Scientists show link between electronic changes and water rearrangement in PCET reaction — ScienceDaily

A team led by Pacific Northwest National Laboratory recorded key stages of a light-induced proton-coupled electron transfer reaction. To do this, the researchers used ultrafast X-ray methods at the Linac Coherent Light Source facility at SLAC National Accelerator Laboratory, ScienceDaily reports. The results were published in the journal Nature Communications.

The process is known as proton-coupled electron transfer, or PCET. In it, a positively charged proton and a negatively charged electron move in a coordinated manner. Similar mechanisms are involved in photosynthesis, catalysis, and biological energy conversion. The coordinated movement of particles may allow molecules to avoid intermediate stages that require additional energy, making reactions faster and more efficient.

X-ray methods and modeling

The scientists studied a ruthenium-based complex that absorbs light and, under acidic conditions, captures a proton from the environment. They combined X-ray absorption spectroscopy, which tracked the movement of electrons between parts of the molecule, with time-resolved X-ray scattering. The second method made it possible to observe the rearrangement of atoms, including the movement of solvent molecules around the reacting molecule.

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Calculations using time-dependent density functional theory and molecular dynamics simulations helped interpret the complex X-ray signals. The results showed that local changes in electronic structure are accompanied by a larger-scale reorganization of the network of water molecules when the molecule captures a proton.

Limitations of the experiment

The authors noted that the proton itself was not observed directly: X-ray scattering primarily detects atoms rich in electrons. They drew conclusions about proton movement based on the consistency of the measurements with theoretical calculations and the recorded rearrangement of the electronic structure and water environment.

The proposed approach may be applied to more complex PCET reactions. According to the authors' assessment, a more detailed understanding of such processes could eventually help develop more efficient catalysts, fuel cells, and flow batteries.