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BP: Fachverband Biologische Physik
BP 24: Posters - Protein Structure and Dynamics
BP 24.13: Poster
Dienstag, 21. März 2017, 14:00–16:00, P1A
Polarization anisotropy of IR spectra reveals geometry of a protonated water cluster — •Jan Daldrop1, Mattia Saita1, Matthias Heyden2, Joachim Heberle1, and Roland Netz1 — 1Fachbereich Physik, Freie Universität Berlin, 14195 Berlin, Germany — 2MPI für Kohlenforschung, 45470 Mülheim an der Ruhr
Infrared spectra for protonated and unprotonated water chains, water slabs and water drops are calculated from ab initio Molecular Dynamics trajectories. For all three water cluster geometries we obtain a pronounced IR continuum band over a wide frequency range in the presence of an excess proton. This continuum band exhibits a strong polarization anisotropy for chains and slabs with maximal adsorption for IR polarization along the water cluster long axes. The continuum band for protonated water chains is shown to be due to charge fluctuation dynamics of the Zundel state ensemble linked to pronounced friction memory effects that decay over 100fs. For proton-conducting proteins, where a water chain traverses the membrane-spanning protein, this anisotropy allows to distinguish proton motion along the water chain from proton motion along the protein or membrane surfaces by the use of polarization and time-resolved IR adsorption spectra. We use the results to interpret our experimental data for the continuum band around ν = 1900 cm*1 of aligned bacteriorhodopsin proteins in membranes during laser-flash initiated proton transfer. Polarization-resolved IR spectroscopy thus allows for the interpretation of IR continuum bands and in particular furthers the microscopic understanding of water-mediated proton-transfer processes.