Subtransition of Multilamellar L-α, Dibehenoyl (Cn=22) Phosphatidylcholine

In multilamellar phospholipids in which the number of carbons per hydrocarbon chain (C n ) is equal to or less than 18, e.g., L-α, Dipalmitoyl phosphatidylcholine (DPPC) for C n =16 and L-α, Distearoyl phosphatidylcholine (DSPC) for C n =18, the subtransition appears only during the heating process under atmospheric pressure after the phospholipids satisfy some special conditions such as the long-term cooling storage around 0°C for more than 72 h. However, the subtransition of multilamellar L-α, Dibehenoyl phosphatidylcholine with C n =22 (abbreviated as DBPC) appears not only during heating, but also in the subsequent cooling run without any special conditions under atmospheric pressure, and it is confirmed that the subtransition of multilamellar DBPC is composed of two phenomena. X-ray scattering analyses indicated changes of hydrocarbon chain packing as the subtransition by the following two-step process; orthorhombic symmetry -orthorhombic symmetry -hexagonal symmetry. These experimental results closely correspond to the phenomena under high pressure, which are obtained from multilamellar DPPC and DSPC conditioned by high-pressure melting above 250 MPa.