Micelles micellar properties

Micellization is a second-order or continuous type phase transition. Therefore, one observes continuous changes over the course of micelle fonnation. Many experimental teclmiques are particularly well suited for examining properties of micelles and micellar solutions. Important micellar properties include micelle size and aggregation number, self-diffusion coefficient, molecular packing of surfactant in the micelle, extent of surfactant ionization and counterion binding affinity, micelle collision rates, and many others. 

Micellar properties are affected by changes in the environment, eg, temperature, solvents, electrolytes, and solubilized components. These changes include compHcated phase changes, viscosity effects, gel formation, and Hquefication of Hquid crystals. Of the simpler changes, high concentrations of water-soluble alcohols in aqueous solution often dissolve micelles and in nonaqueous solvents addition of water frequendy causes a sharp increase in micellar size. 

Van Paassen [57] describes the CMC of some polyether carboxylates with different fatty chains and EO degrees (Fig. 2). In an extensive study, Binana-Limbele et al. [59] investigated the micellar properties of the alkylpolyether carboxylates of the general formula CnH + OCF CH OCI COONa with n = 8, x = 5, and n = 12 and x = 5,1, and 9, by means of electrical conductivity (CMC, apparent micellar ionization degree) and time-resolved fluorescence probing (micelle aggregation number A7) as a function of temperature and surfactant concentration (Table 1). 

Molecules that possess both hydrophilic and hydrophobic structures may associate in aqueous media to form dynamic aggregates, commonly known as micelles. The properties of micellar structures have been discussed in great detail [66-69], but thejr main pharmaceutical application lies in their ability to provide enhanced solubility to compounds lacking sufficient aqueous solubility [70], The ability of a micelle to solubilize compounds of limited aqueous solubility can be understood from consideration of the schematic drawing of Fig. 10a. Above the critical micelle concentration, these molecules orient themselves with the polar ends in interfacing with the aqueous solution and the nonpolar ends at the interior. A hydrophobic core is formed at the interior of the micelle, and hydrophobic solute molecules enter and occupy this region. 

The purpose of this article is to review studies carried out on hemes incorporated inside the micellar cavity, and examine the effect of micellar interaction on the electronic and structural properties of the heme. A comparison of these results with those on the metalloproteins is clearly in order to assess their suitability as models. The article begins with a general introduction to micellar properties, the incorporation of hemes in the micellar cavity, and then discusses results on hemes inside the micelles with different oxidation and spin states, and stereochemistry. The experimental techniques used in the studies on these aqueous detergent micelles are mostly NMR and optical spectroscopy. The present article has therefore a strong emphasis on NMR spectroscopy, since this technique has been used very extensively and purposefully for studies on hemes inside micellar cavities. 

Nagarajan R. Theory of micelle formation quantitative approach to predicting micellar properties from surfactant molecular structure. Surface Sci Ser 1997 70 1-81. 

Mixed surfactant systems are of importance from a fundamental and practical point of view. Therefore, many recent papers have reported on the micellar properties of mixed surfactant solutions. For example, Tokiwa et al. have measured the NMF spectra W Ingram has measured surface tension ( 5). Previously, we have reported the solution properties of anionic-nonlonlc surfactant mixed systems from the point of view of electrical (., 7) and surface tension measurements (8-10), and investigated the mixed micelle formation. 

In a previous publication ( ), results were presented on the micellar properties of binary mixtures of surfactant solutions consisting of alkyldimethylamine oxide (C12 to Cig alkyl chains) and sodium dodecyl sulfate. It was reported that upon mixing, striking alteration in physical properties was observed, most notably in the viscosity, surface tension, and bulk pH values. These changes were attributed to 1) formation of elongated structures, 2) protonation of amine oxide molecules, and 3) adsorption of hydronium ions on the mixed micelle surface. In addition, possible solubilisation of a less soluble 1 1 complex, form between the protonated amine oxide and the long chain sulfate was also considered. 

An early review of micellization in block copolymers was presented by Tuzar and Kratochvfl (1976), and these authors have recently provided an excellent review of the literature up to 1992 (Tuzar and Kratochvfl 1993). Micellar properties of block copolymers were also reviewed by Price (1982). A discussion of micellization was included in the general reviews on block copolymers by Riess et al. (1985) and Brown et al. (1989). Excellent reviews focussed on the solution properties of a particular class of copolymer, i.e. copolymers of polyoxyethylene) with poly(oxypropylene) have been presented by Alexandridis and Hatton (1995) and by Chu (1995) and Chu and Zhou (1996). Micellization and micellar association in related poly(oxyethylene)/poly(oxybutylene) copolymers have been summarized by Booth et al (1997). 

In this present study we report the effect of graded doses of y-irradiation on the properties of the micelles of Pluronic FI27 and on the temperature induced micellar changes which lead to the eventual gelation of these solutions. In view of the batch variability of the micellar properties of poloxamers (3) comparisons have been made with solutions of the same batch which have not been subjected to irradiation. 

Effect of Radiation Dose on Micellar Properties. Figure 1 shows the concentration dependence of the micellar diffusion coefficient at 40° as determined by quasi-elastic light scattering (QELS) for solutions subjected to radiation doses of up to 4.56 Mrad. Limiting diffusion coefficients, D0>were obtained by extrapolation of data for dilute solutions (<0.05%) to zero concentration, the critical micelle concentration (CMC) being negligibly low for this poloxamer ( 1 ). 

Effect of Temperature on Micellar Properties. Figure 5 compares the influence of temperature on the diffusion properties of the micelles in solutions previously irradiated with a dose of 4.56 Mrad with those not subjected to radiation treatment. Hydrated radii calculated from the limiting diffusion coefficients for micelles not treated with radiation remain independent of temperature over the range 25° to 40° (Table III). 

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