Articles de revues : « Micellar catalysi »

1

Cibulka, Radek, Lenka Baxová, Hana Dvořáková, František Hampl, Petra Ménová, Viktor Mojr, Baptiste Plancq et Serkan Sayin. « Catalytic effect of alloxazinium and isoalloxazinium salts on oxidation of sulfides with hydrogen peroxide in micellar media ». Collection of Czechoslovak Chemical Communications 74, n^o 6 (2009) : 973–93. http://dx.doi.org/10.1135/cccc2009030.

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Three novel amphiphilic alloxazinium salts were prepared: 3-dodecyl-5-ethyl-7,8,10-trimethylisoalloxazinium perchlorate (1c), 1-dodecyl-5-ethyl-3-methylalloxazinium perchlorate (2b), and 3-dodecyl-5-ethyl-1-methylalloxazinium perchlorate (2c). Their catalytic activity in thioanisole (3) oxidation with hydrogen peroxide was investigated in micelles of sodium dodecylsulfate (SDS), hexadecyltrimethylammonium nitrate (CTANO3) and Brij 35. Reaction rates were strongly dependent on the catalyst structure, on the type of micelles, and on pH value. Alloxazinium salts 2 were more effective catalysts than isoalloxazinium salts 1. Due to the contribution of micellar catalysis, the vcat/v0 ratio of the catalyzed and non-catalyzed reaction rates was almost 80 with salt 2b solubilized in CTANO3 micelles. Nevertheless, the highest acceleration was observed with non-amphiphilic 5-ethyl-1,3-dimethylalloxazinium perchlorate (2a) in CTANO3 micelles (vcat/v0 = 134). In this case, salt 2a presumably acts as a phase-transfer catalyst bringing hydrogen peroxide from the aqueous phase into the micelle interior. Synthetic applicability of the investigated catalytic systems was verified on semi-preparative scale.

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Khan, Mohammad Niyaz, et Ibrahim Isah Fagge. « Kinetics and Mechanism of Cationic Micelle/Flexible Nanoparticle Catalysis : A Review ». Progress in Reaction Kinetics and Mechanism 43, n^o 1 (mars 2018) : 1–20. http://dx.doi.org/10.3184/146867818x15066862094905.

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The aqueous surfactant (Surf) solution at [Surf] > cmc (critical micelle concentration) contains flexible micelles/nanoparticles. These particles form a pseudophase of different shapes and sizes where the medium polarity decreases as the distance increases from the exterior region of the interface of the Surf/H2O particle towards its furthest interior region. Flexible nanoparticles (FNs) catalyse a variety of chemical and biochemical reactions. FN catalysis involves both positive catalysis ( i.e. rate increase) and negative catalysis ( i.e. rate decrease). This article describes the mechanistic details of these catalyses at the molecular level, which reveals the molecular origin of these catalyses. Effects of inert counterionic salts (MX) on the rates of bimolecular reactions (with one of the reactants as reactive counterion) in the presence of ionic FNs/micelles may result in either positive or negative catalysis. The kinetics of cationic FN (Surf/MX/H2O)-catalysed bimolecular reactions (with nonionic and anionic reactants) provide kinetic parameters which can be used to determine an ion exchange constant or the ratio of the binding constants of counterions.

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Broxton, Trevor J. « Micellar Catalysis of Organic Reactions. XXXVIII A Study of the Catalytic Effect of Micelles of 3-Hydroxymethyl-1-tetradecylpyridinium Bromide on Amide Hydrolysis and Nucleophilic Aromatic Substitution ». Australian Journal of Chemistry 51, n^o 7 (1998) : 541. http://dx.doi.org/10.1071/c98053.

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The preparation of 3-hydroxymethyl-1-tetradecylpyridinium bromide and its use as a catalyst of nucleophilic aromatic substitution and also amide hydrolysis are reported. It was found that the hydroxydehalogenation of nitro-activated aryl halides was much faster in these micelles than in the presence of cetyl(2-hydroxyethyl)dimethylammonium bromide. It was concluded that the increased catalysis of nucleophilic aromatic substitution by this micelle was due to a faster decomposition of the aryl micellar ether which must occur before the phenolate product is released. No such difference in the two micelles was found for amide or thioamide hydrolysis since in these reactions the product amine is produced in the first step of the reaction and decomposition of the acylated micelle is not required in the rate-determining step of the reaction.

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Drennan, Catherine E., Rachelle J. Hughes, Vincent C. Reinsborough et Oladega O. Soriyan. « Article ». Canadian Journal of Chemistry 76, n^o 2 (1 février 1998) : 152–57. http://dx.doi.org/10.1139/v97-226.

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Kinetic studies through stopped-flow spectroscopy were undertaken in the dilute solution range of anionic surfactants where pronounced rate enhancement or inhibition of Ni2+-ligand complexations is often observed at surfactant concentrations much below the critical micelle concentration (CMC). The results are interpreted in terms of Ni-surfactant micelles as the agents responsible for the rate changes in dilute surfactant solution. At higher surfactant concentrations these micelles are transformed into mixed micelles (counterion and size changes), eventually becoming normal surfactant micelles close to the CMC. Surface tension, dye solubility, conductivity, and fluorescent probe investigations support this interpretation.Key words: micellar catalysis, sodium dodecyl sulfate, micelles, critical micelle concentration, premicelles, Ni2+-ligand complexations.

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Broxton, TJ, JR Christie et RPT Chung. « Micellar Catalysis of Organic Reactions. XXVI. SNAr Reactions of Azide Ions ». Australian Journal of Chemistry 42, n^o 6 (1989) : 855. http://dx.doi.org/10.1071/ch9890855.

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The azidodehalogenation of a number of aromatic compounds has been studied in the presence of micelles of cetyltrimethylammonium bromide (ctab). The variation of the observed rate of reaction with ctab concentration has been treated by using the model of Rodenas and Vera to determine the rate constant for reaction in the micellar pseudo-phase, k2m, the binding constant of the substrate to the micelle, Ks, and the nucleophile-micellar counter ion exchange constant KAzBr :. The ratio of the rate constants in the micellar pseudo-phase and in water varied between 0.9 and 52. For reactions involving the production of a dianionic intermediate the largest catalysis was found for compounds containing two nitro groups to stabilize the double negative charge. In addition significant differences in the catalysis were found between compounds having the reaction centre at the micelle-water interface and those for which the reaction centre was more buried inside the micelle. As previously reported the resulting aryl azides undergo cyclization to form a benzofuroxan if a nitro group is located ortho to the azide group. Furthermore, a reversible photochemical reaction was detected for two compounds having a carboxylate group ortho to the azide group.

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Steven, Alan. « Micelle-Mediated Chemistry in Water for the Synthesis of Drug Candidates ». Synthesis 51, n^o 13 (21 mai 2019) : 2632–47. http://dx.doi.org/10.1055/s-0037-1610714.

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Micellar reaction conditions, in a predominantly aqueous medium, have been developed for transformations commonly used by synthetic chemists working in the pharmaceutical industry to discover and develop drug candidates. The reactions covered in this review are the Suzuki–Miyaura, Miyaura borylation, Sonogashira coupling, transition-metal-catalysed CAr–N coupling, SNAr, amidation, and nitro reduction. Pharmaceutically relevant examples of these applications will be used to show how micellar conditions can offer advantages in yield, operational ease, amount of waste generated, transition-metal catalyst loading, and safety over the use of organic solvents, irrespective of the setting in which they are used.1 Introduction2 Micelles as Solubilising Agents3 Micelles as Nanoreactors4 Designer Surfactants5 A Critical Evaluation of the Case for Chemistry in Micelles6 Scope of Review7 Suzuki–Miyaura Coupling8 Miyaura Borylation9 Sonogashira Coupling10 Transition-Metal-Catalysed CAr–N Couplings11 SNAr12 Amidation13 Nitro Reduction14 Micellar Sequences15 Summary and Outlook

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Dahadha, Adnan A., Mohammed Hassan, Tamara Mfarej, Razan Bani Issa, Mohamed J. Saadh, Mohammad Al-Dhoun, Mohammad Abunuwar et Nesrin T. Talat. « The Catalytic Influence of Polymers and Surfactants on the Rate Constants of Reaction of Maltose with Cerium (IV) in Acidic Aqueous Medium ». Journal of Chemistry 2022 (1 juillet 2022) : 1–11. http://dx.doi.org/10.1155/2022/2609478.

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Kinetics of the reaction of maltose with cerium ammonium sulfate were analyzed spectrophotometrically by observing the decrease of the absorbance of cerium (IV) at 385 nm in the presence and absence of polyethylene glycols (600, 1500, and 4000) and polyvinylpyrrolidone (PVP), in addition to anionic micelles of sodium dodecyl sulfate (SDS), cationic micelles of cetyltrimethylammonium bromide (CTAB) and non-ionic micelles of Tween 20 surfactants. Generally, there is little literature about using the polymers (PEGs and PVP) as catalysts in the oxidation-reduction reactions. Therefore, the major target of this work was to investigate the influence of the nature of polymers and surfactants on the oxidation rates of maltose by cerium (IV) in acidic aqueous media, as well as employing the Piszkiewicz model to explain the catalytic effect. The kinetic runs were derived by adaptation of the pseudo first-order reaction conditions with respect to the cerium (IV). The reaction was found to be first-order with respect to the oxidant and fractional-order to maltose and H2SO4. The reaction rates were enhanced in the presence of polymer and micellar catalysis. Indeed, the surfactants were found to work perfectly close to their critical micelle concentrations (CMC). Electrostatic interaction and H-bonding appear to play an influential role in binding maltose molecules to polymer/surfactant micelles, while oxidant ions remain at the periphery of the Stern layer within the micelle.

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Oranli, Levent, Pratap Bahadur et Gérard Riess. « Hydrodynamic studies on micellar solutions of styrene–butadiene block copolymers in selective solvents ». Canadian Journal of Chemistry 63, n^o 10 (1 octobre 1985) : 2691–96. http://dx.doi.org/10.1139/v85-447.

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Hydrodynamic radius of micelles of several block copolymers in different selective solvents (for both types of blocks) was determined from photon correlation spectroscopy. The boundaries of micellar solutions in heptane (good solvent for polybutadiene block) and dimethylformamide (good solvent for polystyrene block) were established for polymers in terms of their molecular mass and block composition. The photon correlation spectroscopy data in combination with intrinsic viscosities of block copolymers in selective solvents were used to determine micellar molecular mass and aggregation number. The influence of temperature on the micelle size was examined. The block copolymer micelles could solubilize a certain amount of insoluble homopolymer within their insoluble core. 1H nmr spectra were examined to study the influence of temperature on micellar systems.

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Wasylishen, Roderick E., Jan C. T. Kwak, Zhisheng Gao, Elisabeth Verpoorte, J. Bruce MacDonald et Ross M. Dickson. « NMR studies of hydrocarbons solubilized in aqueous micellar solutions ». Canadian Journal of Chemistry 69, n^o 5 (1 mai 1991) : 822–33. http://dx.doi.org/10.1139/v91-122.

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Information concerning the solubilization of hydrocarbons in ionic surfactant micelles was obtained from 2H NMR relaxation, 1H NMR chemical shifts, and 1H NMR paramagnetic relaxation measurements. The rotational motion of deuterated hydrocarbons, which is related to the micellar microviscosity at the location of the hydrocarbons, was probed by 2H NMR relaxation. The relaxation data are interpreted using both the two-step and the single-step models, and the results are discussed in terms of the micellar microviscosity and the location of the hydrocarbons in micelles. The location of the hydrocarbons in micelles was further investigated by determining the aromatic ring current-induced 1H chemical shifts along the surfactant alkyl chain and by comparing the 1H spin-lattice relaxation enhancement of the hydrocarbons and the surfactant alkyl chain, induced by Mn2+ on the micellar surface. The hydrocarbons used include benzene, naphthalene, acenaphthalene, triphenylene, cyclohexane, cyclododecane, and tert-butylcyclohexane and the surfactants studied are hexadecyl-, tetradecyl-, and dodecyltrimethylammonium bromide; hexadecyl-, tetradecyl-, and dodecylpyridinium halide; and sodium dodecyl sulfate. The results indicate that the micellar microviscosity at the location of saturated hydrocarbons is approximately 5 cP for both the cationic and anionic micelles, whereas the micellar microviscosity at the location of unsaturated hydrocarbons is much higher. The unsaturated hydrocarbons are found to reside primarily near the surfactant headgroup in the cationic micelles, but are distributed evenly throughout the anionic SDS micelles. The saturated hydrocarbons appear to be located in the interior of the micelles. Key words: NMR, relaxation, solubilization, surfactant, micelle.

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Gebicka, Lidia, et Monika Jurgas-Grudzinska. « Activity and Stability of Catalase in Nonionic Micellar and Reverse Micellar Systems ». Zeitschrift für Naturforschung C 59, n^o 11-12 (1 décembre 2004) : 887–91. http://dx.doi.org/10.1515/znc-2004-11-1220.

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Catalase activity and stability in the presence of simple micelles of Brij 35 and entrapped in reverse micelles of Brij 30 have been studied. The enzyme retains full activity in aqueous micellar solution of Brij 35. Catalase exhibits “superactivity” in reverse micelles composed of 0.1 ᴍ Brij 30 in dodecane, n-heptane or isooctane, and significantly lowers the activity in decaline. The incorporation of catalase into Brij 30 reverse micelles enhances its stability at 50 °C. However, the stability of catalase incubated at 37 °C in micellar and reverse micellar solutions is lower than that in homogeneous aqueous solution.

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Broxton, Trevor J., et Robin A. Coa. « Micellar catalysis of organic reactions. Part 33. Amide hydrolysis in neutral solution in the presence of a copper-containing micelle ». Canadian Journal of Chemistry 71, n^o 5 (1 mai 1993) : 670–73. http://dx.doi.org/10.1139/v93-090.

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The hydrolysis of 5-nitro-2-(trifluoroacetylamino)benzoic acid (1) has been studied at pH 7 in water and in the presence of micelles of cetyltrimethylammonium bromide (ctab) and of copper-containing micelles formed from the reaction of N,N,N′-trimethyl-N′-hexadecylethylenediamine and cupric chloride. It has been found that the hydrolysis of 1 is inhibited by micelles of ctab but strongly catalysed by the copper-containing micelle at this pH. At a higher pH where the hydroxide ion reaction becomes important the reaction is catalysed by micelles of ctab as well, but the catalysis is stronger by the copper-containing micelle. The effect of added sodium chloride on the rate of reaction is shown to be larger for reaction in the presence of ctab than for reaction in the presence of the copper micelles. Also reported are the effects of the buffer concentration on the rate of reaction at various pH for both micelles. It is concluded that the mechanism of reaction in the copper-containing micelle involves a metal-bound hydroxyl rather than a free hydroxide ion loosely associated with the cationic micelle surface. It is interesting that the catalysis of this reaction by the copper-containing micelle is large enough to allow amide hydrolysis at a reasonable rate at neutral pH at ambient temperature.

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Venkateswaran, Krishnan, Mary V. Barnabas, Bill W. Ng et David C. Walker. « Residence-time of muonium at micelles : Effect of added micelles on the reactivity of muonium towards ionic solutes in water ». Canadian Journal of Chemistry 66, n^o 8 (1 août 1988) : 1979–83. http://dx.doi.org/10.1139/v88-319.

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The effective rate constant for the reaction of muonium with NO3−, S2O32−, and Tl+ ions in water is altered by the addition of micelles. There is a decrease when the charge on the micelle is the same as that of the solute and an increase when their charges are opposite. From the magnitude of the effect a mean residence-time for muonium of 2 ns has been deduced for dodecyl sulphate micelles. This suggests there is barely any preferred localization, because 2 ns is smaller, even, than the expected diffusion time if the micelle core is as viscous as reported. This use of muonium atoms to probe the dynamics of micelles seems to support the view that there are regions of low microviscosity and considerable water penetration within the micellar structure.

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Biasutti, M. A., et Juana J. Silber. « Interaction between tetracyanoethylene and naphthalene in reverse micelles of AOT in n-hexane. The electron-donor properties of AOT ». Canadian Journal of Chemistry 74, n^o 9 (1 septembre 1996) : 1603–8. http://dx.doi.org/10.1139/v96-177.

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The electron donor–acceptor (EDA) interaction between TCNE and naphthalene (Naph) in n-hexane and reverse micelles of AOT in n-hexane was studied by UV–visible spectroscopy with the aim of determining the influence of the micellar media on the EDA interaction. The spectra of the mixtures of TCNE–Naph in n-hexane show two typical maxima at 418 and 534 nm, assigned to the formation of a π–π EDA complex. In the micellar media a new band is observed at 398 nm. When the spectra of TCNE in n-hexane are studied in the presence of AOT two new bands at 398 and 418 nm are detected. These bands are consistent with an EDA interaction between TCNE and AOT as n-donor. The stability constants of this interaction were calculated for AOT concentrations below the CMC and in the micellar media at different W(W = [H2O]/[AOT]). The results give evidence of the tendency of AOT to interact very strongly with electron acceptors. Moreover, in the system TCNE–Naph in the micellar media it is shown that Naph and AOT compete to form a complex with TCNE. The formation constants of the complexes of AOT–Naph in the micelle system were determined at W = 0 and 5. Despite the competition of AOT for TCNE the stability constant for the complex TCNE–Naph is higher than in homogeneous media, probably due to the high local concentration of the acceptor in the micelle. Key words: reverse micelles, aerosol-OT, tetracyanoethylene, naphthalene, electron donor–acceptor complexes.

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Favaro, Yvette L., et Vincent C. Reinsborough. « Micellar catalysis in mixed anionic/cationic surfactant systems ». Canadian Journal of Chemistry 72, n^o 12 (1 décembre 1994) : 2443–46. http://dx.doi.org/10.1139/v94-310.

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Dye solubility and stopped-flow kinetic studies were conducted in sodium dodecylsulfate/dodecyltrimethylammonium bromide and sodium dodecylsulfate/decyltrimethylammonium bromide micellar solutions with excess anionic surfactant. The enhanced rate in the presence of anionic micelles of the Ni2+(aq)/pyridine-2-azo-p-dimethylaniline (PADA) complexation reaction was used as a probe of the mixed micellar situation. PADA solubilities and the kinetic parameters derived through the Robinson model for micellar catalysis were consistent with a complete incorporation of the cationic surfactant into the sodium dodecylsulfate micelles.

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JAMES, Stephen R., Sheila SMITH, Andrew PATERSON, T. Kendall HARDEN et C. Peter DOWNES. « Time-dependent inhibition of phospholipase Cβ-catalysed phosphoinositide hydrolysis : a comparison of different assays ». Biochemical Journal 314, n^o 3 (15 mars 1996) : 917–21. http://dx.doi.org/10.1042/bj3140917.

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The properties of three different β-isoforms of phospholipase C (PLC) were analysed using substrate lipids dispersed in phospholipid vesicles, phospholipid–detergent mixed micelles and phospholipid monolayers spread at an air–water interface. Phosphatidylinositol 4,5-bisphosphate hydrolysis went virtually to completion in monolayers, but inositol trisphosphate production was curtailed prematurely in vesicular and micellar assays. Assays were linear for less than 2 min with vesicles; the linear portion could be significantly extended in micelles by increasing the ratio of micelles to enzyme molecules. However, onset of a second lower rate of substrate hydrolysis always occurred when ⩽ 10% of PtdIns(4,5)P2 had been utilized. This was not due to enzyme inactivation in the micellar interface, determined by addition of fresh substrate or fresh enzyme after the slow phase of activity had started, nor was it due to overt product inhibition of PLC or apparent entrapment of PLC at the micelle surface. These results are similar to those seen in assays using bacterial PLC and we suggest that the biphasic kinetics may be due to product-dependent changes in the presentation of substrate lipid to PLC in lamellar assays, leading to reduced activity.

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Augustine, Rimesh, Dae-Kyoung Kim, Ho An Kim, Jae Ho Kim et Il Kim. « Poly(N-isopropylacrylamide)-b-Poly(L-lysine)-b-Poly(L-histidine) Triblock Amphiphilic Copolymer Nanomicelles for Dual-Responsive Anticancer Drug Delivery ». Journal of Nanoscience and Nanotechnology 20, n^o 11 (1 novembre 2020) : 6959–67. http://dx.doi.org/10.1166/jnn.2020.18822.

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A series of ABC triblock poly(N-isopropylacrylamide)75-block-poly(L-lysine)35-block-poly(L-histidine)n (p(NIPAM)75-b-p(Lys)35-b-p(His)N) (N = 35,50,75,100) copolymer bio-conjugates were prepared by combining reversible addition-fragmentation chain transfer polymerization and fast ring-opening polymerization of N-carboxyanhydride a-amino acid using 1,3-dicyclohexylimidazolium hydrogen carbonate as a catalyst. All the resulting triblock copolymers self-assembled into spherical micellar aggregates in aqueous solution, irrespective of the chain length of the histidine block. The micellar aggregates encapsulated the anticancer drug doxorubicin (Dox) and exhibited high drug loading efficiency. Temperature and pH stimuli were applied to investigate the controlled release of Dox. The non-cytotoxic nature of the polymers was investigated using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. Cellular uptake of the Dox-loaded micelles revealed that the micelles successfully release Dox in cancer cells in response to pH- and temperature-induced morphological change. In-vitro studies further confirmed that the Dox-loaded triblock copolymer micelle is an excellent platform for drug delivery.

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MacInnis, Judith A., Greg D. Boucher, R. Palepu et D. Gerrard Marangoni. « The properties of a family of two-headed surfactant systems : the 4-alkyl-3-sulfosuccinates 2. Surface properties of alkyl sulfosuccinate micelles ». Canadian Journal of Chemistry 77, n^o 3 (1 mars 1999) : 340–47. http://dx.doi.org/10.1139/v99-008.

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The micellar properties of a family of two-headed surfactants, the alkyl sulfosuccinates, were investigated employing fluorescence, ultra-violet spectroscopy, and acid-base titrations, as a function of the chain length of the surfactant. Polarity of the micellar interior was investigated using pyrene and the ionic probe 8-anilino-1-naphthalensulfonic acid ammonium salt (ANS). Pyrene I1/I3 ratios were used to probe the microenvironment of the probe in the palisade layer of the micelle. The pKa values of both of the anionic head groups were determined using acid-base titrations. Surface potential measurements were obtained from the measurement of the pKa of the hydrophobic indicator, 7-hydroxycoumarin, at the sulfosuccinate micellar interface. All of these results were used to examine the surface properties of the alkyl sulfosuccinate micelles and the polarity of the micellar interior.Key words: micellization, pKa, surface potential, surface charge density, 7-hydroxycoumarin, pyrene.

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Connolly, Terrence J., et Vincent C. Reinsborough. « Micellar rate enhancement studies in mixed sodium fluorocarbon/hydrocarbon surfactant solutions ». Canadian Journal of Chemistry 70, n^o 6 (1 juin 1992) : 1581–85. http://dx.doi.org/10.1139/v92-194.

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Stopped-flow kinetic studies were conducted in mixed micellar solutions of fluorocarbon and hydrocarbon anionic surfactants to determine the prevalent micellar form. The probe reaction was the Niaq2+/pyridine-2-azo-p-dimethylaniline (PADA) complexation, which is many times accelerated in the presence of anionic micelles. Binding constants for Niaq2+ and PADA partitioning between bulk solution and micelles were determined through the murexide technique and solubility measurements respectively and the molar reaction volume was obtained from the Robinson equation. The three binary surfactant systems investigated had sodium perfluoroheptanoate as the fluorocarbon surfactant while the hydrocarbon surfactants were sodium decylsulfate, sodium nonanesulfonate, and sodium octanesulfonate. The kinetic results were consistent with unimicellar composition in all three systems which was not the behaviour previously found with the sodium octane sulfonate/sodium perfluoroctanoate system. The difference was attributed to closer similarity in the surfactant pair hydrophobicities as revealed through their critical micelle concentrations. Another finding was that mixed micelles synergistically can lead to a much greater solubilization of PADA than is possible through either of the pure surfactants.

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Tee, Oswald S., et Alexei A. Fedortchenko. « Transition state stabilization by micelles : the hydrolysis of p-nitrophenyl alkanoates in cetyltrimethylammonium bromide micelles ». Canadian Journal of Chemistry 75, n^o 10 (1 octobre 1997) : 1434–38. http://dx.doi.org/10.1139/v97-172.

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The cleavage of p-nitrophenyl alkanoates (acetate to octanoate) at high pH is modestly catalyzed by micelles formed from cetyltrimethylammonium bromide (CTAB) in aqueous solution. Rate constants exhibit saturation behaviour with respect to [CTAB], consistent with substrate binding in the micelles. The strength of substrate binding and transition state binding to the micelles increases monotonically with the acyl chain length, and with exactly the same sensitivity. As a result, the extent of acceleration (or catalytic ratio) is independent of the ester chain. These and earlier results are consistent with the reaction centre being located in the Stern layer of the micelle, with the acyl chain of the ester being directed into the hydrophobic micellar interior. The chain length dependence of kinetic parameters found in this work is comparable to that found previously for ester cleavage by cyclodextrins and by various enzymes with hydrophobic binding sites, as well as to that observed for other phenomena involving hydrophobic effects. Keywords: catalysis, ester hydrolysis, micelles, transition state.

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Barclay, Lawrence Ross Coates, Steven Jeffrey Locke et Joseph Mark MacNeil. « Autoxidation in micelles. Synergism of vitamin C with lipid-soluble vitamin E and water-soluble Trolox ». Canadian Journal of Chemistry 63, n^o 2 (1 février 1985) : 366–74. http://dx.doi.org/10.1139/v85-062.

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A study was made of the effect of the inhibitors ascorbic acid (C), α-tocopherol (E), and 6-hydroxy-2,5,7,8-tetramethyl-chroman-2-carboxylate (Trolox, T) on the autoxidation of linoleic acid in 0.50 M sodium dodecyl sulfate (SDS) micelles at pH 7.0 in phosphate buffer. Reactions were thermally initiated at 30 °C in the SDS micelles by a micelle-soluble initiator, di-tert-butylhyponitrite (DBHN). Although water-soluble C alone is an inefficient inhibitor, when combined with micelle-soluble E, it acts synergistically with the latter to extend the efficient antioxidant action of E beyond the sum of the induction periods of C and E acting separately. Similarly C acts synergistically with the water-soluble antioxidant, T. Quantitative studies of these effects under controlled rates of initiation (Ri,) reveal that C functions to regenerate a mole of E (or T) per mole of C used. Kinetic studies show that the rate of autoxidation is first order in micellar linoleic acid and one-half order in micellar DBHN concentrations. Therefore, the classical rate law, −dO2/dt = kp[R—H] (Ri)1/2/(2k1)1/2 is followed. The higher oxidizability (kp/2kt1/2 = 4.48 × 10−2 M−1/2 s−1/2) of linoleate in micelles compared to that in homogeneous solution in chlorobenzene (kp/2kt1/2 = 2.30 × 10−2 M−1/2 s−1/2) is interpreted in terms of the effect of the polar interfacial region of the micelles on a dipolar transition state, R—OŌ: H•R, of the propagation reaction.

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MacInnis, Judith A., R. Palepu et D. Gerrard Marangoni. « A nuclear magnetic resonance investigation of the micellar properties of a series of sodium cyclohexylalkanoates ». Canadian Journal of Chemistry 77, n^o 11 (1 novembre 1999) : 1994–2000. http://dx.doi.org/10.1139/v99-211.

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The micellar properties of a family of surfactants, the sodium cyclohexylalkanoates, have been investigated in aqueous solution using multinuclear NMR spectroscopy. C-13 chemical shift measurements have been used to determine both the cmc values and the micellar aggregation numbers (Ns values) of these surfactants. The cmc values and the degrees of counterion binding were estimated from 23Na chemical shift measurements. The critical micelle concentrations (cmc's) and the aggregation numbers determined from the NMR experiments indicate that these amphiphiles have high cmc's and low aggregation numbers when compared to other single-headed surfactants (most notably the sodium alkanoates). The conformational changes incurred by the carbon atoms upon micelle formation have been deduced from the 13C chemical shift differences (δsurf,mic - δsurf,aq). These results are used to discuss the formation of the aggregates of the sodium cyclohexylalkanoate surfactants as a function of the length of the alkanoate side chain.Key words: micelles, surfactants, NMR spectroscopy, chemical shifts, aggregation numbers, degree of counterion binding, conformational changes.

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Greencorn, David J., Victoria M. Sandre, Emily K. Piggott, Michael R. Hillier, A. James Mitchell, Taryn M. Reid, Michael J. McAlduff, Kulbir Singh et D. Gerrard Marangoni. « Asymmetric cationic gemini surfactants : an improved synthetic procedure and the micellar and surface properties of a homologous series in the presence of simple salts ». Canadian Journal of Chemistry 96, n^o 7 (juillet 2018) : 672–80. http://dx.doi.org/10.1139/cjc-2017-0676.

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The micellar and morphological properties of symmetric, cationic gemini surfactants have been well studied in the literature as a function of nature and type of the spacer group and the length and type of hydrophobic chain. In this paper, we have examined the effects of tail asymmetry on the properties of a series of cationic surfactants, the N-alkyl-1-N′-alkyl-2-N,N,N′,N′-tetramethyldiammonium dibromide. A novel synthetic method is used to prepare a series of these surfactants and the consequences of asymmetry on micellar properties are presented. This new method has been shown to be more efficient, with higher yields of the asymmetric surfactants than the yields of the accepted literature method. The critical micelle concentration values and the micelle sizes of the asymmetric gemini surfactants, 12-4-12, 12-4-10, 12-4-8, and 12-4-6 gemini surfactants, were obtained from conductivity and dynamic light scattering. With increasing chain asymmetry, the size of the micelle increased due to the formation of loose micelles. The addition of NaCl and Na2SO4 to the surfactant solutions increased the aggregate size, and this effect was more pronounced with increasing salt concentrations. These results are interpreted in terms of the effect these ions have on the “compactness” of the micelle structure.

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Stadlbauer, John M., Krishnan Venkateswaran, Hugh A. Gillis, Gerald B. Porter et David C. Walker. « Micelle-induced change of mechanism in the reaction of muonium with acetone ». Canadian Journal of Chemistry 74, n^o 11 (1 novembre 1996) : 1945–51. http://dx.doi.org/10.1139/v96-221.

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Muonium atoms add to the O atom of the carbonyl group of acetone to give the muonated free radical (CH3)2Ċ-O-Mu when the reaction takes place in water or hydrocarbons, but not when the acetone is localized in micelles. Micelles have no effect on the formation of muonated cyclohexadienyl radicals when muonium reacts with benzene under similar conditions. The addition reaction with acetone appears to have been subsumed by a faster alternative reaction in the micellar environment. Evidence is presented for this interpretation rather than for an inhibition of the radical or for a shift in the muon level-crossing resonance spectrum with hydrogen (muonium) bonding, though major shifts are seen for the spectrum of this radical in pure solvents of widely different dielectric constant. It is suggested that muonium's "abstraction" reaction takes over in micelles because significant micelle-induced enhancement effects were previously observed in that type of reaction. The data are consistent with a rate constant for the abstraction reaction of muonium with acetone in micelles of >6 × 108 M−1 s−1. Key words: muonium, kinetic isotope effects, micelle enhancement, H/Mu-addition, H/Mu abstraction.

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Márquez-Villa, José Martín, Juan Carlos Mateos-Díaz, Jorge A. Rodríguez et Rosa María Camacho-Ruíz. « Lipase B from Candida antarctica in Highly Saline AOT-Water-Isooctane Reverse Micelle Systems for Enhanced Esterification Reaction ». Catalysts 13, n^o 3 (28 février 2023) : 492. http://dx.doi.org/10.3390/catal13030492.

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Butyl oleate synthesis by the lipase B from Candida antarctica (CalB) under extreme halophilic conditions was investigated in the present research through the AOT/Water/Isooctane reverse micellar system. The impact of aqueous content (Wo=H2OSurfactant) and NaCl variation on the enzymatic activity of CalB in the butyl oleate reaction in reverse micelles was explored. The results indicated that, based on the increase of NaCl, it is remarkable to achieve higher enzymatic activity up to 444.85 μmolmin at 5 M NaCl and Wo = 10, as the best esterification conditions at pH 7.2 and 30 °C. However, it was clear that butyl oleate synthesis by lipase CalB increased based on the reduction in the average reverse micelle size, where reverse micelle sizes were determined by dynamic light scattering (DLS). This increase in butyl oleate synthesis demonstrated the potential of reverse micelles as systems that enhance mass transport phenomena in heterogeneous biocatalysis. Furthermore, reverse micelles are promising systems for extreme halophilic lipases research.

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Hétu, Daniel, et Jacques E. Desnoyers. « Volumes and heat capacities of transfer of ammonium salts from water to aqueous octyldimethylamine oxide at 25 °C ». Canadian Journal of Chemistry 66, n^o 4 (1 avril 1988) : 767–73. http://dx.doi.org/10.1139/v88-133.

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The effect of an additive on a water–surfactant system can be studied through thermodynamic functions of transfer of the additive from water to aqueous solutions of the surfactant. These thermodynamic functions often go through extrema in the region of the critical micellar concentration (cmc) of the surfactant. As it can be shown with a simple chemical equilibrium model, the general shape of the transfer functions is primarily related to the pair-wise hydrophobic interactions between the additive and the surfactant monomers, to a shift in the monomer–micelle equilibrium and to the distribution of the additive between the aqueous phase and the micelles. Medium and electrostatic effects are also possible, especially with ionic systems. To separate these effects and identify the salts which distribute themselves in the micelles, the volumes and heat capacities of transfer of hydrophobic ammonium salts from water to aqueous solutions of dimethyloctylamine oxide have been investigated. The short chain salts have only a small effect on monomer–micelle equilibrium by salting out the monomers, whereas the more hydrophobic ones participate also to the micellization process, shifting more strongly the surfactant monomer–micelle equilibrium.

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Hils, Christian, Ian Manners, Judith Schöbel et Holger Schmalz. « Patchy Micelles with a Crystalline Core : Self-Assembly Concepts, Properties, and Applications ». Polymers 13, n^o 9 (4 mai 2021) : 1481. http://dx.doi.org/10.3390/polym13091481.

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Crystallization-driven self-assembly (CDSA) of block copolymers bearing one crystallizable block has emerged to be a powerful and highly relevant method for the production of one- and two-dimensional micellar assemblies with controlled length, shape, and corona chemistries. This gives access to a multitude of potential applications, from hierarchical self-assembly to complex superstructures, catalysis, sensing, nanomedicine, nanoelectronics, and surface functionalization. Related to these applications, patchy crystalline-core micelles, with their unique, nanometer-sized, alternating corona segmentation, are highly interesting, as this feature provides striking advantages concerning interfacial activity, functionalization, and confinement effects. Hence, this review aims to provide an overview of the current state of the art with respect to self-assembly concepts, properties, and applications of patchy micelles with crystalline cores formed by CDSA. We have also included a more general discussion on the CDSA process and highlight block-type co-micelles as a special type of patchy micelle, due to similarities of the corona structure if the size of the blocks is well below 100 nm.

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ul Haq, Naveed, Muhammad Usman, Ajaz Hussain, Zahoor Hussain Farooqi, Muhammad Saeed, Sadia Hanif, Muhammad Irfan, Mohammad Siddiq et Usman Ali Rana. « Partitioning of reactive yellow 86 between aqueous and micellar media studied by differential absorption spectroscopy ». Canadian Journal of Chemistry 95, n^o 6 (juin 2017) : 697–703. http://dx.doi.org/10.1139/cjc-2016-0442.

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The present study describes the partitioning of a reactive dye, reactive yellow 86, between aqueous and micellar media of a cationic surfactant (cetyltrimethyl ammonium bromide, CTAB), as well as an anionic surfactant (sodium dodecyl sulphate, SDS). In a systematic investigation, we have recorded the UV–vis absorption spectra of the dye as a function of surfactant’s concentration above and below the critical micelle concentration (CMC). Absorption spectra display a red shift in the case of CTAB and a hypochromic shift upon using SDS. The partition coefficient (Kx) was calculated using differential absorption data, and the value of free energy of partition (ΔGp) was calculated using this Kx value. The results revealed that the dye is solubilized in CTAB micelles to a greater extent than in SDS micelles.

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Mullally, Maria K., et D. Gerrard Marangoni. « Micellar properties of zwitterionic surfactant - alkoxyethanol mixed micelles ». Canadian Journal of Chemistry 82, n^o 7 (1 juillet 2004) : 1223–29. http://dx.doi.org/10.1139/v04-022.

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The micelle formation process for a zwitterionic surfactant, N-dodecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate (ZW3-12), has been investigated in a series of mixed solvents consisting of different concentrations of ethoxylated alcohols and polymers. The critical micelle concentrations (cmc values) of the aggregates were determined by fluorescence spectroscopy, and the surfactant aggregation numbers were obtained from luminescence probing experiments. The cmc values for ZW3-12 changed very little in the presence of increasing amounts of poly(ethyleneoxide) (PEO) in the mixed solvent. In the case of the ethoxylated alcohol ZW3-12 systems, the cmc values and aggregation numbers decreased systematically with increasing alcohol concentration. However, the cmc values of the mixed micelles showed little dependence on the number of ethylene oxide (EO) groups at constant alcohol concentration. These results are compared with the well-studied sodium dodecylsulfate ethoxylated alcohol, and dodecyltrimethylammonium bromide ethoxylated alcohol mixed micellar systems and to SDSPEO systems and are discussed in terms of the contribution of the EO groups to the hydrophobic interactions. Key words: zwitterionic surfactant, alcohols, mixed micelles, luminescence probing.

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Broxton, TJ. « Micellar Catalysis of Organic Reactions. XXXI. A Study of the Effects of Micelles of Cetyltrimethylammonium Bromide on Some SNAr Reactions in Aqueous Binary Mixtures ». Australian Journal of Chemistry 44, n^o 5 (1991) : 667. http://dx.doi.org/10.1071/ch9910667.

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The effect of micelles of cetyltrimethylammonium bromide ( ctab ) on the SNAr reactions of 1-fluoro-2,4-dinitrobenzene (1), 2-fluoro-5-nitrobenzoate (2) and 4-fluoro-3-nitrobenzoate (3) with sodium hydroxide in aqueous binary mixtures with several alcohols has been studied. Two products were detected in all of these reactions: the phenol from reaction with hydroxide ions, and an aryl alkyl ether from reaction with the alkoxide ions. Micelles of ctab increased the percentage yield of the ether product at the expense of the phenol for compounds (1) and (2) in most of the binary mixtures used. For compound (3), however, micelles of ctab had little effect on the product distribution. These differences were attributed to differences in the orientation of substrates (2) and (3) when solubilized by micelles of ctab . Very high yields of the ether were obtained for the reaction of compound (1) with hydroxide ions in trifluoroethanol /water mixtures, and this was attributed to the considerable ionization of trifluoroethanol which was the most acidic alcohol used in this work. The lowest yield of the ether product was obtained in reactions of compound (1) with hydroxide ions in propan-2-ol/water mixtures since propan-2-ol was the least acidic alcohol used. These results are compared with those previously reported for the reaction of compound (1) in the presence of hydroxy-functionalized micelles and β- cyclodextrin. In the presence of micelles of ctab the aryl alkyl ethers derived from compounds (1) and (2) underwent a subsequent SNAr reaction with hydroxide ions during which the alkoxide ion was displaced. For compound (3) no subsequent reaction of the ether was detected in the presence of micelles of ctab . This was also attributed to the orientation of this product within the micelle. The reaction centre was buried in the micellar interior, and hence was shielded from a subsequent reaction. The rates of this subsequent reaction for compound (1), and of the decomposition of micellar aryl ethers and of cyclodextrin aryl ethers derived from compound (1), are also compared. The increase in the yield of the ether product in the presence of micelles was attributed to the increased ionization of alcohols in the presence of cationic micelles.

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IONESCU, Lavinel G., Danil A. R. Rubio et Elizabeth Fatima De Souza. « MICELLAR CATALYZED HYDROLYSIS OF LITHIUM p-NITROPHENYL ETHYL PHOSPHATE (LiPNEF) AND THE PSEUDO PHASE ION EXCHANGE MODEL ». SOUTHERN BRAZILIAN JOURNAL OF CHEMISTRY 4, n^o 4 (20 décembre 1996) : 59–82. http://dx.doi.org/10.48141/sbjchem.v4.n4.1996.61_1996.pdf.

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The hydrolysis of lithium p-nitrophenyl ethyl phosphate (LiPNEF) was studied at 25°, 35°, and 45 °C by spectrophotometric techniques in the presence of micelles of cetyltrimethylammonium bromide (CTAB), sodium hydroxide, and salt. The concentration of NaOH used varied from 0,050 to 5,00 M and the NaCl ranged from 0,0050 to 0,030 M. Pseudo-first order rate constants (kw) and second-order rate constants (k2) and activation parameters such as Ea, ΔH≠, ΔG≠, and ΔS≠ were measured. The system was also studied by tensiometric, viscosity, and quasi-elastic light scattering methods. At low concentrations of NaOH (below 0,55 M), the reaction can be explained in terms of conventional models of micellar catalysis, including the pseudo-phase ion exchange model. For a higher concentration of NaOH, conventional models of micellar catalysis are not applicable. In fact, at high hydroxide concentration, the system no longer contains micelles but liquid crystalline mesophases, and a model analogous to phase transfer catalysis appears to be more appropriate.

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Lunkim, Kimkholhing, M. Niraj Luwang et Sri K. Srivastava. « Quantitative Analysis of Dye Decolourization Reactions in Mixed Micellar Systems of Sodium Dodecyl Sulfate with Tween-20, Tween-80, and Triton X-100 ». Australian Journal of Chemistry 65, n^o 2 (2012) : 153. http://dx.doi.org/10.1071/ch11454.

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The reaction of triphenylmethane dye (ethyl violet) with hydroxyl ion has been investigated in absence and presence of micelles. In micellar solutions, the solubilization of dye carbocation is observed. The reaction rate constant follows pseudo-first order kinetics with respect to the nucleophile. In presence of sodium dodecyl sulfate (SDS) micelles, an inhibitory effect is observed due to repulsion of the nucleophile to the strongly bound dye carbocation in the negatively charged SDS aggregate. The presence of nonionic surfactant reduces the inhibitory effect of the anionic SDS micelles. Quantitative analysis of the micellar data obtained has been done by applying a positive cooperativity model of enzyme catalysis. The value of n (index of cooperativity) has been found to be greater than 1 for all systems under study. The presence of solvents such as ethanol, n-propanol, and n-butanol reduces the inhibitory effect of the micelles.

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Tang, Christina, et Bridget T. McInnes. « Cascade Processes with Micellar Reaction Media : Recent Advances and Future Directions ». Molecules 27, n^o 17 (31 août 2022) : 5611. http://dx.doi.org/10.3390/molecules27175611.

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Reducing the use of solvents is an important aim of green chemistry. Using micelles self-assembled from amphiphilic molecules dispersed in water (considered a green solvent) has facilitated reactions of organic compounds. When performing reactions in micelles, the hydrophobic effect can considerably accelerate apparent reaction rates, as well as enhance selectivity. Here, we review micellar reaction media and their potential role in sustainable chemical production. The focus of this review is applications of engineered amphiphilic systems for reactions (surface-active ionic liquids, designer surfactants, and block copolymers) as reaction media. Micelles are a versatile platform for performing a large array of organic chemistries using water as the bulk solvent. Building on this foundation, synthetic sequences combining several reaction steps in one pot have been developed. Telescoping multiple reactions can reduce solvent waste by limiting the volume of solvents, as well as eliminating purification processes. Thus, in particular, we review recent advances in “one-pot” multistep reactions achieved using micellar reaction media with potential applications in medicinal chemistry and agrochemistry. Photocatalyzed reactions in micellar reaction media are also discussed. In addition to the use of micelles, we emphasize the process (steps to isolate the product and reuse the catalyst).

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Boucher, Gregory D., Aaron C. MacDonald, Brent E. Hawrylak et D. Gerrard Marangoni. « Article ». Canadian Journal of Chemistry 76, n^o 9 (1 septembre 1998) : 1266–73. http://dx.doi.org/10.1139/v98-165.

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A family of two-headed surfactants, the disodium 4-alkyl-3-sulfonatosuccinates, has been synthesized by the monoesterification of maleic anhydride and the addition of sodium bisulfite to the corresponding monoester. The properties the micelles formed by these compounds in aqueous solution, and the conformations of the chains comprising the micellar interior, have been investigated using a combination of 1-D nmr experiments and homonuclear and heteronuclear 2-D nmr techniques. The critical micelle concentrations (cmc's) and the aggregation numbers determined from the nmr experiments indicate that, in agreement with the earlier literature on other two-headed surfactant systems, these amphiphiles have high cmc's and low aggregation numbers when compared to single-headed surfactants of comparable chain length. All these results are interpreted in terms of the effect of adding a second headgroup to a single-headed, single-tailed surfactant.Key words: micelles, surfactants, nmr spectroscopy, chemical shifts, aggregation numbers.

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Huang, H., et R. E. Verrall. « Thermodynamics of micellization and solubilization in systems of water – sodium n-alkylcarboxylates – alkoxyethanols at 25 °C ». Canadian Journal of Chemistry 75, n^o 11 (1 novembre 1997) : 1445–62. http://dx.doi.org/10.1139/v97-174.

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The apparent molar volumes and adiabatic compressibilities, [Formula: see text] of carboxylate surfactants, CnNa (n = 8, 10, 12), in aqueous solutions in the absence and presence of medium-chain-length alkoxyethanols, C4EOX (EO = ethylene oxide group, X = 0–4), and of alkoxyethanols, [Formula: see text] in aqueous solutions in the absence and presence of surfactant, were determined at 25 °C from density and sound velocity measurements as a function of both the surfactant and alcohol concentrations. The partial molar volumetric properties of CnNa and the transfer functions of C4EOX from water to aqueous surfactant solutions were calculated from the apparent molar properties. Values of the thermodynamic parameters of micellization for CnNa, i.e., the critical micelle concentration, the partial molar property of the monomer at infinite dilution, [Formula: see text] and in the micellar state, [Formula: see text] were obtained from simulations of the experimental data, [Formula: see text] using a mass-action model. As expected, these properties are strongly dependent on the surfactant chain length. The distribution coefficient of C4EOX between the micelle and aqueous phases, KD, and the change in the molar property of alcohols due to micellization, [Formula: see text] extracted from fitting the transfer function data of C4EOX using a chemical equilibrium model, show that the solubilization of alkoxyethanols in carboxylate micelles is enhanced by increasing the surfactant chain length and the number of EO groups in the alcohol. The deeper penetration of C4EOX into the micelles of longer chain surfactants is associated with increasingly stronger interactions between surfactant head groups and EO segments of the alcohol on (or near) the micelle surface. Aggregation numbers of CnNa–C4EOX mixed micelles show that addition of a small amount of C4EOX has little effect on the structure of the micelles formed from C8Na and C10Na, but leads to significant change in C12Na micelles. Keywords: sodium carboxylate salts, alkoxyethanols, partial molar volume and compressibility, transfer functions, distribution coefficient, mean aggregation number.

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Gracie, Kim, Dale Turner et R. Palepu. « Thermodynamic properties of micellization of sodium dodecyl sulfate in binary mixtures of ethylene glycol with water ». Canadian Journal of Chemistry 74, n^o 9 (1 septembre 1996) : 1616–25. http://dx.doi.org/10.1139/v96-179.

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Micellar properties of sodium dodecyl sulfate (SDS) in aqueous mixtures of ethylene glycol (EG) were determined using techniques such as conductivity, density, EMF, surface tension, viscosity, ultrasonic velocity, and spectroscopy (fluorescence). The effective degree of disssociation of micelles (α) was determined using three different methods. Thermodynamics of micellization were obtained from the temperature dependence of critical micelle concentrations (cmc) values. The difference in Gibbs energies of micellization [Formula: see text] of SDS, between water and mixed solvent systems, was calculated to evaluate the influence of cosolvent on the micellization process. Surfactant aggregation numbers (Ns) obtained from static fluorescence quenching methods indicated a decrease in the aggregation numbers with increasing concentration of ethylene glycol in the binary solvent mixtures. In addition, the micropolarity of the micellar interior was determined from the pyreneI1/I3 ratios. These values were consistent with a decrease in the micropolarity surrounding the probe molecule as the EG content in the solvent mixture was increased. Key words: thermodynamics, micellization, aggregation numbers, ultrasonic velocity, degree of dissociation.

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Cruz Barrios, Eliandreina, Kyra V. Penino et Onofrio Annunziata. « Diffusiophoresis of a Nonionic Micelle in Salt Gradients ; Roles of Preferential Hydration and Salt-Induced Surfactant Aggregation ». International Journal of Molecular Sciences 23, n^o 22 (8 novembre 2022) : 13710. http://dx.doi.org/10.3390/ijms232213710.

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Diffusiophoresis is the migration of a colloidal particle in water driven by concentration gradients of cosolutes such as salts. We have experimentally characterized the diffusiophoresis of tyloxapol micelles in the presence of MgSO4, a strong salting-out agent. Specifically, we determined the multicomponent-diffusion coefficients using Rayleigh interferometry, cloud points, and dynamic-light-scattering diffusion coefficients on the ternary tyloxapol–MgSO4–water system at 25 °C. Our experimental results show that micelle diffusiophoresis occurs from a high to a low salt concentration (positive diffusiophoresis). Moreover, our data were used to characterize the effect of salt concentration on micelle size and salt osmotic diffusion, which occurs from a high to a low surfactant concentration. Although micelle diffusiophoresis can be attributed to the preferential hydration of the polyethylene glycol surface groups, salting-out salts also promote an increase in the size of micellar aggregates, ultimately leading to phase separation at high salt concentration. This complicates diffusiophoresis description, as it is not clear how salt-induced surfactant aggregation contributes to micelle diffusiophoresis. We, therefore, developed a two-state aggregation model that successfully describes the observed effect of salt concentration on the size of tyloxapol micelles, in the case of MgSO4 and the previously reported case of Na2SO4. Our model was then used to theoretically evaluate the contribution of salt-induced aggregation to diffusiophoresis. Our analysis indicates that salt-induced aggregation promotes micelle diffusiophoresis from a low to a high salt concentration (negative diffusiophoresis). However, we also determined that this mechanism marginally contributes to overall diffusiophoresis, implying that preferential hydration is the main mechanism causing micelle diffusiophoresis. Our results suggest that sulfate salts may be exploited to induce the diffusiophoresis of PEG-functionalized particles such as micelles, with potential applications to microfluidics, enhanced oil recovery, and controlled-release technologies.

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Singh, R. K. London. « Micellar Effects on Nucleophilic Addition Reaction and Applicability of Enzyme Catalysis Model ». E-Journal of Chemistry 9, n^o 3 (2012) : 1181–87. http://dx.doi.org/10.1155/2012/129436.

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This study describes the effect of anionic and cationic micelles on nucleophilic addition reaction of rosaniline hydrochloride (RH) with hydroxide under pseudo-first order condition. Strong inhibitory effect is observed due to SDS micelle, whereas CTAB catalysed the reaction. This is explained on the basis of electrostatic and hydrophobic interactions which are simultaneously operating in the reaction system. The kinetic data obtained is quantitatively analysed by applying the positive cooperativity model of enzyme catalysis. Binding constants and influence of counterions on the reaction have also been investigated.

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Procházka, Karel, Hélène Delcros et Geneviève Delmas. « A light scattering and calorimetric study of micelle formation by a polystyrene -b-hydrogenated polyisoprene block copolymer in a binary solvent (pentane–cyclopentane) ». Canadian Journal of Chemistry 66, n^o 4 (1 avril 1988) : 915–18. http://dx.doi.org/10.1139/v88-155.

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A light scattering and calorimetric study was made of micelle formation by a polystyrene-b-hydrogenated polyisoprene in a binary mixture. The polymer 0.42 weight percent PS, is unassociated in cyclopentane (c-C5) but forms micelles with a PS core in n-pentane, a non-solvent for PS. Light scattering measurements and heats of mixing, obtained over the binary composition range at a polymer concentration higher than the c.m.c., show that the solution changes from the unassociated to the micellar state for solutions richer in pentane than 0.4 volume fraction. Using heats of mixing of the corresponding homopolymers, the heat of micellization is found to be −5.1 + 0.3 J g−1, a value which supports the model of an enthalpy driven process of micellization.

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Ortega, Francisco, et Elvira Rodenas. « Counterion micellar effects upon the reaction of low-spin diimine iron(II) complexes ». Canadian Journal of Chemistry 67, n^o 2 (1 février 1989) : 305–9. http://dx.doi.org/10.1139/v89-050.

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The rate of reaction of tris(1,10-phenanthroline)iron(II) ion (1a), tris(3,4,7,8-tetramethyl-1,10-phenanthroline)iron(II) ion (1b), and tris(4,7-diphenhyl-1, 10-phenanthroline)iron(II) ion (1c) with hydroxide ion, in cationic micelles, is strongly affected by the concentration of micellar counterion in solution. The reaction of la in CTACl is modestly speeded up by the addition of added KCl, while the reactions of 1b and 1c are strongly inhibited by the addition of large amounts of KCl and KBr to micellar solutions of CTACl and CTABr, respectively. These rate effects fit the pseudophase-ion exchange model, assuming the binding of the substrates to the micelles depends upon the counterion concentration. Keywords: counterion micellar effects, low-spin diimine iron(II) complexes.

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Landry, Josette M., D. Gerrard Marangoni, Michael D. Lumsden et Robert Berno. « 1D and 2D NMR investigations of the micelle-formation process in 8-phenyloctanoate micelles ». Canadian Journal of Chemistry 85, n^o 3 (1 mars 2007) : 202–7. http://dx.doi.org/10.1139/v07-008.

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The micellization process of sodium 8-phenyloctanoate in a deuterated aqueous solution was studied, using 1H NMR spectroscopy and two-dimensional (2D) nuclear Overhauser enhancement spectroscopy (NOESY). 1H NMR spectra, acquired for the sodium 8-phenyloctanoate before and after the critical micelle concentration (CMC) value, showed that large chemical-shift changes were observed for both the aromatic proton peaks and the peaks for the methylene protons near the terminal phenyl group. The plots for the methylene protons near the headgroup do not show these large chemical-shift changes. These observations support the view that the terminal phenyl ring of the surfactant is primarily located in the micellar interior. The 2D NOESY experiments show significant cross-peaks, between the phenyl protons and the methylene protons of the surfactant, that substantiate the conclusions on those drawn from NMR aromatic solute induced shift (ASIS) experiments on the same and similar systems. All these observations are consistent with the Gruen model of the micelle and previous NMR NOESY experiments for other surfactant systems.Key words: surfactants, micelles, NMR, NOESY.

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Martinek, Karel, Iliya V. Berezin, Yurii L. Khmelnitski, Natalya L. Klyachko et Andrei V. Levashov. « Micellar enzymology : Potentialities in applied areas (biotechnology) ». Collection of Czechoslovak Chemical Communications 52, n^o 10 (1987) : 2589–602. http://dx.doi.org/10.1135/cccc19872589.

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Micellar enzymology, a new trend in molecular biology, studies the catalysis by enzymes entrapped into hydrated reversed micelles of surfactants (detergents, phospholipids) in organic solvents. The effect of solubilization on enzymatic properties is briefly considered. Applications of such biocatalytic systems in fine organic syntheses, in clinical and chemical analyses, and in medicine, as well as probable future trends in biotechnology are discussed.

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Ilhami, Fasih Bintang, Kai-Chen Peng, Yi-Shiuan Chang, Yihalem Abebe Alemayehu, Hsieh-Chih Tsai, Juin-Yih Lai, Yu-Hsuan Chiao, Chen-Yu Kao et Chih-Chia Cheng. « Photo-Responsive Supramolecular Micelles for Controlled Drug Release and Improved Chemotherapy ». International Journal of Molecular Sciences 22, n^o 1 (25 décembre 2020) : 154. http://dx.doi.org/10.3390/ijms22010154.

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Development of stimuli-responsive supramolecular micelles that enable high levels of well-controlled drug release in cancer cells remains a grand challenge. Here, we encapsulated the antitumor drug doxorubicin (DOX) and pro-photosensitizer 5-aminolevulinic acid (5-ALA) within adenine-functionalized supramolecular micelles (A-PPG), in order to achieve effective drug delivery combined with photo-chemotherapy. The resulting DOX/5-ALA-loaded micelles exhibited excellent light and pH-responsive behavior in aqueous solution and high drug-entrapment stability in serum-rich media. A short duration (1–2 min) of laser irradiation with visible light induced the dissociation of the DOX/5-ALA complexes within the micelles, which disrupted micellular stability and resulted in rapid, immediate release of the physically entrapped drug from the micelles. In addition, in vitro assays of cellular reactive oxygen species generation and cellular internalization confirmed the drug-loaded micelles exhibited significantly enhanced cellular uptake after visible light irradiation, and that the light-triggered disassembly of micellar structures rapidly increased the production of reactive oxygen species within the cells. Importantly, flow cytometric analysis demonstrated that laser irradiation of cancer cells incubated with DOX/5-ALA-loaded A-PPG micelles effectively induced apoptotic cell death via endocytosis. Thus, this newly developed supramolecular system may offer a potential route towards improving the efficacy of synergistic chemotherapeutic approaches for cancer.

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Tee, Oswald S., et Ogaritte J. Yazbeck. « Transition state stabilization by micelles : thiolysis of p-nitrophenyl alkanoates in cetyltrimethylammonium bromide micelles ». Canadian Journal of Chemistry 78, n^o 8 (1 août 2000) : 1100–1108. http://dx.doi.org/10.1139/v00-113.

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Thiolysis of p-nitrophenyl esters (acetate to decanoate) by the anion of 2-mercaptoethanol (ME) is catalyzed by micelles of cetyltrimethylammonium bromide (CTAB) in aqueous solution. At fixed [ME], the observed rate constants (kobs) show saturation with respect to added [CTAB], consistent with ester binding in the micelles. Plots of kobs vs. [ME] are linear in the absence and in the presence of the CTAB, and analysis of the slopes of the plots afford rates constants for thiolate ion attack on the esters in the aqueous phase (kN) and in the micellar phase (kcN). The strengths of substrate binding and transition state binding to the micelles are strongly correlated, with a slope of unity, because they have the same dependence on the ester chain. Consequently, the catalytic ratios (kcN/kN) are independent of the length of the ester. Similar behaviour is found for thiolysis by the dianions of mercaptoacetic acid, 3-mercaptopropionic acid, and cysteine, and also for ester cleavage by the anions of glycine and 2,2,2-trifluoroethanol, as earlier for cleavage by hydroxide ion. The results are consistent with Kirby's dissection of transition state binding into "passive" and "dynamic" components. The passive component involves hydrophobic binding of the ester chain which is more or less the same as in the substrate binding. The dynamic component is associated with reaction in the Stern layer of the micelle, and its magnitude varies with the nucleophiles because of differences in their ease of exchange between the aqueous medium and the Stern layer.Key words: catalysis, esters, thiolysis, micelles.

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Stavber, Gaj. « The Road to Greener Applied Organic Synthesis : Performing Organic Reactions in Micelle-Based and Host-Guest Aqueous Nanoreactors ». Australian Journal of Chemistry 63, n^o 5 (2010) : 849. http://dx.doi.org/10.1071/ch10051.

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The micellar and supramolecular catalysis of organic reactions in water, utilizing nanometre-sized micelles of ionic, non-ionic amphiphiles or host-guest inclusion complexes using appropriate host macrocyclic molecules able to accommodate a hydrophobic organic substrates are taken under a brief account. A focus on Heck-type C-C couplings, ring closing metathesis, and halo-transformations of organic compounds in aqueous environment, is presented.

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Wood, Alex B., Daniel E. Roa, Fabrice Gallou et Bruce H. Lipshutz. « α-Arylation of (hetero)aryl ketones in aqueous surfactant media ». Green Chemistry 23, n^o 13 (2021) : 4858–65. http://dx.doi.org/10.1039/d1gc01572a.

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α-Arylations can be run under micellar catalysis conditions using a Pd(i) pre-catalyst together with KO-t-Bu as base. Sequences using this coupling along with as many as four additional steps can be carried out in a 1-pot fashion, all in water.

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Bunton, Clifford A., Houshang J. Foroudian, Nicholas D. Gillitt et Christy R. Whiddon. « Dephosphorylation and aromatic nucleophilic substitution in nonionic micelles. The importance of substrate location ». Canadian Journal of Chemistry 76, n^o 6 (1 juin 1998) : 946–54. http://dx.doi.org/10.1139/v98-093.

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Reactions of OH- and F- with p-nitrophenyl diphenyl phosphate (pNPDPP) are inhibited by very dilute dodecyl (10) and (23) polyoxyethylene glycol (C12E10 and C12E23, respectively), but rate constants become independent of surfactant concentrations at concentrations above the critical micelle concentration. Low charge density anions, e.g., ClO4-, inhibit and low charge density cations, e.g., (n-C7H15)4N+, accelerate reactions, probably by controlling concentrations of nucleophiles in the palisade layer. Diphenyl phosphorofluoridate, generated by attack of F-, is not detected but is rapidly hydrolyzed to phenyl phosphorofluoridate or diphenyl phosphate ion with loss of phenol or F-. The products are different in DMSO containing modest amounts (<15 vol%) of water and no surfactant and are phenyl phosphorofluoridate and difluorophosphate ions generated by attack of F- on the initial phosphorofluoridate. These differences are consistent with the micellar palisade layer being water-rich. Although the nonionic surfactants do not intervene nucleophilically in reactions of pNPDPP, considerable amounts of ether are formed in the reaction of 2,4-dinitrochlorobenzene (DNCB), in C12E10 and C12E23 at high pH by attack of alkoxide ion with the relatively hydrophilic DNCB located close to the micellar surface. The differences in the chemistries of reactions of pNPDPP and DNCB appear to be associated largely with differences in locations of these substrates in the nonionic micelles.Key words: fluoridates, p-nitrophenyl diphenyl phosphate, 2,4-dinitrochlorobenzene, nonionic micelles, palisade layer.

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Razak, Norazizah Abd, et M. Niyaz Khan. « Kinetics and Mechanism of Nanoparticles-Catalyzed Piperidinolysis of Anionic Phenyl Salicylate ». Scientific World Journal 2014 (2014) : 1–7. http://dx.doi.org/10.1155/2014/604139.

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The values of the relative counterion (X) binding constantRXBr(=KX/KBr, whereKXandKBrrepresent cetyltrimethylammonium bromide, CTABr, micellar binding constants ofXv-(in non-spherical micelles),v=1,2, and Br−(in spherical micelles)) are 58, 68, 127, and 125 forXv−=1−, 12−, 2−, and22-, respectively. The values of 15 mM CTABr/[NavX] nanoparticles-catalyzed apparent second-order rate constants for piperidinolysis of ionized phenyl salicylate at 35°C are 0.417, 0.488, 0.926, and 0.891 M−1 s−1forNavX= Na1, Na21, Na2, and Na22, respectively. Almost entire catalytic effect of nanoparticles catalyst is due to the ability of nonreactive counterions,Xv-, to expel reactive counterions,3−, from nanoparticles to the bulk water phase.

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Dolcet, C., et E. Rodenas. « An electrostatic approach to negatively charged substrate reactions with hydroxide ion in cationic CTAB micelles ». Canadian Journal of Chemistry 68, n^o 6 (1 juin 1990) : 932–38. http://dx.doi.org/10.1139/v90-145.

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An electrostatic treatment is presented to explain the experimental kinetic data we obtained for the basic hydrolysis of the negatively charged substrates acetylsalicylic acid and 3-acetoxy-2-naphthoic acid. This treatment, based on the non-linearized Poisson–Boltzmann equation, considers specific interactions between the counterions and the micellar surface and explains the displacement of these substrates from the micellar to the aqueous phase through bromide counterion addition. Keywords: electrostatic approach, cationic CTAB micelles.

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Broxton, TJ, JR Christie et SM Mannas. « Micellar Catalysis of Organic-Reactions. XXI. A Comparison of the Catalytic Activity of Micelles of Cetyltrimethylammonium Bromide and Sulfate on Ester, Amide and Carbamate Hydrolyses ». Australian Journal of Chemistry 41, n^o 3 (1988) : 325. http://dx.doi.org/10.1071/ch9880325.

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The basic hydrolyses of phenyl acetate, N,4-dimethyl-N-(3′- nitrophenyl ) benzamide , methyl N-methyl-N-(4′-nitrophenyl) carbamate and methyl N-(3′,5′-dinitrophenyl)-N-methylcarbamate have been studied in cationic micelles of cetyltrimethylammonium bromide (ctab) and sulfate (ctas). Hydrolysis of phenyl acetate and the 4′-nitro carbamate, which involve rate-determining hydroxide attack, exhibit weak catalysis by both micelles, and the observed rates in each micelle are similar. The hydrolysis of the benzamide and the 3′,5′-dinitro carbamate, which involve rate determining C-N bond breaking, show larger catalysis, and, furthermore, micelles of ctab are more effective than micelles of ctas. The observed rates can be explained by the pseudo-phase kinetic model. For reactions involving rate-determining hydroxide attack, the calculated second-order rate constants in micelles of ctab and ctas are similar and much less than those for reaction in water. For reactions involving rate-determining C-N bond breaking the calculated second-order rate constants in micelles of ctab are greater than in micelles of ctas, and similar to those for reaction in water.

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Wang, Hui, Ambra Maria Fiore, Christophe Fliedel, Eric Manoury, Karine Philippot, Maria Michela Dell'Anna, Piero Mastrorilli et Rinaldo Poli. « Rhodium nanoparticles inside well-defined unimolecular amphiphilic polymeric nanoreactors : synthesis and biphasic hydrogenation catalysis ». Nanoscale Advances 3, n^o 9 (2021) : 2554–66. http://dx.doi.org/10.1039/d1na00028d.

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Triphenylphosphine-stabilised rhodium nanoparticles embedded in well-defined core-crosslinked micelles have been generated and used in aqueous biphasic catalysis. The conditions allowing core confinement and efficient catalyst recycle are outlined.

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