The influence of mono-and bivalent anions and micelle/submicellar clusters of different ionic and nonionic surfactants on the hydrolysis of malachite green (MG + ) was studied in the presence of low alkali concentrations. Large polarizable I − ion and bivalent SO 4 2− ion show specific interaction toward MG + with the formation of dye−anion ion-pair resulting in a retardation of the reaction rate. Tensiometric studies for anionic surfactants sodium dodecyl sulfate (SDS) and dioctyl sodium sulfosuccinate (AOT) in the presence of dye indicate the formation of ion-pair micelles which subsequently break down to form normal micelles. A change of the absorbance value accompanied by a red shift in the electronic spectra with increase in surfactant concentration also evidenced the formation of ion-pair. The observed rate inhibition by the anionic surfactants and the interaction behavior/nature of binding between the dye and surfactant in the premicellar region have been analyzed in terms of different kinetic models. The Piszkiewicz cooperativity index (n) suggests 1:1 association between the anionic surfactant monomer and MG + in the submicellar cluster. A catalyzing effect for the cationic surfactant, cetyltrimethylammonium bromide (CTAB), was noticed in the post-CMC region leading toward a limiting reaction rate, and the Menger−Portonoy pseudophase model was employed to explain the behavior with evaluation of the binding parameter. The nonionic surfactant poly(oxyethylene) (20) sorbitan monolaurate (Tween 20) exerts inhibition effect on the hydrolysis reaction which may be explained qualitatively by the dearth of HO − ions in the vicinity of the micelle-bound dye and quantitatively in light of the pseudophase model. Different equilibrium constants and binding constant parameters suggest appreciable binding between the dye and surfactant monomer/micelles owing to electrostatic/hydrophobic interactions.

In the submicellar solution of anionic surfactants sodium dodecyl sulfate (SDS) and dioctyl sodium sulfosuccinate (AOT), the alkaline fading of methyl violet (MV+) carbocation has been studied spectrophotometrically in the temperature range 293–308 K. The interaction behavior of the dye carbocation with the anionic surfactant and the observed submicellar rate retardation is consistent with the ion pair and subsequent ion‐pair micelle formation. The change in the spectral pattern along with a change in the peak intensity and shoulder intensity with increasing surfactant concentrations indicates the shifting of the equilibrium between the helical and distorted helical isomers of MV+ owing to the existence of dye–surfactant ion pair, ion‐pair micelles, and dye‐embedded micelles. This dynamic dye–surfactant ion‐ion interaction has been corroborated by the tensiometric studies. The decrease in the fading rate and the change in the spectral pattern in the presence of anion, especially I–, support the existence of the dye–anion interaction. The premicellar rate inhibition and the corresponding interaction have been accounted for by the use of two kinetic models namely, Olson–Simonson and Piszkiewicz cooperativity models. The cooperativity index value suggested a 1:1 dye–surfactant association in both the surfactants. The ratio of the concentration of the premicellar complex and the free dye cation indicates appreciable binding. The kinetic and thermodynamic parameters associated with the dye–surfactant complex have been explained in terms of dye–surfactant, dye–water, and surfactant–water interactions.

The kinetics of the oxidative degradation of D-fructose by nanoparticles of MnO 2 has been studied in dilute sulfuric acid medium and also in the presence of surfactants of cetyl trimethyl ammonium bromide (CTAB), Triton X-100 (TX-100), and Tween 20. Amorphous nanoparticles of MnO 2 in the form of spherical particulates of size 50-200 nm, as detected by a transmission electron microscope, have been found to exist, supported on two-dimensional gum acacia sheets. The reaction is first order in MnO 2 but complex order with respect to fructose and H + . The reaction is inhibited due to adsorption of reaction products on the surface of MnO 2 nanoparticles. The reaction takes place through an intermediate complex formation between -D-fructopyranose and protonated MnO 2 . A one-step two-electron transfer reaction ultimately leads to the formation of an aldonic acid and formic acid. The entropy of activation plays the key role for the reaction in the absence of surfactants. In the surfactant-mediated reaction, partitioning of both the reactants takes place between the aqueous and micellar pseudophases and reaction occurs following Berezin's model. Binding of fructose with the surfactants in the Stern/palisade layer takes place through the ion-dipole interaction and H-bonding while protonated MnO 2 remains at the outer side of the Stern/palisade layer within the micelle. Both the enthalpy and entropy changes associated with the fructose-water interaction, fructose-micelle interaction, and micelle-water interaction finally control the fructose-micelle binding.

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