Soft-Matter Nanodomains Enable C2-H/D Exchange in Imidazolium Ionic Liquids

Water-mediated proton transfer depends on both composition and local organization. Here, C2-H/D exchange of imidazolium ionic liquids, undetectable in bulk ionic-liquid/D2O controls over 96-99 h, becomes observable within nonionic Igepal CO-520 (Ig-520) reverse-micellar nanodomains. Composition-specific formulations were selected to provide comparable apparent hydrodynamic diameters (DH = 6.8 ± 0.2 nm). 1H NMR directly monitored depletion of the imidazolium C2-H resonance, while FTIR supported formation of the corresponding C-D vibration in 1-butyl-3-methylimidazolium tetrafluoroborate and thiocyanate. Increasing hydration lowered the method-specific apparent exchange rates obtained independently from both methods but increased the NMR-derived long-time exchange fraction, F∞. The thiocyanate salt exchanged faster, whereas the tetrafluoroborate salt reached the larger F∞. This rate-extent divergence shows that hydration and anion identity regulate kinetic response and long-time exchange outcome differently within the integrated Ig-520/cyclohexane nanodomain environment.