Key Points:
- A researcher has spent 17 years working on a better answer as to how protons move through water than the gold-standard Grotthuss Mechanism.
- His findings revealed the proton moves through water in trains of three water molecules, but the theory was not immediately accepted by the community.
- A new study confirms the original findings, and puts an end to the 200-year-old mystery of proton movement.
How does a proton move through water? In 1806, Theodor Grotthuss proposed his theory, which became known as the Grotthuss Mechanism. Over the years, many others attempted an updated solution realizing that, strictly speaking, Grotthuss was incorrect. Still, it remained the standard text-book answer—until now.
Until Ehud Pines saw the realization of 17 years of dogged research into the subject.
"The debates on the Grotthuss mechanism and the nature of proton solvation in water have grown heated, as this is one of the most basic challenges in chemistry,” said Pines. “Understanding this mechanism is pure science, pushing the boundaries of our knowledge and changing one of our fundamental understandings of one of nature's most important mass and charge transport mechanisms."
Pines suggested, based on his experimental studies at Ben-Gurion University, that the proton moves through water in trains of three water molecules. The proton train "builds the tracks" underneath them for their movement and then disassembles the tracks and rebuilds them in front of them to keep going. It's a loop of disappearing and reappearing tracks that continues endlessly.
While in recent years additional theoretical studies confirmed Pines' findings of the hydrated proton accommodated by a chain of three water molecules, most of the global scientific community working in the field remained reluctant to accept Pines' emerging model.
So, Pines asked collaborators at the Max Born Institute in Germany to try to replicate his experiments to confirm the findings. The X-ray absorption (XAS) experiment measured the effect of the proton charge on the structure of the inner electrons of the waters’ single oxygen atoms. As predicted, it was found that three water molecules are most affected by the presence of the proton, each to a different extent, and, together with the proton, form protonated 3-water molecules chains or "trains.”
"Everyone thought about this problem for over 200 years, so that was a sufficient challenge to me to decide to take it up. Seventeen years later, I am gratified to most likely have found and demonstrated the solution," said Pines.
Information provided by Ben-Gurion University.