Self-Assembly in Lipidic Particles - Self-Assembled Supramolecular Architectures: Lyotropic Liquid Crystals - page 128

5.1 INTRODUCTION

In the literature, the biological relevance of lipidic nonlamellar structures in
various cells has been pointed out (Almsherqi et al., 2006; de Kruijff, 1997;
Deng et al., 2002; Ellens et al., 1989; Luzzati, 1997; Patton and Carey, 1979).
As an example, Patton and Carey (1979) observed the formation of bicontinu-
ous cubic phases during fat digestion. These self-assembled nanostructures
were also explored in a variety of cells as a result of cell stress, starvation,
or lipid and protein alterations (Almsherqi et al., 2006; Deng et al., 2002).
Moreover, there is a growing body of evidence concerning the crucial role of
peptides (such as viral peptides) and proteins for inducing the lamellar to
nonlamellar structural transitions in biological cells (Colotto and Epand, 1997;
Ellens et al., 1989; Siegel, 1999). For instance, these transitions are considered
as a keystone element in the fi rst steps of the fusion process (Colotto and
Epand, 1997; Ellens et al., 1989).
The characterization of real biological systems is considered a diffi cult task
due to their complexity. Therefore, the physicochemical properties of model,
biologically relevant, binary or ternary lamellar and nonlamellar phases (de
Kruijff et al., 1997; Hyde et al., 1997; Lewis et al., 1998; Lindblom and Rilfors,
1989; Ortiz et al., 1999; Yaghmur et al., 2007) as well as their corresponding
nanostructured dispersions have received considerable attention (Angelova
et al., 2005; Barauskas et al., 2005; Gustafsson et al., 1996; Larsson, 2000;
Rizwan et al., 2007; Spicer, 2004). In this context, numerous investigations have
been carried out on the physicochemical properties and the phase behavior
of biologically relevant surfactant-like lipid-water systems (Barauskas and
Landh, 2003; de Campo et al., 2004; Larsson, 1983; Lindblom et al., 1979;
Lutton, 1965; Qiu and Caffrey, 1998, 1999), particularly the temperature-water
content phase diagrams of various binary monoglyceride-water systems
(Larsson, 1983; Lindblom et al., 1979; Lutton, 1965). Among these systems, we
have recently investigated the monolinolein (MLO)-water binary mixture (de
Campo et al., 2004), which forms reverse isotropic micellar solution (L 2 ),
lamellar (L α ), inverted - type hexagonal (H 2 ), and cubic (V 2 ) liquid crystalline
phases within a feasible experimental temperature range (i.e., 20-94°C) (Fig.
5.1 ). V 2 is a three-dimensional (3D) bicontinuous phase composed of bilayers
that separate aqueous channel networks, and this phase has an infi nite periodic
minimal surface (IPMS). An MLO-water system has two types of bicontinu-
ous cubic phases depending on the water content, that is, the cubic assemblies
with the Ia3d (the gyroid type, C G ) and the Pn3m (the diamond type, C D )
symmetries. The H 2 consists of hydrophilic cylinders in a continuous nonpolar
matrix composed of the MLO hydrocarbon tails.
Recent studies (de Campo et al., 2004; Guillot et al., 2006; Moitzi et al., 2007;
Sagalowicz et al., 2006; Salonen et al., 2007; Yaghmur and Glatter, 2009;
Yaghmur et al., 2005, 2006a,b) have been focused on the formation and char-
acterization of various emulsions in which the droplets consisted of well-
defi ned nanostructures. This required an exchange of either the kinetically
stabilized oil droplets in normal oil-in-water (O/W) emulsions or the internal