After 17 years of research, scientist solves one of the holy grails of physical chemistry

Prof. Ehud Pines is an iconoclast. What else can you call a scientist who spent 17 years doggedly searching for the solution to a 200-plus-year-old chemical problem that he believed never received a satisfactory answer using methods no other scientist believed had they could lead to the truth? Now he’s being confirmed when the prestigious journal Angewandte Chemie published a cover article detailing how his experiment was replicated by another research group, while X-raying it to reveal the solution that Prof. Pines was all along for has argued.

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.

Prof. Ehud Pines, based on his experimental studies at Ben-Gurion University of the Negev together with his PhD student Eve Kozari and theoretical studies by Prof. Benjamin Fingerhut on the structure of Prof. Pines’ protonated water clusters, proposed that the proton moves in trains of three water molecules through water. 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, however, according to Prof. 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 Prof. 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 transforming 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 corroborated Prof. Pines’ findings about the hydrated proton captured by a chain of three water molecules, most of the global scientific community working in the field has remained reluctant to support Prof. Pines ‘ Accepting emerging model for proton solvation and motion in water. Therefore, Prof. Pines turned to long-time employees of 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 multi-million dollar specialized equipment funded by the European Research Council – confirmed Prof 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 Prof. 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 am satisfied that I most likely found and demonstrated the solution,” says Prof. 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 Prof. Pines but is only an oddity compared to the revelation that this fundamental mechanism is one of the most common understand and basic processes in nature.