Plenarvorträge - DPG-Tagungen

Arbeitskreis Biologische Physik Freitag
(ME-switch).
The resulting model reveals different mechanism of phase separation acting
on different length scales, namely phase separation driven by proteinlipid
interaction as well as phase separation due to enzymatic activity. In
addition, we find also oscillatory behavior and traveling domains.
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Complex Crystal Growth of CaCO3 controlled by Diblock-
Copolymer Solutions — •Antje Reinecke 1 , Helmut Cölfen 1 ,
and Hans-Günther Döbereiner 1,2 — 1 Max-Planck-Institut für
Kolloid- und Grenzflächenforschung, D-14424 Potsdam — 2 Department
of Biology, Columbia University, New York, NY 10027
The morphology of CaCO3 crystals grown from Na2CO3 and CaCl2
solutions in a double jet reactor is extensively modified in the presence
of Poly(ethyleneoxide)-block-Poly(methacrylic acid). We observe growth
via rod, dumbell and final sphere morphologies using electron and phasecontrast
microscopy. It is well known that diblock-copolymer additives
influence strongly crystal shapes. However, so far, detailed morphological
sequences during crystal growth have not been reported. For the first
time, we present a quantitative characterization of crystal shapes and
their growth dynamics. Extensive phase-contrast microscopy studies are
statistically analyzed to provide the dynamics of shape distributions over
time. Electron microscopy gives high resolution images of faceted crystal
shapes. We correlate crystal morphology to dynamic free ion concentration
measurements using Ca ++ sensitive electrodes.
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Giant Hexagonal Superstructures in Diblock-Copolymer
Membranes — •Wojciech Gó´zd´z 1 , Christopher Haluska 2 ,
Hans-Günther Döbereiner 2,3 , Stephan Förster 4 , and Gerhard
Gompper 3 — 1 Institute of Physical Chemistry, PAS, Warsaw —
2 Max-Planck-Institut für Kolloid- und Grenzflächenforschung, Potsdam
— 3 Department of Biology, Columbia University, New York — 4 Institut
für Physikalische Chemie, Universität Hamburg
In aqueous solutions, amphiphilic diblock copolymers self-assemble into
bilayer membranes similar to phospholipid membranes. Such membranes
can form spherical vesicles called polymersomes in analogy to liposomes,
vesicles built from lipid molecules. We have discovered a new type of
polymersomes, characterized by a genus of the order of one hundred.
The genus describes the number of holes or handles in a vesicle. We have
studied the properties of the high-genus polymersomes both experimentally
and theoretically. We are particularly interested in the structure
of the polymersome walls, which resemble locally a hexagonal network
of passages. The structure of the walls can be altered by applying thermodynamic
stimuli, for example temperature. A few types of ordered
structures which form the wall of polymersomes have been observed experimentally,
such as connected spheres, connected spindles, narrow and
wide passages. The transition between different structures is predicted
and the phase diagram is calculated [1]. The theoretical calculations are
in good agreement with the experiments.
1. C. Haluska et al. , Phys. Rev. Lett., 89(2002), 238302
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Slow Relaxation Dynamics of Tubular Polymersomes after
Thermal Quench — •Antje Reinecke 1 and Hans-Günther
Döbereiner 1,2 — 1 Max-Planck-Institut für Kolloid- und Grenzflächenforschung,
D-14424 Potsdam — 2 Department of Biology,
Columbia University, New York, NY 10027
Morphological shape changes of giant tubular vesicles prepared from
the diblock copolymer polybutadiene- (32)-b-polyethylene oxide(20)
(PB-PEO) in aqueous solution after thermal quenches between 10 and
50K were monitored via quantitative phase-contrast microscopy [1].
Reducing the temperature leads to extremely slow sequential beading
of the tubes where the formation of necks starts symmetrically at
the two ends. We characterize the neck diameters and find that the
necks close one by one with effective velocities on the order of a few
tens of nanometers per minute. The necks do not close continuously,
but rather their radii decrease in time in a sequence of exponential
decays between intermediate plateaus. The slow dynamics is a result of
the high membrane surface viscosity of PB-PEO. Sequential beading
is rationalized via a cascade of metastable shapes determined by the
bending elastic energy of the tubular polymersomes.
[1] A. Reinecke, H.-G. Döbereiner, Langmuir 19, 605-608 (2003)
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Advanced Flicker Spectroscopy of Fluid Membranes — •Hans-
Günther Döbereiner 1,2 , Gerhard Gompper 3 , Christopher K.
Haluska 1 , Daniel M. Kroll 4 , Peter G. Petrov 1,5 , and Karin A.
Riske 1 — 1 Max-Planck-Institut für Kolloid- und Grenzflächenforschung,
14424 Potsdam — 2 Dept. of Biology, Columbia University, New York,
NY 10027, USA — 3 IFF, Forschungszentrum Jülich, 52425 Jülich, —
4 Dept. of Medicinal Chemistry, University of Minnesota, Minneapolis,
Minnesota 55455, USA — 5 School of Physics, University of Exeter, EX4
4QL, UK
The bending elasticity of a fluid membrane is characterized by its modulus
and spontaneous curvature. We present a new method, advanced
flicker spectroscopy of giant nonspherical vesicles, which makes it possible
to simultaneously measure both parameters for the first time [1]. Our
analysis is based on the generation of a large set of reference data from
Monte Carlo simulations of randomly triangulated surfaces. As an example
of the potential of the procedure, we monitor thermal trajectories
of vesicle shapes and discuss the elastic response of zwitterionic membranes
to transmembrane pH gradients. Our technique makes it possible
to easily characterize membrane curvature as a function of environmental
conditions.
[1] Phys. Rev. Lett. 91, 048301-4 (2003)
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Mechanisms of pattern formation during T cell adhesion
— •Thomas Weikl — Max-Planck-Institut für Kolloid- und
Grenzflächenforschung, 14424 Potsdam
T cells form intriguing patterns during adhesion to antigen-presenting
cells. The patterns at the cell-cell contact zone are composed of two types
of domains, which either contain short TCR/MHCp receptor-ligand complexes
or the longer LFA-1/ICAM-1 complexes. The final pattern consists
of a central TCR/MHCp domain surrounded by a ring-shaped LFA-
1/ICAM-1 domain, while the characteristic pattern formed at intermediate
times is inverted with TCR/MHCp complexes at the periphery of
the contact zone and LFA-1/ICAM-1 complexes in the center. We have
developed a statistical-mechanical model of cell adhesion and propose a
novel mechanism for the T cell pattern formation. Our mechanism for
the formation of the intermediate inverted pattern is based (i) on the initial
nucleation of numerous TCR/MHCp microdomains, and (ii) on the
diffusion of free receptors and ligands into the contact zone. Due to this
inward diffusion, TCR/MHCp microdomains at the rim of the contact
zone grow faster and form an intermediate peripheral ring for sufficiently
large TCR/MHCp concentrations. According to our model, the formation
of the final pattern with a central TCR/MHCp domain requires
active cytoskeletal transport processes, which agrees with experimental
findings.
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DNA in situ hybridization detection by gold conjugated
nanoparticles and Atomic Force Microscopy — •Gabriella
Teti 1 , Konstantin Agelopoulos 2 , Burkhard Brandt 2 , Stefan
Thalhammer 1 , and Wolfgang Heckl 1 — 1 Department Geo- und
Umweltwissenschaften, Ludwig Maximilians Universitaet-Muenchen —
2 Institut klinische Chemie und Laboratoriumsmedizin, Westf*lische
Wilhelms-Universitaet Muenster
The localization of specific molecules in biological samples continues
to be important for the basic and applied biological research. Immunocytochemistry
and in situ hybridization of nucleic acids are key methods.
For high resolution localization of specific DNA sequences in situ
on biological samples, a study based on the combination of atomic force
microscope (AFM) and DNA in situ hybridization technique has been
proposed. The DNA probes were labelled with digoxigenin and the detection
system was based on antibodies against digoxigenin conjugated
with gold particles. In some cases the gold labelling was amplified by a
colloidal silver enhancement. Compared to high resolution electron microscopy,
AFM generates topographic and three-dimensional images on a
nanometre scale in ambient and liquid conditions without destroying the
sample morphology. The experimental approach was demonstrated on
specific probes against human leukaemia, epidermal growth factor receptor
on human metaphase chromosomes and specific oligonucleotides on
stretched plasmid DNA. Finally, we suggest potential applications based
on our results for high-resolution physical mapping of human genes and
disease correlated genes.