RIPPLE PHASE-STABILITY IN LIPID SYSTEMS THAT FORM INTERDIGITATED BILAYERS

Interdigitated bilayer phases have been unambiguously shown to occur i n phospholipid systems. The presence of the interdigitated bilayer pha se is influenced by the character of the lipids present in the bilayer and the structure of the solvent at the bilayer-solvent interface. Ph ase structures and transitions involving interdigitated phases are exa mined using real time x-ray diffraction. The synthetic lipids 1,2 O-di hexadecylphosphatidylcholine (DHPC) in water and dipalmitoylphosphatid ylcholine (DPPC) in ethanol/water or 1 M KSCN have been previously sho wn to form an interdigitated gel state bilayer phase. The dynamic phas e sequence observed for DHPC in water was found to be: L(c)(inter) --> L(beta)(inter) --> P(beta) --> L(alpha). The dynamic phase sequence o bserved for DPPC in ethanol/water or 1 M KSCN was found to not contain a ripple (P(beta)) phase. It can be concluded that changes in the ord ering of the solvent structure at the bilayer-solvent interface can pr event the dynamic formation of the rippled bilayer phase.