Observing catalysis at the single molecule level

Is it possible to really see individual molecules in action as they are involved in a chemical reaction at a surface? And can we, in this way, get a complete understanding of reaction mechanisms, at the resolution of atoms? The importance of studying chemical reactions at surfaces has very recently been highlighted when Gerhard Ertl was awarded the Nobel Prize in chemistry for elucidating mechanisms of chemical processes on heterogeneous catalysts. Although ground-breaking, these studies were carried out under ultra-high vacuum (UHV), being an unrealistic condition for conventional chemical or biological reactions which usually occur in a liquid medium. The aim of my Vidi proposal is to initiate a new line of research at the interface of chemistry and physics, in which I intend to develop the concept of understanding chemical reactions at the highest detail possible at solid-liquid interfaces. Towards this goal I propose to apply a new technique to study catalysis at the single molecule level: Scanning Tunneling Microscopy (STM) in a liquid-cell, in which conditions that are commonly applied in chemical laboratory processes can be closely resembled. In observing chemical reactions at the single molecule level, I propose to investigate: (i) a multistep epoxidation reaction, by imaging changes in single MnIII-porphyrin catalysts at a solid-liquid interface upon their oxidation by O2 to MnIV-oxo species, and the subsequent transfer of oxygen atoms from the species to alkenes that are added to the liquid; (ii) towards a higher level of complexity: to image reactants and products in a cascade reaction, using two catalysts adsorbed at the same interface, in which an epoxidation reaction catalyzed by MnIII-porphyrins is followed by an epoxide ring-opening by alcohols catalyzed by SnIV-porphyrins; (iii) highly topical "click" reactions, in which the mechanism of the coupling of azides to alkynes catalyzed by CuI-catalysts will be unraveled.