After more than two centuries of speculation, researchers at Yale University have successfully observed the movement of protons through water. In a groundbreaking study published on September 11, 2023, the team detailed their innovative approach to track and measure protons, shedding light on a fundamental process that plays a crucial role in various scientific applications.
Innovative Techniques Unveiled
Using a custom-built, 30-foot-long mass spectrometer, the researchers devised a method to analyze how protons traverse charged water molecules. This instrument, which took years to develop, allowed the team to benchmark the speed of proton movement within a molecular system where protons have limited space to hide. Senior author Mark Johnson, a chemist at Yale, stated, “We show what happens in a tiny molecular system where there is no place for the protons to hide.”
Despite the long-standing understanding that protons facilitate charge transport in water, their minute size and quantum mechanical properties have made them challenging to observe directly. Johnson noted, “They aren’t polite enough to stay in one place long enough to let us observe them easily.” Instead, protons are thought to conduct charge through an atomic-scale relay mechanism, hopping from molecule to molecule.
Understanding Proton Transport
To visualize the proton movement, Johnson and his team utilized 4-aminobenzoic acid, an organic molecule capable of accepting an extra proton at two distinct sites. These sites can be identified by the color of light they absorb, providing a unique opportunity to observe proton transfer. Co-lead author Payten Harville, a postdoctoral researcher at Yale, explained that protons could only “get from one docking site to the other [by hitching] a ride on a water network ‘taxi.’”
During the experiment, the team attached the 4-aminobenzoic acid molecules to six water molecules. The mass spectrometer then analyzed each reaction at a rate of ten times per second, utilizing precisely timed lasers to gather data on proton movement. Although the study did not capture the intermediate steps of the proton’s journey, it established stringent parameters for future investigations, according to Johnson.
“We’re able to provide parameters that will give theorists a well-defined target for their chemical simulations,” he noted. This development holds the potential to enhance the precision of experiments in fundamental chemistry, offering researchers a means to challenge existing theoretical models.
As scientists have long recognized the significance of protons in various processes—from energy storage to biological functions—this breakthrough marks a pivotal advancement in understanding molecular systems. It took science 200 years to achieve this milestone, and researchers anticipate that refining this methodology will further accelerate discoveries in the field.