ABSTRACT
GMO is a polar lipid and thus an amphiphilic molecule, with a waxy texture at room temperature and a characteristic odor. It swells to form several types of liquid-crystalline phases; a temperaturedependent phase diagram of the GMO-water system is described in several studies (4-6). When a small amount of water (5% w/w) is added to GMO at 37
°
C, it causes the formation of reversed micelles (L
) with very low viscosity. The introduction of additional water leads to phase changes to a lamellar phase (L,
∼
8 to 15 % w/w water
content at 37
°
C) and cubic phase (Q,
∼
20 to 35% w/w water content at 37
°
C). The reversed hexagonal phase (H
) is observed only at temperatures exceeding 90
°
C. The structure of the cubic phase is called bicontinuous because
it consists of a curved three-dimensional network of lipid bilayers, separating two congruent water channel networks (7). Two different cubic phases have been identified in the binary system of GMO and water. The cubic phase with lower water content (20 to 34% w/w at 25
°
C) produces a body-centered lattice (8), while the cubic phase formed with higher water content (33 to 40% w/w at 25
°
C) causes the formation of a primitive lattice (9). These structures were described as infinite periodic minimal surfaces (IPMS) with space groups of
Ia3d
and
Pn3m
and for the body-centered lattice and space group of
Im3m
for the primitive lattice (10). These space groups correspond to the three fundamental cubic IPMS, the gyroid structure (G), diamond structure (D), and Schwarz’s octahedral periodic surface (P), respectively. After reaching an equilibrium with respect to water content, the cubic phase can coexist with excess water without disruption of its intact structure (4).
