Exploring the Recognition Mechanism of Surfactant–Cyclodextrin Complex Formation: Insights from SPR Studies on Temperature and Ionic Liquid Influence

This study examines the kinetics and thermodynamics of the inclusion complex (IC) formation between sodium dodecylbenzenesulfonate (SDBS) and amine-modified β-cyclodextrin (βCD–NH2) using surface plasmon resonance (SPR) and theoretical analysis. We determined a binding constant of 103 L mol–1 for the thermodynamically stable complex ([βCD–NH2/SDBS]°) within the temperature range of 285.2–301.2 K. The thermodynamic analysis revealed a transition from entropy-driven to enthalpy-driven behavior with increasing temperature. The rate constant for IC formation was approximately 102 M–1 s–1, with the residence time decreasing from 14.08 s at 285.2 K to 6.13 s at 301.2 K. We observed the formation of an activated complex ([βCD–NH2/SDBS]‡), with energetic parameters indicating temperature dependence. At 285.2 K, the activated enthalpy change was positive, while at 301.2 K, it was negative. The dissociation energetic parameters remained temperature-independent. Additionally, increasing concentrations of the ionic liquid 1-butyl-3-methylimidazolium chloride influenced the SDBS tail’s conformation and penetration into the βCD–NH2 cavity at the activated state. These findings provide insights into the complexation mechanism and the effects of the temperature and ionic liquids on IC formation.