Invited Paper NT+BI-WeM9
Using Neutron Spectroscopy to Study Collective Dynamics of Biological and Model Membrane Systems

Wednesday, October 17, 2007, 10:40 am, Room 618

The spectrum of fluctuations in biomimetic and biological membranes covers a large range of time and length scales, ranging from the long wavelength undulation and bending modes of the bilayer with typical relaxation times of nanoseconds and lateral length scales of several hundred lipid molecules, down to the short-wavelength, picosecond density fluctuations involving neighboring lipid molecules. New developments and improvements in neutron scattering instruments, sample preparation and environments and, eventually, the more and more powerful neutron sources open up the possibility to study collective excitations, i.e. phonons, in artificial and biological membranes. The goal of this project is to seek relationships between collective dynamics on various length scales on the one hand, and macroscopic phenomena such as trans-membrane transport, pore opening, and membrane fusion on the other hand. The combination of various inelastic neutron scattering techniques enlarges the window of accessible momentum and energy transfers - or better: accessible length and time scales - and allows one to study structure and dynamics on length scales ranging from the nearest-neighbor distances of lipid molecules to length scales of more than 100 nm, covering time scales from about 0.1 ps to almost 1 μs. The fluctuations are quantified by measuring the corresponding dispersion relations, i.e. the wave vector-dependence of the excitation frequencies or relaxation rates. Because biological materials lack an overall crystal structure, in order to fully characterize the fluctuations and to compare experimental results with membrane theories, the measurement must cover a very large range of length and time scales. By using multiple instruments, from spin-echo to triple-axis spectrometers, we have successfully probed these fluctuations over the desired range of length and time scales.^1-5

¹M.C. Rheinstädter, C. Ollinger, G. Fragneto, F. Demmel and T. Salditt, Phys. Rev. Lett. 93, 108107, 1-4 (2004).
²Maikel C. Rheinstädter, Wolfgang Häußler and Tim Salditt, Phys. Rev. Lett. 97, 048103, 1-4 (2006).
³Maikel C. Rheinstädter, Tilo Seydel, Franz Demmel and Tim Salditt, Phys. Rev. E 71, 061908, 1-8 (2005).
⁴Maikel C. Rheinstädter, Tilo Seydel and Tim Salditt, Phys. Rev. E 75, 011907, 1-5 (2007)
⁵Maikel C. Rheinstädter, Tilo Seydel, Wolfgang Häußler and Tim Salditt, J. Vac. Soc. Technol. A 24, 1191-1196 (2006).