Hydration effect on the structure of dioleoylphosphatidylcholine bilayers

In situ enersgy dispersive x-ray diffraction was used to study the effect of hydration on the structure of dioleoylphosphatidylcholine (DOPC) bilayers in the biologically relevant liquid-crystalline phase. A broad range of relative humidity (RH) was investigated (0.45<RH<1) and two hydration regimes were found. From RH=0.45 up to RH= 0.94, the structure of DOPC bilayers was found to change slightly. At RH 0.94, a distinctive structural change was observed. From RH=0.94 up to full hydration, a strong increase in the head group size, coupled with a marked decrease in the hydrophobic core thickness, was observed. Possible molecular mechanisms underlying experimental observations are discussed.