Presence Of Anionic Micelles Research Articles

Modulation of Analytical Performance of a Bifunctional Optical Probe at the Micelle‐Water Interface: Selective Sensing of Histidine in Biological Fluid

AbstractBifunctional bis(indolyl)methane (BIM) derivatives with free carboxylic acid groups have been synthesized for the detection of heavy metal pollutants in the aqueous medium. Unlike in water, compounds in the presence of anionic micelle, showed color change from red to yellow specifically in the presence of Cu2+ ions. The incorporation of ionic surfactants could selectively block one of the binding sites, thereby improved the selectivity. In addition, large local concentration of metal ions (Cu2+) at micelle‐water interface of anionic surfactant improved the sensitivity. Metal ion binding at carboxylic acid (donor site) end not only alter the charge transfer state of the molecules, but also modify the self‐assembly property of probe molecules in the aqueous medium. The sensitivity as well as selectivity of the probes towards Cu2+ was found to be dependent on the number of carboxylic acid units on the central aryl ring. Further, the in‐situ formed Cu2+‐complex was involved for the ppb level recognition of histidine, an amino acid essential for protein biosynthesis and enzymatic activities. Finally, the present system was involved in the analysis of residual Cu2+ contents in natural water samples and histidine in the human urine sample.

Kinetic study on the oxidation of Phenyl Vinyl Sulfide with Iron(III)-Polypyridyl complexes in the presence of Anionic Micelle

Kinetic study on the oxidation of Phenyl Vinyl Sulfide with Iron(III)-Polypyridyl complexes in the presence of Anionic Micelle

Inclusion of two push-pull N-methylpyridinium salts in anionic surfactant solutions: a comprehensive photophysical investigation.

Two N-methylpyridinium salts with push-pull properties have been investigated in the aqueous solution of anionic micelles of sodium dodecyl sulfate (SDS) and potassium p-(octyloxy)benzenesulfonate (pOoBSK) surfactants. These molecules are known to be extremely sensitive to the local environment, with their absorption spectrum being subjected to a net negative solvatochromism. These compounds are also characterized by an excited state deactivation strictly dependent on the physical properties of the chemical surrounding, with the formation of intramolecular charge-transfer (ICT) states accordingly stabilized. Thanks to steady-state and femtosecond resolved spectroscopic techniques, the photophysical properties of these molecules in the presence of anionic micelles have been fully characterized and an efficient permeation within the micellar aggregates can thus be inferred. The extent of the changes in the photophysical properties of these molecules (with respect to what is observed in water) is an indicator of the medium experienced in the nanoheterogeneous solutions: enhanced fluorescence emissions, reduced Stokes shifts and slowed-down excited state decays strongly confirm the confinement within a scarcely polar and restraining environment. The slightly different behavior shown in the two types of micelles can be ascribed to a peculiar interaction between the aromatic moiety of the surfactant and that of the cations. Additionally, the inclusion promotes the solubilization of these poorly water-soluble salts, which is alluring in their promising use as DNA binders for antitumor purposes. Thus, the anionic micelles allowed the solubilization of the pyridinium salts under investigation, which in turn allowed the characterization of the nonhomogeneous medium established by the micellar aggregates.

Interaction of antihypertensive drug amiloride with metal ions in micellar medium using fluorescence spectroscopy

Steady state and life time fluorescence spectroscopy have been employed to study the interaction of antihypertensive drug amiloride with biologically important metal ions i.e. Cu2+, Fe2+, Ni2+ and Zn2+ in various micellar media (anionic SDS (sodium dodecyl sulfate), nonionic TX-100 (triton X-100) and cationic CTAB (cetyl trimethyl ammonium bromide)). It was observed that fluorescence properties of drug remain unaltered in the absence of micellar media with increasing concentration of metal ions. However, addition of Cu2+, Fe2+ and Ni2+ caused fluorescence quenching of amiloride in the presence of anionic micelle, SDS. Binding of drug with metal ions at the charged micellar interface could be the possible reason for this pH-dependent metal-mediated fluorescence quenching. There were no remarkable changes observed due to metal ions addition when drug was present in cationic and nonionic micellar medium. The binding constant and bimolecular quenching constant were evaluated and compared for the drug–metal complexes using Stern–Volmer equation and fluorescence lifetime values.

Kinetics of hydrolysis of procaine in aqueous and micellar media

AbstractThe kinetics of alkaline hydrolysis of procaine under the pseudo–first‐order condition ([OH−] ≫ [procaine]) has been carried out. N,N‐Diethylaminoethanol and p‐aminobenzoate anion were obtained as the hydrolysis product. The rate of hydrolysis was found to be linearly dependent upon [NaOH]. The addition of cationic cetyltrimethylammonium bromide (CTAB), dodecyltrimethylammonium bromide (DDTAB) and tetradecyltrimethylammonium bromide, and anionic sodium dodecyl sulfate (SDS) micelles inhibited the rate of hydrolysis. The maximum inhibitive effect on the reaction rate was observed for SDS micelles, whereas among the cationic surfactants, CTAB inhibited most. The variation in the rate of hydrolysis of procaine in the micellar media is attributed to the orientation of a reactive molecule to the surfactant and the binding constant of procaine with micelles. The rate of hydrolysis of procaine is negligible in DDTAB micelles. The observed results in the presence of cationic micelles were treated on the basis of the pseudophase ion exchange model. The results obtained in the presence of anionic micelles were treated by the pseudophase model, and the various kinetic parameters were determined. © 2012 Wiley Periodicals, Inc. Int J Chem Kinet 45: 1–9, 2013

Kinetic studies on sodium dodecyl sulfate micelle inhibited reactions of triphenylmethyl carbocations with cyanide ion

The kinetics of the decolorization reactions of triphenylmethane dyes (BG, MG and PRH) with the cyanide ion (nucleophile) were studied in the presence of anionic micelles of sodium dodecyl sulfate (SDS). The reactions follow pseudo-first order kinetics. The rate constant depends on surfactant concentration. SDS micelles inhibit the overall rate of the reaction between the dye carbocation with the nucleophile. Quantitative analysis of the micellar data obtained has been done by applying a positive cooperativity model of enzyme catalysis. For all the dyes under study, the value of n (index of cooperativity) has been found to be greater than one. The inhibitory effect has been explained in terms of hydrophobic and electrostatic interactions of various species present in the reaction systems.

S-Nitrosocaptopril formation in aqueous acid and basic medium. A vasodilator and angiotensin converting enzyme inhibitor

The reaction of S-nitrosocaptopril (NOcap) formation was studied in both aqueous acid and basic medium. Captopril (cap) reacts rapidly with nitrous acid in strong acid medium to give the stable--in the timescale of the experiments--NOcap. The kinetic study of the reaction involving the use of stopped-flow, shows that at low sodium nitrite (nit) concentration, the reaction is first-order in both [nit], [H(+)], and is strongly catalysed by Cl(-) or Br(-) (= X(-)): rate = (k(3) + k(4)[X(-)])[H(+)][nit][cap]. In aqueous buffered solution of acetic acid-acetate the reaction rate is much slower and the decomposition of NOcap was observed; however, the rate of NOcap decay is more than 30-fold slower than its formation. In aqueous basic medium of carbonate-hydrogen carbonate buffer, as well as in alkaline medium, the kinetics of the nitroso group (NO) transfer from tert-butyl nitrite (tBN) to cap was studied using either conventional or stopped flow methods. In mild basic medium, the NOcap decomposes. The NOcap formation is first-order in both tBN and cap concentrations, and the reaction rate increases with pH until to, approximately, pH 11.5, above which value it becomes pH independent or even invariable with the [OH(-)]. Kinetic results show that the thiolate ion of cap is the reactive species. In fact, the presence of anionic micelles of sodium dodecyl sulfate (SDS) inhibits the reaction due to the separation of the reagents; whereas, cationic micelles of tetradecyltrimethylammonium bromide (TTABr) catalyse the reaction at low surfactant concentration due to reagents concentration in the small volume of the micelle. The rate equation is: rate = k(f) K(SH)[cap][tBN]/(K(SH) + [H(+)]). The rate of NOcap decomposition in mild basic medium is first-order in both [cap] and [NOcap], and decreases on increasing pH; but, in alkaline medium the NOcap is stable within the timescale of the experiments. Based on the results, the NOcap decomposition yields the disulfide compound that is formed in the nucleophilic attack of the -SH group of cap to the sulfur electrophilic center of NOcap, -S-N=O. The resulting rate equation is: rate = k(d)[H(+)][cap][NOcap]/(K(SH) + [H(+)]).

ChemInform Abstract: Kinetics and Mechanism of Intramolecular General Base-Catalyzed Alkanolysis of Phenyl Salicylate in the Presence of Anionic Micelles

ChemInform Abstract: Kinetics and Mechanism of Intramolecular General Base-Catalyzed Alkanolysis of Phenyl Salicylate in the Presence of Anionic Micelles

A study on the adsorption characteristics of an amphiphilic phenothiazine drug on activated charcoal in the presence of surfactants

In this paper the adsorption of amphiphilic phenothiazine drug Thioridazine hydrochloride (THCl) on Activated charcoal (AC) surface was studied in aqueous solutions. The effects of different types of surfactants anionic sodium dodecylsulfate (SDS) and lithium dodecylsulfate (LiDS), cationic cetyltrimethyl ammonium bromide (CTAB) and nonionic TritonX-100 (TX-100) micelles on the adsorption were reported. It was found that the Langmuir isotherm appears to fit the isotherm data better than the Freundlich isotherm. The adsorption of THCl was reduced in the presence of cationic CTAB bearing the same charge as THCl while presence of SDS and LiDs did not change significantly adsorption capacity of THCl on AC except the shape of the isotherm. The presence of TX-100 micelles significantly increased adsorption of THCl on AC. Kinetic measurements showed that the adsorption equilibrium of THCl was attained within 30 min in aqueous media while in the presence of 10 mM anionic micelles the adsorption equilibrium of THCl reached the equilibrium almost in 1 min. The kinetics of adsorption in view of three kinetic models i.e. the first-order Lagergren model, the pseudo-second-order model and the intraparticle diffusion model has been discussed. The adsorption rate constants of THCl onto AC in the presence of anionic micelles are higher than in aqueous media for both kinetics models and the second-order model provides the best correlation of data in the absence and presence of micelles. In order to gain further insight into the adsorption mechanism of THCl on AC, association of THCl with surfactants was also studied by absorption spectra. Binding constants of THCl to micelles were calculated by means of Benesi–Hildebrand Equation to provide more precise comparison of the effect of surfactants on the adsorption of THCl.

Tautomerization of 2-acetylcyclohexanone in assemblies of cationic surfactants

The kinetic study of the keto-enol interconversion of 2-acetylcyclohexanone (ACHE) has been performed in organic solvents such as dimethylsulfoxide, 1-propanol, 2-propanol, methanol, dioxane, tetrahydrofuran and acetonitrile, as well as in aqueous micellar solutions of the cationic surfactants tetradecyltrimethylammonium chloride and tetradecyltrimethylammonium bromide at 25 °C. Either the solvent-assisted or H+-catalyzed reaction rates of tautomerization are reduced in both organic solvents and in micellar medium. In 70% v/v solvent–water or at fixed concentration of any cationic surfactant, the observed rate constant moderately increases with [H+]. The nitrosation of the enol has also been studied in micellar solutions of both cationic and anionic surfactants. Under experimental conditions of first-order dependence on [H+], [nitrite], and [X−] (X = Cl or Br), the presence of cationic micelles reduces strongly the rate of nitrosation, whereas in the presence of anionic micelles, the first-order rate constant, ko, goes through a maximum on increasing the surfactant concentration.

ミセル系におけるキノリン誘導体の蛍光消光（原標題は英語）

The halide-sensitive fluorescence probe, 6-methoxy-N-alkylquinolinium, was prepared to investigate the behavior of counterion dissociation in micellar aqueous solution. Fluorescence was quenched by halide ions based on linear Stern-Volmer plots. The plots indicated a distinct break at cmc of cationic surfactants containing halide counterions. The slope of Stern-Volmer for 6-methoxy-N-ethylquinolinium (MEQ) decreased beyond cmc owing to micellar counterion binding. The quenching efficiency of 6-methoxy-N-dodecylquinolinium (C12MQ) increased significantly beyond cmc with surfactant concentration. The fluorescence of micellar solubilized C12MQ would thus appear to be quenched effectively by halide ions at the micellar surface. These ions were found to function effectively as a quencher in cationic micelle systems, but to have no effect on amphiphilic probe fluorescence in the presence of anionic micelles. Repulsive electrostatic interactions are thus shown to occur between halide ions and anionic micelles containing probes.

Influence of sodium dodecyl sulfate on the reaction between nile blue a and hydrogen peroxide

The influence of the anionic surfactant sodium dodecyl sulfate on the rate of the reaction between the cationic form of Nile Blue A and hydrogen peroxide was investigated in the pH range from 5 to 8.5. A retardation of the oxidation of Nile Blue A with hydrogen peroxide of three orders of magnitude was observed at pH 8.5 in the presence of anionic micelles compared to the kinetic data in water. The retardation effect was less pronounced at lower pH values. These effects were explained by the electrostatic interaction of the species involved in the reaction with the negatively charged micellar surface and their effective separation in the vicinity of the micellar surface.

Unusual Rate Enhancement in the Hydroxide Ion-Catalyzed Hydrolysis of N-Phthaloylglycine in the Presence of Anionic Micelles

Pseudo-first-order rate constants (kobs) for hydrolysis of ionized N-phthaloylglycine (NPG) at a constant [NaOH] and 30 °C increase nearly 50% with an increase in the total concentration of sodium dodecyl sulfate ([SDS]T) from 0.0 to 0.2 M. The hydrolysis of NPG involves -OH and anionic NPG as the reactants. The increase in [NaBr] from 0.01 to 0.4 0 M increases kobs by nearly 44% at 0.004 M NaOH and 30 °C. Pseudo-first-order rate constants (kobs ) increase by nearly 50% with an increase in [KCl] from 0.0 to 0.1 M at 0.003 and 0.004 M NaOH and 30 °C. The increase in [SDS]T from 0.0 to 0.3 M decreases kobs for hydrolysis of phthalimide at 0.01 M NaOH and 35 °C by nearly 10%. The attempt is also made to explain pseudo-first-order rate constants in terms of interfacial hyroxide ion concentration calculated from the Boltzmann equation using interfacial electrical potential.

Influence of sodium dodecyl sulfate micelles on the kinetics of complex formation between Pd(H 2O) 42+ and glutathione

The kinetics of the complex formation between Pd(H 2O) 4 2+ and glutathione was investigated in the presence of sodium dodecyl sulfate in the acidity range from 2 M HClO 4 to pH 5. Acceleration (from 2 M HClO 4 to pH 3.5) and retardation (3.5 < pH < 5) of the complex formation in the presence of anionic micelles was observed compared with the kinetic data in aqueous solution. These effects were explained by the electrostatic interaction of the reacting species with negatively charged micellar surface and their effective concentration and/or separation in the vicinity of micellar surface.

Influence of sodium dodecyl sulphate micelles on the kinetics of complex formation between Pd(H2O)42+ andS-carboxymethyl-L-cysteine

The kinetics of complex formation between Pd(H2O)42+ and S-carboxymethyl-L-cysteine (SCMCH2) was investigated in the presence of sodium dodecyl sulphate in the acidity range between 2 M HClO4 and pH 5. Although the mechanism was not affected by the presence of anionic micelles, retardation (2·2 < pH < 5) and acceleration (pH < 2·2) of the complex formation were observed compared with its rate in aqueous solution. These effects were interpreted in terms of the long-range electrostatic interactions between the negatively charged micellar surface and ligand species which can be in different ionic forms depending on the pH.

Unusual Rate Enhancement in the Hydroxide-Ion-Catalyzed Cleavage of Acetyl Salicylate Ion (Aspirin Anion) in the Presence of Anionic Micelles

The reaction rate studies on the hydrolytic cleavage of acetyl salicylate ion (AS-) within the [-OH] range 0.010-0.025 M reveal AS- and -OH as the reactants. The effects of micelles of sodium dodecyl sulfate (SDS) on observed pseudo-first-order rate constants (kobs) for the hydrolytic cleavage of AS- have been studied at different [OH-]. At a constant [OH-], the rate constants (kobs) follow an empirical relationship: kobs = C + F [SDS]T where [SDS]T represents total SDS concentration. The magnitudes of C and F increase with an increase in [OH-]. These data are explained in terms of the pseudophase model of the micelle.

Preconcentration of aniline derivatives from aqueous solutions using micellar-enhanced ultrafiltration

The preconcentration of aniline derivatives present in aqueous solutions containing ionic surfactants was performed using the micellar-enhanced ultrafiltration technique. The efficiency of the analyte recovery in the surfactant-rich retentate was significantly improved by exploiting the electrostatic, hydrophobic and specific interactions between the aggregates and the solute molecules. By working at low pH, in the presence of anionic micelles, the quantitative retention of amines having different substituent groups can be achieved. The enriched sample can be analysed directly using high-performance liquid chromatography.

Micellar rate enhancement studies in mixed sodium fluorocarbon/hydrocarbon surfactant solutions

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.

Effects of non-ionic and anionic micellar aggregates on the kinetics of the iridium(IV) oxidation of monosubstituted malonic acids

The kinetics of the electron-transfer reaction between the hexachloroiridate(IV) ion and phenylmalonic acid have been studied in the absence and in the presence of non-ionic (Triton X-100, Triton X-102, Triton X-165, C10E6, C12E6, C14E6, C12E10, C12E23) and anionic (sodium dodecyl sulfate, sodium tetradecyl sulfate) micelle-forming surfactants over a wide acidity and surfactant concentration range at 25.0 °C and ionic strength 0.05 mol dm–3. A number of kinetic measurements using benzylmalonic acid as reducing agent have also been performed. The redox reactions exhibit a first-order dependence on both the reductant and oxidant concentrations. The reaction rate in the absence of surfactants decreases as the hydrogen-ion concentration increases. In the presence of non-ionic micelles the oxidation process is retarded by an increase in either the acidity or the surfactant concentration. The inhibitory effects of these micellar aggregates upon the reaction rate depend on the hydrophobic micellar environment and the number of the ethoxy groups of the non-ionic surfactants. In the presence of anionic micelles a retarding effect has been observed only with sodium tetradecyl sulfate for the benzyl derivative. Binding constants of the neutral reductant species have been estimated by kinetic measurements. A mechanism for the electron-transfer reactions examined is suggested.

Kinetics and mechanism of intramolecular general base‐catalyzed alkanolysis of phenyl salicylate in the presence of anionic micelles

AbstractThe alkanolysis of ionized phenyl salicylate, PS−, has been studied in the presence and absence of micelles of sodium dodecyl sulphate, SDS, at 0.05 M NaOH, 30 or 32°C and within the alkanol, ROH, (ROH = HOCH2CH2OH and CH3OH) contents of 15–74 or 92%, v/v. The alkanolysis of PS− involves intramolecular general base catalysis. At a constant concentration of SDS, [SDS]T, the observed pseudo first‐order rate constants, kobs, for the reactions of ROH with PS− obtained at different concentration of ROH, [ROH]T, obey the relationship: kobs = k[ROH]T/(1 + KA[ROH]T) where k is the apparent second‐order rate constant and KA is the association constant for dimerization of ROH molecules. Both k and KA decrease with increase in [SDS]T. At a constant [ROH]T, the rate constants, kobs, show a decrease of nearly 2‐fold with increase in [SDS]T from 0.0–0.3M. These results are explained in terms of pseudo‐phase model of micelle. The rate constants for alkanolysis of PS− in micellar pseudophase are insignificant compared with the corresponding rate constants in aqueous‐alkanol pseudophase. This is attributed largely to considerably low value of [ROH] in the specific micellar environment where micellar bound PS− molecules exist. The increase in [ROH]T decrease the value of the binding constant of PS− with SDS micelle. The effects of anionic micelles on the rates of alkanolysis of PS− are explained in terms of the porous cluster micellar structure.