Fung Kayleigh L Y, Skowron Stephen T, Hayter Ruth, Mason Stephen E, Weare Benjamin L, Besley Nicholas A, Ramasse Quentin M, Allen Christopher S, Khlobystov Andrei N
School of Chemistry, University of Nottingham, University Park, Nottingham NG7 2RD, UK.
SuperSTEM Laboratory, SciTech Daresbury Campus, Keckwick Lane, Daresbury WA4 4AD, UK.
Phys Chem Chem Phys. 2023 Mar 29;25(13):9092-9103. doi: 10.1039/d2cp05183d.
We report experimental methodologies utilising transmission electron microscopy (TEM) as an imaging tool for reaction kinetics at the single molecule level, in direct space and with spatiotemporal continuity. Using reactions of perchlorocoronene (PCC) in nanotubes of different diameters and at different temperatures, we found a period of molecular movement to precede the intermolecular addition of PCC, with a stronger dependence of the reaction rate on the nanotube diameter, controlling the local environments around molecules, than on the reaction temperature (-175, 23 or 400 °C). Once initiated, polymerisation of PCC follows zero-order reaction kinetics with the observed reaction cross section of 1.13 × 10 nm (11.3 ± 0.6 barn), determined directly from time-resolved TEM image series acquired with a rate of 100 frames per second. Polymerisation was shown to proceed from a single point, with molecules reacting sequentially, as in a domino effect, due to the strict conformational requirement of the Diels-Alder cycloaddition creating the bottleneck for the reaction. The reaction mechanism was corroborated by correlating structures of reaction intermediates observed in TEM images, with molecular weights measured by using mass spectrometry (MS) when the same reaction was triggered by UV irradiation. The approaches developed in this study bring the imaging of chemical reactions at the single-molecule level closer to traditional concepts of chemistry.
我们报道了利用透射电子显微镜（TEM）作为成像工具的实验方法，用于在直接空间中以时空连续性研究单分子水平的反应动力学。通过研究不同直径的纳米管中以及不同温度下全氯并五苯（PCC）的反应，我们发现PCC分子间加成反应之前存在一段分子运动期，并且反应速率对纳米管直径的依赖性更强，纳米管直径控制着分子周围的局部环境，而不是反应温度（-175、23或400°C）。一旦引发，PCC的聚合遵循零级反应动力学，观察到的反应截面为1.13×10 nm（11.3±0.6靶恩），这是直接从以每秒100帧的速率采集的时间分辨TEM图像序列中确定的。由于狄尔斯-阿尔德环加成反应严格的构象要求为反应制造了瓶颈，聚合反应显示从单个点开始，分子依次反应，如同多米诺效应。当通过紫外线照射引发相同反应时，通过将TEM图像中观察到的反应中间体结构与使用质谱（MS）测量的分子量相关联，证实了反应机理。本研究中开发的方法使单分子水平的化学反应成像更接近传统化学概念。
