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aktualisiertes pdf - DPG-Tagungen

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Fachsitzungen<br />

– Hauptvorträge –<br />

SYND 1 Sitzung 1<br />

Zeit: Donnerstag 14:00–16:00 Raum: HS 332<br />

Hauptvortrag SYND 1.1 Do 14:00 HS 332<br />

Theory and Design of Multidimensional IR Pulse Experiments<br />

— •Christoph Scheurer — Lehrstuhl für<br />

Theoretische Chemie, TU München, 85748 Garching<br />

Femtosecond visible and infrared (IR) multiple-pulse techniques<br />

based on the control and manipulation of multiple<br />

quantum coherences provide new tools to probe the structure<br />

and dynamics of complex molecular assemblies. The control<br />

over time delays in a pulse sequence yields multidimensional<br />

spectra with increased resolution and information content<br />

as compared to 1-D experiments. Structural and dynamical<br />

information is contained in the position, shape, and temporal<br />

evolution of cross and diagonal peaks that are due to<br />

anharmonicities in the underlying system Hamiltonian and<br />

its coupling to the environment. Ultrafast laser pulses thus<br />

allow to obtain picosecond snapshot pictures of the molecular<br />

structure along dynamic trajectories. These experiments<br />

are theoretically best described in the framework of the density<br />

matrix formalism. In the weak-field limit a multiplepulse<br />

experiment can be conveniently represented by a set<br />

of double-sided Feynman diagrams. The design of multidimensional<br />

vibrational spectroscopies can draw upon analogy<br />

with liquid or solid state nuclear magnetic resonance (NMR)<br />

spectroscopy which are well established for studying structure<br />

and dynamics of complex systems on slower timescales.<br />

Hauptvortrag SYND 1.2 Do 14:30 HS 332<br />

Investigating Ultrafast Peptide Dynamics by 2D-IR<br />

Spectroscopy — •Peter Hamm, Jens Bredenbeck,<br />

and Jan Helbing — Universität Zürich, Physikalisch<br />

Chemeisches Institut, Winterthurerstr. 190, 8075 Zürich,<br />

Schweiz<br />

Recent work has shown that two-dimensional infrared (2D-<br />

IR) spectroscopy might be a valuable experimental complement<br />

to existing tools to study conformation of small peptides<br />

in the solution phase. 2D-IR spectroscopy allows one<br />

to measure the couplings between certain vibrational modes,<br />

which are related to the relative orientation of the peptide<br />

units, and hence allows one to extract structural information.<br />

Great progress has been achieved recently in resolving the<br />

structure, structural distribution and structural fluctuations<br />

of a small peptide, trialanine. The most promising potential<br />

of 2D-IR spectroscopy is its intrinsic high time resolution (1<br />

ps), which freezes in all motions of a peptide backbone. On<br />

the one hand, this allows one to resolve rapidly exchanging<br />

conformations of an equilibrium ensemble of peptides. On the<br />

other hand, one can monitor how a non-equilibrium ensem-<br />

195<br />

ble evolves in time with 1 ps time resolution. The emerging<br />

possibilities of 2D-IR spectroscopy will be discussed.<br />

Hauptvortrag SYND 1.3 Do 15:00 HS 332<br />

Simulation of conformational dynamics and energy<br />

transfer in peptides — •Yuguang Mu, Phuong<br />

Nguyen, and Gerhard Stock — Institut für Physikalische<br />

und Theoretische Chemie,J. W. Goethe-Universität,<br />

Marie-Curie-Str. 11, D-60439 Frankfurt<br />

Recent multidimensional vibrational experiments have provided<br />

a wealth of new information on peptides and proteins.<br />

To study the correlations between spectra and peptide<br />

dynamics and to obtain a microscopic understanding<br />

of the phenomena, molecular dynamics (MD) simulations of<br />

various small peptides in aqueous solution have been performed.<br />

From these simulations, time-dependent correlation<br />

functions reflecting vibrational dephasing, energy transfer<br />

and energy relaxation are computed and compared to experiment.<br />

Furthermore, nonequilibrium MD simulations of<br />

laser-induced peptide dynamics are presented and analyzed.<br />

The validity and accuracy of nowadays available MD models<br />

and methods are discussed.<br />

Hauptvortrag SYND 1.4 Do 15:30 HS 332<br />

Ultrafast Conformational Dynamics in Cyclic Peptides<br />

— •Josef Wachtveitl — Goethe-Universität<br />

Frankfurt, Institut für Physikalische und Theoretische<br />

Chemie, Marie-Curie-Straße 11, 60439 Frankfurt am Main<br />

Structural changes of peptides containing a modified<br />

azobenzene dye(AMPB) are studied with ultrafast spectroscopy.<br />

AMPB peptides represent a new class of molecules<br />

where the photoisomerizable dye azobenzene is linked to the<br />

peptide moiety via a flexible methylene spacer. The ultrafast<br />

reactions in the femtosecond to nanosecond time domain<br />

are investigated for the optical switch AMPB, a linear and<br />

cyclic octapeptide and a bicyclic octapeptide containing an<br />

additional disulfide bridge. These molecules with increasing<br />

conformational constraints, are studied for the cis to trans<br />

and the trans to cis photoreactions. For the cis to trans reaction<br />

the isomerization of the chromophore occurs fast in<br />

the 1 ps range, while it is slower (10 ps range) in the trans<br />

to cis reaction. In all peptides the structural changes of the<br />

chromophore lead to modifications in the peptide structure<br />

in the 10 ps to 1 ns time range. The results indicate that the<br />

chromophore AMPB acts simultaneously as a fast molecular<br />

switch and as a sensor for initial conformational dynamics in<br />

the peptide.

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