2025-09-11 イェール大学
(Photo by Allie Barton)
＜関連情報＞
- https://news.yale.edu/2025/09/11/pinning-down-protons-water-basic-science-success-story
- https://www.science.org/doi/10.1126/science.ady1723
微水和4-アミノ安息香酸における水媒介プロトン移動の微小正則動力学 Microcanonical kinetics of water-mediated proton transfer in microhydrated 4-aminobenzoic acid
Abhijit Rana, Payten A. Harville, Thien Khuu, and Mark A. Johnson
Science Published:11 Sep 2025
DOI:https://doi.org/10.1126/science.ady1723
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. —Jake S. Yeston
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.
