Exploring the Recognition\nMechanism of Surfactant–Cyclodextrin\nComplex Formation: Insights from SPR Studies on Temperature and Ionic\nLiquid Influence

This study examines the kinetics and thermodynamics of\nthe inclusion\ncomplex (IC) formation between sodium dodecylbenzenesulfonate (SDBS)\nand amine-modified β-cyclodextrin (βCD–NH<sub>2</sub>) using surface plasmon resonance (SPR) and theoretical analysis.\nWe determined a binding constant of 10<sup>3</sup> L mol<sup>–1</sup> for the thermodynamically stable complex ([βCD–NH<sub>2</sub>/SDBS]°) within the temperature range of 285.2–301.2\nK. The thermodynamic analysis revealed a transition from entropy-driven\nto enthalpy-driven behavior with increasing temperature. The rate\nconstant for IC formation was approximately 10<sup>2</sup> M<sup>–1</sup> s<sup>–1</sup>, with the residence time decreasing from 14.08\ns at 285.2 K to 6.13 s at 301.2 K. We observed the formation of an\nactivated complex ([βCD–NH<sub>2</sub>/SDBS]<sup>‡</sup>), with energetic parameters indicating temperature dependence. At\n285.2 K, the activated enthalpy change was positive, while at 301.2\nK, it was negative. The dissociation energetic parameters remained\ntemperature-independent. Additionally, increasing concentrations of\nthe ionic liquid 1-butyl-3-methylimidazolium chloride influenced the\nSDBS tail’s conformation and penetration into the βCD–NH<sub>2</sub> cavity at the activated state. These findings provide insights\ninto the complexation mechanism and the effects of the temperature\nand ionic liquids on IC formation.