Evan Wyn-Jones

The use of ion-selective electrodes to determine the effective degree of micelle dissociation in tetradecylpyridinium bromide solutions

A surfactant membrane electrode selective to the tetradecylpyridinium cation has been constructed and used with various ion-selective electrodes to evaluate the effective degree of micelle dissociation of tetradecylpyridinium bromide micelles. Four different approaches have been used to evaluate this parameter and in three cases the results are consistent.

The construction and characteristics of drug-selective electrodes. Applications for the determination of complexation constants of inclusion complexes with α- and β-cyclodextrins including a kinetic study

Ion-selective membrane electrodes selective to the drugs chlorpromazine, dicyclomine, imipramine, desipramine and propranolol hydrochlorides have been constructed using a modified poly(vinyl chloride) membrane which has ionic end-groups as ion-exchange sites and which was cast using a solid polymeric plasticiser. These drug electrodes show excellent Nernstian responses in the concentration range 10–2–10–7 mol dm–3 and their selectivity coefficients with respect to each other, as well as their workable pH range have been investigated. The electrodes have also been used to determine the complexation constants of chlorpromazine and dicyclomine hydrochlorides with both α- and β-cyclodextrins. In all cases a 1:1 complex was observed. The kinetics associated with the formation of the complex involving α-cyclodextrin and dicyclomine hydrochloride have also been investigated using the ultrasonic technique.

Thermodynamic and kinetic parameters associated with the exchange process involving alcohols and micelles

The partition coefficients of the alcohols butan-1-ol → hexan-1-ol between water and cetyltrimethylammonium bromide micelles have been obtained from solubility experiments. These results have been combined with previously obtained ultrasonic relaxation data to derive the kinetic and thermodynamic parameters associated with the exchange process involving alcohol molecules and cetyltrimethyl ammonium bromide micelles. Bearing in mind the simplicity of the approaches taken to interpret the equilibrium and kinetic measurements, there is remarkable self-consistency in the data.

Kinetics of micellization from ultrasonic relaxation studies

The kinetics of micelle formation for a range of ionic surfactants in aqueous solution have been investigated using the ultrasonic relaxation technique. In order to understand the concentration dependance of both the relaxation time and the relaxation strength, and other aspects of the relaxation data, it was necessary to modify our previous two state kinetic model describing micellisation. In this new theoretical treatment the interchange of the monomers to and from the micelles is assumed to be an adsorption mechanism governed by the fundamental kinetic principles introduced by Langmuir in his adsorption theory. Finally we have reconsidered the origin of the chemical relaxation observed in detergent solutions resulting from temperature- and pressure-jump experiments.

Comparison of energy barrier data from dielectric, n. m. r. and ultrasonic techniques

Abstract Energy barriers for intramolecular motions have been determined for eight compounds in polystyrene matrices by dielectric absorption techniques in the

Equilibrium and kinetic studies associated with the interaction between sodium dodecyl sulfate and polyvinylpyrrolidone in aqueous solution

Binding isotherms for various sodium dodecyl sulfate–polyvinylpyrrolidone mixtures have been constructed from electrochemical measurements involving a dodecyl sulfate-selective membrane electrode. It was found that once the surfactant starts to bind to the polymer, small surfactant aggregates are formed. These aggregates grow in size until the polymer becomes fully saturated after which ‘free’ micelles are formed in solution. The degree of counterion dissociation was also measured using an electrode selective to the sodium counterion. The surfactant concentration at the start of binding and at the onset of the formation of free micelles was also determined using gel filtration. Finally the kinetics of the binding process were measured using ultrasonic relaxation measurements.

Analysis of the fast relaxation times for micelle kinetics taking into account new EMF data

The analysis of the concentration dependence of the fast relaxation time associated with monomer/micelle exchange in several ionic surfactants has been carried out using different modifications of the original Annianson and Wall relaxation equation and taking into account new emf data from surfactant-selective electrode measurements. In most of the published work describing the analysis of the fast relaxation time it has been normal practice to assume that in the micellar region the monomer surfactant concentration is constant and equal to the c.m.c. On the other hand, the electrode measurements have clearly shown that the surfactant monomer concentration decreases significantly in the micellar region. The micellar parameters that can be derived from the analysis of the fast relaxation times are very different when these two conditions are realised.

Kinetic and equilibrium studies associated with the aggregation of non-ionic surfactants in non-polar solvents

The aggregation properties of poly(oxyethylene)alkyl ether, non-ionic surfactants (CnEOm), have been studied in the non-polar solvents heptane and decane using light scattering, vapour pressure osmometry and ultrasonic relaxation methods. The results show that the degree of association is low and only small aggregates (N≈ 5–15) are present. The aggregation numbers increase with EO size, and are slightly larger in decane than in heptane. Alkyl chain size has no influence on aggregation. Only at high concentrations does the association phenomenon resemble the behaviour expected from micellar solutions.

Kinetic and equilibrium studies associated with the formation of inclusion compounds involving n-butanol and n-pentanol in aqueous cyclodextrin solutions

The equilibrium constants associated with the inclusion compounds of n-butanol and n-pentanol with α-cyclodextrin in aqueous solutions have been measured using the head-space analysis technique involving gas chromatography. These data confirm that a 1:1 inclusion complex is formed. The kinetics associated with the formation of these inclusion compounds have been studied using the ultrasonic relaxation method. From a detailed analysis of relaxation data it is clear that the kinetics of the process do not conform to the simple behaviour suggested by the equilibrium experiments. In addition there are also discrepancies between values of the volume change of the reaction determined independently from relaxation and density data. The significance of these results is discussed in terms of a two-step mechanism for the formation of the complex.

Electrochemical studies of cationic drug inclusion complexes with α- andβ-cyclodextrins

Drug membrane selective electrodes have been constructed for the cationic drug propranolol hydrochloride, diphenhydramine hydrochloride, diphenylpyraline hydrochloride and also chlorcyclizine hydrochloride. The characteristics of these drug selective electrodes have been evaluated and the electrodes used to measure equilibrium constants of the inclusion compounds involving the drugs with both α- andβ-cyclodextrins. The enthalpies and entropies associated with the formation of the inclusion complexes have also been estimated from the temperature dependence of the equilibrium constants.