https://phys.org/news/2022-09-scientist-holy-grails-physical-chemistry.html

How does a proton move through water?

Although the Grotthuss Mechanism as proposed by Theodor Grotthuss in 1806 has been largely understood to be incorrect for many years, it is only now that evidence for an alternative emerging model for proton solvation and movement in water has been produced.

“The debates on the Grotthuss mechanism and the nature of proton solvation in water have grown heated,” says Prof. Pines, “as this is one of the most basic challenges in chemistry. 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.”

An innovative 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 by Prof. Pines, 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.”

An understanding of the hydrated proton is fundamental to many chemical (e.g., acid-base chemistry) and biological (e.g., bioenergetics and enzyme catalysis) processes.