Hexagonal Hn phase

Figure 8-12 (A) 31P NMR spectra of different phospholipid phases. Hydrated soya phosphatidylethanolamine adopts the hexagonal Hn phase at 30°C. In the presence of 50 mol% of egg phosphatidylcholine only the bilayer phase is observed. At intermediate (30%) phosphatidylcholine concentrations an isotropic component appears in the spectrum. (B) Inverted micelles proposed to explain "lipidic particles" seen in freeze fracture micrographs of bilayer mixture of phospholipids, e.g., of phosphatidylethanolanine + phosphatidylcholine + cholesterol. From de Kruijft et al.m Courtesy of B. de Kruijft.

INTERACTIONS BETWEEN LAMELLAR AND INVERTED HEXAGONAL Hn PHASE OF CL/DNA COMPLEXES AND ANIONIC GIANT LIPOSOMES MIMICKING THE CELL PLASMA MEMBRANE... 

Fig. 4 Elongation of the R3 phosphate ester chain of the cationic PC results in nonlamellar phase formation. Small-angle X-ray diffraction patterns recorded at 20° C show (a) lamellar La (b) cubic Pn3m (c) inverted hexagonal Hn phases formed by dioleoyl cationic PCs with ethyl, hexyl and octadecyl R3 chains, respectively, diCl8 1 -EPC [19], diC18 l-C6PC [20] and diC18 l-C18PC [21]...

J. M. Seddon, Structure of the inverted hexagonal (Hn) phase and non-lamellar transitions of lipids, Biochim. Biophys. Acta, 1990,1031, 1-69. 

Figure 4.2 Lipid phases, (a) Gel (Lp) lamellar phase, (b) Liquid-crystalline Lj) or fluid lamellar phase, (c) Inverted hexagonal (Hn) phase, (d) Hexagonal phase. [Reproduced from R.B. Gennis (1989) Biomernbranes Molecular Structure and Function. Springer New York, (p. 41), with permission]...

Essentially the same consideration appUes to an inverted bicontinuous cubic phase (Qn) and an inverted hexagonal (Hn) phase, which are usually formed with lipids with long hydrophobic chains. Qn and Hn phases have recently received growing attention in the pharmaceutical or biological fields, for instance, as new carriers for drug-deUvery systems, and matrices for membrane protein crystallization [37-42]. The conventional (e.g., monoolein) Qn phase, however, often transforms into a soUd phase at low temperatures around 4°C [43-47], where temperature-sensitive proteins or actives are most preferably handled and preserved. It has recently been confirmed that isoprenoid-chained lipids can in fact give a range of Qn phases that are stable at low temperatures [13]. 

FIGURE 2.16 Lipid polymorphism of phosphatidylethanolamine inverted micelles and hexagonal Hn phases. Taper lipids such as phosphatidylethanolamine (PE) have a higher propensity to form micellar rather than bilayer structures. In the plasma membrane, PE can induce curvature effects and hexagonal (Hn) phase formation. 

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