Interdigitated phases

Several other examples of drug-membrane interactions have been reported. Using X-ray diffraction techniques, interactions with tetracyclines [75], pindolol [76], and chlorpromazine [77, 78] have been described. In these studies, it was shown that in the presence of chlorpromazine the bilayer thickness or lipid head group separation in DPPC liposomes is only 30 A, which is about 20 A smaller than two fully extended DPPC molecules. Chlorpromazine produced an interdigitated phase, which is in agreement with the observed effect of chlorpromazine on the shape of erythrocytes. 

Siminovitch et al., 1987). By comparing DPPC dispersed in water (which does not exist in an interdigitated phase) and DPPC dispersed in perdeuterated glycerol (which was known to be in an interdigitated phase at low temperature), Levin and collaborators showed that the interdigitated phase can be monitored by studying the Raman intensity ratios 1(2850)/I(2880) and I(2932)/f(2880) (Levin et al., 1985). 

Concerning IR spectroscopy, it was demonstrated by high-pressure FTIR that the spectra of the non-interdigitated and those of the interdigitated phase exhibit marked differences in terms of splitting of the methylene scissoring band ()CH2 around 1468 cm and its correlation field component CH2. 

FIGURE 8.6 Schematic drawing of the structure of an ordered bulk heterojunction, showing two interdigitated phases sandwiched between the two electrodes. 

ID ordered lamellar phases are known as gel states, and occur when phospholipids are arranged into bilayers that then stack into a multilayer with each bilayer separated by water. The fatty acid alkyl side-chains are stiff and extended, as in the 3D and 2D lamellar crystal phases, but may undergo hindered rotations about their chain axes. There are a number of types of ID ordered lamellar phases depending upon the tilt angle 0 these are (0 = 0), (0 > 0) and an interdigitated phase L i (0 = 0) where fatty acid alkyl side-chains from different monolayers overlap with each other (Figure 1.91). One other ID ordered lamellar phase, Lg, is known, in which the fatty acid alkyl side-chains cease to be linear but adopt a helical conformation. 

Electroformed GUVs have proved to be a unique system for visualizing the effects of lipid membrane phase transitions on a dosed single bilayer. In addition, DMPC GUVs have been used in studies of interdigitated phase formation, induced by ethanol and temperature variations [22]. 

Figure 7. Interdigitated phases fonned by phosphatidylcholines with two chains of unequal length or by pliosphatidylcholines with ether linkages [14-16).

Detailed x-ray diffraction studies on polar liquid crystals have demonstrated tire existence of multiple smectic A and smectic C phases [M, 15 and 16]. The first evidence for a smectic A-smectic A phase transition was provided by tire optical microscopy observations of Sigaud etal [17] on binary mixtures of two smectogens. Different stmctures exist due to tire competing effects of dipolar interactions (which can lead to alternating head-tail or interdigitated stmctures) and steric effects (which lead to a layer period equal to tire molecular lengtli). These... 

Fig. 7. Different types of interphases. (a) Contact interphases, as produced for example by transcrystalline growth or enhanced adlayer crosslinking in the adhesive phase, (b) Diffusion interphases, as produced by interdigitation or interdiffusion of chains from either or both phases.

OS 41a] [R 19] ]P 30] A study was undertaken to compare extended (1 h) processing in small vials (2 cm ) with short-time (100 s) continuous micro reactor and mini-batch (10 cm ) operation for 10 different substrates (C4-C8 alcohols) which were reacted with rhodium(I)-tris(m-sulfophenyl)phosphane [111]. The vials were either directly filled with the two phases yielding a bilayered fluid system with small specific interfaces or by interdigital micro mixer action yielding an emulsion with large specific interfaces. 

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