Micellar flexibility

Other approaches can be used to form polymetallic assemblies under thermodynamic control. One of the simplest is to exploit micellar structures that encapsulate lanthanide ions. For instance, during our early studies on lanthanide emission in the NIR, we used reverse micelles derived from sodium bis(2-ethylhexyl) sulpho-succinate to control the solvation of lanthanide ions [37]. While this approach gives great flexibility, micellar assembhes tend not to be well defined, meaning that a range of species exist in solution at any time. 

The approach we have developped in this study could be applied to other systems in which the hydrocarbon chains are known to be very flexible (micellar systems, for instance). Further works are needed in particular to developp new theoretical models and new experiments on crystalline models of bilayers would be of first importance. 

It has also been pointed out that percolation is hindered by molecules stiffening the micellar interface, such as cholesterol, whereas it is favored by molecules that make the interface more flexible, such as gramicidin and acrylamide [263]. 

Capillary zone electrophoresis (CZE) is the most common electrophoretic separation technique due to its simplicity of operation and its flexibility. It is the standard mode for drug analysis, identification of impurities, and pharmacokinetic studies. Other separation modes, such as capillary isotachopho-resis (CITP), micellar electrokinetc chromatography (MEKC), capillary electrochromatography (CEC), capillary gel electrophoresis (CGE), capillary isoelectric focusing, and affinity capillary electrophoresis (ACE), have then-advantages in solving specific separation problems, since the separation mechanism of each mode is different. 

Addition of Kryptofix 222 and Kronenether to reverse micellar system induces no changes in the droplet size and an increase in the droplet-droplet interactions. The complexation of cations Na of AOT led to a decrease in counterion binding, and consequently repulsive interactions between polar head groups of AOT surfactant are increasing. This could induce a more flexible interface of reverse micelles. 

The highly flexible nature of the micellar reaction cavities has been... 

Bilayers are preferentially formed for Ns = 0.5...1. Lipids that form bilayers cannot pack into micellar or cylindrical structures because of their small head group area and because their alkyl chains are too bulky to fit into a micelle. For bilayer-forming lipids this requires that for the same head group area a a, and chain length Lc, the alkyl chains must have twice the volume. For this reason lipids with two alkyl chains are likely to form bilayers. Examples are double-chained phospholipids such as phophatidyl choline or phophatidyl ethanolamine. Lipids with surfactant parameters slightly below 1 tend to form flexible bilayers or vesicles. Lipids with Ns = 1 form real planar bilayers. At high lipid concentration this leads to a so-called lamellar phase. A lamellar phase consist of stacks of roughly parallel planar bilayers. In some cases more complex, bicontinuous structures are also formed. As indicated by the name, bicontinuous structures consist of two continuous phases. 

R. Nagarajan, Are large micelles rigid or flexible a reinterpretation of viscosity data for micellar solutions, J. Colloid Interface Sci. 90 (1982) 477-486. 

Fully saturated alkyl chains are extremely flexible, with a difference in energy between a trans C-C bond and gauche+ or gauche states of only = 0.8 kT at room temperature. Therefore, the methylene chain of a typical surfactant (e.g. SDS) can exist in a large number of low energy conformations in a micellar aggregate. 

Most systems examined to date have employed the AOT anionic reversed micellar system (366-370). In one case, amylase was extracted using trioctylmethylammonium chloride (cationic surfactant) in isooctane (375) while in another, catalase was extracted using a cationic DTAB/octane/hexanol reversed micelle (377). In our own research, we have successfully employed nonionic Igepal CO-530 -CCl, cationic CTAB - hexanol, and zwitterionic lecithin - CC1, reversed micellar systems in the extraction of some amino acids and proteins (379). The availability of such a pool of different charge-type micellar systems allows one flexibility in the development of such extraction schemes. In fact, preliminary results seem to indicate that better extractions are obtainable in some instances via use of zwitterionic reversed micellar media (379). 

The separation of anions by the use of a cationic micellar mobile phase results in a high degree of flexibility not available from other methods of ion chromatography. The importance of micelles in the mobile phase lies in their ability to participate in the partitioning mechanism. The three equilibria involved in micellar chromatography are schematically represented in Figure 1. The elution behaviour of the anionic solute depends on three partition coefficients K p, the partition coefficient between the bulk mobile phase and and the micelle K nn the partition coefficient between the bonded phase and the micelle and K mpi the partition coefficient between the bonded phase and the bulk mobile phase. 

A common industrial practice used to avoid oscOlations is to seed the first reactor with small-diameter seed particles produced earber in batch reactors. By then keeping the emulsifier concentration below the CMC one avoids further micellar generation and simply grows the seed particles. Although in some cases this may introduce additional flexibility in that a... 

As remarked earlier, the nonlinear viscoelastic behavior of entangled wormy micellar solutions is similar to that of entangled flexible polymer molecules. Cates and coworkers (Cates 1990 Spenley et al. 1993, 1996) derived a full constitutive equation for entangled wormy micellar solutions, based on suitably modified reptation ideas. The stress tensor obtained from this theory is (Spenley et al. 1993)... 

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