Effect of microheterogeneous environments of CTAB, Triton X‐100, and Tween 20 on the oxidative degradation of d‐fructose by nanoparticles of MnO₂

Abstract

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.

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

“…The enthalpy (ΔH 0 ) and entropy (ΔS 0 ) changes associated with the binding between Tween 20 and MG + were evaluated from the linear plot of lnK MG+ against 1/T, and the values are −24.9 ± 5.5 kJ mol −1 and −22.1 ± 0.5 J K −1 mol −1 , respectively. Tween 20 is polar nonionic surfactant owing to the presence of poly(oxyethylene) and hydroxyl groups in its structure 30 and hence remains hydrated in aqueous medium. When Tween 20 binds with MG + , water molecules are released from the solvation layer of Tween 20 with absorption of energy and increase of entropy 31 due to this structure-breaking process, and at the same time release of energy also takes place due to the structure formation through hydrophobic binding with a decrease in entropy.…”

Evidence of formation of dye–surfactant ion pair micelle in the anionic surfactant mediated alkaline fading of methyl violet carbocation

“…The rates of different reactions are influenced by the presence of self‐aggregated surfactants 3–6 or even by the surfactant monomers 7,8 themselves by forming different types of association with the reactant molecules through electrostatic, hydrophobic, or H‐bonding interactions. The submicellar aggregate or the micellar system may either catalyze or inhibit the rate of the reaction depending on the nature of the reacting species as well as the nature of the binding 8,9 . In the submicellar system, the electric charges on the surfactant monomer, and the substrate play a very important role in the formation of premicellar aggregate which ultimately influences the rate of reaction 10 …”