Phase bilayer structure

Poly-a-chloroacrylatcs do not exhibit Sc phases, only Sax phases. "Bilayer structures (Sai) are observed at shoit spacers (n 2). Despite their phases, the polymers 3a-3d could not be proved to be ferroelectric. No spontaneous polarization could be measured because of misalignment in the samples [14]. 

Similarly, N-allcylammonium [28] and alkylphosphonium [29] salts form lamellar phases with smectic bilayer structures. In both cases. X-ray scattering also showed the isotropic liquid not to be completely disordered and still displaying similar features to the mesophase. Buscio et al. [28] showed that in N-allcylammonium chlorides the feature was not only much broader than that observed in the mesophase but increased in width with decreasing chain length. 

We note that the bilayer smectic phase which may be formed in main-chain polymers with two odd numbered spacers of different length (Fig. 7), should also be polar even in an achiral system [68]. This bilayer structure belongs to the same polar symmetry group mm2 as the chevron structure depicted in Fig. 17b, and macroscopic polarization might exist in the tilt direction of molecules in the layer. From this point of view, the formation of two-dimensional structure of the type shown in Fig. 7, where the polarization directions in neighbouring areas have opposite signs, is a unique example of a two dimensional antiferroelectric structure. 

Upon the spontaneous rearrangement of anhydrous phospholipids in the presence of water into a hydrated bilayer structure, a portion of the aqueous phase is entrapped within a continuous, closed bilayer structure. By this process water-soluble compounds are passively entrapped in liposomes. The efficiency of encapsulation varies and depends, for example, on the method of preparation of liposomes and the phospholipid concentration during preparation. Different parameters can be used to describe the encapsulation efficiency ... 

The multilamellar bilayer structures that form spontaneously on adding water to solid- or liquid-phase phospholipids can be dispersed to form vesicular structures called liposomes. These are often employed in studies of bilayer properties and may be combined with membrane proteins to reconstitute functional membrane systems. A valuable technique for studying the properties of proteins inserted into bilayers employs a single bilayer lamella, also termed a black lipid membrane, formed across a small aperture in a thin partition between two aqueous compartments. Because pristine lipid bilayers have very low ion conductivities, the modifications of ion-conducting... 

A simple consideration of the synclinic banana phases in the context of the prior discovery of the Soto Bustamante-Blinov achiral antiferroelectric bilayer is illuminating. In Figure 8.28, the achiral antiferroelectric SmAPA bilayer structure is illustrated on the left. The layers are horizontal and normal to the plane of the page, and the tilt plane is vertical and normal to the plane... 

Qualitatively, the bilayer structures that result from DPD simulations are reasonable [65], In the simulation box, it is possible to find a stable bilayer in which the head groups shield the apolar core from the water phase. This means that the model effectively features a start-and-stop mechanism for... 

At the most fundamental level, monolayers of surfactants at an air-liquid interface serve as model systems to examine condensed matter phenomena. As we see briefly in Section 7.4, a rich variety of phases and structures occurs in such films, and phenomena such as nucleation, dendritic growth, and crystallization can be studied by a number of methods. Moreover, monolayers and bilayers of lipids can be used to model biological membranes and to produce vesicles and liposomes for potential applications in artificial blood substitutes and drug delivery systems (see, for example, Vignette 1.3 on liposomes in Chapter 1). 

Although the lipid bilayer structure is quite stable, its individual phospholipid and sterol molecules have some freedom of motion (Fig. 11-15). The structure and flexibility of the lipid bilayer depend on temperature and on the kinds of lipids present. At relatively low temperatures, the lipids in a bilayer form a semisolid gel phase, in which all types of motion of individual lipid molecules are strongly constrained the bilayer is paracrystalline (Fig. ll-15a). At relatively high temperatures, individual hydrocarbon chains of fatty acids are in constant motion produced by rotation about the carbon-carbon bonds of the long acyl side chains. In this liquid-disordered state, or fluid state (Fig. 11—15b), the interior of the bilayer is more fluid than solid and the bilayer is like a sea of constantly moving lipid. At intermediate temperatures, the lipids exist in a liquid-ordered state there is less thermal motion in the acyl chains of the lipid bilayer, but lateral movement in the plane of the bilayer still takes place. These differences in bilayer state are easily observed in liposomes composed of a single lipid,... 

Phospholipid(s) 379, 380,382 - 387, 392. See also Specific substances bilayer diagram 391 head groups, functions of 396 inverted hexagonal phase 397 31P NMR 397 non-bilayer structures 397 Phosphomannomutase 654 Phosphomutases 526 Phosphonamidate 626s... 

In addition to the properties of micelles described above, vesicles, which are bilayer structures and can be considered to be model membranes, separate two distinct aqueous phases an entrapped or inner water pool and the bulk aqueous phase. In principle, therefore, electron transfer may be possible across the bilayer and the sites of hydrogen and oxygen production in a water splitting system can be separated spatially. 

The existence of a forbidden water layer thickness range, which seems to be a general phenomenon with these gel phases, might be relevant to cell adhesion and equilibrium distances at cell contact. The gel represents one type of lipid bilayer structure that occurs in membranes (see below), and, because of the dominance of neutral lipid molecules, the... 

End-to end dimers of 210 incorporating a fluorinated spacer segment (compound 211) form only a nematic and two different types of SmA phases, one with bilayer structure, the other an interdigitated one. This phase transition was attributed to a change of the molecular conformation from folded (bent), stabilized by segregation of the RF-segments (SmA(HT)), to linear, favored by reduced conformational mobility and steric effects (SmA(LT)) [368]. 

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