Dodecyltrimethylammonium Chloride Micelles Research Articles

Photoionization of 3-Methylindole Embedded in Sodium Dodecyl Sulfate and Dodecyltrimethylammonium Chloride Micelles: Migration of Electrons Generated in Micelle Cores and Their Solvation in Outside Water

Electrons were generated in the core of micelles formed by negatively charged sodium dodecyl sulfate (SDS) or positively charged dodecyltrimethylammonium chloride (DTAC) by photoionization of 3-methylindole embedded in the core. The electrons were hydrated after they moved out of the core to the outer aqueous phase. These processes were monitored with femtosecond time-resolved absorption spectroscopy. The migration of electrons from the micelle core to the outer aqueous phase was faster than the instrumental response time of 200 fs. Hot electrons in the aqueous phase were produced in ≤320 fs. There was no significant difference observed for the micellar solutions of negatively charged SDS and positively charged DTAC, or for water. The geminate recombination between the electrons and the radical cations was hindered to a large extent once the electrons hydrated at the outer aqueous phase were separated from the radical cations remaining in the micelle core.

Molecular dynamics study of the aggregation rate for zwitterionic dodecyldimethylamine oxide and cationic dodecyltrimethylammonium chloride micelles

We studied dynamic scaling law for the early stage domain growth in the micelle aggregation process of dispersed surfactant molecules in water for zwitterionic dodecyldimethylamine oxide (DDAO) and cationic dodecyltrimethylammonium chloride (DTAC) based on all-atomistic molecular dynamics calculations. For both surfactants, the aggregation number N increases in proportion to tα′, where t and α′ are the simulation time and exponent of the dynamic scaling, respectively. When the aggregation is controlled by diffusion, it follows the well-known Lifshitz–Slyozov (LS) law giving the exponent α′ = 1. The values of α′ obtained for DDAO and DTAC are 0.6 and 0.3, respectively, indicating that the aggregation rate is suppressed compared with purely diffusion controlled LS process. The aggregation of DDAO and DTAC may be partly controlled by electrostatic interaction between the aggregates.

Physico-chemical Investigation of Mixed Micelle Formation Between Tetradecyltrimethylammonium Bromide and Dodecyltrimethylammonium Chloride in Water and Aqueous Solutions of Sodium Chloride

Conductometric measurements have been employed to gain a detailed insight into the interactions between two cationic surfactants, tetradecyltrimethylammonium bromide (TTAB) and dodecyltrimethylammonium chloride (DTAC), in water and in an aqueous solution of sodium chloride. The experimental data were analyzed according to Rubingh’s model within the framework of the pseudophase separation model. The evaluated values of critical micelle concentration (cmc) were found to be lower than their corresponding cmcid values, signifying attractive interactions involving both components in the solutions. The micellar mole fractions (\( X_{1}^{\text{Rub}} \)) of TTAB evaluated by Rubingh’s model were always larger than the ideal values (\( X_{1}^{\text{id}} \)), signifying the higher involvement of TTAB in mixed micelles of TTAB and DTAC. Activity coefficients (\( f_{ 1}^{\text{Rub}} \) and \( f_{ 2}^{\text{Rub}} \)) were always below one in all cases signifying synergism in the mixed micelles. All the outcomes point to synergism and attractive interactions in the mixed systems. Values of excess Gibbs energy were evaluated by employing Rubingh’s model (\( \Delta G_{\text{ex}}^{\text{Rub}} \)) and the \( \Delta G_{\text{ex}}^{\text{Rub}} \) values obtained are negative. The values of \( \Delta H_{\text{m}}^{\text{o}} \) and \( \Delta S_{\text{m}}^{\text{o}} \) reveal that hydrophobic interaction is expected to be the binding force between TTAB and DTAC in aqueous media at lower temperatures, while both hydrophobic interactions as well as exothermic interactions are involved at higher temperatures. The interaction forces between the surfactants were found to be enhanced in the presence of NaCl.

Molecular dynamics study of stability and disintegration of long rod-like micelles: Dodecyltrimethylammonium chloride in solutions of hydroxybenzoates

Abstract Recently it was found out that different positions of the hydroxylic group on hydroxybenzoate anions (HB) crucially affect the thermodynamics of the self-organization of the cationic surfactant dodecyltrimethylammonium chloride (DTAC) and also the structure of resulting aggregates. In our previous work, the properties of stable long cylindrical DTAC micelles in the presence of NaHB at 1:1 DTAC/NaHB molar ratio in aqueous solutions were investigated by atomistic molecular dynamics simulations. In the present work, we first study the decay of cylindrical DTAC micelles in water without added salt and then extend our research to systems with low NaHB concentrations (DTAC/NaHB molar ratios of 4:1 and 2:1) in order to approach the real experimental conditions more closely. The geometry and structural properties of DTAC micelles in water are investigated, and also the decomposition of long cylindrical micelles and the solvent accessible surface area of micelles is discussed. We observe that the initial DTAC micelle without NaHB quickly disintegrates into smaller stable spherical micelles. At the 2:1 DTAC/NaHB molar ratio we find all initial DTAC micelles to remain stable; however, their geometry deviates significantly from initial cylindrical one. Furthermore, it is observed that o-HB induces a more ordered internal structure of the micelle, and is more strongly oriented than the other two isomers, which agrees well with the experiments and observations reported in our previous work. When the NaHB concentration is decreased to 4:1 DTAC/NaHB molar ratio, an initial DTAC micelle disintegrates forming smaller aggregates of spherical or elongated shapes regardless of the nature of the HB isomer present. The microscopic structure of the resultant micelles is very similar to the structure observed at higher NaHB concentration, however, the effect of HB ions is smaller. It was also observed that the micelle remains stable longer in the presence of o-HB than in the presence of the other two isomers.

Structure and Stability of Long Rod-like Dodecyltrimethylammonium Chloride Micelles in Solutions of Hydroxybenzoates: A Molecular Dynamics Simulation Study.

The relative position of the hydroxylic and carboxylic groups in the isomeric hydroxybenzoate (HB) anions is experimentally known to have a large impact on the thermodynamics of micellization of cationic surfactants, such as dodecyltrimethylammonium chloride (DTAC), and on the structure of the resulting micelles. To understand the effect of the different isomers on the molecular level, we employed atomistic molecular dynamics simulations to study systems containing infinitely long cylindrical DTAC micelles in aqueous solutions of the sodium salts of all three isomers of HB at a temperature and a pressure of 298.15 K and 1 atm. In all studied systems, the number of DTAC unimers is identical to the number of HB anions. At this concentration, the initially cylindrical micelles remain stable, irrespective of the nature of the isomer, whereas micelles rapidly disintegrated in the absence of HB anions. The HB isomers decrease the line density of unimers along the micellar axis and its concomitant thickness in the order o-HB > m-HB > p-HB. It is further observed that o-HB anions penetrate more deeply into the micellar core, induce a more ordered internal structure of the micelle, and are oriented more strongly than the other two isomers. In addition, the ortho isomer shows two different preferential orientations with respect to the radial direction of the cylindrical micelle; it can either be incorporated almost completely into the micelle or it can be attached through hydrogen bonding to one of those o-HB anions that are already incorporated into the micelle, and thus stick out of the micellar surface.

Time evolution of monomers and aggregates of a polymethine dye probe the dynamics of model vesicles and micelles

Time-resolved absorption (plus turbidity) spectra of the dye FDID in DDAB vesicles, illustrating the slow-dynamics disaggregation: H-aggregate → monomer. • An anionic polymethine dye is incorporated in model bicationic vesicles/micelles. • In colloidal structures, absorption spectra detected dye monomers and H-aggregates. • In the presence of the lipid DDAB, H-aggregates slowly disaggregated into monomers. • A mechanism for the above disaggregation was proposed from kinetic/absorption data. • The dye sensed the exchanging dynamics of surfactant(s) between colloids and water. An anionic polymethine dye (a fluoro-oxonol abbreviated FDID), which forms monomers and oligomers according to the surrounding medium, is used in this work to probe the stability and dynamics of bicationic colloidal nanostructures, namely micelles and vesicles. Using pure water as the reference solvent (medium 1 ), five aqueous colloidal media of the lipid–detergent system DDAB–DTAC (didodecyldimethylammonium bromide–dodecyltrimethylammonium chloride) were analyzed: pre-micelle DTAC media ( 2 ); pure DTAC micelles ( 3 ); DDAB–DTAC micelles ( 4 ); DDAB–DTAC vesicles ( 5 ); and pure DDAB vesicles ( 6 ). In systems 4–6 , containing the double-chained DDAB, FDID showed a slow-dynamics disaggregation, H-aggregates → monomers. The kinetics of this transition was followed by running UV–vis absorption spectra along time. The transition lifetimes τ increased in the order τ medium 3 ≪ τ media 4,5 < τ medium 6 , reflecting the much faster mobility of the single-chained DTA + long ion, as compared to that of the more hydrophobic, double-chained, DDA + . This paper showed that FDID can probe the exchanging dynamics of the DDA + /DTA + long cations between the water phase and the colloidal nanostructures.

Effect of Counterions on the Shape, Hydration, and Degree of Order at the Interface of Cationic Micelles: The Triflate Case

Specific ion effects in surfactant solutions affect the properties of micelles. Dodecyltrimethylammonium chloride (DTAC), bromide (DTAB), and methanesulfonate (DTAMs) micelles are typically spherical, but some organic anions can induce shape or phase transitions in DTA(+) micelles. Above a defined concentration, sodium triflate (NaTf) induces a phase separation in dodecyltrimethylammonium triflate (DTATf) micelles, a phenomenon rarely observed in cationic micelles. This unexpected behavior of the DTATf/NaTf system suggests that DTATf aggregates have unusual properties. The structural properties of DTATf micelles were analyzed by time-resolved fluorescence quenching, small-angle X-ray scattering, nuclear magnetic resonance, and electron paramagnetic resonance and compared with those of DTAC, DTAB, and DTAMs micelles. Compared to the other micelle types, the DTATf micelles had a higher average number of monomers per aggregate, an uncommon disk-like shape, smaller interfacial hydration, and restricted monomer chain mobility. Molecular dynamic simulations supported these observations. Even small water-soluble salts can profoundly affect micellar properties; our data demonstrate that the -CF3 group in Tf(-) was directly responsible for the observed shape changes by decreasing interfacial hydration and increasing the degree of order of the surfactant chains in the DTATf micelles.

Spectroscopical properties of a DTAF-labeled hydrophilic–hydrophobic copolymer in water and surfactant micelles

Emulsion copolymerization of hydrophilic α-tert-butoxy-ω-vinylbenzyl-polyglycidol macromonomer with styrene yields core–shell microspheres and a water-soluble copolymer fraction. This copolymer has a higher content of hydrophilic polyglycidol attested by 1H NMR. Further information is acquired by labeling the copolymer with 5-(4,6-dichlorotriazinyl)aminofluorescein (DTAF) and making absorption and fluorescence studies. The acquired data on aqueous solution of labeled copolymer without (L) and with micelles of dodecyltrimethylammonium chloride (LD), sodium dodecylsulfate (LS) and hexaethyleneglycol mono n-dodecyl ether (LE) reveal that the dianionic and anionic tautomers of the DTAF-label are apparent and concordant with the recorded spectrophotometric pKa values. The emission intensities, quantum yields and lifetimes obey the sequence LE < LS < L < LD. They are along with the increasingly deprotonated forms of the fluorophore and unveil that the micelle-label interactions depend on the surfactant.

Aggregation and disaggregation of anionic aluminum phthalocyanines in cationic pre-micelle and micelle media: A fluorescence study

Abstract The interactions of two anionic aluminum phthalocyanines (Pcs), the tetrasulfonated (AlPcS 4 ) and the monosulfonated (AlPcS 1 ) species, with the cationic detergent n -dodecyltrimethylammonium chloride (DTAC) were investigated. These studies were performed by UV–visible absorption, steady-state and transient-state fluorescence, fluorescence lifetime imaging microscopy (FLIM), and fluorescence correlation spectroscopy (FCS). For both AlPcS 4 and AlPcS 1 , large complexes of Pc–DTAC were formed at low surfactant concentrations, in the pre-micelle range. These complexes were visualized by the FLIM technique, directly in a drop of the sample. As the DTAC concentration increased, the size of the complexes decreased significantly. Above the detergent critical micelle concentration ( CMC ≈ 22 mM), highly fluorescent monomers of both AlPcS 4 and AlPcS 1 were found to be strongly bound to the DTAC micelles surface: large equilibrium binding constants, K b = 3.5 × 10 5 and 6.2 × 10 4 , were obtained for AlPcS 4 and AlPcS 1 , respectively. The aggregation/disaggregation behavior of phthalocyanines likely results from a delicate balance in the system, between hydrophobic attractions (Pc–Pc) and electrostatic attractions (anionic Pc macrocycles – cationic DTAC headgroups) and repulsions (between anionic sulfonated groups of Pc macrocycles).

Characterization of metal nanoparticles prepared by photoreduction in aqueous solutions of various surfactants using UV–vis, EXAFS and SAXS

Photoreduction formation mechanisms of metal particles (gold (Au) and platinum (Pt) particles) in aqueous surfactant solutions of dodecyltrimethylammonium chloride (DTAC) and polyethylene glycol lauryl ether (PEG) have been studied by transmission electron microscopy (TEM), small-angle X-ray scattering (SAXS), and extended X-ray absorption fine structure (EXAFS) measurements. EXAFS results confirmed the metallic nature of the nanoparticles, and showed that the average particle size significantly depends neither on the metal species nor on the charged properties (cationic, anionic, or nonionic) of surfactants. The SAXS analysis indicated that the structure of DTAC and PEG micelles could be fitted with the hard-sphere model having the interaction radius R HS and the spherically shaped core–shell structure. At the beginning of the photoirradiation, the increase of the SAXS intensity at q < 1.0 nm −1 was not due to the change of the size and shape of the produced metal particles, but due to the increase in number of produced metal particles in the growth process. Once the radius of metal particles produced during the photoirradiation exceeded a radius ( R shell) of the individual micelles, the metal particle growth was noticeably accelerated and the larger aggregates were formed, which were not stabilized by adsorbed surfactant molecules on their metal surface.

Catalytic conversions in aqueous media: Part 3. Biphasic hydrogenation of polybutadiene catalyzed by Rh/TPPTS complexes in micellar systems

Water-soluble Rh/TPPTS complexes [TPPTS = P(C 6H 4- m-SO 3Na) 3] are active catalysts (TOF > 1200 h −1) for the biphasic hydrogenation of the completely water-insoluble heavy polybutadiene (PB) in single micelles formed by the cationic surfactant dodecyltrimethylammonium chloride (DTAC), or mixed micelles created by DTAC with either non-ionic or anionic surfactants. The reaction proceeds under mild conditions ( T = 100 °C, P H 2 = 20 bar ) at a molar ratio of P/Rh = 3 and C C units/Rh = 1000 within 20 min and at a rhodium concentration of only 10 ppm in water. The pH of the aqueous catalyst solution markedly influenced the activity. High catalytic activities were achieved under neutral conditions whereas at acidic or basic conditions the catalytic activity dramatically decreased. The hydrogenation rate depends critically on the microstructure of PB and the nature of micellar catalysis. The 1,4-units content of PB plays a major role for performing the catalytic hydrogenation reaction in single or mixed micellar systems for obtaining maximum reactivity. When the PB possesses a high 1,4-units content (98.0 wt% of 1,4-units and 2.0 wt% of 1,2-units) higher reaction rates were achieved in mixed micellar systems created by DTAC/Brij-35 surfactants compared to the rates observed in single DTAC micelles. In contrast, with PB starting material consisting of 61.0 wt% of 1,2-units and 39.0 wt% of 1,4-units higher reaction rates were obtained in single DTAC micelles compared to those rates achieved in mixed micellar systems.

Fluorescence of 1,3-Di(1-pyrenyl)propane probe incorporated into human serum albumin protein enforced conformations of the probe

Steady-state and time-resolved fluorescence spectra of 1,3-di (1-pyrenyl)propane (1 Py-(3)-1 Py) incorporated into macromolecules of human serum albumin (HSA), into micelles of dodecyltrimethylammonium chloride (DTAC), and dissolved in 1,4-dioxane were compared. The steady-state fluorescence spectra indicated that in all the mentioned environments, upon excitation of lPy-(3)-lPy, light was emitted from the single pyrene chromophores (lPy*) and from the lPy, lPy* excimers. The time-resolved fluorescence emission registered at 480 nm (excimer emission) for lPy-(3)-lPy in the DTAC micelles and dissolved in 1,4-dioxane allowed to monitor formation of excimer with time constant τ1 = 40.0 ns and 9.6 ns, for lPy-(3)-lPy in the DTAC micelles and in 1,4-dioxane, respectively. However, when the lPy-(3)-lPy probe was located inside of the macromolecules of HSA, only the decay of emission was observed for excimer with our set-up (f > 2 ns after excitation). The instantaneous formation of excimer, unrelated to the decay of monomer excitation, indicates that the considerable fraction of lPy-(3)-lPy in the hydrophobic pockets of HSA is present as the ground state dimer. The red shift (ΔΔ = 8 nm) and broadening of UV absorption for lPy-(3)-lPy in HSA (when compared with absorption lPy-(3)-lPy in 1,4-dioxane) and comparison of excitation spectra of lPy-(3)-lPy in HSA and in 1,4-dioxane also indicate that label molecules bound to some sites of HSA are in the ground state in the dimer conformation. Moreover, the close values of the ratios of intensities of monomer emission to excimer emission, registered 2 ns (5 ns gate) after excitation pulse with duration 300 ps and at the steady-state conditions, indicate that the interconversion between conformers of lPy-(3)-lPy inside of the macromolecules of HSA is slow in comparison with the decay time of Py chromophore in the excited state in HSA (two-exponential decay with decay times τ1 = 2.41 ns, τ2 = 69.0 ns). Thus, ratios of the intensities of monomer and excimer emissions of lPy-(3)-lPy in HSA do not allow to obtain any information on the local microfluidity inside of the protein macromolecules but could be used for discrimination between different conformations of the probe, possibly located in different protein pockets.

Interactions between Water-Soluble Polymers and Surfactants: Effect of the Polymer Hydrophobicity. 1. Hydrophilic Polyelectrolytes

The binding of DTAC (dodecyltrimethylammonium chloride) to two polyelectrolytes of differing hydrophobicity, the alternated copolymers poly(maleic acid-co-methyl vinyl ether) and poly(maleic acid-co-butyl vinyl ether) referred to as PS1 and PS4, respectively, has been investigated by potentiometry with a surfactant ion-specific electrode, by time-resolved fluorescence quenching, by fluorescence anisotropy, and by viscosimetry. The surfactant binding isotherms, the number of surfactants (N) making up polymer-bound aggregates, the lifetime of pyrene (τ2) in these aggregates, and their microviscosity (ηi) were thus obtained as a function of the surfactant concentration and copolymer neutralization degree α, which determines its electrical charge density. As observed in other studies, the binding is cooperative in the whole range of α for PS1 and for α ⩾ 0.5 for PS4. Aggregation numbers, pyrene lifetimes, and aggregate microviscosities were all found to be independent of the surfactant concentration but to depend strongly on α. N increased with α for PS1 but decreased for PS4. For PS1, τ2 and ηi increased when α decreased, i.e. with decreasing micelle size. The comparison of the τ2 values obtained with DTAC and dodecyltrimethylammonium bromide in the presence of PS1 revealed that the surfactant counterions are expelled from the surface of polymer-bound aggregates. This leads to a model where polymer chains tightly wrap around aggregates with their charged groups in contact with surfactant charged groups. The difference of behavior between PS1 and PS4 is attributed to the contribution of hydrophobic interactions between PS4 butyl side chains and surfactant alkyl chains. This contribution is small in the case of PS1, where binding is of essentially electrostatic nature. The high microviscosity of polymer-bound aggregates relative to free DTAC micelles is attributed to the electrostatic binding of surfactant ions to the polyelectrolyte and to the presence of the polymer main chain at the aggregate surface. The large values of the pyrene fluorescence lifetime are the result of the high microviscosity of the bound aggregates, which slows down the diffusive motion of reactants (probe and quencher, or any other reactant) in the aggregates and thus makes quenching (and other) processes much less efficient than in free micelles.

Volume behavior of mixed micelles of dodecyltrimethylammonium chloride and bromide

Volume behavior of mixed micelles of dodecyltrimethylammonium chloride and bromide

Electron spin resonance, electron spin echo, and electron nuclear double resonance studies of the photoreduction yield of a series of alkylmethylviologens in sodium dodecyl sulfate and dodecyltrimethylammonium chloride micelles: effect of the alkyl chain length of the viologen

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTElectron spin resonance, electron spin echo, and electron nuclear double resonance studies of the photoreduction yield of a series of alkylmethylviologens in sodium dodecyl sulfate and dodecyltrimethylammonium chloride micelles: effect of the alkyl chain length of the viologenHugh J. D. McManus, Young Soo Kang, and Larry KevanCite this: J. Phys. Chem. 1992, 96, 13, 5622–5628Publication Date (Print):June 1, 1992Publication History Published online1 May 2002Published inissue 1 June 1992https://doi.org/10.1021/j100192a078RIGHTS & PERMISSIONSArticle Views80Altmetric-Citations14LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (2 MB) Get e-Alerts

Volume behavior of mixed micelles of dodecyltrimethylammonium chloride and bromide

Densities of aqueous solutions of mixtures of dodecyltrimethylammonium chloride (DTAC) and dodecyltrimethylammonium bromide (DTAB) have been measured as a function of total molality at constant composition and the apparent molar volumes of the mixtures were derived from the density data. The partial molar volumes of monomeric surfactant mixtures, the molar volumes of mixed micelles, and the volumes of formation of mixed micelles were evaluated and are compared with those for decyltrimethylammonium bromide (DeTAB) and DTAB mixtures. The partial molar volumes of monomeric surfactant mixtures and the molar volumes of mixed micelles are observed to depend linearly on the monomer and micelle compositions, respectively. Although the volume of formation of mixed micelles of the DeTAB-DTAB mixture depends on the micellar composition, that of the DTAC-DTAB mixture is observed to be almost independent of the micellar composition. This suggests that the volumes of the counter ions in the micellar solutions are almost equal to those in the monomeric solutions.

The use of the n-(9-anthroyloxy) stearic acid to probe the water content of sodium dodecyl sulfate, dodecyltimethylammonium chloride, and triton X-100 micelles

Quenching of the n-(9-anthroyloxy) stearic acids ( n = 2, 6, 9, and 12) fluorescence by water is used to evaluate the water content in the vicinity of the anthroate chromophore in micelles of sodium dodecyl sulfate (SDS), dodecyltrimethylammonium chloride (DTAC), and Triton X-100. The mean locations of the probes in the three micelles are evaluated from the ring current effects of the anthracene ring on the 1H-NMR resonances of the surfactant protons. It is found that there is practically no water in the hydrocarbon core of the Triton X-100 and the DTAC micelles while in SDS micelles water seems to penetrate further down to the β carbon of the surfactant molecule. Water concentrations obtained from fluorescence decays are compared with those obtained from the response of the emission spectra of the same probes to changes in the solvent polarity.

Micellar Accelerated Reduction of Ethylenediaminetetraacetatocobaltate(III) by 1-Benzyl-1,4-dihydronicotinamide

Abstract The electrostatic and hydrophobic effects of ionic micelles on the reduction of ethylenediaminetetraacetato cobaltate(III) ([Co(edta)]−) by 1-benzyl-1,4-dihydronicotinamide (BNAH) were investigated with dodecyltrimethylammonium chloride (DTAC) and/or sodium dodecyl sulfate (SDS). Cationic DTAC accelerated the reduction of [Co(edta)]−, while anionic SDS retarded the reaction. The micellar effects of DTAC on the present reaction at 30°C were kinetically analyzed by using the ion-exchange model and the Berezin’s approach: the evaluated rate constant, (1.0±0.1–1.1±0.4)×10−4 mol−1 dm3 s−1, for the micellar-phase reaction was ten times smaller than that, 1.46×10−3 mol−1 dm3 s−1, for the aqueous-phase one. This fact was well-explained by the electron-transfer rate constant calculated with the experimentally determined redox potentials of BNAH and [Co(edta)]−. The cationic DTAC micelles, however, resulted in considerably larger value (3.58×10−3 mol−1 dm3 s−1) of overall reaction rate constant than that (1.46×10−3 mol−1 dm3 s−1) of nonmicellar one, because the apparent concentrations of the reactants in the micellar phase increased remarkably by condensation of BNAH and [Co(edta)]− to the micelles through the hydrophobic interaction and the electrostatic interaction, respectively.

Micellar effects on the reduction of tris(acetylacetonato)cobalt (III) by 1-benzyl-1,4-dihydronicotinamide with ionic surfactants

The reduction of tris(acetylacetonato)cobalt(III)[Co(acac)3] by 1-benzyl-1,4-dihydronicotinamide (BNAH) has been studied in 4–100%(v/v) methanol-borate buffer with or without surfactants of anionic sodium dodecylsulphate (SDS) or cationic dodecyltrimethylammonium chloride (DTAC) micelles. The second-order reaction rate decreases on increased methanol content of the solvent system and in the presence of the surfactant micelles in the reaction system; it is retarded in the order of DTAC > SDS > none, and the rate constants of the electron transfer in the micellar pseudophase are 15–70 times smaller than that in the bulk aqueous phase. The binding constants of BNAH to SDS and DTAC micelles were determined to be 236 and 102 mol–1 dm3, respectively, at 30 °C by fluorescence measurements. It was also well reflected, by the estimated values of the activation parameters, that the micellar reaction of both the incorporated reactants [BNAH and Co(acac)3] proceeded at the water-micelle interface, in which low polar environments suppress the reaction through the unfavourable orientation of the reactants and the destabilization of the transition state of the reaction.

A study of competitive counterion binding to micelles using the acid-catalyzed reaction of hydrogen peroxide with iodide ions

The reaction involving the acid-catalyzed reduction of hydrogen peroxide by iodide ions has been used to study the competitive counterion binding of hydrogen ions to sodium dodecyl sulfate (SDS) micelles and iodide ions to both dodecyltrimethylammonium bromide (DTAB) and dodecyltrimethylammonium chloride (DTAC) micelles. It has been demonstrated that a pseudophase ion-exchange model can be employed to quantitatively describe, within certain limits, the competitive counterion binding in these ionic micellar systems. Ion-exchange constants have been determined for the hydrogen/sodium ion-exchange at the surface of SDS micelles, the iodide/bromide ion-exchange at the surface of DTAB micelles, and the iodide/chloride ion-exchange at the surface of DTAC micelles. These ion-exchange constants are 1.3 ± 0.4, 3.1 ± 0.3, and 8.2 ± 0.8, respectively.