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 L(c), phase, gel L(beta), (or L(beta) ) phase, interdigitated gel L(beta I) phase, ripple gel P-beta, phase, liquid crystalline L(alpha) phase, cubic Q phase, hexagonal H-II 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, Marcelja 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.