Aqueous micellar solutions

In this approach, developed by Tanaka et al. (90, 91), n-Bu4N+ salts of the clusters [Fe4S4(SQH4-p-R)4] with strongly hydrophobic substituents (e.g., R = n-CgHn) in Me SO or DMF solutions were added to buffered aqueous solutions containing micellar reagents such as Triton X-100 or dodecyltrimethylammonium chloride. The cluster resides in a partially aqueous environment in the hydrophobic interior of the micelle. Potentials are shifted 400 mV in the positive direction when compared to the values 

A reaction system consisting of a Fe(II) salt, BSA, Ne2S, and 2-mer-captoethanol afforded a dark brown solution whose absorption spectrum ( max 420 nm) had the appearance of a [4Fe-4S] + cluster (96). Formation of additional BSA-bound Fe-S species cannot be discounted, however. The albumin-cluster protein showed weak hydrogenase activity in the form of dihydrogen evolution in the presence of reduced methyl viologen (96). The protein was not further characterized. 

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As a result of the micellar environment, enzymes and proteins acquire novel conformational and/or dynamic properties, which has led to an interesting research perspective from both the biophysical and the biotechnological points of view [173-175], From the comparison of some properties of catalase and horseradish peroxidase solubilized in wa-ter/AOT/n-heptane microemulsions with those in an aqueous solution of AOT it was ascertained that the secondary structure of catalase significantly changes in the presence of an aqueous micellar solution of AOT, whereas in AOT/n-heptane reverse micelles it does not change. On the other hand, AOT has no effect on horseradish peroxidase in aqueous solution, whereas slight changes in the secondary structure of horseradish peroxidase in AOT/n-heptane reverse micelles occur [176],... 

Levonantradol (8.4) was synthesized with the intention to introduce a basic amino function into the heterocycle in the hope of obtaining water-soluble salts. Although the solubility of the hydrochloride is not good it was possible to get stable aqueous micellar solutions with the aid of emulsifiers [145] and the compound made its way as an injectable into clinical trials, but never was approved. 

Aqueous micellar solutions, i.e. solutions containing a surfactant at a concentration above its critical micelle concentration, have been studied extensively during the last decade, in part from curiosity, and because of the possibility of providing unique chromatographic selectivity compared to conventional RPC [345-349]. Above the critical micelle concentration individual surfactant molecules self-aggregate to form structures known as micelles which are microscopically... 

Epoxidation of cyclooctene and other alkenes with Oxone (KHSO5) was promoted effectively in an aqueous micellar solution of an amphiphilic ketone (3.3).52 The amphiphilic ketone can be easily derived from hepta(ethylene glycol) monodecyl ether. 

The bimolecular rate constants were determined (Burke 2001) for the repair of carotenoid radical cations by trolox, ascorbic, ferrulic, and uric acids from the pulse radiolysis studies of carotenoids in aqueous micellar solutions (see Table 14.10). 

Figure 1 shows the Raman spectrum of Hb obtained with 406.7-and 413.1-nm excitation and the spectrum of monomeric, four-coordinate Ni protoporphyrin in aqueous micellar solution (9). Excitation at 413.1 nm is at resonance with the red component of the split Soret band of Ni-reconstituted hemoglobin at 406.7 nm the blue component of the Soret band is selectively probed. Comparison of the spectra shows that two sets of marker line frequencies exist. One set (labeled 4 in Figure 1) is enhanced by resonance with the blue Soret component the other set (labeled 5) is enhanced by excitation of the red Soret component. Thus, the shifts in the core-size lines in going from set 4 - 5 are -39 cm (i/-q at 1657 cm ), -20 cm cm ), and -34 cm 1 19 cm ). 

The micelle-encapsulated six coordinated bis(pyridinato) iron(II) complexes of protoporphyrin and OEP have been reported by addition of pyridine to the four coordinate ferrous complex in aqueous micellar solution. The optical spectrum of [Fe(II)(PP)(Py)2] in micelle (Fig. 10) is identical to S = 0 six-coordinate bis(pyridinato) iron(II) porphyrin complex [3]. The magnetic moment measurements in solution confirm their diamagnetic nature. The HNMR spectra are also characteristic low-spin iron(II) resonances (S = 0) with shifts lying in the diamagnetic region (Table 2). 

A general observation from the HNMR studies on micelle-encapsulated heme is that the line width of the heme protons increases significantly in the micellar solutions compared to those in simple solutions. The change in linewidths of heme methyl protons in micelles is not as large in low-spin Fe(III) hemes as in the high-spin ones. The linewidths in four-coordinate and five-coordinate complexes of ferrous hemes in aqueous micellar solutions are also quite broad compared to those observed in benzene solutions [12, 61], but are similar to those of hemoproteins [2,62]. We examine below the origin and implications of the linewidth change in micellar solutions. 

Nowick JS, Chen JS. Molecular recognition in aqueous micellar solution—adenine thymine base-pairing in SDS micelles. J Am Chem Soc 1992 114 1107-1108. 

Since their effective diffusivities are of the same magnitude as those of micellar solutions, the hquid crystalUne phases, though viscous, do not significantly hinder surfactant dissolution for these rather hydrophihc surfactants. Indeed, a drop of Ci2(EO)6 having Ro = 78 pm dissolved completely in only 16 s at 30 °C. Rapid dissolution is favored because free energy decreases as the surfactant is transferred from the Hquid surfactant phase L2 to liquid crystals) to aqueous micellar solution and the aggregate shape approaches that of a dilute Li phase, where its free energy is minimized at this temperature. 

Aqueous micellar solutions of many nonionic surfactants, with an increase in temperature, become turbid over a narrow temperature range, which is referred to as their cloud-point [17,277]. Above the cloud-point temperature, such solutions separate into two isotropic phases. Cloud-point extraction (CPE) is also referred to as a particular case of ATPE [278,279] and more specifically as aqueous micellar two-phase systems [10,277]. Very recently, in an extensive review, Quina and Hinze [280] have discussed in detail the emergence of CPE as an environmentally benign separation process, highlighting the basic features, experimental protocols, recent applications, and future trends in this area. 

Though CPE has many advantages [10], some problems remain to be solved such as (1) limited number of surfactants, (2) high cloud-point, and (3) strong hydrophobic nature. In an attempt to overcome some of these limitations, Tani et al. [281] proposed a new method that involves solubilization of hydrophobic membrane proteins into aqueous micellar solutions of alkylglucosides, followed by phase separation induced by the addition of a water-soluble polymer such as poly(ethylene)glycol (PEG) and dextran T-500. Using this approach they could carry out the whole procedure from solubilization to phase separation at 0 °C. 

Hydrophobic substances added to an aqueous micellar solution tend to be entrapped into the oily interior, and if the substance contains a fiuorofor, its fluorescence properties may change drastically upon entrapment, due to the change... 

Chemical procedures that produce less waste or less hazardous waste are said to be green because they reduce harmful environmental effects. In chemical analyses with dithizone, you can substitute aqueous micelles (Box 26-1) for the organic phase (which has traditionally been chloroform, CHC13) to eliminate chlorinated solvent and the tedious extraction.2 For example, a solution containing 5.0 wt% of the micelle-forming surfactant Triton X-100 dissolves 8.3 X 10 5M dithizone at 25°C and pH < 7. The concentration of dithizone inside the micelles, which constitute a small fraction of the volume of solution, is much greater than 8.3 X 10 5M. Aqueous micellar solutions of dithizone can be used for the spectrophotometric analysis of metals such as Zn(II), Cd(Il), Hg(Il), Cu(ll), and Pb(II) with results comparable to those obtained with an organic solvent. 

MM Delgado Zamarreno, A Sanchez Perez, MC Gomez Perez, J Hernandez Mendez. Automatic determination of liposoluble vitamins in butter and margarine using Triton X-100 aqueous micellar solution by liquid chromatography with electrochemical detection. Anal Chim Acta 315 201-208, 1995. 

One potential application of the work on oriented nematic phases of rodlike molecules is to solutions containing cylindrical micelles. Orientation could be achieved by a shear field or perhaps by an electric field. Gotz and Heckman (9) confirmed the existence of anisotropic electrical conductivity for a concentrated surfactant solution in a shear field. They used their results to show that the solution contained cylindrical rather than platelike micelles. Of course, the magnitude of the electrical conductivity in an aqueous micellar solution should be quite different from that in the nematic phase of an organic material. So the conditions for and types of electrohydrodynamic instabilities could be different as well. 

Winsor (17) describes how electrical conductivity varies during addition of an alcohol to an aqueous micellar solution containing some solubilized oil. Conductivity initially decreases as mixed (and probably larger) micelles containing both surfactant and alcohol are formed. When liquid crystal (presumably having a lamellar structure) starts to appear in equilibrium with the micellar solution, conductivity decreases even faster. As more alcohol is added, the aqueous solution disappears, only liquid crystal is present, and the conductivity reaches a minimum. Addition of still more alcohol results in the appearance of an oil-continuous micellar solution and an increase in conductivity. Eventually all liquid crystal disappears, the increase in conductivity ceases, and conductivity... 

Solubilizing Capacity of Surfactant Micelles and Distribution Coefficient of Timobesome Acetate in Aqueous Micellar Solutions at 25°C Solubilizing Capacity Distribution ... 

The term photoredox axial ligand addition is used in instances when a stable molecule (e.g. 02, NO) is coordinated to an electronically excited complex. As one of the rare examples of this kind of reactions, the visible-light-induced reversible formation of dioxygen adducts of Co(TPP) and its derivatives occurring in aqueous micellar solutions at room temperature, can be shown (the encapsulation of the complexes into Triton X micelles is a key factor of the reactions)... 

Quinquethiophene gave an inclusion complex in perhydrotripheny-lene with emission at 2.52 and 2.37 eV (97CPL(278)146). The absorption and emission characteristics of a hetero-chalcone derivative, 3-(4 dimethylaminophenyl)-l-(2-thienyl)prop-2-en-l-one (59), in aqueous micellar solutions of sodium dodecy sulfate (SDS), cetyltrimethylammo-nium bromide (CTAB), and Triton X-100 (TX-100) as well as in (3-CD solutions were reported (08PPS257). 

Alkaline hydrolysis rates of a series of thiophenyl 4-X-benzoates (47 X = H, Me, N02) was significantly enhanced in the presence of cyclodextrins (CDs), and this was attributed to strong binding of the benzoyl moiety within the CD cavity and covalent catalysis by secondary hydroxy groups of the CDs (48).63 The effect of MeCN and MeOH on the alkaline hydrolysis of acetylsalicylic acid in aqueous micellar solutions was reported.64 Butylaminolysis of p-nitrophenyl acetate in chlorobenzene in the presence of different kinds of phase-transfer catalysts (crown ethers and gly-mes) supported the existence of a novel reaction pathway exhibiting a first-order dependence on the concentration of the phase-transfer catalyst and a second-order... 

Solvent and concentration effects on keto-enol tautomerization have been investigated in DMSO-water mixtures and aqueous micellar solutions, for 2-acetylcyclo-hexanone and 2-acetyl-1-tetralone.286 Dramatic rate increases aboves 60% DMSO content have been explained in terms of solvent structure solvent polarity alone cannot rationalize the effect. 

Another new approach combines MAE with the use of an aqueous surfactant solution as the extracting phase. This new technique is called microwave-assisted micellar extraction (MAME). This procedure is based on the well-known solubilization capacity of aqueous micellar solutions toward water-insoluble or sparingly soluble organic compounds. As a general rule, nonionic surfactants are usually the most effective, showing greater solubilization capacities that rapidly increase with the solubilization kinetics as the cloud-point temperature of the solution is raised. 

The confinement of a relatively large number of dye molecules in the small volume of a nanoparticle may trigger collective phenomena otherwise not observable in bulk solution. This has been demonstrated by Prasad and coworkers in the case of an ORMOSIL pH sensor.69 The PEBBLEs contain a naphthalenylvinylpyridine derivative (NVP) as pH-sensitive fluorescent dye which has been functionalized with a triethoxysilane anchor by reaction with an excess of (3-isocyanatopropyl)triethoxysi-lane (ICTES). The sol-gel polymerization in aqueous micellar solution of the NVP-ICTES derivative with VTES gives spherically shaped 33 nm silica nanoparticles in which the dye is covalently linked to the silica matrix and uniformly distributed in the nanoparticle volume. The NVP dye responds ratiometrically to protons, with a... 

Two-color photoionization through the triplet manifold has also been reported for biphenyl in aqueous micellar solution [80]. 

Aqueous micellar solutions were first used as mobile phases in LC in 1980. A micellar solution is one that contains a surfactant at a concentration above the critical micelle concentration, about 10-2 M. The nature of micelles and their use in analytical chemistry, including chromatography, has been recently described.82... 

Extractions Based on the Phase Separation Behavior of Aqueous Micellar Solutions. The extraction and concentration of components in an aqueous mixture can sometimes be effected via use of appropriate surfactant systems that are capable of undergoing a phase separation as a result of altered conditions (i.e. temperature or pressure changes, added salts or other species, etc.). Two general types of such surfactant extraction systems will be described (i) those based on the cloud point phenomenon and (ii) those based on coacervation formation. 

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