The file SCdbltraj.gif contains a trajectory of skin lipid double bilayer 
(112 CER, 112 CHOL, and 64 FFA) in excess water (5250 molecules). The 
water molecules are not shown.

There are 50 frames separated by 20ns. To prepare the animation,
periodic boundary condition was removed and molecules were shifted 
such that the center of mass of the lipids remain fixed.

Color scheme: carbon (cyan), hydrogen (white), nitrogen (blue), oxygen (red).

Majority of the molecules are represented with bonds. Four CHOL that 
exchange between the leaflets are highlighted with orange colors.
Two CER molecules on the top bilayer also are highlighted by
drawing with larger spheres. 

There is a subpopulation of CHOL at the bilayer mid-plane that is
in dynamic equilibrium with the majority population embedded in the
ordered leaflets. The disordered chain arrangement, and lower
mass density at the bilayer mid-plane allow fast diffusion of
CHOL. CER at the outer leaflets undergo a slithering movement and
can reorient its head group. In contrast, CER in the inner leaflets
are hydrogen bonded with lipids in adjacent leaflet and have
little flexibility in head-group region.