This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Some of nature's most important chemical reactions rely on the coupled movement of negatively and positively charged particles. These processes play central roles in photosynthesis, catalysis and biological energy conversion yet remain difficult to observe.
Now, a research team led by the Department of Energy's Pacific Northwest National Laboratory, in collaboration with colleagues at SLAC National Accelerator Laboratory and several academic labs, has captured snapshots of these events triggered when light strikes a molecule. The findings, published in Nature Communications, could help researchers better understand and ultimately design better flow batteries, fuel cells and catalysts. The research team focused on the coupled movement of positively charged particles called protons with negatively charged electrons.
This coordinated energy transfer is among the most efficient known and, in plants, is used to capture the sun's energy and convert it into stored energy, among other processes in nature. By moving electrons and protons in a coordinated fashion, molecules can bypass energetically costly intermediate steps. This makes reactions faster and dramatically more energy efficient.
In this case, the research team focused on how changes in a molecule's electronic structure, the addition of a proton and the surrounding water environment are linked during the reaction. Despite studying this interplay for decades, no one had previously captured it in a single study with both local and structural sensitivity. Advanced X-ray methods available at the Linac Coherent Light Source at SLAC, combined with state-of-the-art quantum chemistry calculations and molecular dynamics simulations, gave unprecedented insight into this crucial process.
PNNL experimental chemical physicist Elisa Biasin, former PNNL scientist Abdullah Kahraman and PNNL theorists Niranjan (Niri) Govind and Amity Andersen, together with their collaborators, used a combination of ultrafast X-ray spectroscopy, scattering and advanced simulations to capture key steps in a light-driven proton-coupled electron transfer reaction, or PCET. This combined approach reveals, for the first time with structural sensitivity, how gaining a proton reshapes a molecule's electronic structure at specific sites and reorganizes the surrounding water environment. "We have captured for the first time how electronic changes associated with proton transfer are coupled to reorganization of the surrounding solvent," said Biasin.
"This gives us a new way to understand how molecules and their environments evolve together during fundamental chemical transformations." PCET is a workhorse in nature, allowing plants to harvest light for photosynthesis and animals to efficiently metabolize food for energy, among other essential energy-conversion processes. In the experimental system on which the team focused, the basic mechanism is well understood. However, in some PCET reactions, there continues to be debate about the order of movement of protons and electrons.
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