Phase transitions and polymorphism in phospholipids

An assembly of phospholipids dispersed in water exhibits a variety of phases in a narrow temperature range, i.e., subgel Lc. phase, gel Lβ. (or Lβ) phase, interdigitated gel Lβ1 phase, ripple gel Pβ. phase, liquid crystalline Lα phase, cubic Q phase, hexagonal HII phase, etc. The characteristics of the structures in these phases are discussed. Some of the phase transitions are considered in terms of the critical packing parameter developed by Israelachvili, Marčelja and Horn (Quart. Rev. Biophys, 13, 121 ((1980)). For much further consideration, heterogeneity in the bilayer structure of phospholipids should be taken into account. In connection with this nature, the importance of a sequential mechanism in the phase transitions of phospholipids is pointed out.