Cubic inverted structure

Lyotropic lamellar (La) liquid crystals (LC), in a form of vesicle or planar membrane, are important for membrane research to elucidate both functional and structural aspects of membrane proteins. Membrane proteins so far investigated are receptors, substrate carriers, energy-transducting proteins, channels, and ion-motivated ATPases [1-11], The L liquid crystals have also been proved useful in the two-dimensional crystallization of membrane proteins[12, 13], in the fabrication of protein micro-arrays[14], and biomolecular devices[15]. Usefulness of an inverted cubic LC in the three-dimensional crystallization of membrane proteins has also been recognized[16]. 

There are two types of spinel, normal and inverted. Normal spinels have all the A ions in tetrahedral sites and all B ions in octahedral coordination. When the structures are inverted, the divalent A ions and half of the trivalent B ions are in the octahedral sites while the remaining B ions have tetrahedral coordination. Both normal and inverted spinels have the same cubic structure (space group Fd3m). 

Mercury selenide is a zero-gap material (semimetal). The lowest conduction band minimum and the top of the valence band are degenerate at the center of the Brillouin zone (Fg). The F level, which for most cubic semiconductors is the conduction band minimum and has an energy larger than that of the Fg state, is found to be below the Fg state in HgSe ( negativ energy gap , inverted band structure). 

Lyotropic liquid crystaDine phases are formed in concentrated mixtures of amphiphilic molecules and water. The common and well-studied lyotropic liquid crystalline phases are lamellar (La), hexagonal (normal. Hi or inverted H2) and normal or inverted cubic (bicontinuous or micellar) structures. 

FIG. 7 Structures of various liquid-crystalline phases of membrane lipids. (A) Normal hexagonal phase (Hi) (B) lamellar phase (C) inverted hexagonal phase (Hu). Cubic phases consisting of (D) spherical, (E) rod-shaped, and (F) lamellar units. The hydrocarbon regions are shaded and the hydrophilic regions are white. (Reprinted by permission from Ref. 11, copyright 1984, Kluwer Academic Publishers.)... 

In the Hn phase and in the inverted micellar cubic phase, the water associated with the polar headgroups is trapped inside a ring structure and is not in rapid exchange with bulk water [18]. In a bicontinuous cubic phase, however, there is a continuous network of aqueous channels. 

Cyclic carbohydrates with two alkyl chains (e.g. 1,2-dialkyl (or 1,2-diacyl) glycerol 8 a (sug=Glcp, Galp) present structural similarities with glycerophospho-lipids. They form complex mesophases such as bicontinuous cubic phases, inverted hexagonal phases or myelin figures [58-61]. Other dialkyl derivatives... 

In tetrahedral and cubic symmetry, the crystal-field levels are inverted, giving a single orbital state lowest. For dl in an octahedral field, the 4F state also has the single orbital state lowest, so we would expect the d1 configuration in a tetrahedral or cubic field to behave in a similar fashion and fit the spin Hamiltonian given in Eq. (158) solved for S=f. For most of the examples listed in Table XV, the tetrahedral symmetry is not distorted so that D = E=0 and no fine structure is reported. The 5=f character of the spin state is revealed in these cases by the fact that Eq. (80) must be added to the spin Hamiltonian to explain the ESR results on d1 in tetrahedral and cubic fields (131). For Co2+ in Cs3CoCl5, D= —4.5 cm-1 (222) and in CdS, D > 2 cm-1 (223). 

Argentite is probably die most important primary silver mineral. However, it maintains its cubic (isometric) characteristic only above 179 C (354°F). Upon cooling, the inward structure inverts to a noil-isometric form, usually orthorhombic, yet retaining its original outward form. It is, therefore, a paramorph after argentite, known as acanthite. 

This behavior of the DPoPE/cationic PC mixtures is not surprising, because both the double bonds and hydrocarbon chain length variations are known to have considerable effect on the lamellar-to-nonlamellar transitions in lipids [113]. A specific structural characteristic of lipid arrays that exhibits distinct change around the chain length of 14 carbons is the formation of inverted bicontinuous cubic phases Qn. The latter phases tend to form in diacyl or dialkyl phospholipids... 

Micellar solutions are isotropic microstructured fluids which form under certain conditions. At other conditions, liquid crystals periodic in at least one dimension can form. The lamellar liquid crystal phase consists of periodically stacked bilayers (a pair of opposed monolayers). The sheetlike surfactant structures can curl into long rods (closing on either the head or tail side) with parallel axes arrayed in a periodic hexagonal or rectangular spacing to form a hexagonal or a rectangular liquid crystal. Spherical micelles or inverted micelles whose centers are periodically distributed on a lattice of cubic symmetry form a cubic liquid crystal. 

Figure 11.10. Structure of dispersed self-assembly particles. The original cryo-TEM image is shown at the top with schematic representation of the structure below the images. Particles shown are (a) micelles, (b) vesicle, (c) inverted bicontinuous cubic and (d) reverted hexagonal phase particle. Adapted from Sagalowicz et al. 2006a.

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