Somewhere inside the Department of Energy's Pacific Northwest National Laboratory in Richland, Washington, a beam of light hit a tiny molecule — and for the first time ever, scientists watched the water around it rearrange itself to do the work of life. The team captured molecular-level snapshots showing exactly how a molecule's electronic structure, a newly arriving proton, and the surrounding water all change together in a single choreographed moment.
This coordinated dance is called proton-coupled electron transfer, or PCET. It sounds technical, but it happens every time a plant turns sunlight into stored energy and every time your body turns food into fuel. It is among the most efficient energy transfers known in nature, because moving protons (positively charged particles) and electrons (negatively charged particles) together lets molecules skip expensive intermediate steps. That makes reactions faster and far more energy-efficient.
Scientists had studied this interplay for decades, but no one had ever captured a combined view of the local electronic changes and the water reorganization in a single experiment. Now, a team led by PNNL — with SLAC National Accelerator Laboratory and several university partners — has done both at once. Using ultrafast X-ray spectroscopy and scattering at SLAC's Linac Coherent Light Source, combined with quantum chemistry calculations and molecular dynamics simulations, they captured the key steps of a light-driven PCET reaction. The work was published in Nature Communications.
The team included PNNL experimental chemical physicist Elisa Biasin, former PNNL scientist Abdullah Kahraman, and PNNL theorists Niranjan "Niri" Govind and Amity Andersen, along with collaborators. One big open question has always been the order of events: do protons and electrons move at the same moment? At which molecular site? And how does the surrounding water help a proton hop along? Because electrons and protons move almost unimaginably fast, and water reorganizes in ways that are notoriously hard to watch, the answers stayed hidden — until these instruments and simulations lined up with theory.
"We have captured for the first time how electronic changes associated with proton transfer are coupled to reorganization of the surrounding solvent," Biasin said. The new approach gives researchers a way to probe how molecules and their environments evolve together during fundamental chemical transformations.
The payoff could be practical. Because PCET powers so much of energy conversion, understanding it better could help engineers design more efficient catalysts, fuel cells, and flow batteries — devices that store energy in liquid chemicals. By answering old questions about how water helps protons move, this work opens a clearer path toward cheaper, faster, cleaner energy storage built on nature's own tricks.