CAREER: Direct Interrogation of Proton-Coupled Electron Transfer Reaction Dynamics and Mechanisms with Cryogenic Ion and Ultrafast Vibrational Spectroscopies

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With support from the Chemical Structure, Dynamics, and Mechanisms-A (CSDM-A) Program in the Division of Chemistry, Dr. Joseph Fournier and his group at Washington University in St. Louis are using sophisticated laser techniques to study very fast chemical reactions. Specifically, Dr. Fournier’s group is investigating a special class of reactions in which protons and electrons simultaneously move from one molecule to another. These reactions are at the heart of many fundamental biological and chemical processes, including photosynthesis and cellular respiration, but are difficult to study with existing experimental methods. In order to overcome such difficulties, Dr. Fournier and his students are developing a new approach that allows them to directly track the reactions in real time with molecular-level detail. The results of their measurements help to unravel and quantify the most important factors that drive these reactions, which is vital information for understanding key biological processes and for developing new molecules for applications in green energy and chemical synthesis. The project also includes an effort to modernize physical chemistry education at the undergraduate and graduate levels, as well as outreach events that introduce St. Louis-area high school students to the ways in which the quantum mechanical behavior of atoms and molecules affects the world around us. Catalytic processes driven by proton-coupled electron transfer (PCET) reactions are ubiquitous in chemistry and biology, yet the current understanding of these reactions and the ability to quantitatively predict mechanisms and reaction dynamics involving PCET remains limited. Dr. Fournier and his team are using a suite of infrared spectroscopy techniques to study PCET reactions for a series of biomimetic model complexes. These spectroscopic techniques include gas-phase cryogenic ion vibrational spectroscopy (CIVS), solution-phase two-dimensional infrared spectroscopy (2DIR), as well as the development and implementation of a novel approach called time-resolved cryogenic ion vibrational spectroscopy (TR-CIVS). The TR-CIVS measurements will systematically probe well-defined systems in the gas phase with both high frequency resolution and ultrafast temporal resolution, with the goal of characterizing the elusive proton transfer coordinate in more detail than previously possible. The experiments target the identification of transient intermediates and the dynamics of their formation, and will probe the role of tunneling and low-frequency hydrogen-bonding modes in the proton transfer process. This work aims to provide important insight for understanding PCET mechanisms and to aid in the development of new computational models that predict how the chemical architecture of catalytic systems determines their reactive properties.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.