Micellar medium

It should be noted that charged micelles create medium polarity, which is a very important factor for the ion-radical formation. The reaction of bilirubin with peroxy radicals is a prominent example. In biological systems, bilirnbin acts as an antioxidant. It has also been claimed that it is a 

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A micelle-bound substrate will experience a reaction environment different from bulk water, leading to a kinetic medium effect. Hence, micelles are able to catalyse or inhibit organic reactions. Research on micellar catalysis has focused on the kinetics of the organic reactions involved. An overview of the multitude of transformations that have been studied in micellar media is beyond the scope of this chapter. Instead, the reader is referred to an extensive set of review articles and monographs" ... 

Analogously, the effect of micelles on the rate of the unimolecular retro Diels-Alder reaction has been studied. Also here only a modest retardation" or acceleration" is observed. Likewise, the presence of micelles has been reported to have a modest influence on an intramolecular Diels-Alder reaction . Studies on the endo-exo selectivity of a number of different Diels-Alder reactions in micellar media lead to comparable conclusions. Endo-exo selectivities tend to be somewhat smaller in micellar solutions than in pure water, but still are appreciably larger than those in organic media In contrast, in microemulsions the endo-exo selectivity is reduced significantly" ... 

Jaeger and co-workers studied the regioselectivity of the reaction of a surfactant diene with a surfactant dienophile in micellar media" ". The orientational effects in the aggregates could result in an increase in the regjoselectivity in aqueous solutions of these compounds as compared to the reaction in organic media. 

Nucleophilic aromatic photosubstitution reactions in aqueous solutions and in micellar media has been investigated extensively.42... 

Dialkylanthracene-containing squaraine dyes 17 show intense absorption and emission in the NIR region (720-810 nm) [74]. They are compatible with aqueous environments and show substantial enhancement of quantum yields and fluorescence lifetimes in hydrophobic and micellar media, suggesting that these dyes can be potentially useful as fluorescent probes in biological applications, e.g., for imaging of hydrophobic domains such as cell membranes. 

Shamsipur and Jalali described a simple and accurate pH metric method for the determination of two sparingly soluble (in water) antifungal agents miconazole and ketoconazole in micellar media [17]. Cetyltrimethylammonium bromide and sodium dodecyl sulfate micelles were used to solubilize these compounds. The application of this method to the analysis of pharmaceutical preparation of the related species gave satisfactory results. Simplicity and the absence of harmful organic solvents in this method make it possible to be used in the routine analyses. 

Recently, Porter et al. (1986b, 1988) have reported the synthesis of both meso- and ( )-forms of a series of two-chain carbonyl diacids made by joining two pentadecanoic acid units by a carbonyl group at the 3,3, 6,6, 9,9 and 12,12 positions, 3,5-didodecyl-4-oxoheptanedioic acid (C-15 3,3 ), 6,8-dinonyl-7-oxotridecanedioic acid (C-15 6,6 ), 9,11-dihexyl-10-oxononadecanedioic acid (C-15 9,9 ) and 12,14-dipropyl-13-oxopentacosanedioic acid (C-15 12,12 ), respectively. The diacids were used to probe further the question of stereochemical preference in two-chain amphiphiles. The method used for examining the diastereomeric preference was equilibration by base-catalyzed epimerization in homogeneous, bilayer and micellar media. This method allows for stereoselection based on hydrophobic/hydrophilic considerations rather than classic steric size effects. 

In the following sections the most important features of the organized media that are most frequently used in chemiluminescent reactions (micellar media and cyclodextrins) will be summarized as well as their influence on various chemiluminescent systems, including their corresponding applications in chemical analysis. 

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. 

Spectrophotometric Determination of Pd(II) In Micellar Media by Sodium-l-Methyl-l-Propylthioxanthate... 

A direct method has been developed for the spectrophotometeric determination of Pd(II) with sodium-1-methyl-l-propylthioxanthate as a complexing reagent in the micellar media. Beer s law was obeyed in the concentration range 0.84-7.5pg/mL for Pd(II) under the optimized conditions. Calibration curve was constructed at the absorption maxima (/.m(ix) i.e. 370nm for Pd(II). Sandell s sensitivity and molar absorptivity have been found to be 0.0060pg/cm2 and 8.6xl04 L/mol/cm for Pd(II). The developed method has been found to be quite simple, rapid, sensitive and reproducible results were obtained. 

Figure 4.4. (A) Stale diagram showing the loss of excitation energy via radiationless decay through the d-d state. (B) Temperature dependence of the lifetime of Ru(bpy)ji+ in a micellar media. The solid line is the best fit using a thermally activated deactivation via the d-d state. (Reprinted from Ref. 15 with permission. Copyright 1986 American Chemical Society.)...

W. J. Dressick, K. I. Raney, J. N. Demas, and B. A. DeGraff, Properties ofosmium(II) photosensitizers in aqueous and sodium lauryl sulfate micellar media, Inorg. Chem. 23, 875-880 (1984). 

Last time, electron-transfer reactions were frequently performed in micellar media. Analyzing temperature effects on electron transfer from aromatic amines to coumarins in aqueous Trilon X-100 micelles, Kumbhakar et al. (2006) deduced that the two-dimensional electron-transfer (2DET) model is more suitable to explain the results obtained than the conventional electron-transfer theories. The model is detailed in the article by Kumbhakar et al. (2006) and references therein. 

Micellar media created by sodium dodecyl sulfate or cetyltrimethylammon-ium bromide have also a positive effect on the ortho selectivity [262,269-271]. In a recent article, the PFR of 1-naphthyl acetate in aqueous solutions of an antenna polyelectrolyte like poly(sodium styrenesulfonate-co-2-vinylfluorene) has been reported, which, in addition to the micellar effect, also provides singlet sensitization by means of fluorene chromophores. In this particular case, the occurrence of in-cage versus out-of-cage processes can be clearly correlated with the different packing of the microdomains, which depends on the molar fraction of monomers in the antenna copolymer [272]. 

The fluorinated 4-quinoline antibiotic ciprofloxacin (295) is known to interact with iron-containing drugs and mineral supplements. Stability constants have been determined for complex formation of iron(III) with ciprofloxacin, presumably acting as a bidentate 0,(9-donor, in aque-ous " and in micellar media. 

Acid-base equilibrium in ferric heme complexes inside micelles shows a distinct dependence on the micellar media. The existence of isosbestic points suggests... 

On the basis of the lipases numerous applications, also on an industrial scale, have been shown using an enzyme from this family. Table 3 summarises some applications of a popular lipase, often used in reverse micellar media, the Candida rugosa lipase. 

TABLE 17 Relative Quantum Yields and t/c Ratios from 97 in Isotropic and Micellar Media 308]... 

Hydrophobic species bearing hydrocarbon chains present vitamin B12 or vitamin B6 type activity [5.37]. Such systems lend themselves to inclusion in membrane or micellar media. They thus provide a link with catalysis in more or less organized media such as membranes, vesicles, micelles, polymers [5.39-5.41] (see Section 7.4). Water soluble cyclophanes showing, for example, transaminase [5.42], acetyl transfer [5.43], pyruvate oxidase [5.44] or nucleophilic substitution [5.45] activity have been described. 

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