Kinetic investigations on alkaline fading of malachite green in the presence of micelles and reverse micelles

Nanostructured Colloidal Solutions of Malachite Green Formulated: Nonlinear Optical Properties and Simulation

Malachite green (MG) is a dye that has been presented to use as photosensitizers for photodynamic therapy (PDT). Nonlinear absorption coefficient (β) and nonlinear refractive index (n₂) of MG formulations with micelles and its encapsulation are studied aiming PDT. Encapsulation of MG was prepared by the mixture of water droplet in the continuous phase of oil, stabilized with surfactant. MG interacts with micelles and reverses micelle (RM), and the results are related to the size and concentration of micelles, RM, surfactant charge types. At low capsule size, the 1/β linearly increases by the increase of volume fraction of water droplet, while, an exponential behavior was observed in the higher capsule size.

Influence of Anions and Micelle and Submicellar Aggregates on the Alkaline Hydrolysis of Malachite Green: Tensiometric, Spectrophotometric, and Kinetic Investigations

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 SO₄^2- 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.

Alkaline Hydrolysis of Methyl Decanoate in Surfactant-Based Systems

Surfactant-modified reaction systems are one approach to perform organic reactions with water as the solvent involving hydrophobic reactants. Herein, the alkaline hydrolysis of the long-chain methyl decanoate in cationic and nonionic surfactant-modified systems is reported. The physicochemical behavior of the reaction mixture and the performance of the alkaline hydrolysis were systematically investigated. In water as the solvent, the reaction is slow, but at elevated temperatures, the alkaline hydrolysis of methyl decanoate is accelerated because the reaction product sodium decanoate acts as an ionic surfactant, leading to an increased solubility of methyl decanoate in the aqueous phase. The rate can be significantly increased by the addition of surfactants as solubilizers. In nonionic TX-100 solutions, the reaction rate can be increased by a factor of about 100 for a surfactant concentration of 5 wt %. If cationic surfactants are applied, the reaction rate can be further increased due to the electrostatic interaction between the hydroxide ions in solution and the charged head groups of the cationic micelles.

Kinetic exploration supplemented by spectroscopic and molecular docking analysis in search of the optimal conditions for effective degradation of malachite green

The degradation of malachite green (MG) by an alkaline hydrolytic process has been explored spectrophotometrically.