1,721,028 research outputs found
Energetics of adhesion cluster formation in the context of biological membranes
No full textThe orchestration of cellular adhesion is an intricate process that involves a multitude of specialized proteins but at the same time follows a simple physical plan. It is still not totally known why cells create clusters of bonds to adhere on a substrate. Besides experimental methods to study cellular adhesion there exist several different theoretical models to describe the stability of focal adhesion clusters. The model proposed in this work makes it possible to understand the formation of adhesion bond clusters. It explains the emergence of a long-range bond-bond attraction that originates from the finite membrane elasticity as the driving force of cluster growth. In combination with a thermally driven bond disintegration such a model will eventually be able to explain the kinetic stability of finite size bond clusters. The model extends conventional two-state models where bonds are either open or closed by introducing a rich scenario of metastable states associated with hysteretic behavior in the bond closure and rupture dynamics.CRC "Collective Behavior of Soft and Biological Matter" [937
Salty Water in KOH-Doped Hexagonal Ice: a Proton and Deuteron NMR Study
No full textWater doped with 10(-2) mol of KOH was cooled to temperatures at which most of the solution freezes to form hexagonal ice. Using proton and deuteron spin-lattice relaxometry as well as static field gradient diffusometry, it was found that a liquid-like phase coexists with the crystal down to below 200 K. The ionic dopants are expelled from the crystalline phase and form a KOH-enriched aqueous solution probably in the form of inclusions within the ice crystal. Its self-diffusion coefficient is only slightly smaller than that of nominally pure water. Motional correlation times were determined on the basis of spin-lattice relaxation times and compared with previous electrical conductivity and calorimetry results.Deutsche Forschungsgemeinschaft [BO1301/7
NMR Study of Local and Long Range Dynamics of Adsorbed Water in Zeolite NaY(Br)
No full textThe dynamics of partially deuterated water in zeolite NaY(Br) are investigated by a combination of several NMR methods for two different loadings, 4 water molecules and 18 water molecules per supercage. Information on local dynamics is obtained by H-1 and H-2 NMR spin-lattice relaxation, H-2 NMR solid-echo spectra and H-2 NMR stimulated echo decay curves. The water long range diffusion has been studied by H-1 NMR static field gradient experiments. The most important findings are as follows: The mechanism of water dynamics depends strongly on the degree of loading. This is clearly reflected in both, local and long range motion. The intermediate H-2 NMR spectra might be explained referring to a model proposed by O'Hare et al.: It is based on two different populations of water molecules performing tetrahedral jumps respectively C-2-flips of their OH bonds. Alternative models for the local water dynamics, distorted tetrahedral jumps and a distribution of correlation times, are also discussed.Deutsche Forschungsgemeinschaft [FU 308/10
Dynamics of Glass Forming Ammonia Hydrates
No full textThe dielectric relaxation of ammonia-water mixtures was studied for a range of NH3 mole fractions x. For 0.01 250 K, line up smoothly with those of pure water. The relaxation behavior of glass forming ammonia hydrates was also investigated using nuclear magnetic resonance techniques including deuteron relaxometry and stimulated-echo spectroscopy, as well as static field-gradient proton diffusometry. These experiments yielded additional insights into the rotational and translational dynamics of ammonia hydrates
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