Ionic Liquid-Mediated Modulation of Zwitterionic Micelles and Their Catalytic Performance in the Decarboxylation of...

Zwitterionic micelles and ionic liquids play an important role as organized media that can tune interfacial properties and modulate reaction environments in aqueous solutions. Understanding how these systems influence reaction kinetics is essential for elucidating catalytic mechanisms. This work investigates the catalytic effects of zwitterionic micelles on the decarboxylation of the 6-nitrobenzisoxazole-3-carboxylate anion (6-NBIC) and correlates kinetic parameters with the physicochemical properties of the self-assembled systems. Two classes of zwitterionic surfactants were examined: sulfobetaines (SB3-n) and an imidazolium-based surfactant (ImS3-14), the latter solubilized in aqueous solution by the ionic liquid BMIMBr. Critical micelle concentrations, interfacial properties, hydrodynamic diameters (4.7-7.7 nm), zeta potentials, and local micropolarity were determined. The micelles significantly enhanced reaction rates relative to aqueous solution, yielding intrinsic micelle/water rate ratios (k _M/k _W) of 376, 363, and 260 for SB3-14, SB3-14/BMIMBr, and ImS3-14/BMIMBr, respectively. Thermodynamic activation parameters in micellar systems revealed lower ΔS ^‡ values than in aqueous solution, indicating more rigid transition states, along with reductions of approximately 10 kcal mol^-1 in the activation energy. Specific ion effects at the micelle-water interface also modulate catalytic behavior by influencing zeta potential, ion-micelle interactions, and 6-NBIC/BMIM⁺ ion-pairing. These findings deepen the understanding of the mechanisms governing the catalytic effects of micellar systems in decarboxylation reactions.