Alexander Otten

European Synchrotron Radiation Facility, Grenoble, Rhône-Alpes, France

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Publications (5)15.29 Total impact

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    ABSTRACT: DNA condensation in vivo usually requires proteins and/or multivalent salts. Here, we explore the in vitro compaction of DNA by cationic dendrimers having an intermediate size and charge. The dynamic assembly of DNA-dendrimer mesophases is discernible due to the laminar flow in a specially designed X-ray compatible microfluidic device. The setup ensures a nonequilibrium ascent of reactant concentration, and the resulting progression of DNA compaction was detected online using microfocused small-angle X-ray diffraction. The evolution of a DNA-dendrimer columnar square mesophase as a function of increasing dendrimer content is described. Additionally, in regions of maximum shear, an unexpected high-level perpendicular ordering of this phase is recorded. Furthermore, these assemblies are found to be in coexistence with a densely packed DNA-only mesophase in regions of excess DNA. The latter is reminiscent of dense packing found in bacteriophage and chromosomes, although surprisingly, it is not stabilized by direct dendrimer contact.
    No preview · Article · Aug 2007 · Biomacromolecules
  • Rolf Dootz · Alexander Otten · Sarah Köster · Bernd Struth · Thomas Pfohl
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    ABSTRACT: Combining microfluidics with x-ray microdiffraction and Raman microscopy, the dynamic behaviour of soft matter, with specific consideration of the molecular structure, can be investigated. Microfluidic systems enable a reduction of sample volume and shorter reaction times. By performing experiments under continuous microflow, material damage is avoided and the influence of external stress on biomacromolecules can be analysed. The generated elongated flow induces alignment of the investigated materials, allowing for an improved structural characterization. Here, the dynamics of the compaction of DNA by polypropyleneimine dotriacontaamine dendrimers, generation 4 is studied. As a consequence of the laminar flow inside the microchannels, highly defined, diffusion-controlled compaction of the DNA occurs enabling the study of different states of the reaction during one measurement by varying the observation position in the channels. The evolution of a columnar mesophase with an in-plane square symmetry is monitored by x-ray microdiffraction and the molecular interaction between the two reactants is traced using Raman microscopy, leading to a more profound comprehension of the condensation reaction. The experimental results are in accordance with finite element method simulations of the flow and diffusion profiles in the elongated flow device.
    No preview · Article · Apr 2006 · Journal of Physics Condensed Matter
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    ABSTRACT: The combination of X-ray microdiffraction and microfluidics is used to investigate the dynamic behaviour of soft materials. A microfocused X-ray beam enables the observation of the influence of droplet formation on the nanostructure of a smectic liquid crystal in water. Using a hydrodynamic focusing device, the evolution of the intercalation of DNA into multilamellar membranes can be studied. Owing to the elongational flow at the centre of this device, alignment of the material is induced which allows for an improved structural characterization. Furthermore, the influence of strain applied to these materials can be tested.
    No preview · Article · Dec 2005 · Journal of Synchrotron Radiation
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    ABSTRACT: We report on the application of microfocussing on a non specific beamline. The ID10B beamline at the ESRF was originally designed for surface diffraction experiments. A special Fresnel phase zone plate opens a new field of wide scientific interest to the beamline.
    No preview · Article · May 2004
  • Alexander Otten · Stephan Herminghaus
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    ABSTRACT: This work describes the investigation of the physical basis of the amazing water repellence of some plant leaves, which is in addition to self-cleaning properties known as the "Lotus effect". Two rather different possible mechanisms are proposed, which are suggested to cover the main physics in a majority of superhydrophobic systems. These concepts are illustrated with two different types of plant leaves as well as a model surface carrying carbon nanotube aggregates.
    No preview · Article · Apr 2004 · Langmuir