Miscibility gap in fluid dimyristoylphosphatidylcholine : cholesterol as "seen" by x rays - art. no. 051914

A binary mixture of dimyristoylphosphatidylcholine (DMPC) and cholesterol d isplays a fluid miscibility Sap under excess water conditions. Effects due to the imperfect miscibility of the two amphiphiles are studied near to and far from thermodynamic equilibrium by time-resolved small angle x-ray diff raction. The experiment discloses that this mixture phase separates when le aving the miscibility gap upon heating, a transition that is not included i n current phase diagrams. This transition appears to be reversible and show s a temperature hysteresis of only a few degrees. We suggest a model in whi ch the transition is driven with increasing temperature by a movement of th e cholesterol away from the hydrophilic-hydrophobic interface toward the hy drophobic core of the bilayer.