Elvira Rodenas

The determination of some physical properties of reverse CTAB micelles in 1-hexanol

Abstract Aggregation numbers and water pool radii of the L 2 region of the cetyltrimethylammonium bromide (CTAB)/1-hexanol/ H 2 O system have been studied by carrying out fluorescence quenching measurements using 4-(1-pyrenyl)butyric acid as a probe and N -cetylpyridinium chloride as a quencher. The water pool radii of these reverse micelles depend mainly on the water content while the aggregation numbers only depend on the surfactant amount. Conductimetric measurements and light scattering measurements at 90° for the system are also given. Both sets of results are related to the layer thickness where surfactant and co-surfactant are located. Ion distribution inside the water pool and the surface potential have been calculated using the non-linearized Poisson—Boltzmann equation. The surface charges per square metre of micelles obtained for the L 2 region are always smaller than 21 mC m −2 .

Influence of CTAB/1-butanol micelles on crystal violet basic hydrolysis

Abstract The influence of CTAB/1-BuOH micelles (hexadecyltrimethylammonium bromide1-butanol) on Crystal Violet basic hydrolysis has been studied. The kinetic results can be explained by means of the pseudophase kinetic model. The results strongly suggest that incorporation of 1-butanol to cationic CTAB micelles displaces the substrate from the micellar into the aqueous phase. Different theoretical approaches are discussed in order to explain the results.

Physical properties of cetylpyridinium chloride micelles and their behaviour as reaction media

The physical properties of cetylpyridinium chloride micelles (CPyCl) in aqueous solution have been obtained by steady-state fluorescence quenching and conductivity measurements; the influence on the basic hydrolysis of a positively charged substrate (Crystal Violet) and a negatively charged substrate [5,5′-dithiobis(2-nitrobenzoic) acid], has been studied. The kinetic results are explained on the basis of an electrostatic treatment that considers the ion distribution around the micelles according to the Poisson–Boltzmann (PB) non-linearized equation with specific interactions between the ions in solution and the micellar surface.

Acid hydrolysis of reduced form of nicotin-adenin dinucleotide in sodium dodecyl sulfate micelles

Abstract The acid hydrolysis of NADH in SDS micelles has been studied. SDS concentrations near the CMC produce a catalytic effect on the reaction while higher concentrations produce an inhibitory effect. The results are analyzed on the basis of the micellar pseudo-phase—ion exchange kinetic model. The inhibition effect at high SDS concentrations is related to the amount of reactive ions that the micelles withdraw from the aqueous phase and the catalysis observed at SDS concentrations near the CMC has been explained by a premicellar equilibrium between the substrate in aqueous phase and the free monomers of surfactant. Values for the micellar surface effective dielectric constant, the CMC, and the aggregation number have been obtained with flourescence measurements and the fraction of neutralized micellar surface with conductivity measurements. HCl addition decreases the CMC and the micellar surface effective dielectric constant and it increases the micellar aggregation number.

Benzene, toluene, and cyclohexane incorporation into hexadecyltrimethylammonium bromide micelles: Effect on the basic hydrolysis of crystal violet

Abstract Oil incorporation into CTAB micelles produces different effects on the basic hydrolysis of Crystal Violet. Benzene and toluene inhibit the reaction while cyclohexane produces a catalytic effect on the reaction. The highest amount of oil that can be incorporated into CTAB micelles in aqueous phase has been used and the physical properties of the micelle, such as the CMC and the fraction of neutralized micellar head groups, does not change significantly with the oil solubilization. The results have been analyzed on the basis of the pseudophase ion-exchange kinetic model and by considering ion distribution around the CTAB micelles according to the nonlinearized Poisson-Boltzmann equation. The fraction of micellar head groups neutralized and the critical micelle concentration have been obtained from conductivity measurements.

Methanol and ethanol oxidation by chromium(VI) in aqueous perchloric acid

SummaryOxidation of short-chain alcohols (MeOH and EtOH) by CrVI in concentrated aqueous HClO4 does not fit pseudo-first order rate equations, but results can be expressed in a two-exponential equation. A reaction mechanism based upon a chromate ester intermediate in equilibrium with the protonated alcohol and the chromic acid, suitable for a longer chain alcohol, does not account for kinetic results. A new mechanism is considered involving an intermediate reaction between chromic and perchloric acids.

Hydroxide ion specific adsorption on cetyltrimethylammonium bromide micelles explains kinetic data

Abstract The aim of this paper is to show an improvement of the electrostatic kinetic model that was previously developed to explain kinetic data for micellar systems. The new treatment considers specific interactions between all the ions in solution and the micellar surface and it is used to explain the kinetic data for cetyltrimethylammonium bromide micelles.

Kinetics of the reaction of tris(4,7-diphenyl-1,10-phenanthroline-disulphonate)iron(II) ion with hydroxide ion in water

SummaryThe kinetics of the hydrolysis of the tris(4,7-diphenyl-1,10-phenanthrolinedisulphonate)iron(II) ion has been studied. The results are consistent with a consecutive reaction mechanism with a reversible step, and from the analysis of the kinetic results the rate constants have been determined.

Kinetic study of keratin cystine reduction in W/O microemulsion media

Abstract The reduction kinetics of hair cystine was studied in water-in-oil-type microemulsion media and compared with that in aqueous media. A model microemulsion of the system water/sodium dodecylsulfate/ n -pentanol/ n -dodecane was chosen. Different concentrations of reducing agent, thioglycolic acid, were incorporated in the model microemulsion and in water. Cystine reactivity was evaluated by the cysteine formation as a function of treatment time. The reaction kinetics were described by a pseudo-first-order model for both media, microemulsions and aqueous solutions.

Micellar effect upon the reaction of tris(4,7-diphenyl-1,10-phenanthrolinedisulphonato)iron(II) ion with hydroxide in water

SummaryReaction of tris(4,7-diphenyl-1,10-phenanthrolinedisulphonato)iron(II) ion with hydroxide ion is strongly accelerated by cationic micellar systems. Kinetics both in water and in cationic micelles are consistent with a mechanism of consecuive reactions with a reversible step, and the rate constants have been determined. Results in micelles are explained in terms of thepseudo-phase ion-exchange and mass-action kinetics models, and they show that micelles speed the reaction by an authentic catalytic effect by stabilization of transition state of the reaction.