Scientist solves one of the holy grails of physical chemistry


BEER-SHEVA, ISRAEL – Professor Ehud Pines is an iconoclast. What else can you call a scientist who spent 17 years doggedly searching for the solution to a chemistry problem more than 200 years old that he believed had never received a satisfactory answer, using methods no other scientist believed that they could lead to the truth? Now he’s confirmed as the most respected applied Chemistry diary published a lengthy front-page article how his experiment was replicated by another research group while being X-rayed to reveal the solution Pines has been arguing for all along.

The question is: how does a proton move through water? In 1806 Theodor Grotthuss presented his theory, which became known as the Grotthuss mechanism. Over the years many others tried an updated solution, realizing that Grotthuss was strictly wrong, but it remained the standard textbook answer. Until now.

Pines proposed that the proton moves through water in trains, based on his experimental studies at Ben-Gurion University of the Negev along with his PhD student Eve Kozari and theoretical studies by Professor Benjamin Fingerhut on the structure of Pines’ protonated water clusters three water molecules. The proton train “builds the tracks” beneath them for their movement, and then dismantles and rebuilds the tracks in front of them to keep going. It is an endless loop of disappearing and reappearing tracks. Similar ideas have been put forward by a number of scientists in the past, but according to Pines they have not been assigned to the correct molecular structure of the hydrated proton, which leads to the promotion of the Grotthuss mechanism through its unique trimeric structural properties.

“The debates about the Grotthuss mechanism and the nature of proton solvation in water have become heated,” says Pines, “as this is one of the most fundamental challenges in chemistry. Understanding this mechanism is pure science, pushing the frontiers of our knowledge and altering one of our fundamental understandings of one of nature’s most important mass and charge transport mechanisms.”

While additional theoretical studies in recent years have confirmed Pines’ findings about the hydrated proton captured by a chain of three water molecules, most scientists working in the field worldwide have been reluctant to accept Pines’ emerging model for the solvation and motion of to accept protons in water. So Pines turned to longtime collaborators at the Max Born Institute in Germany. They assembled an international research team led by Dr. Erik Nibbering, and repeated the experiment, this time examining the chemical system. The X-ray experiment – which required specially designed equipment costing millions of dollars and was funded by the European Research Council – confirmed Pines’ findings. The X-ray absorption (XAS) experiment measured the effect of the proton charge on the structure of the inner electrons of the individual oxygen atoms of water. As predicted by Pines, three water molecules were found to be most affected by the presence of the proton, each to different degrees, and together with the proton form protonated 3-water molecule chains or “trains”.

“Everyone has been thinking about this problem for over 200 years, so that was enough of a challenge for me to decide to tackle it. Seventeen years later, I’m very happy to have most likely found and demonstrated the solution,” says Pines.

The next edition of the college chemistry textbooks may replace the description of the Grotthuss mechanism with the “Pines mechanism,” an idea that tickles Pines but is only an oddity compared to the revelation that this basic mechanism is one of the most common and fundamental ones understand processes in nature.

– This press release was originally published on the website of Ben Gurion University of the Negev


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