Rostock 2019 – scientific programme

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MO: Fachverband Molekülphysik

MO 11: Photochemistry

MO 11.5: Talk

Wednesday, March 13, 2019, 11:45–12:00, S HS 001 Biologie

Steering proton transfer pathways of the bifunctional photoacid 7-hydroxyquinoline — •Marius-Andrei Codescu and Erik T. J. Nibbering — Max-Born-Institut für Nichtlineare Optik und Kurzzeitspektroskopie, Max-Born-Str. 2A, 12489 Berlin

Acid-base neutralization reactions in protic solvents typically occur through proton exchange pathways consisting of a solvent bridge connecting acid and base. Bifunctional photoacids have both proton donating and accepting sites, enabling real-time probing of proton exchange through a well-defined number of solvent molecules. For 7-hydroxyquinoline (7HQ), compelling evidence pointed to initial proton abstraction by the quinoline N site from the methanol solvent, followed by methoxide transport to the OH-site, making it an proton hole transport [Hoffmann et al., J. Phys. Chem. A 120, 9378 (2016)]. This strongly contrasts to the generally accepted picture of an excess proton transport pathway initiated at the OH-site. Here we show that by adding formate anion to 7HQ in methanol, the dominant proton transport pathway of 7HQ changes from a transmission of proton holes to that of excess protons. We follow the reaction dynamics by probing IR-active marker modes of 7HQ and of formic acid with femtosecond time resolution, and determine the local parameters that open up the excess proton transport route. Our findings may provide insight into proton transport pathways of transmembrane proton channel proteins.