将羰基中的氧转移到邻近的碳中心。
在氧活化成三氟烯酸烯后，钯和降冰片烯的协同催化使氮加入到邻近的碳上，同时用氢化物取代三氟烯酸烯。然后水解产生所需的移位酮。该方案非常适合于药物优化过程中复杂分子的后期变异。
Abstract
Chemists devote tremendous effort to the precise placement of oxygens in molecular frameworks. Wu et al. report a convenient method to shift the oxygen in a carbonyl group to an adjacent carbon center. After activation of the oxygen to an alkenyl triflate, cooperative catalysis by palladium and norbornene adds nitrogen to the neighboring carbon while displacing the triflate with hydride. Hydrolysis then produces the desired shifted ketone. The protocol is well suited to late-stage variation of complex molecules during drug optimization.
催化化学
Catalytic chemistry
Scalable Birch reduction with lithium and ethylenediamine in tetrahydrofuran
锂和乙二胺的可伸缩伯奇还原
作者：JAMES BURROWS, SHOGO KAMO, AND KAZUNORI KOIDE
链接：
https://www.science.org/doi/10.1126/science.abk3099
摘要
半个多世纪以来，伯奇还原法被广泛应用于碱金属在两个完全相反的碳位上对芳基环进行部分还原。然而，在这种条件下，苛性气氨需要冷凝。此后Benkeser开发的一种变体使用了更安全的液体乙二胺，但易于过度减少。通过在四氢呋喃溶剂中稀释乙烯二胺，现在作者获得了与伯奇条件相当的选择性，但不需要冷凝氨。
Abstract
The Birch reduction has been widely used for more than half a century to achieve partial reduction of aryl rings by alkali metals at just two diametrically opposed carbon sites. However, the conditions require condensation of caustic gaseous ammonia. A variation developed soon afterward by Benkeser used safer liquid ethylene diamine but was prone to overreduction. By diluting ethylene diamine in tetrahydrofuran solvent, Burrows et al. now obtain selectivities comparable to Birch conditions but without the need for condensed ammonia.
Enantioselective catalytic 1,2-boronate rearrangements
对映选择性催化硼酸酯重排
作者：HAYDEN A. SHARMA, JAKE Z. ESSMAN AND ERIC N. JACOBSEN
链接：
https://www.science.org/doi/10.1126/science.abm0386
摘要
马特森反应通过将卤代烃（如广泛使用的二氯甲烷）与硼上的烷基取代基偶联而产生碳-碳键。作者报道了该反应的不对称催化作用。他们的催化剂，由手性硫脲、硼酯和烷基锂碱衍生而来，似乎可以通过其锂中心加速氯化物的提取。该产物仍然含有氯，可以通过立体定向置换进一步修饰，生成各种各样的三取代手性中心。
Abstract
The Matteson reaction produces carbon–carbon bonds by coupling halocarbons such as widely available dichloromethane with an alkyl substituent on boron. Sharma et al. report asymmetric catalysis of this reaction. Their catalyst, derived from a chiral thiourea, a boronic ester, and an alkyl lithium base, appears to accelerate a chloride abstraction step through its lithium center. The product, still bearing a chloride, can be further modified through stereospecific displacement to generate a wide variety of trisubstituted chiral centers.
大气化学
Atmospheric chemistry
A surface-promoted redox reaction occurs spontaneously on solvating inorganic aerosol surfaces
溶剂化无机气溶胶表面自发发生的表面促进氧化还原反应
作者：XIANGRUI KONG, DIMITRI CASTARÈDE, ERIK S. THOMSON, ANTHONY BOUCLY, LUCA ARTIGLIAMARKUS AMMANNIVAN GLADICH, AND JAN B. C. PETTERSSON
链接：
https://www.science.org/doi/10.1126/science.abc5311
摘要
界面氧化还原化学在气体分子和气溶胶粒子的形成中起着重要的作用。
然而，对这些非均相过程的描述是具有挑战性的，并且在化学动力学模型中往往被忽略。利用常压X射线光电子能谱结合分子动力学模拟，作者发现，在典型的无机气溶胶硫酸铵表面的溶剂化过程的第一阶段，表面促进了自发氧化还原化学。
一些意想不到的物质被确认为硫酸盐还原铵氧化反应的可能产物，这可能有助于解决大气化学中的一些持久难题。研究结果对污水处理和其他工业技术的发展也有一定的指导意义。
Abstract
Interfacial redox chemistry plays an important role in the formation of gas molecules and aerosol particles. However, the characterization of such heterogeneous processes is challenging, and they are often omitted in chemical kinetics models. Using ambient-pressure x-ray photoelectron spectroscopy combined with molecular dynamics simulations, Kong et al. discovered spontaneous redox chemistry promoted by the surface at the first stages of the solvation process on a typical inorganic aerosol surface of ammonium sulfate (see the Perspective by Ruiz-Lopez). Several unexpected species have been identified as being possible products of a sulfate-reducing ammonium oxidation reaction, and this may help to resolve some of the enduring conundrums of atmospheric chemistry. The present results could also be useful for the development of wastewater treatments and other industrial technologies.
Abating ammonia is more cost-effective than nitrogen oxides for mitigating PM2.5 air pollution
缓解PM2.5空气污染，减氨比减氮氧化物更具成本效益
作者：BAOJING GU, LIN ZHANG, RITA VAN DINGENEN, MASSIMO VIENO, HANS JM VAN GRINSVENXIUMING ZHANG, SHAOHUI ZHANG, YOUFAN CHENSITONG WANGMARK A. SUTTON
链接：
https://www.science.org/doi/10.1126/science.abf8623
摘要
直径2.5微米及以下的大气颗粒物（PM2.5）污染是人类死亡的主要原因，控制其产生是卫生政策的重点。氮氧化物是PM2.5的重要前体，一直是污染控制项目的重点。
现在作者研究表明，减少氨排放也是减少PM2.5的一个重要组成部分，减少氨排放的社会效益大大超过成本。因此，减少氨的排放将是氮氧化物和二氧化硫控制的一种具有成本效益的补充。
Abstract
Particulate air pollution 2.5 micrometers or smaller in size (PM2.5) is a major cause of human mortality, and controlling its production is a health policy priority. Nitrogen oxides are an important precursor of PM2.5 and have been a focus of pollution control programs. However, Gu et al. now show that abating ammonia emissions is also an important component of PM2.5 reduction, and the societal benefits of abatement greatly outweigh the costs. Reducing ammonia emissions thus would be a cost-effective complement to nitrogen oxides and sulfur dioxide controls.
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