  Extensive microscopic molecular dynamics simulations have been performed to
study the effects of short-chain alcohols, methanol and ethanol, on two
different fully hydrated lipid bilayer systems in the fluid phase at 323 K. It
is found that ethanol has a stronger effect on the structural properties of the
membranes. In particular, the bilayers become more fluid and permeable: Ethanol
molecules are able to penetrate through the membrane in typical time scales of
about 200 ns whereas for methanol that time scale is considerably longer, at
least of the order of microseconds. We find good agreement with NMR and
micropipette studies. We have also measured partitioning coefficients and the
rate of crossing events for alcohols, i.e., typical time scale it takes for a
molecule to cross the lipid bilayer and to move from one leaflet to the other.
For structural properties, two-dimensional centre of mass radial-distribution
functions indicate the possibility for quasi long-range order for
ethanol-ethanol correlations in contrast to liquid-like behaviour for all other
combinations.
