Induction of an interdigitated gel phase in fully hydrated phosphatidylcholine bilayers

Abstract

Several surface active small molecules induce an unusual phase in dipalmitoylphosphatidylcholine (DPPC) suspensions. In this phase, the lipid hydrocarbon chains from apposing monolayers interpenetrate or interdigitate. A structural analysis by X-ray diffraction shows that with incorporation of the drug chlorpromazine, the bilayer thickness, or lipid headgroup separation, in DPPC liposomes is only 30 Å, which is about 20 Å smaller than two fully-extended DPPC molecules. This interdigitated phase may be a more general phenomenon than previously believed, as several other molecules, both charged and uncharged, such as tetracaine and benzyl alcohol, can cause the lipid hydrocarbon chains to interpenetrate.