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Register a new userCollective Dynamics of Lipid Membranes studied by Inelastic Neutron Scattering
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We have studied the collective short wavelength dynamics in deuterated DMPC bilayers by inelastic neutron scattering. The corresponding dispersion relation $hbaromega$(Q) is presented for the gel and fluid phase of this model system. The temperature dependence of the inelastic excitations indicates a phase coexistence between the two phases over a broad range and leads to a different assignment of excitations than that reported in a preceding inelastic x-ray scattering study [Phys. Rev. Lett. {bf 86}, 740 (2001)]. As a consequence, we find that the minimum in the dispersion relation is actually deeper in the gel than in the fluid phase. Finally, we can clearly identify an additional non-dispersive (optical) mode predicted by Molecular Dynamics (MD) simulations [Phys. Rev. Lett. {bf 87}, 238101 (2001)].
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We present the first inelastic neutron scattering study of the short wavelength dynamics in a phospholipid bilayer. We show that inelastic neutron scattering using a triple-axis spectrometer at the high flux reactor of the ILL yields the necessary resolution and signal to determine the dynamics of model membranes. The results can quantitatively be compared to recent Molecular Dynamics simulations. Reflectivity, in-plane correlations and the corresponding dynamics can be measured simultaneously to gain a maximum amount of information. With this method, dispersion relations can be measured with a high energy resolution. Structure and dynamics in phospholipid bilayers, and the relation between them, can be studied on a molecular length scale.
Lipid membranes form the barrier between the inside and outside of cells and many of their subcompartments. As such, they bind to a wide variety of nano- and micrometer sized objects and, in the presence of strong adhesive forces, strongly deform and envelop particles. This wrapping plays a key role in many healthy and disease-related processes. So far, little work has focused on the dynamics of the wrapping process. Here, using a model system of micron-sized colloidal particles and giant unilamellar lipid vesicles with tunable adhesive forces, we measure the velocity of the particle during its wrapping process as well as the forces exerted on it by the lipid membrane. Dissipation at the contact line appears to be the main factor determining the wrapping velocity and time to wrap an object.
We report a high energy-resolution neutron backscattering study to investigate slow motions on nanosecond time scales in highly oriented solid supported phospholipid bilayers of the model system DMPC -d54 (deuterated 1,2-dimyristoyl-sn-glycero-3-phoshatidylcholine), hydrated with heavy water. This technique allows to discriminate the onset of mobility at different length scales for the different molecular components, as e.g.@ the lipid acyl-chains and the hydration water in between the membrane stacks, respectively, and provides a benchmark test regarding the feasibility of neutron backscattering investigations on these sample systems. We discuss freezing of the lipid acyl-chains, as observed by this technique, and observe a second freezing transition which we attribute to the hydration water.
We report a high energy-resolution neutron backscattering study to investigate slow motions on nanosecond time scales in highly oriented solid supported phospholipid bilayers of the model system DMPC -d54 (deuterated 1,2-dimyristoyl-sn-glycero-3-phoshatidylcholine), hydrated with heavy water. Wave vector resolved quasi-elastic neutron scattering (QENS) is used to determine relaxation times $tau$, which can be associated with different molecular components, i.e., the lipid acyl chains and the interstitial water molecules in the different phases of the model membrane system. The inelastic data are complemented both by energy resolved and energy integrated in-situ diffraction. From a combined analysis of the inelastic data in the energy and time domain, the respective character of the relaxation, i.e., the exponent of the exponential decay is also determined. From this analysis we quantify two relaxation processes. We associate the fast relaxation with translational diffusion of lipid and water molecules while the slow process likely stems from collective dynamics.
We present data on the magnetic and magneto-elastic coupling in the hexagonal multiferroic manganite LuMnO3 from inelastic neutron scattering, magnetization and thermal expansion measurements. We measured the magnon dispersion along the main symmetry directions and used this data to determine the principal exchange parameters from a spin-wave model. An analysis of the magnetic anisotropy in terms of the crystal field acting on the Mn is presented. We compare the results for LuMnO3 with data on other hexagonal RMnO3 compounds.
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