Scientists have seen for the first time the connection of electron and proton transfer with water
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- Scientists have seen for the first time the connection of electron and proton transfer with water
Many energy conversion processes in nature depend on the coordinated movement of electrons and protons. However, it is extremely difficult to simultaneously observe changes inside the reacting molecule and the restructuring of the environment due to the high speed of such processes. Now, using ultrafast X-ray techniques, researchers have been able to trace the key stages of a similar reaction in water. How electrons, protons and water simultaneously participate in energy transfer is described in the Izvestia article.
Electron, proton and water: how did you manage to see the reaction in real time
The study was published in the scientific journal Nature Communications. Scientists have studied proton and electron transfer, which underlies many energy conversion processes. To do this, they used a model ruthenium complex and triggered the reaction with a light pulse.
The researchers were able to sequentially trace how the electron distribution changes after excitation, and then the protonation of the nitrogen atom in the molecule occurs. Simultaneously with these changes, the nearest shell of water molecules around the complex was rebuilt. In particular, a change in the hydrogen bonds between the molecule and water was observed.
The water was part of the mechanism: what was happening around the molecule
When the complex was excited by light, the electron density was redistributed and predominantly localized on a certain part of the molecule. After about 460 ps (picoseconds), it was subsequently protonated. At the same time, the arrangement of the surrounding water molecules changed.
In the initial state, nitrogen atoms interacted with water through hydrogen bonds of the same type. After the proton was attached, the structure of these bonds changed: interactions between the protonated nitrogen atom and the oxygen atoms of water were formed. Calculations showed that a significant part of the solvent rearrangement occurred directly near the site of the molecule that received the proton.
Ultrafast X-ray: how scientists caught an almost imperceptible movement
To get this picture, the researchers combined several methods at once. Femtosecond optical spectroscopy made it possible to track changes in the state of a molecule, X—ray absorption spectroscopy - changes in the electronic structure in the region of a particular atom, and temporarily resolved X—ray scattering - rearrangement of the molecular environment.
The experimental data were then compared with calculations of the electronic structure and molecular dynamic models. This approach made it possible to link changes in the electron density with changes in the first solvation shell, the immediate environment of a molecule made of water.
Eliza Biasin, an experimental physics chemist at the Pacific Northwest National Laboratory
For the first time, we were able to capture how the electronic changes associated with proton transfer are combined with the reorganization of the surrounding solvent. This gives us a new way to understand how molecules and their environment co-evolve during fundamental chemical transformations.
Previously, it was possible to study certain features of such processes indirectly, but at the same time it was much more difficult to trace changes in the electronic structure, protonation and rearrangement of the solvent. The authors have shown that combining X-ray methods can provide structural information about the successive stages of proton and electron transfer.
From photosynthesis to batteries: why it was necessary to disassemble the reaction
Proton and electron transfer is associated with catalytic reactions, bioenergetics, and energy conversion. Similar processes are involved, in particular, in photosynthesis and other biological systems, where charge movement is combined with proton movement.
The researchers note that the developed approach can be used to study more complex proton and electron transport mechanisms. In the future, such knowledge may help to better control such reactions in the development of catalysts, artificial photosynthesis systems and energy conversion technologies.
At the same time, the current work was performed on a model complex of ruthenium, so the results obtained cannot be directly transferred to all biological and technological systems.
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