The question of how precisely protons move through water in an electric field has fascinated scientists for centuries. Now, more than 200 years after the phenomenon’s last major revelation, scientists have some clarity.
In 1806, Theodor Grotthuss put forward a hypothesis, which came to be known as the Grotthus mechanism for ‘proton jump’, about how a charge could flow through a solution of water.
Although Grotthuss’s hypothesis was very progressive for its time, arriving before protonsor even the actual structure of water, were even known: researchers today have known for a long time that it did not provide a complete understanding of what happened at the molecular level.
The latest findings on the subject may have cracked the mystery by solving the electronic structures of hydrated protons that have remained elusive for so long.
The findings suggest that protons move through water in ‘trains’ of three water molecules, with ‘tracks’ built in front of the train as it goes and stop once it passes.
This loop can continue indefinitely to transport protons through water. While the idea was previously suggested, the new study assigns a different molecular structure that is a better fit for Grotthuss’ proposed solution, according to the study’s authors.
“Debates about the Grotthuss mechanism and the nature of proton solvation in water have become heated, as this is one of the most basic challenges in chemistry.” says chemist Ehud Pines from Ben-Gurion University of the Negev in Israel.
The new study is compelling because it combines a theoretical approach with physical experimentation. made possible by recent technological advances. The researchers used a X-ray absorption spectroscopy (XAS) to monitor how proton charges affected electrons on individual oxygen atoms in water.
As predicted, the impact was greatest on three water molecules, although to different degrees on each individual molecule. within the trimeric group. The researchers found the groups of three molecules forming chains with the proton.
The researchers also incorporated quantum-level chemical calculations and simulations to determine interactions between protons and neighboring water molecules as the protons move through the liquid.
“Understanding this mechanism is pure science, pushing the boundaries of our knowledge and changing one of our fundamental interpretations of one of nature’s most important mass and charge transport mechanisms.” says pines.
The discovery plays into many other chemical processesincluding photosynthesis, cellular respiration and energy transport in hydrogen fuel cells.
It is not only the solution that is remarkable, but also how the researchers were able to arrive at it: testing and validating theoretical predictions against experimental results, and vice versa, in a long and winding process that has taken nearly two decades from start to finish. .
“Everyone thought about this problem for over 200 years, so it was enough of a challenge that I decided to tackle it.” says pines. “Seventeen years later, I am pleased to have found and demonstrated the solution.”
The research has been published in International edition of Angewandte Chemie.
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