Berlin 2015 – scientific programme

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O: Fachverband Oberflächenphysik

O 60: Dielectric and Molecular/Water Interfaces

O 60.4: Talk

Wednesday, March 18, 2015, 15:45–16:00, MA 043

Ultrafast Interfacial Reorientational Dynamics of a Leucine Side Chain — •Michael Donovan, Mischa Bonn, Ellen Backus, and Tobias Weidner — Max Planck Institute for Polymer Research, Ackermannweg 10 Mainz, Germany 55128

Proteins possess fluctuating structural features which are important for their function. At interfaces, protein motions may be different than in bulk, and this can affect protein function when in contact with surfaces. We utilize surface specific probes to study the interfacial behavior of protein side chains. As a model system we studied the reorientational dynamics of hydrophobic leucine side chains at the air-water interface. We followed ultrafast reorientational motions of excited methyl groups pointing into the hydrophobic phase using femtosecond SFG pump probe methods. Specifically, orthogonally polarized mid IR pump pulses excite molecular vibrations, and interfacial dynamics are followed by watching the temporal evolution of an interface specific sum frequency generation (SFG) probe pulse until the signal recovers to its steady state value. First, the dynamics of a charged Leucine monolayer are followed through time resolved SFG, and later the dynamics of leucine in an alpha helical and beta sheet peptide are followed. It is shown that these fast reorientational motions can act as probes of the local interfacial environment of the side chain.