Motional Coherence in Fluid Phospholipid Membranes

Modern experimental and computational techniques give access to collective molecular properties and raise the fundamental question of coherence in biology. While incoherent systems are systems wherein each particle is a separate, localized entity interacting with others through collisions and other energy exchanges, in a coherent regime particles lose their individual identity. Even in simple models, a biological system must be considered as an array of units interacting through coherent reactions. Coherence must therefore possibly be considered as a fundamental property of biomolecular systems. By employing high energy-resolution neutron backscattering, combined with in-situ diffraction, we have investigated slow molecular motions on nanosecond time scales in the fluid phase of phospholipid model membrane of DMPC [1]. A cooperative structural relaxation process was observed. Combined with results from a 0.1 microsecond long all atom molecular dynamics simulation, we found that correlated dynamics in lipid membranes occurs over several lipid distances, spanning a time interval from pico- to nanoseconds. [1] Rheinstadter et al., accepted for Phys. Rev. Lett., http://arXiv.org/abs/0809.3040.