Pinning down protons in water — a basic science success story

Amazing stuff! Towards hydrogen power!

"The movement of protons through electrically charged water is one of the most fundamental processes in chemistry. It is evident in everything from eyesight to energy storage to rocket fuel — and scientists have known about it for more than 200 years.

But no one has ever seen it happen. Or precisely measured it on a microscopic scale.

Now, [researchers] ... — for the first time — set benchmarks for how long it takes protons to move through six charged water molecules. The discovery, made possible with a highly customized mass spectrometer that has taken years to refine, could have far-reaching applications for researchers in years to come. ..."

Unfortunately, the link to the research paper in the article below is broken. My guess is that this is the paper titled "Microcanonical Kinetics of Water-Mediated, Long Range Proton Transfer in Microhydrated 4-Aminobenzoic Acid". Google Scholar can not find this paper, but Google search found it.

From the abstract:

"Editor’s summary

Proton transfer is perhaps the most fundamental chemical reaction, underlying numerous more complex transformations in both biochemical and synthetic systems. The process often involves a network of numerous water molecules. To home in on the details in a well-controlled context, Rana et al. studied interconversion of two protonated isomers, or protomers, of 4-aminobenzoic acid in small water clusters. By measuring the kinetics of proton migration between nitrogen and oxygen sites with well-resolved spectroscopic signatures, the authors were able to establish precise benchmarks for future modeling. ...

Abstract

Isolated cluster systems can help to elucidate the molecular level description of water-mediated proton transfer. Protonation of neutral 4-aminobenzoic acid (4ABA) occurs at the acid (O-protomer) and amine (N-protomer) functionalities, yielding two distinct species with relative energies dependent on the degree of hydration.

Here, we measured the rates of intramolecular proton transfer in 4ABAH+·(H2O)6 ions upon protomer-selective vibrational excitation of initially cold (6 K) cluster ions isolated in a cryogenic ion trap. Interconversion rates were observed on the microsecond time scale.

These results quantify the kinetics of proton transfers in the context of a closed, finite system at well-defined internal energies and therefore provide experimental benchmarks for theoretical efforts that are being developed to treat relatively slow, highly cooperative solvent-mediated chemical processes."

Pinning down protons in water — a basic science success story | Yale News "In a new study, ... team set measurable parameters on the movement of protons in water — shedding new light on one of basic science’s most enduring enigmas."

Microcanonical kinetics of water-mediated proton transfer in microhydrated 4-aminobenzoic acid (no public access)

Payten Harville, left, Abhijit Rana, and Mark Johnson (three of the authors) operate a customized mass spectrometer that has been adapted to enable multiple interactions with carefully timed pulses of laser light.