X-RAY-DIFFRACTION MEASUREMENTS OF DIPALMITOYLPHOSPHATIDYLCHOLINE AS A FUNCTION OF PRESSURE

Results of the first X-ray diffraction measurements of the lamellar periodicity of dipalmitoylphosphatidylcholine as a function of pressure are presented. Below the gel transition the periodicity decreases with increasing pressure. Above the transition, the periodicity increases with increasing pressure at a rate ∼10 times that below the gel transition. This discovery is interpreted in terms of the relative compressibility within and perpendicular to the bilayer plane. We find the gel transition temperature, Tm, is elevated with pressure. We determine dPm dTm ≅ 48 atm./oC and is constant with pressure. In addition, we find coexistance of gel and liquid crystalline phases near the transition as a function of pressure. We believe these measurements to represent the first observation of the gel transition as a function of pressure using a structural technique. © 1978.