The metathesis reaction, studied by single-molecule chemistry

教科书中对化学反应的描述依赖于单分子的转化，但化学家很少在这样的浓度水平上进行实验。理解化学需要很大程度的抽象，才能从材料的物理性质推断分子性质。因此，直接接触分子动力学不仅有助于增加有关反应机理和途径的知识，而且还可能有助于简化对化学的总体理解。最近，该方案的作者用单分子荧光光谱研究了众所周知的双键环氧化反应。在他们的实验中，他们利用了荧光探针分子在转化过程中发射波长的变化，并在通向环氧化物的反应途径中发现了一个未知的分叉。这些实验是在耐有机溶剂的特殊反应室中使用单分子灵敏的TIRF显微镜进行的。在应用项目中，我们计划将这种实验方法转移到Ru催化的复分解反应中。尽管这种催化在大量的合成应用中得到了很好的理解，但最初的反应值得进一步研究，因为初步实验揭示了缔合反应和解离反应机理的线索。本项目的目的是让化学家熟悉单分子化学的机会，例如基于Ru的复分解催化剂的模棱两可的激活。我们计划通过跟踪固定靶标上的荧光轨迹来研究磷化氢解离在区域选择性中的作用。通过使用微流控技术，可以控制更多化学品的供应。

The description of chemical reaction in textbooks relies on the transformation of single molecules, but chemists hardly perform experiments on suchlike concentration levels. Understanding chemistry requires a huge level of abstraction in deducing molecular properties from physical properties of the material. Thus, direct access to molecular dynamics will not only help adding knowledge about reaction mechanisms and pathways but may also help simplifying the understanding of chemistry in general. Recently, the authors of this proposal studied the well-known epoxidation of double bonds by single-molecule fluorescence spectroscopy. In their experiments, they exploited the change of the emission wavelength of a fluorescent probe molecule during the transformation and found a yet unknown bifurcation in the reaction pathway to the epoxide. The experiments were carried out in special reaction chambers resistive to organic solvents using a single-molecule sensitive TIRF-microscope.In the applied project we plan to transfer this experimental approach to the ruthenium-catalyzed metathesis reaction. Despite the catalysis being well-understood for a plethora of synthetic applications, the initial reaction deserves further investigation as preliminary experiments revealed hints to both the associative and the dissociative reaction mechanism. The aim of the present project is to familiarize chemists with the opportunities of single-molecule chemistry, exemplified on the ambiguous activation of ruthenium-based metathesis catalysts. We plan to address the role of phosphine dissociation in the regioselectivity by following fluorescence trajectories on immobilized targets. Controlled supply of further chemicals is warranted by use of microfluidics.