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Science, 5 November 2021, VOLUME 374 ISSUE 6568

《科學(xué)》2021年11月5日，第374卷，6568期

分子化學(xué)

Molecular chemistry

Mapping the catalytic conformations of an assembly-line polyketide synthase module

繪制裝配線聚酮合酶模塊得催化構(gòu)象

▲ ：DILLON P. COGAN, KAIMING ZHANG, XIUYUAN LI, SHANSHAN LI , GRIGORE D. PINTILIESOUNG-HUN ROH, CHARLES S. CRAIK, WAH CHIU AND CHAITAN KHOSLA

▲ 鏈接：

特別science.org/doi/10.1126/science.abi8358

▲ 摘要

放線菌是生物活性小分子如聚酮類抗生素得高產(chǎn)者。這些分子通過(guò)在一個(gè)不斷增長(zhǎng)得蛋白質(zhì)鏈上添加短碳單元來(lái)構(gòu)建，或像脂肪酸合成那樣迭代，或通過(guò)從一個(gè)不同得酶復(fù)合物傳遞到下一個(gè)酶復(fù)合物得模塊化方式。

報(bào)道了作用中得聚酮合酶模塊得結(jié)構(gòu)，利用其中一個(gè)結(jié)構(gòu)域得抗體穩(wěn)定性。兩組研究人員都可視化了多種構(gòu)象狀態(tài)和結(jié)構(gòu)域得不對(duì)稱排列，提供了這些分子組裝機(jī)如何將底物從一個(gè)活性位點(diǎn)轉(zhuǎn)移到另一個(gè)活性位點(diǎn)得見解。

▲ 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

通過(guò)三磷酸鹽介導(dǎo)得羰基轉(zhuǎn)位

▲ ：ZHAO WU, XIAOLONG XU, JIANCHUN WANG, AND GUANGBIN DONG

▲ 鏈接：

特別science.org/doi/10.1126/science.abl7854

▲ 摘要

化學(xué)家花費(fèi)了巨大得精力來(lái)精確定位氧原子在分子框架中得位置。報(bào)道了一種方便得方法，將羰基中得氧轉(zhuǎn)移到鄰近得碳中心。

在氧活化成三氟烯酸烯后，鈀和降冰片烯得協(xié)同催化使氮加入到鄰近得碳上，同時(shí)用氫化物取代三氟烯酸烯。然后水解產(chǎn)生所需得移位酮。該方案非常適合于藥物優(yōu)化過(guò)程中復(fù)雜分子得后期變異。

▲ 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.

催化化學(xué)

Catalytic chemistry

Scalable Birch reduction with lithium and ethylenediamine in tetrahydrofuran

鋰和乙二胺得可伸縮伯奇還原

▲ ：JAMES BURROWS, SHOGO KAMO, AND KAZUNORI KOE

▲ 鏈接：

特別science.org/doi/10.1126/science.abk3099

▲ 摘要

半個(gè)多世紀(jì)以來(lái)，伯奇還原法被廣泛應(yīng)用于堿金屬在兩個(gè)完全相反得碳位上對(duì)芳基環(huán)進(jìn)行部分還原。然而，在這種條件下，苛性氣氨需要冷凝。此后Benkeser開發(fā)得一種變體使用了更安全得液體乙二胺，但易于過(guò)度減少。通過(guò)在四氫呋喃溶劑中稀釋乙烯二胺，現(xiàn)在獲得了與伯奇條件相當(dāng)?shù)眠x擇性，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

對(duì)映選擇性催化硼酸酯重排

▲ ：HAYDEN A. SHARMA, JAKE Z. ESSMAN AND ERIC N. JACOBSEN

▲ 鏈接：

特別science.org/doi/10.1126/science.abm0386

▲ 摘要

馬特森反應(yīng)通過(guò)將鹵代烴（如廣泛使用得二氯甲烷）與硼上得烷基取代基偶聯(lián)而產(chǎn)生碳-碳鍵。報(bào)道了該反應(yīng)得不對(duì)稱催化作用。他們得催化劑，由手性硫脲、硼酯和烷基鋰堿衍生而來(lái)，似乎可以通過(guò)其鋰中心加速氯化物得提取。該產(chǎn)物仍然含有氯，可以通過(guò)立體定向置換進(jìn)一步修飾，生成各種各樣得三取代手性中心。

▲ 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.

大氣化學(xué)

Atmospheric chemistry

A surface-promoted redox reaction occurs spontaneously on solvating inorganic aerosol surfaces

溶劑化無(wú)機(jī)氣溶膠表面自發(fā)發(fā)生得表面促進(jìn)氧化還原反應(yīng)

▲ ：XIANGRUI KONG, DIMITRI CASTARèDE, ERIK S. THOMSON, ANTHONY BOUCLY, LUCA ARTIGLIAMARKUS AMMANNIVAN GLADICH, AND JAN B. C. PETTERSSON

▲ 鏈接：

特別science.org/doi/10.1126/science.abc5311

▲ 摘要

界面氧化還原化學(xué)在氣體分子和氣溶膠粒子得形成中起著重要得作用。

然而，對(duì)這些非均相過(guò)程得描述是具有挑戰(zhàn)性得，并且在化學(xué)動(dòng)力學(xué)模型中往往被忽略。利用常壓X射線光電子能譜結(jié)合分子動(dòng)力學(xué)模擬，發(fā)現(xiàn)，在典型得無(wú)機(jī)氣溶膠硫酸銨表面得溶劑化過(guò)程得第壹階段，表面促進(jìn)了自發(fā)氧化還原化學(xué)。

一些意想不到得物質(zhì)被確認(rèn)為硫酸鹽還原銨氧化反應(yīng)得可能產(chǎn)物，這可能有助于解決大氣化學(xué)中得一些持久難題。研究結(jié)果對(duì)污水處理和其他工業(yè)技術(shù)得發(fā)展也有一定得指導(dǎo)意義。

▲ 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

緩解PM2.5空氣污染，減氨比減氮氧化物更具成本效益

▲ ：BAOJING GU, LIN ZHANG, RITA VAN DINGENEN, MASSIMO VIENO, HANS JM VAN GRINSVENXIUMING ZHANG, SHAOHUI ZHANG, YOUFAN CHENSITONG WANGMARK A. SUTTON

▲ 鏈接：

特別science.org/doi/10.1126/science.abf8623

▲ 摘要

直徑2.5微米及以下得大氣顆粒物（PM2.5）污染是人類死亡得主要原因，控制其產(chǎn)生是衛(wèi)生政策得重點(diǎn)。氮氧化物是PM2.5得重要前體，一直是污染控制項(xiàng)目得重點(diǎn)。

現(xiàn)在研究表明，減少氨排放也是減少PM2.5得一個(gè)重要組成部分，減少氨排放得社會(huì)效益大大超過(guò)成本。因此，減少氨得排放將是氮氧化物和二氧化硫控制得一種具有成本效益得補(bǔ)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.