  Lipid membranes in a physiological context cannot be understood without
taking into account their mobile environment. Here, we report on 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). This technique allows
discriminating the Q-dependent onset of mobility and provides a benchmark test
regarding the feasibility of dynamical neutron scattering investigations on
these sample systems. Apart from freezing of the lipid acyl-chains, we could
observe a second freezing temperature that we attribute to the hydration water
in between the membrane stacks. The freezing is lowered several degrees as
compared to (heavy) bulk water.
