Publication Details

M. Trapp, T. Gutberlet, F. Juranyi, M. Tehei, L. van Eijck, T. Unruh & J. Peters (2010). Quasielastic and elastic scattering studies of aligned DMPC multilayers at different hydrations. American Conference on Neutron Scattering Ottawa, Canada, Oral presentation and student travel grant, 27 June 2010.


Lipid model membranes such as 1,2-Dimyristoyl-sn-Glycero-3-Phosphocholine (DMPC) serve as role models for their more complex counterparts in biological systems. Quasielastic neutron scattering (QENS) [1-3], inelastic neutron scattering (INS) [4] and neutron spin echo spectroscopy (NSE) [5] have been employed to study local as well as collective dynamics of these membranes on a ps-ns time scale. Most of these studies lack a systematic investigation of the behavior of the model membranes in dependence on their hydration. We now started a detailed investigation of hydration effect on model membrane systems. The complexity of the dynamics can be further reduced by selective deuteration, which allows to distinguish between dynamics of different part of the lipid molecules. In the here presented work we have used chain deuterated DMPC-d54 to study the dynamics of the lipid head group. To probe both dynamics in the plane of the membrane and perpendicular to it, the samples were prepared on cleaned silicon wafers. The hydration for the two samples was adjusted by hydrating them for pure D2O and from a saturated salt solution respectively, resulting in two different states of hydration (repeat distance d=62.5 Å with 15 water molecules per lipid and d = 54.9 Å with 9 water molecules per lipid, respectively). The alignment and mosaicity were checked prior to the measurements for all samples by neutron diffraction and was found to be below 1°. QENS experiments were performed at the time-of-flight spectrometer TOFTOF at the research reactor FRMII in Munich (energy resolution: 56 μeV FWHM) in the temperature range from 5°C to 30°C to cover the main phase transition from the Pβ gel phase to the liquid crystalline Lα phase of DMPC which occurs around 23°C. Elastic incoherent neutron scattering (EINS) measurements were performed at the high momentum transfer backscattering spectrometer IN13 (energy resolution 8 μeV FWHM) and the cold neutron backscattering spectrometer IN16 (energy resolution 0.9 μeV FWHM) both at the Institut Laue-Langevin (ILL), Grenoble. For the QENS experiment elastic incoherent structure factors (EISF) and diffusion constants were extracted, which indicate that hydration has a clear influence on the mobility of this system [6]. The integrated intensities from the EINS experiments showed a shift of the main phase transition as a function of hydration which coincides with a change of the slopes of the mean square displacements [7]. In addition to earlier QENS [1-3] and backscattering [8] investigations, these experiments extend our knowledge of model membrane systems. References [1] S. König et al., J.Phys.II France, 2 (1992) 1589-1615 [2] M.C. Rheinstädter et al., Phys. Rev. E 75 (2007) 011907 [3] S. Busch et al., JACS 132, (2010), 3232-3233 [4] M.C. Rheinstädter et al., Phys Rev. Lett. 93 (2004) 108107 [5] M.C. Rheinstädter et al., Phys. Rev. Lett. 97 (2006) 048103 [6] M. Trapp et al., in preperation [7] M. Trapp et al., Spectrosc.-int. J., accepted (2010) [8] M.C. Rheinstädter et al., Phys. Rev. E 71 (2005) 061908 (2002)