The microscopic dynamics of lipids in biomembranes is of special relevance in the study of chemical reactions produced in cells. The mechanism of the exchange of a model lipid molecule between both sides of a flexible bilayer membrane or flip-flop in an aqueous environment has been studied by computer simulation using the recently developed transition path sampling technique, since flip-flop transitions are infrequent events of the lipid dynamics. In addition, structural changes in the membrane have been investigated at ambient conditions and for increasing temperature. Our results highlight the cooperative effort of the whole system in order to allow a lipid molecule to cross the bottleneck in configuration space associated with the transition state of the flip-flop event. Within the time interval of the transition, all molecules of the system significantly change the frequency of their molecular motions.

• Received 9 February 2004

DOI:https://doi.org/10.1103/PhysRevE.69.061918