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Fachsitzungen
– Hauptvorträge –
SYND 1 Sitzung 1
Zeit: Donnerstag 14:00–16:00 Raum: HS 332
Hauptvortrag SYND 1.1 Do 14:00 HS 332
Theory and Design of Multidimensional IR Pulse Experiments
— •Christoph Scheurer — Lehrstuhl für
Theoretische Chemie, TU München, 85748 Garching
Femtosecond visible and infrared (IR) multiple-pulse techniques
based on the control and manipulation of multiple
quantum coherences provide new tools to probe the structure
and dynamics of complex molecular assemblies. The control
over time delays in a pulse sequence yields multidimensional
spectra with increased resolution and information content
as compared to 1-D experiments. Structural and dynamical
information is contained in the position, shape, and temporal
evolution of cross and diagonal peaks that are due to
anharmonicities in the underlying system Hamiltonian and
its coupling to the environment. Ultrafast laser pulses thus
allow to obtain picosecond snapshot pictures of the molecular
structure along dynamic trajectories. These experiments
are theoretically best described in the framework of the density
matrix formalism. In the weak-field limit a multiplepulse
experiment can be conveniently represented by a set
of double-sided Feynman diagrams. The design of multidimensional
vibrational spectroscopies can draw upon analogy
with liquid or solid state nuclear magnetic resonance (NMR)
spectroscopy which are well established for studying structure
and dynamics of complex systems on slower timescales.
Hauptvortrag SYND 1.2 Do 14:30 HS 332
Investigating Ultrafast Peptide Dynamics by 2D-IR
Spectroscopy — •Peter Hamm, Jens Bredenbeck,
and Jan Helbing — Universität Zürich, Physikalisch
Chemeisches Institut, Winterthurerstr. 190, 8075 Zürich,
Schweiz
Recent work has shown that two-dimensional infrared (2D-
IR) spectroscopy might be a valuable experimental complement
to existing tools to study conformation of small peptides
in the solution phase. 2D-IR spectroscopy allows one
to measure the couplings between certain vibrational modes,
which are related to the relative orientation of the peptide
units, and hence allows one to extract structural information.
Great progress has been achieved recently in resolving the
structure, structural distribution and structural fluctuations
of a small peptide, trialanine. The most promising potential
of 2D-IR spectroscopy is its intrinsic high time resolution (1
ps), which freezes in all motions of a peptide backbone. On
the one hand, this allows one to resolve rapidly exchanging
conformations of an equilibrium ensemble of peptides. On the
other hand, one can monitor how a non-equilibrium ensem-
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ble evolves in time with 1 ps time resolution. The emerging
possibilities of 2D-IR spectroscopy will be discussed.
Hauptvortrag SYND 1.3 Do 15:00 HS 332
Simulation of conformational dynamics and energy
transfer in peptides — •Yuguang Mu, Phuong
Nguyen, and Gerhard Stock — Institut für Physikalische
und Theoretische Chemie,J. W. Goethe-Universität,
Marie-Curie-Str. 11, D-60439 Frankfurt
Recent multidimensional vibrational experiments have provided
a wealth of new information on peptides and proteins.
To study the correlations between spectra and peptide
dynamics and to obtain a microscopic understanding
of the phenomena, molecular dynamics (MD) simulations of
various small peptides in aqueous solution have been performed.
From these simulations, time-dependent correlation
functions reflecting vibrational dephasing, energy transfer
and energy relaxation are computed and compared to experiment.
Furthermore, nonequilibrium MD simulations of
laser-induced peptide dynamics are presented and analyzed.
The validity and accuracy of nowadays available MD models
and methods are discussed.
Hauptvortrag SYND 1.4 Do 15:30 HS 332
Ultrafast Conformational Dynamics in Cyclic Peptides
— •Josef Wachtveitl — Goethe-Universität
Frankfurt, Institut für Physikalische und Theoretische
Chemie, Marie-Curie-Straße 11, 60439 Frankfurt am Main
Structural changes of peptides containing a modified
azobenzene dye(AMPB) are studied with ultrafast spectroscopy.
AMPB peptides represent a new class of molecules
where the photoisomerizable dye azobenzene is linked to the
peptide moiety via a flexible methylene spacer. The ultrafast
reactions in the femtosecond to nanosecond time domain
are investigated for the optical switch AMPB, a linear and
cyclic octapeptide and a bicyclic octapeptide containing an
additional disulfide bridge. These molecules with increasing
conformational constraints, are studied for the cis to trans
and the trans to cis photoreactions. For the cis to trans reaction
the isomerization of the chromophore occurs fast in
the 1 ps range, while it is slower (10 ps range) in the trans
to cis reaction. In all peptides the structural changes of the
chromophore lead to modifications in the peptide structure
in the 10 ps to 1 ns time range. The results indicate that the
chromophore AMPB acts simultaneously as a fast molecular
switch and as a sensor for initial conformational dynamics in
the peptide.