Crystal structures micellar

Typically, micelles tend to be approximately spherical over a fairly wide range of concentration above the c.m.c., but often there are marked transitions to larger, non-spherical liquid-crystal structures at high concentrations. Systems containing spherical micelles tend to have low viscosities, whereas liquid-crystal phases tend to have high viscosities. The free energies of transition between micellar phases tend to be small and, consequently, the phase diagrams for these systems tend to be quite complicated and sensitive to additives. 

In Sections II and III, the crystal structure of rhodopsin is briefly reviewed and compared with the dynamic structure in micellar solutions and membranes as inferred from the biophysical methods mentioned above. A structural model of the cytoplasmic surface derived from solution NMR of peptides has been presented (Ifeagle et al., 1997 Katagadda et al., 2001), but this approach does not provide direct information on... 

Collectively, all of the data obtained on the solution structure with SDSL, sulfhydryl reactivity, and disulfide cross-linking kinetics strongly support the conclusion that the structure of the TM7-H8 sequence investigated is very similar in the crystal and micellar solution state. In solution, the H8 helix is sandwiched between the hydrophobic/aqueous interface on one side and residues 325-328 of the C-terminal tail on the other. 

Lipid cubic (51) and sponge (52) phases, as well as bicelles (53), are alternatives to detergents that have been applied successfully to membrane protein crystallization. In these instances, the protein is embedded in a lipid bilayer environment, which is considered more natural compared with the detergents that form micellar phases. In the recent high-resolution crystal structure of the human 32 adrenergic G-protein-coupled receptor, lipid cubic phase was used with necessary cholesterol and 1,4-butandiol additives (54). The cholesterol and lipid molecules were important in facilitating protein-protein contacts in the crystal. 

Chapter five introduces highly organized, quasi one-dimensional crystals, namely micellar rod and vesicular tubular fibres. They are compared to equally fascinating liquid threads found in viscoelastic gels and to phospholipid tubules. These membraneous assemblies build a bridge to the secondary structures of... 

Ionic surfactants with two long (six or more carbons) alkyl chains have high VH values relative to lc, and probably do not form spherical micelles. They have values of n that increase with surfactant concentration, the increase becoming more pronounced with increase in the length of the chains. Some of these micellar solutions are in equilibrium with lamellar liquid crystal structures (Lianos, 1983). 

The lyotropic liquid crystals have been studied as a separate category of liquid crystals since they are mostly composed of amphiphilic molecules and water. The lyotropic liquid-crystal structures exhibit the characteristic phase sequence from normal micellar cubic (IJ to normal hexagonal (Hi), normal bicontinuous cubic (Vi), lamellar (1 ), reverse bicontinuous cubic (V2), reverse hexagonal (H2), and reverse micellar cubic (I2). These phase transitions can occur, for instance, when increasing the apolar volume fraction [9], or decreasing the polar volume fraction of the amphiphilic molecule, for example, poly(oxyethylene) chain length in nonionic poly(oxyethylene) alkyl (oleyl) or cholesteryl ether-based systems (10, 11). 

Methanogenic bacteria, 158 Methanoic acid, 1,351 Methanolysis, 477, 478 Methods, lUPAC, 249 Methoxystearic acids, 467 Methyl esters, physical properties, 349,350, 351, 353,477 Methyl glucosides, 280 Methyl group, van der Waals radius, 346 a-Methylene group, 484 Methyloctadecanoic acids, crystal structures, 15, 347, 348 Methylsterols in fats, 105 Metridiidae, 147 Micellar solutions, 357 Micrococcus lysodeikticus, 35, 46, 47 Microemulsions, 329-32 Migratory grasshopper, 145 Milk fat, 23,51, 60,113-18,167-69,397, 556-57... 

This chapter presents recent papers (June 2004-May 2005) that focus on the N.M.R. techniques used to elucidate micro structural features and dynamics of self-assembled systems. As reported in the analogous chapter of last year/ here the relevant concepts and acronyms related to liquid crystals and micellar solutions will be briefly revised. 

Some authors [348,349] suggested that a possible explanation of the phenomenon can be the formation of a surfactant lamella liquid-crystal structure inside the film. Such lamellar micelles are observed to form in surfactant solutions, however, at concentrations much higher than those used in the experiments with stratifying films. The latter fact makes the explanation with a lamella liquid crystal problematic. Nikolov et al. [280,350,351] observed stratification not only with micellar surfactant solutions but also with suspensions of latex particles of micellar size. The stepwise changes in the film thickness were approximately equal to the diameter of the spherical particles contained in the foam film [280—282,352]. The experimental observations show that stratification is always observed. 

Mixed micellar solutions of enantiomeric ABA or BAB block copolymers exhibited very different gelation behavior and crystal structure. As the third system, the micellar solutions of AB block copolymers, PLLA-PEG and PDLAPEG, were examined for the hydrogel formation. The AB system is similar to ABA in that the B-blocks form the corona shape in micelles as illustrated in Figure 1, while having a similarity with BAB because the mobility of the core A-blocks is similar to each other. 

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