Cmc = critical micellar concentration

Monomer/Micelle Equilibrium Mixtures of surfactants, like any surfactant species in an aqueous solution, give rise to monomer or micelle aggregates provided that the concentration reaches a minimum value, called the critical micellar concentration (CMC). The micelles thus formed are mixed, i.e. made up of the different surfactant species in solution. 

In order to separate neutral compounds, Terabe et al. [13] added surfactants to the buffer electrolyte. Above their critical micellar concentration (cmc), these surfactants form micelles in the aqueous solution of the buffer electrolyte. The technique is then called Micellar electrokinetic capillary chromatography, abbreviated as MECC or MEKC. Micelles are dynamic structures consisting of aggregates of surfactant molecules. They are highly hydrophobic in their inner structure and hydrophilic at the outer part. The micelles are usually... 

The levels of PAF synthesis and release are also modulated by levels of extracellular albumin. In the absence of albumin, neutrophils (stimulated with fMet-Leu-Phe) synthesise only low levels of PAF within 1-2 min of stimulation. In the presence of 0.25% albumin, PAF synthesis is increased, and up to half of this may be released with 5% albumin, rates of synthesis and release are increased further and sustained over a 30-min period. Newly-synthesised PAF is reincorporated by neutrophils into membrane lipids and is therefore poorly soluble in aqueous media. Thus, extracellularly added albumin will bind to cell-associated PAF and effectively solubilise it at concentrations below its critical micellar concentration (CMC). This will effectively enhance the PAF release rate, which will decrease the concentration of cell-associated PAF thus, the rate of biosynthesis will be sustained. 

AP has been used to probe micellar media (Saroja et al., 1998). The probe is located at the micellar interface and is well suited to monitoring micellar aggregation. In fact, the sharp change in the fluorescence intensity versus surfactant concentration allows the critical micellar concentration (CMC) to be determined. Excellent agreement with the literature values was found for anionic, cationic and nonionic surfactants. The electroneutrality of 4-AP and its small size are distinct advantages over ionic probes like ANS or TNS. 

Micelles tend to aggregate, and there are many ways to measure their concentration, including surface tension measurements. The midpoint of the concentration range over which micellar aggregation occurs is called the critical micellar concentration (CMC). Below the CMC, added bile-salt molecules dissolve in the form of monomers above the CMC, added bile-salt molecules form micelles, leaving the monomeric concentration essentially constant. The pH at which CMC formation occurs is called the critical micellar pH, (CMpH). Table 1.1 lists values for some of the bile acids mentioned in this review. 

The presence of a fluoroalkyl chain renders the molecule more hydrophobic and enhances its amphiphilic character by lowering the superficial pressure and the critical micellar concentration (CMC) (Figure 6.49). On the other hand, these chains do not cause any specific toxicity, and the hemostatic activity is often lowered. 

With short chain derivatives, the forces of repulsion are higher than the ones of attraction the curvature is high and spherical micelles are formed at a concentration called the critical micellar concentration (cmc). This concentration can be detected by a change in the physico-chemical properties of the solution (e.g. surface tension, Fig. 3 a). Above a characteristic temperature (referred as Krafft temperature), the tensio-active molecules are infinitely soluble in the form of micelles (Fig. 3 b). 

Most of the studies on thermodynamics of mixed micellar systems are based on the variation of the critical micellar concentration (CMC) with the relative concentration of both components of the mixed micelles (1-4). Through this approach It Is possible to obtain the free energies of formation of mixed micelles. However, at best, the sign and magnitude of the enthalpies and entropies can be obtained from the temperature dependences of the CMC. An Investigation of the thermodynamic properties of transfer of one surfactant from water to a solution of another surfactant offers a promising alternative approach ( ), and, recently, mathematical models have been developed to Interpret such properties (6-9). 

Surfactants having a positive curvature, above a given concentration usually called the critical micellar concentration, cmc, self-assemble to form oil-in-water aggregates called normal micelles. The surfactant most often used is sodium dodecyl sulfate, Na(DS) or SDS. To make particles, the counterion of the surfactant is replaced by ions which participate in the chemical reaction. These are called functionalized surfactants. 

Micelles and vesicles can be formed above a certain concentration. For instance, small micelles are formed above critical micellar concentration, cmc. (The latter abbreviation is often used for critical vesicle concentration, too. However, sometimes a more general term critical aggregate concentration, cac is also applied.) Bilayers of specific amphiphiles with two tails are typical of the central part of cell membranes discussed in some detail in the next chapter. Studying artificial mono- and bilayers (uniform or with built in pores) is indispensable for gaining information about the structure and functioning of cell membranes involving the transport through them. 

The initial concentration, C0, in square centimeters, was determined directly from the area under the curve of a synthetic boundary trace. Although usual practice is to place solvent in one cell and the solution in the other, the solvent used in this work was a solution of bile salt slightly above its critical micellar concentration, CMC (15), usually 0.5 gram per 100 ml. The solution, which was placed in the other cell, was a more concentrated solution (1.5 to 5.0 grams per 100 ml.). Therefore, since both the solvent and the solution were saturated with monomers, C0 represents an initial concentration difference of bile salts in the micellar phase. The pertinent data for each equilibrium ultracentrifugation experiment are presented in Table I. 

Plots of surface tension versus concentration for n-pentanol [49], LiCl (based on Ref. [50]), and SDS in an aqueous medium at room temperature are shown in Fig. 3.7. The three curves are typical for three different types of adsorption. The SDS adsorption isotherm is typical for amphiphilic substances. In many cases, above a certain critical concentration defined aggregates called micelles are formed (see Section 12.1). This concentration is called the critical micellar concentration (CMC). In the case of SDS at 25°C this is at 8.9 mM. Above the CMC the surface tension does not change significantly any further because any added substance goes into micelles not to the liquid-gas interface. 

A temperature-composition phase diagram for a surfactant solution is a characteristic phase diagrarr that delineates the conditions under which crystalline surfactant, monomers, or micelles will exist. On the phase diagram shown in Figure 12.5 (Smirnova, 1995), L represents the liquid phase, S the solid phase, and )(the surfactant mole fraction. The critical micellar temperature, CMT, is deLned as the line between the crystalline and micellar phases. Micelle formation occurs at temperatures greater than the CMT. The critical micellar concentration, CMC, line separates the micellar and... 

Amphiphilic molecules (surfactants) can assemble into nanoscopic supramolecular structures with a hydrophobic core and a hydrophilic shell micellar arrangement. As surfactant concentration is increased in aqueous solutions, the separated molecules aggregate into micelles upon reaching a concentration interval known as the critical micellar concentration (CMC). 

Critical Micellar Concentration (cmc) and Area per Molecule (o) at the Dodecane/Aqueous Phase Interface for Different Extractants and Salinities... 

Critical micellar concentrations (CMCs) of sucrose fatty acid esters have been determined by various methods, for mixtures and for pure derivatives (Table III).95,126,390 395 Studies on the lyotropic properties of sucrose... 

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