For the first time in over two centuries, scientists have directly observed the movement of protons through water. A team from Yale University published their groundbreaking findings in the journal Science on September 11, 2023. This study marks a significant advancement in understanding how protons, which carry a positive charge, travel through water molecules.
The research team developed a sophisticated method using a customized 30-foot-long mass spectrometer. This device allows for the separation of elements by mass and took years to refine. With it, the researchers were able to measure the speed of protons moving through six charged water molecules.
Unraveling a Long-Standing Mystery
Despite being fundamental to various scientific processes, the behavior of protons in water remained elusive. Protons play critical roles in many areas, including “everything from eyesight to energy storage to rocket fuel,” as noted by the researchers. Yet, their minuscule size and quantum mechanical properties make them exceedingly difficult to track.
Mark Johnson, senior author of the study and a chemist at Yale, explained, “They aren’t polite enough to stay in one place long enough to let us observe them easily.” Protons are thought to conduct charge through an atomic-scale relay mechanism, wherein they jump from molecule to molecule, complicating observation.
Innovative Tracking Methodology
To visualize this process, Johnson and his colleagues utilized 4-aminobenzoic acid, an organic molecule that can accept an additional proton at two distinct sites. These sites can be differentiated by their light absorption characteristics, according to Payten Harville, a postdoctoral researcher and co-lead author of the study.
The team connected the 4-aminobenzoic acid molecules to the six water molecules. In this setup, protons can only transition between the two sites by transferring via a water network, described as a “taxi” for protons. When the protons “hitch” a ride, the mass spectrometer analyzes each reaction ten times per second, employing precisely timed lasers.
While this experiment has not yet captured every intermediate step of the proton’s movement through water, it establishes stringent parameters for future studies. Johnson highlighted that the findings will provide theorists with “well-defined targets for their chemical simulations,” which have often lacked experimental validation.
If this technology can be adapted beyond Yale’s customized spectrometer, it could significantly enhance the precision of experiments in fundamental chemistry. Given that it has taken scientists 200 years to reach this point, further refinements may come more swiftly.
