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To improve the efficiency of cyclodextrins as carotenoid carriers, the kinetics and thermodynamics of the inclusion complex formation between modified β-cyclodextrin (βCD-NH2) and β-carotene (βCT) were studied using surface plasmon resonance (SPR) at pH 7.4 and theoretical calculations. The observed dissociation rate of the [βCD-NH2/βCT]° inclusion complex is small (2.59 × 1 0 - 1 s - 1 ), indicating that βCD-NH2 only interacted with the βCT ionone group to form inclusion complex. The βCD-NH2/βCT binding constant is 2.80 × 1 0 4 Lmol - 1 (at 298.15 K), and its temperature dependence indicates that the [βCD-NH2/βCT]° formation is driven by hydrophobic interactions ( Δ H ∘ = 28.83 kJ l - 1 and T Δ S ∘ = 54.21 kJ l - 1 ) caused mainly by the βCT end group desolvation. In contrast, the formation of the [βCD-NH2/βCT]‡ activated complex via association between free molecules and dissociation of [βCD-NH2/βCT]° occurred with the overcoming of an energy barrier ( E a ‡ = 40.77 kJ mol - 1 and E d ‡ = 11.94 kJ l - 1 ) and decrease in entropy ( T Δ S a ‡ = - 11.70 kJ l - 1 and T Δ S d ‡ = - 65.92 kJ l - 1 ). [ABSTRACT FROM AUTHOR]

Preferential solvation participate in various supramolecular self-assembly processes, whose thermodynamic properties can be modulated by the addition of ionic liquids (ILs). However, the effects of these liquids on the thermodynamics of the host-guest complexation process remain unexplored. In this study, the thermodynamic properties of the complexation between 1-dodecylpyridinium cations (C 12 Py+) and β-cyclodextrin (βCD) species in aqueous solutions with different concentrations of 1-alkyl-3-methylimidazolium halides (C n mimX) were investigated by isothermal titration calorimetry. In water, C 12 Py+ and βCD form a 1:1 inclusion complex, which is enthalpically (Δ H i c o = −9.2 ± 0.1 kJ mol−1) and entropically (T Δ S i c o = 16.1 ± 0.2 kJ mol−1) favorable. However, in IL aqueous solutions, all the βCD―C 12 Py+ thermodynamic parameters of the complexation change and this IL effect is dependent on the carbon chain length of C n mim+ cations. ILs with shorter alkyl chains (C n mim+, n ≤ 4) decreases the system entropy, while ILs with longer alkyl chains (C n mim+, n ≥ 6) reduce the enthalpy values. These effects are attributed to i) preferential solvation of surfactant tails by ILs; ii) ability of the ILs to modify the 3D water structure and iii) inclusion of IL molecules into the inner cavities of βCD. [ABSTRACT FROM AUTHOR]

[Display omitted] • β-cyclodextrin/resveratrol inclusion kinetic differs from β-cyclodextrin/RESAn1. • This kinetic difference become from desolvation process of interacting molecules. • Desolvation process affected mainly the kinetic entropic parameters. • Chemical structural differences effect occurs mainly on the association step. • Isokinetic compensation was observed only for the free molecules' association. The determination of the kinetics of inclusion processes is significant for the application of inclusion complexes as carriers for bioactive molecules. We determined the kinetic parameters of inclusion between modified β-cyclodextrin (β-CD- N H 2) and the polyphenols resveratrol (RES) and its structural analog (RESAn1), using the real-time analysis of surface plasmon resonance. The association and dissociation rate constants (k a and k d) showed that RESAn1 inclusion and its dissociation from β-CD- N H 2 were faster than a similar process for RES (k a β - C D - NH 2 / R E S A n 1 = 3.10∙104 ± 0.14 M−1s−1, k a β - C D - NH 2 / R E S =1.87∙103 ± 0.11 M−1s−1; k d β - C D - NH 2 / R E S A n 1 =0.39 ± 0.02 s−1, k d β - C D - NH 2 / R E S =0.30 ± 0.02 s−1, at 25 °C). The activated complex formation was also affected by the structural differences between the polyphenols, as showed by the activation energies of the association step (E act , a β - C D - NH 2 / R E S = 14.81 ± 0.64 kJ∙mol−1, E act , a β - C D - NH 2 / R E S A n 1 = −15.01 ± 0.75 to 82.35 ± 4.47 kJ∙mol−1). These effects of polyphenol structural differences are due to the desolvation process of interacting molecules. These results elucidate the role of small group to the dynamics of the molecular inclusion of β-CD. [ABSTRACT FROM AUTHOR]

[Display omitted] • βCD interacts with the hydrophobic and hydrophilic parts of the Brij surfactants. • The length of the tail and head group affect the stability of the complexes. • The inclusion process is enthalpy-driven. • Complexes formed with the more hydrophobic surfactants self-associate in solution. • Ionic liquids promote the self-association of all complexes. The thermodynamic study of inclusion complexes formed between cyclodextrin and surfactants gives valuable information about how the hydrophobic/hydrophilic balance affects the complex formation. Although various surfactants have been used with this purpose, there is a lack of thermodynamic data about the formation of complexes between β-cyclodextrin (βCD) and the nonionic Brij surfactants. Moreover, the effect of ionic liquids (IL) on this system has not yet been reported. Isothermal titration calorimetry was used for determining the thermodynamic parameters and stoichiometry of the complexes formed, in the absence and presence of 1-butyl-3-methylimidazolium chloride (C 4 mimCl). The dynamic light scattering technique was used for complementing the results. Both the tail and head group of the surfactants was included by βCD, and the complexes' stability followed the order: Brij 78 > Brij 58 ≈ Brij 56 > Brij 76. The standard enthalpy and entropy change were negative for all complexes, indicating the process is enthalpy-driven. The increase of the surfactants' hydrophilicity didn't affect the complexes' stability, while the increase of the hydrophobicity induced the formation of inclusion complex aggregates with 200–270 nm. Finally, the increase of C 4 mimCl concentration do not affect the complex stability but increase the enthalpy and entropy change associated with the inclusion complex formation. [ABSTRACT FROM AUTHOR]