Ultrafast Proton Transfer Pathways Mediated by Amphoteric Imidazole

MA Codescu and T Kunze and M Weiss and M Brehm and O Kornilov and D Sebastiani and ETJ Nibbering, JOURNAL OF PHYSICAL CHEMISTRY LETTERS, 14, 4775-4785 (2023).

DOI: 10.1021/acs.jpclett.3c00595

Imidazole, being an amphoteric molecule, can act bothas an acidand as a base. This property enables imidazole, as an essential buildingblock, to effectively facilitate proton transport in high-temperatureproton exchange membrane fuel cells and in proton channel transmembraneproteins, enabling those systems to exhibit high energy conversionyields and optimal biological function. We explore the amphotericproperties of imidazole by following the proton transfer exchangereaction dynamics with the bifunctional photoacid 7-hydroxyquinoline(7HQ). We show with ultrafast ultraviolet-mid-infrared pump-probespectroscopy how for imidazole, in contrast to expectations basedon textbook knowledge of acid-base reactivity, the preferentialreaction pathway is that of an initial proton transfer from 7HQ toimidazole, and only at a later stage a transfer from imidazole to7HQ, completing the 7HQ tautomerization reaction. An assessment ofthe molecular distribution functions and first-principles calculationsof proton transfer reaction barriers reveal the underlying reasonsfor our observations.

Return to Publications page