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.