Mixed micelles effect

Yoshida K, Dubin PL. Complex formation between polyacrylic acid and cationic/nonionic mixed micelles effect of pH on electrostatic interaction and hydrogen bonding. Colloid Surf A 1999 147 161-167. 

Inspired by the many hydrolytically-active metallo enzymes encountered in nature, extensive studies have been performed on so-called metallo micelles. These investigations usually focus on mixed micelles of a common surfactant together with a special chelating surfactant that exhibits a high affinity for transition-metal ions. These aggregates can have remarkable catalytic effects on the hydrolysis of activated carboxylic acid esters, phosphate esters and amides. In these reactions the exact role of the metal ion is not clear and may vary from one system to another. However, there are strong indications that the major function of the metal ion is the coordination of hydroxide anion in the Stem region of the micelle where it is in the proximity of the micelle-bound substrate. The first report of catalysis of a hydrolysis reaction by me tall omi cell es stems from 1978. In the years that... 

The substituents at C-2, C-3 within diene 97 and those at C-1, C-2 within dienophiles 98-100 are electronically and/or sterically equivalent with respect to diene and dienophile reaction centers, respectively, and therefore cycloaddition should not display regiochemical bias in the absence of orientational effects. The Diels-Alder reactions of 97 prepared in situ with 98-100 gave an excess of 101 (Scheme 4.19) [70b], which are the expected regioisomers if the reagents react in their preferred orientations within a mixed micelle with an ammonium head group at the aggregate-water interface and the remainder in the micelle interior. 

FIGURE 3 Effect of the amount of cholesterol on the particle size. Phosphatidylcholine/cholesterol liposomes were prepared by the octyl glucoside dilution technique. The begin concentration of the mixed micelles was 150 mM octyl glucoside and 10 mM phosphatidylcholine in 10 mM tris(hydroxymethyl)aminomethane and 0.9% NaCl, pH 7.4. Dilution was performed with an automatic titration unit at a dilution rate (= dilution factor, relative to the initial volume, per unit of time) of 0.026 sec"l ( a and ) or 0.69 sec l ( and o). Mean diameters after dilution and ) and after filtration ( L and q) are repi sented. (Adapted from Jiskoot et al, 1986a.)... 

A. (1986a). Preparation of liposomes via detergent removal from mixed micelles by dilution. The effect of bilayer composition and process parameters on liposome characteristics, Pharm. Weekbl. 

Rundlett, K. L. and Armstrong, D. W., Effect of micelles and mixed micelles on efficiency and selectivity of antibiotic-based capillary electrophoretic separations, Anal. Chem., 67, 2088, 1995. 

The absorption of drugs from the rectal [32] cavity has been studied in some detail. Muranishi et al. [34] have shown that a significant increase in the absorption and lymphatic uptake of soluble and colloidal macromolecules can be achieved by pretreating the rectal mucosal membrane with lipid-nonionic surfactant mixed micelles. They found no evidence of serious damage of the mucosal membrane. Davis [30] suggested that the vaginal cavity could be an effective delivery site for certain pharmaceuticals, such as calcitonin, used for the treatment of postmenopausal osteoporosis. 

Mixed Micellization and Desorption Effects on Propagation of Surfactants in Porous Media... 

As suggested above, the main recovery mechanism of surfactants retained in the rock can be interpreted as a micellization phenomenon inside the pores. Upon contact with micelles from the desorbent agent, the adsorbed surfactants are solubilized in the form of mixed micelles. This also explains the effectiveness of the desorbent still observed at low concentration (0.27% in Test 3 in Table in, concentration much higher than the CMC of NP 30 EO equal to 0.016%). 

The critical micellar concentrations of anionic/nonionic surfactant mixtures examined are low in a saline medium, so that, at the concentrations injected in practice, the chromatographic effects resulting from the respective adsorption of monomers are masked. Such surfactants propagate simultaneously in the medium in the form of mixed micelles. 

Sierra, M.B., Morini, M.A., Schulz, P.C., Junquera, E. and Aicart, E. (2007) Effect of double bonds in the formation of sodium dodecanoate and sodiumlO-undecenoate mixed micelles in water. Journal of Physical Chemistry B, 111 (40), 11692-11699. 

Murakami and Kondo (1975) reported that the cationic micelle is quite effective for the pyridoxal-catalyzed elimination of S-phenylcysteine. The significant rate acceleration was explained by the binding of the Schiff s base to the micelle phase, followed by the efficient proton abstraction by hydroxide ion at the micelle surface. According to Gani et al. (1978), mixed micelles of CTAB and dodecylamine hydrochloride are good models for the site accommodating pyridoxal 5 -phosphate in glycogen phosphorylase, since the micelles can imitate well the formation of SchifT s bases in hydrophobic environments. 

Shao Z, Mitra AK (1994) Bile salt-fatty acid mixed micelles as nasal absorption promoters. III. Effects on nasal transport and enzymatic degradation of acyclovir prodrugs. Pharm Res 11 243-250. 

Similar experiments with PEG-phosphatidyl ethanolamine mixed micelles with a core-incorporated amphiphilic " In- or Gd-loaded chelating agent PAP demonstrated fast and efficient gamma and MR visualization of different compartments of the lymphatic system. Upon subcutaneous administration, the micelles penetrate the lymphatics and effect visualization (Figure 6). Micelles mostly stay within the lymph fluid rather than accumulate in the nodal macrophages (because of protective effect of surface PEG fragments) and rapidly move via the lymphatic pathway. 

Among the purposes of this paper is to report the results of calorimetric measurements of the heats of micellar mixing in some nonideal surfactant systems. Here, attention is focused on interactions of alkyl ethoxylate nonionics with alkyl sulfate and alkyl ethoxylate sulfate surfactants. The use of calorimetry as an alternative technique for the determination of the cmc s of mixed surfactant systems is also demonstrated. Besides providing a direct measurement of the effect of the surfactant structure on the heats of micellar mixing, calorimetric results can also be compared with nonideal mixing theory. This allows the appropriateness of the regular solution approximation used in models of mixed micellization to be assessed. 

Calorimetric measurements can be used to obtain heats of mixing between different surfactant components in nonideal mixed micelles and assess the effects of surfactant structure on the thermodynamics of mixed micellization. Calorimetry can also be successfully applied in measuring the erne s of nonideal mixed surfactant systems. The results of such measurements show that alkyl ethoxylate sulfate surfactants exhibit smaller deviations from ideality and interact significantly less strongly with alkyl ethoxylate nonionics than alkyl sulfates. 

It is clear from equation (7) that the addition of a second surfactant results in further decrease in y the essential requirements being a not too small adsorption of the second surfactant. Whether it replaces the first surfactant or is adsorbed in addition to it is immaterial, just as it is not essential for the two surfactants to form a complex. If the two surfactants are of the same type e.g. both water soluble anionic surfactants, they will form mixed micelles and this will lower the activity of the second surfactant added and decrease both its Fand dp. However, if the two surfactants are different in nature, e.g. one predominantly water soluble and the other oil soluble, they will only slightly affect each other s activity and their combined effect on the interfactial tension may be large enough to bring y to zero at finite concentrations. 

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