Role of tilt order in the asymmetric ripple phase of phospholipid bilayers- art. no. 055705

We present the electron density map of the asymmetric ripple phase of dilau roylphosphatidylcholine. We find that the primary feature characterizing th e "asymmetry" of the rippled bilayers is the difference in the bilayer thic kness in the two arms, and not the asymmetry of the bilayer height profile as is generally assumed. This difference in the bilayer thickness can be at tributed to a mean tilt of the hydrocarbon chains of the lipid molecules al ong the direction of the ripple wave vector. We propose a Landau theory for this phase which takes into account the anisotropic elastic properties of a bilayer with tilt order.