Plenarvorträge - DPG-Tagungen

Symposium Life Sciences on the Nanometer Scale - Physics Meets Biology Mittwoch
optical properties of the whole complex.
SYLS 3.22 Mi 16:00 B
Ab-initio vibrational analysis of the secondary structure of proteins
— •Lars Ismer 1 , Joel Ireta 1 und Jörg Neugebauer 2 —
1 FHI Berlin — 2 Universität Paderborn
For a detailed understanding of protein functionality an accurate description
of their dynamical properties is crucial. However, so far ab-initio
based studies on realistic structures going beyond the primary structure
are rare, particularly with respect to vibrational properties. We have therefore
performed a full ab-initio DFT-PBE based harmonic vibrational
analysis of infinite poly-alanine and -glycine chains in two different secondary
conformations: the infinite α-helical conformation, as model for the
most ubiquitous native secondary conformation stabilized by hydrogen
bonds (hb) and the fully extended conformation (FES), as a reference
system where hb’s are absent. By comparing the phonon dispersion relation
of α-helix and FES we were able to extract a direct ”fingerprint”
of the hb’s and their cooperativity in specific high frequent vibrational
branches. We also observed that constraining the peptide chain to the
helical conformation leads to significant blue-shifts in the low frequent
backbone vibrations. A thermodynamic analysis based on these results
revealed that the vibrational contributions of the free energy significantly
lower the stability of the α-helix with respect to the FES by about 0.8
kcal/mol at 300K.
SYLS 3.23 Mi 16:00 B
Optical characterisation of artifical confinements for protein
folding — •Johannes Hohlbein 1 , Ulrike Rehn 1 , and Ralf B.
Wehrspohn 2 — 1 Max-Planck-Institute of Microstructure Physics,
Weinberg 2, 06120 Halle, Germany — 2 Department of Physics,
University of Paderborn, Warburger Str. 100, 33098 Paderborn,
Germany
We present a new method to characterize in-situ the optical thickness
of porous alumina films by the use of photoluminescence-induced Fabry-
Pèrot-interferences. Additionally we show, that the use of different electrolytes
yields different photoluminescence pattern. A second experiment
allows to determine the degree of filling of the pores by a liquid which is
of importance when using the pores as templates for protein folding. First
studies of the influence of geometrical confinement on protein folding will
be presented.
Porous oxide growth on aluminium under anodic bias in various electrolytes
has been studied for nearly 50 years. Recently, porous anodic
alumina (PAA) films have been used to prepare nanostructures for a
wide range of applications. In order to use porous alumina as template
for protein folding in-situ optical measurements of their thickness as well
as the degree of filling are required. It has been shown, that porous alumina
exhibits a photoluminescence (PL) signal. We will use the PL pattern
to determine the thickness and the degree of filling by Fabry-Pèrotinterferences.
SYLS 3.24 Mi 16:00 B
Neuronale Synchronität in biologisch plausiblen exzitatorischen
Netzwerken: Entstehung und Modulation — •K. Kube 1 , V.
Spravedlyvyy 1 , A. Herzog 1 , B. Michaelis 1 , A. de Lima 2 , T.
Opitz 2 , T. Voigt 2 , A. Reiher 3 , A. Krtschil 3 , S. Günther 3 , H.
Witte 3 und A. Krost 3 — 1 Institut für Elektronik, Signalverarbeitung
und Kommunikationstechnik, Otto-von-Guericke-Universität Magdeburg
— 2 Institut für Physiologie, Otto-von-Guericke-Universität Magdeburg
— 3 Institut für Experimentelle Physik, Otto-von-Guericke-Universität
Magdeburg
Detaillierte Kompartimentmodelle von Einzelneuronen sind oft benutzt
worden, um das Gehirn als modulare elektrische Apparatur darzustellen.
Wir präsentieren eine biologisch realistische Simulation von
Netzwerk-Eigendynamik, wie sie in Zellkulturen des frühen zerebralen
Kortex von Wirbeltieren abläuft. Dabei wird die Entwicklung der
natürlichen Vernetzungstruktur nachgebildet, in der verschiedene funktionelle
Neuronentypen interagieren. Ausgehend von spontaner elektrischer
Aktivität einzelner Neurone werden in massiven Simulationen Eigenarten
der elektrischen Dynamik des Netzwerks und deren gezielte
Beeinflussung gezeigt sowie mit der in-vitro-gemessenen Aktivität verglichen,
die in Verbindung mit zellulären Lernmechanismen (Hebb-LTP)
wechselwirken können, um sich an Muster äußerer Reize anzupassen. Abschließend
wird diskutiert, auf welche Art man in spontan feuernden Zellen,
die über zufällige, rekurrente Strukturen von Netzwerken verbunden
werden, von Organisation sprechen kann.
SYLS 3.25 Mi 16:00 B
Protein adsorption on tailored substrates — •Hubert Mantz,
Anthony W. Quinn, and Karin Jacobs — Experimental Physics,
Saarland University, POB 151 150, 66041 Saarbrücken
It has long been established that bacterial plaque plays an essential role
in the development of oral diseases such as dental caries. Dental plaque
consists of a diversity of different components, which makes it difficult to
determine the mechanism for their formation and growth. Understanding
them would enhance the field of preventative dentistry enabling restorative
materials to be tailored to resist bacterial attachment or have some
antibacterial effect.
We try to get an insight in these mechanisms by using ellipsometry, a
non-destructive optical method for determining film thickness and optical
properties of the sample to be studied. These experiments can measure
the adsorption kinetics of purified salivary proteins on tailored substrates.
By using AFM and wettability analysis, the composition of the surfaces
can be controlled and described.
SYLS 3.26 Mi 16:00 B
Picosecond dynamics of bacterial porins investigated by
quasi-elastic neutron scattering — •Marie Plazanet 1 , Cecile
Bon 2 , Franck Gabel 3 , Sylviane Julien 2 , Peter Timmins 1 ,
and Guiseppe Zaccai 3 — 1 Institut Laue Langevin, 6 rue Jules
Horowitz, 38042 Grenoble Cedex 9, France — 2 CNRS/IPBS, 205 route
de Narbonnes, 31077 Toulouse cedex, France — 3 IBS, 41, rue Jules
Horowitz, 38027 Grenoble Cedex 1, France
The survival of bacteria requires a continuous exchange of molecules
across the cell wall. Porins, a large class of membrane proteins, are involved
in the transport of small hydrophilic molecules across the outer
membrane. Porins have peculiar structural features; they fold in a multistranded,
closed beta-sheet, exposed to the hydrophobic membrane core
on one side and an aqueous channel on the other. Dynamics of these extremely
stable proteins clearly modulate the pore activity (i.e. biological
activity of the porin), and there is good evidence that this dynamics is
modulated by the dynamics of the lipids surrounding the porins.
Experiments have been undertaken on outer membrane fractions of
E.Coli, with the natural asymmetric lipid distribution (lipopolysaccharides
in the outer leaflet and various phospholipids in the inner leaflet).
Samples enriched in porins and samples depleted in porins have been investigated
to probe both lipid and porin contribution. While data are still
under study, preliminary results show that both systems clearly exhibit
very different dynamics on the pico-second timescale. A brief comparison
with corresponding results on the bacteriorhodospsin, a representative of
the membrane proteins folded in an helix-bundle, will be done.
SYLS 3.27 Mi 16:00 B
Controlled proliferation of living cells on UV-light modified polymers
— •Thomas Gumpenberger 1 , Johannes Heitz 1 , Dieter
Baeuerle 1 und Christoph Romanin 2 — 1 Angewandte Physik, Universitaet
Linz, Austria — 2 Biophysik, Universitaet Linz, Austria
We demonstrated the controlled proliferation of human umbilical endothelial
cells (HUVEC) on UV-light modified polymer samples. The polymers
under investigation were either polytetrafluoroethylene (PTFE)
or polyethyleneterephtalate (PET), which are among the most frequently
employed biomaterials in reconstructive medicine. The PTFE surfaces
were modified by exposure to the ultraviolet (UV) light of a Xe2*-excimer
lamp at a wavelength of 172 nm in an ammonia atmosphere. The irradiation
led to an efficient exchange of the F-atoms in the surface by other
chemical moieties. In-vitro, this resulted in a significant increase in the
number of adhering cells 1 day after seeding and in the formation of a
confluent cell layer after 3 to 8 days. The results were comparable or even
better than those obtained on standard polystyrene petri-dishes used in
cell cultivation. Similar studies were performed on PET.
SYLS 3.28 Mi 16:00 B
Electrolytic fabrication of SNOM aperture-sensors — •Carola
Haumann, Christoph Pelargus, Robert Ros, and Dario Anselmetti
— Experimental Biophysics and Applied Nanosciences, Faculty
of Physics, Bielefeld University, Universitaetsstrasse 25, 33615 Bielefeld,
Germany
The resolution achievable with scanning near-field optical microscopy
(SNOM) is determined by the optical quality of the near-field sensors.
We present a method to fabricate reproducibly aperture probes with diameters
in the sub 100nm range by solid state electrolysis. The method,
originally invented by A. Bouhelier et al., was further developed by in-