Martin Kimmig

University of Freiburg, Freiburg, Baden-Württemberg, Germany

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Publications (9)43.12 Total impact

  • ChemInform 11/2010; 22(44):35-35. DOI:10.1002/chin.199144035
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    ABSTRACT: ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
    ChemInform 02/2010; 25(8). DOI:10.1002/chin.199408035
  • M. Kimmig, G. Strobl, B. Stuehn
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    ABSTRACT: Analysis of measurements of the static scattering function by electron and X-ray diffraction, of the dynamic scattering law by neutron scattering, and of infrared and Raman spectra points at the important role of twin helix-reversal defects for the molecular dynamics in the intermediate phase and high-temperature phase (modifications IV and I) of poly(tetrafluoroethylene). In contrast to single helix-reversal defects, these twin defects constitute a local perturbation which can move along the chain without affecting remote units. One species, the ''coherent'' twin defect, possesses a particularly low formation energy, since it retains the twist long-range order along the chain. Formation of the defects occurs mainly in the intermediate phase. In the high-temperature phase a saturation is observed. The steep increase in the defect concentration in the intermediate phase followed by the equilibration in the high-temperature phase can be understood as a transition between a disordered state controlled by intra- and intermolecular forces to one which is only determined by the intramolecular potentials. In spite of the disorder in the helices, an orientational short-range order is retained for sequences in adjacent chains. The degree of order is related to the defect concentration. The reorientation of the CF2 group resulting from the formation and motion of the twin defects occurs with rates in the range of 10-100 GHz. Orientational short-range order leads to a slowing down.
    Macromolecules 04/2002; 27(9). DOI:10.1021/ma00087a017 · 5.93 Impact Factor
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    ABSTRACT: Osteopontin (OPN) is a chemotactic protein that attracts immune cells, to inflammatory sites. The sensitization phase of allergic cutaneous contact hypersensitivity (CHS) requires the migration of Langerhans cells/dendritic cells (LCs/DCs) from skin to draining lymph nodes. Characterizing OPN function for LC/DC migration we found upregulated OPN expression in hapten sensitized skin and draining lymph nodes. OPN induces chemotactic LC/DC migration, initiates their emigration from the epidermis, and attracts LCs/DCs to draining lymph nodes by interacting with CD44 and alphav integrin. Furthermore, OPN-deficient mice have a significantly reduced CHS response that correlates with an impaired ability of OPN-deficient mice to attract LCs/DCs to draining lymph nodes. In conclusion, OPN is an important factor in the initiation of CHS by guiding LCs/DCs from skin into lymphatic organs.
    Journal of Experimental Medicine 12/2001; 194(9):1219-29. · 13.91 Impact Factor
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    ABSTRACT: Osteopontin (OPN) is a chemotactic protein that attracts immune cells, to inflammatory sites. The sensitization phase of allergic cutaneous contact hypersensitivity (CHS) requires the migration of Langerhans cells/dendritic cells (LCs/DCs) from skin to draining lymph nodes. Characterizing OPN function for LC/DC migration we found upregulated OPN expression in hapten sensitized skin and draining lymph nodes. OPN induces chemotactic LC/DC migration, initiates their emigration from the epidermis, and attracts LCs/DCs to draining lymph nodes by interacting with CD44 and αv integrin. Furthermore, OPN-deficient mice have a significantly reduced CHS response that correlates with an impaired ability of OPN-deficient mice to attract LCs/DCs to draining lymph nodes. In conclusion, OPN is an important factor in the initiation of CHS by guiding LCs/DCs from skin into lymphatic organs.
    Journal of Experimental Medicine 11/2001; 194(9):1219-1230. DOI:10.1084/jem.194.9.1219 · 13.91 Impact Factor
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    ABSTRACT: Rotations of the molecules about their long axis constitute an important part in the complex pattern of internal motions in the rhombohedral phase of perfluoro‐n‐eicosane (C20F42). Dynamical studies were performed by quasielastic and inelastic neutron scattering. Spectra were determined in a range of strong diffuse scattering. They show a superposition of librations (δE≂1–2 meV) and rotational diffusion (δE≂10–100 μeV). Reorientation rates exhibit a slowing down on approaching the transition to the low temperature phase (Tc=200 K). As indicated by this slowing down, by the nonexponential relaxation function, and also an intensity enhancement at the Bragg‐positions, rotations occur correlated between neighboring molecules. The state of motion can be simulated by molecular dynamics calculations performed for a two‐dimensional lattice of coupled rotators.
    The Journal of Chemical Physics 11/1993; 99(10):8105-8114. DOI:10.1063/1.465636 · 3.12 Impact Factor
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    ABSTRACT: Poly- and oligotetrafluoroethylenes exhibit at room temperature a high molecular mobility in the crystalline state. A detailed analysis of the molecular motion is possible by measuring the static and dynamic structure factor using x-ray and neutron scattering. The onset of diffusive molecular dynamics coincides in poly- and oligotetrafluoroethylenes with an orderdisorder phase transition. — In PTFE the prevalent relaxational mode is a double helix reversal. Occurrence of helix reversals leads to a characteristic change in the static structure factor S(q), indicating a loss of azimuthal correlation within the chain. A quasieelastic line in the dynamic structure factor S(q, ω) can be associated with motion of helix reversals. Six-fold symmetry (around the chain axis) of the intensity distribution of the diffusive scattering indicates an intermolecular correlation of rotational motion. — In C20F42 the phase transition at 200 K is mainly connected with the onset of rotational motion. Additionally, longitudinal diffuse motion sets in at the phase transition. This mode shows an increasingly collective character on approaching the phase transition.
  • Heinz Schwickert, Gert Strobl, Martin Kimmig
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    ABSTRACT: Perfluoro-n-eicosane (n-C20F42) passes through three different solid modifications, called M(T < 146 K), I(146 < T < 200 K), and R(T > 200 K). Structures of the phases M and R were characterized by x-ray scattering experiments. Crystals are built up by rectangular layers. In modification M layers are set up by arrays of right-handed and left-handed (15/7-) helices in alternate succession. The unit cell is monoclinic (a = 9.65 angstrom, b = 5.70 angstrom, c = 28.3 angstrom, and beta = 97-degrees; space group Pa). In modification R molecules are highly mobile. There is no ordering with regard to the helix handedness. Molecules resemble cylindrical objects and are packed in a hexagonal dense mode. Regular layer stacking results in crystals with rhombohedral symmetry (a = b = 5.70 angstrom, c = 85.00 angstrom, gamma = 120-degrees; space group R 3mBAR).
    The Journal of Chemical Physics 08/1991; 95(4):2800-2806. DOI:10.1063/1.460931 · 3.12 Impact Factor
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    ABSTRACT: The defect structure in the rhombohedral modification R of perfluoro-n-eicosane has been analyzed in a temperature-dependent x-ray and neutron scattering study. The analysis was based on an evaluation of Bragg-reflection intensities and of the diffuse scattering. Different components of disorder were detected and characterized. At the transition from the low temperature phase to modification R, rotation of the molecules about their long axes sets in. As shown by the azimuthal distribution of the diffuse scattering, rotations occur cooperatively with correlations between neighbors. The Debye–Waller factors measured for the layer reflections are indicative for a moderate roughening of the interfaces due to a restricted longitudinal diffusive motion. Molecules are perturbed by the formation of helix reversal defects. Evaluation of the diffuse scattering yields the associated finite azimuthal correlation length. There is also evidence for a continuous slow untwisting of the helix. With increasing temperature, it approaches the all-trans form.
    The Journal of Chemical Physics 08/1991; 95(4):2807-2816. DOI:10.1063/1.460932 · 3.12 Impact Factor