Changes in Hydrocarbon Chains and Head Groups in Distearoyl Phosphatidylcholine at 4th and 3rd Transitions under High Pressure

The highly ordered conformation of hydrocarbon chain packing with orthorhombic symmetry in L-α-distearoyl phosphatidylcholine under high pressure is confirmed using wide angle X-ray diffraction and Raman scattering. With an increase in temperature under high pressure, two phase transitions (the 4th and 3rd counted from the well known main and pre-transitions) convert the hydrocarbon chain packing from orthorhombic to quasi-hexagonal via, briefly, quasi-orthorhombic symmetry. This behavior is closely related to the movement of the head group and the occurrence of the gauche bond in the intrachain of phospholipids. These phenomena occur after the phospholipid is pressed above about 250 MPa and heated once above its melting point.