Reversed cubic phase

Figure 4.9 The phase diagram of the CMO/ ethanol/water ternary system at 25°C. The phase boundaries of the one-phase regions are drawn with solid lines. The phases indicated are lamellar phase (U), bicontinuous reverse cubic phase (V), and three isotropic phases miceiiar isotropic phase (L), sponge phase (L3), and the new Ql phase. The marked sampies A-H contain constant 10 wt% ethanoi and they iie in a...

Uddin, M.H., Rodriguez, C., Watanabe, K., Lopez-Quintela, A., Kato, T., Furukawa, H., Harashima, A., and Kunieda, H. (2001) Phase Behavior and formation of reverse-cubic-phase-based emulsion in water/poly(oxyethylene) poly (dimethylsiloxane) surfactants/ silicone oil systems. Langmuir, 17, 5169-5175. 

Phases built up of discrete aggregates include the normal and reversed micellar solutions, micellar-type microemulsions, and certain (micellar-type) normal and reversed cubic phases. However, discrete self-assemblies are also important in other contexts. Adsorbed surfactant layers at solid or liquid surfaces may involve micellar-type structures and the same applies to mixed polymer-surfactant solutions. 

IPMS has also been a useful tool in the description of the structure of bicontinuous reversed cubic phases of lipids (7). The symmetries of bicon-tinuous cubic phases are classified by their space group, which is determined by X-ray diffraction. Three different symmetries, of interest here, are known for bicontinuous cubic membrane lipids namely., laSd, Pn3m and ImSm. 

Due to the similarities between the structure of the PLB and the bicontinuous reversed cubic phases PLB has been suggested to be of a cubic structure. This hypothesis is supported by the Bndings that the PLB lipid... 

La, lamellar phase Hn, reversed hexagonal phase l2, bicontinuous reversed cubic phase. 

The phase relationship between the most commonly known tetragonal phase CaC2-I and phase(s) II (or III) is still in question. CaC2-I transforms reversibly into the cubic phase IV, as does the phase (II -r) III. It is interesting to note that the cubic phase IV seems to have a memory for its respective precursor phase (III or I) that is regained after cooling down phase IV. The synthesis of... 

Bicontinuous cubic phase Lamellar phase Bicontinuous cubic phase Reverse hexagonal columnar phase Inverse cubic phase (inverse micellar phase)... 

We are approaching the final part of the book, concerned with cellular models based on vesicles. The main keywords are now compartment and (if this word exists) compartmentation. The biological potential of these aggregates is closely related to their physical properties, and for this reason some of these basic characteristics will first be briefly considered. Also, to give a proper background to these properties, it may be useful to compare various kinds of compartments, such as micelles, reverse micelles, cubic phases, and vesicles. This will be useful to understand better biochemical reactions in vesicles, which will be dealt with in the next chapter. 

Depending on temperature, transitions between distinct types of LC phases can occur.3 All transitions between various liquid crystal phases with 0D, ID, or 2D periodicity (nematic, smectic, and columnar phases) and between these liquid crystal phases and the isotropic liquid state are reversible with nearly no hysteresis. However, due to the kinetic nature of crystallization, strong hysteresis can occur for the transition to solid crystalline phases (overcooling), which allows liquid crystal phases to be observed below the melting point, and these phases are termed monotropic (monotropic phases are shown in parenthesis). Some overcooling could also be found for mesophases with 3D order, namely cubic phases. The order-disorder transition from the liquid crystalline phases to the isotropic liquid state (assigned as clearing temperature) is used as a measure of the stability of the LC phase considered.4... 

FIGURE 4.2 Schematic illustration of 2 x 2 x 2 unit cells of a lipid/water phase with gyroid cubic symmetry. In reversed bicontinuous cubic phases the lipid bilayer membrane separates two intertwined water-filled subvolumes resembling 3D arrays of interconnected tunnels. Black box (right) represents an enlargement of a part of the folded liquid crystalline lipid bilayer membrane structure. 

The lipidic cubic phase has recently been demonstrated as a new system in which to crystallize membrane proteins [143, 144], and several examples [143, 145, 146] have been reported. The molecular mechanism for such crystallization is not yet clear, but the interfacial water and transport are believed to play an important role in nucleation and crystal growth [146, 147], Using a related model system of reverse micelles, drastic differences in water behavior were observed both experimentally [112, 127, 128, 133-135] and theoretically [117, 148, 149]. In contrast to the ultrafast motions of bulk water that occurs in less than several picoseconds, significantly slower water dynamics were observed in hundreds of picoseconds, which indicates a well-ordered water structure in these confinements. 

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