化学家首次改变单个分子中原子间的键

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Fig. 1 Images of single molecules obtained by high-resolution atomic force microscopy. Selectively and reversibly the molecular structure in the center can be transformed to the structure on the right or on the left, by voltage pulses applied form the tip of a scanning probe microscope. Credit: Leo Gross/IBM

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Fig. 2 Schematic of the tip induced reactions. By voltage pulses from the tip of a scanning probe microscope, different molecular transformations are triggered selectively. The color of the arrows indicates the value of voltage pulses used to trigger selectively the different transformations. Credit: Florian Albrecht/IBM

据物理学家组织网（Phys.org）2022年7月15日报道，化学家首次可以改变单个分子中原子间的化学键（Chemists change the bonds between atoms in a single molecule for the first time）。上述由美国国际商用机器公司（International Business Machine简称IBM）的利奥·格罗斯（Leo Gross）提供的图片，是通过高分辨率原子力显微镜（high-resolution atomic force microscopy）获得的单分子图像。通过从扫描探针显微镜（scanning probe microscope）的尖端施加电压脉冲，可以选择性和可逆地将中心的分子结构转变为右侧或左侧的结构。

来自IBM欧洲研究院（IBM Research Europe）、西班牙圣地亚哥孔波斯特拉大学（Universidade de Santiago de Compostela）和德国雷根斯堡大学（University of Regensburg）的一个研究小组首次改变了单个分子中原子之间的键。相关研究结果于2022年7月14日已经在《科学》（Science）杂志网站发表，详见：

Florian Albrecht, Shadi Fatayer, Iago Pozo, Ivano Tavernelli, Jascha Repp, Diego Peña, Leo Gross. Selectivity in single-molecule reactions by tip-induced redox chemistry. Science, 2022, 377 (6603): 298-301. DOI: 10.1126/science.abo6471. Published 14 Jul 2022.  https://doi.org/10.1126/science.abo6471.

在此论文中，该小组描述了他们的方法和可能的用途。在同一期杂志上，伊戈尔·阿拉布金（Igor Alabugin）和胡朝伟（Chaowei Hu音译）发表了一篇观点文章，概述了该团队所做的工作。详见：Igor Alabugin, Chaowei Hu. A Swiss Army knife for surface chemistry. Science, 2022, 377 (6603): 261-262. DOI: 10.1126/science.abq2622. Published 14 Jul 2022. https://dx.doi.org/10.1126/science.abq2622.

正如伊戈尔·阿拉布金和胡朝伟所指出的那样，目前制造复杂分子（complex molecules）或分子装置（molecular devices）的方法通常相当具有挑战性。他们将其比作将一盒乐高玩具（Legos）倾倒在洗衣机中，并希望建立一些有用的连接。在这项新的努力中，该研究团队通过使用扫描隧道显微镜（scanning tunneling microscope简称STM）来打破分子中的键，然后通过创建新键来定制分子，从而大大简化了这项工作——这是化学上的第一。

可以通过视频观看尖端诱导反应示意图（Fig. 2）。通过扫描探针显微镜尖端的电压脉冲，可以选择性地触发不同的分子转变。箭头的颜色表示用于选择性触发不同变换的电压脉冲值。

该团队的工作涉及将样品材料放入扫描隧道显微镜（scanning tunneling microscope），然后使用极少量的电来破坏特定的键。更具体地说，他们首先从四元环的核中抽出4个氯原子作为起始分子。然后，他们将STM的尖端移到C—CI键上，用电击断开化学键。对其他C—CI键和C—C键对这样做导致了一个双自由基（diradical）的形成，这使得六个电子可以自由地用于形成其他键。在一项创造新分子的测试中，研究小组随后利用自由电子（和一定剂量的高压）形成对角C—C键，从而产生弯曲的炔烃（bent alkyne）。在另一个例子中，他们施加一定量的低电压以形成环丁二烯环（cyclobutadiene ring）。

研究人员注意到，他们的工作是由IBM苏黎世实验室（IBM's laboratory in Zurich）的格尔德·宾宁（Gerd Binnig）和海因里希·罗雷尔（Heinrich Rohrer）领导的团队开发的超高精度隧道技术实现的。他们建议，他们的技术可以用来更好地理解氧化还原化学（redox chemistry），并创造新的分子种类。

上述介绍，仅供参考。欲了解更多信息，敬请注意浏览原文或者相关报道。

分子碰撞过程中观察到的键选择反应（Bond-selective reactions observed during molecular collisions）

Tip-induced organic reactions（DOI: 10.1126/science.abo6471）

Control over the reaction products of a unimolecular transformation on a surface have been induced and visualized with a scanning tunneling microscope (STM) tip. Albrecht et al. synthesized a tetrachlorotetracene molecule and absorbed it on a thin salt layer grown on copper (see the Perspective by Alabugin and Hu). Under cryogenic conditions, voltage pulses from the STM tip led to the elimination of the chlorine atoms and produced intermediates with a large central ring. Subsequent voltage pulses created other isomers of this molecule, a diyne and a chrysene-based bisaryne, in reactions that could be reversed with opposite polarity pulses. —PDS

Abstract（DOI: 10.1126/science.abo6471）

Controlling selectivity of reactions is an ongoing quest in chemistry. In this work, we demonstrate reversible and selective bond formation and dissociation promoted by tip-induced reduction-oxidation reactions on a surface. Molecular rearrangements leading to different constitutional isomers are selected by the polarity and magnitude of applied voltage pulses from the tip of a combined scanning tunneling and atomic force microscope. Characterization of voltage dependence of the reactions and determination of reaction rates demonstrate selectivity in constitutional isomerization reactions and provide insight into the underlying mechanisms. With support of density functional theory calculations, we find that the energy landscape of the isomers in different charge states is important to rationalize the selectivity. Tip-induced selective single-molecule reactions increase our understanding of redox chemistry and could lead to novel molecular machines.

Abstract (DOI: 10.1126/science.abq2622)

To construct complex molecules and molecular devices, tiny, atomic-sized objects must be brought together and connected in a precise way. For better or for worse, this daunting task is still mostly done in a manner likened to putting Lego blocks in a washing machine and hoping that the quintillions of molecules somehow end up assembling themselves into the desired product, either by complete chance or under the guidance of other molecular-sized objects—i.e., catalysts. On page 298 of this issue, Albrecht et al. (1) show how a single molecule can be transformed into three distinct products depending on the voltage pulses from the tip of a scanning tunneling microscope (STM). Notably, the three products can be repeatedly interconverted with a high degree of control.