Microcanonical kinetics of water-mediated proton transfer in microhydrated 4-aminobenzoic acid.
basic_science · Level V
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- Record sourced from PubMed, PMID 40934335.
- Also identified by DOI 10.1126/science.ady1723.
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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 (<i>O</i>-protomer) and amine (<i>N</i>-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<sup>+</sup>·(H<sub>2</sub>O)<sub>6</sub> 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.