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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]

To explore in vivo application of quantum dots (QDs), it is essential to understand the dynamics and energetics of interactions between QDs and proteins. Here, surface plasmon resonance (SPR) and molecular docking were employed to investigate the kinetics and thermodynamics of interactions between human serum albumin (HSA) and CdTe QDs (~3 nm) functionalized with mercaptopropionic acid (MPA) or thioglycolic acid (TGA). Kinetic analysis showed that HSA–QD interactions involved transition-complex formation. Despite the structural similarities between MPA and TGA, the [HSA−CdTe@TGA]‡ formation by association of free HSA and QDs demanded 70% more energy and higher entropic gain (E a − TGA ‡= 65.10 and T ∆ S a − TGA ‡= 28.62 kJ mol−1) than the formation of [HSA−CdTe@MPA]‡ (E a − MPA ‡ = 38.13 and T ∆ S a − MPA ‡ = 0.53kJ mol−1). While the [HSA−CdTe@MPA]° dissociation required higher energy and lower entropy loss (E d − MPA ‡ = 49.96 and T ∆ S d − MPA ‡ = − 32.18kJ mol−1) than the [HSA−CdTe@TGA]° dissociation (E d − TGA ‡= 30.78 and T ∆ S d − TGA ‡= − 51.12 kJ mol−1). The stability of [HSA−QDs]° was independent of the temperature and functionalizing group. However, the enthalpic and entropic components were highly affected by the substitution of MPA (ΔH ° = − 11.83 and TΔS ° = 32.72 kJ mol−1) with TGA (ΔH ° = 34.31 and TΔS ° = 79.73 kJ mol−1). Furthermore, molecular docking results indicated that the metal site on the QDs contributes to the stabilization of [HSA−QDs]°. Therefore, differences in QD functionalization and surface coverage densities can alter the HSA–QD interaction, thus their application. [Display omitted] • Human serum albumin (HSA) binds to CdTe quantum dots (QD) with high affinity. • [HSA − CdTe @ MPA]° stable complex formation was enthalpic and entropically favorable. • [HSA − CdTe @ TGA]° stable complex formation was entropically driven. • The QD surface coverage highly affects the thermodynamic and kinetic parameters. • The HSA-QD interaction mechanism is altered by the QD surface coverage density. [ABSTRACT FROM AUTHOR]

Life manifestation is mainly based on biopolymer-ligand molecular recognition; therefore, the elucidation of energy and speed associated with protein-ligand binding is strategic in understanding and modulating biological systems. In this study, the interactions between methylene blue (MB) or azure A (AZA) dyes and bovine lactoferrin (BLF) were investigated by surface plasmon resonance, fluorescence spectroscopy, and isothermal titration microcalorimetry. Despite the molecular similarities between the dyes, the BLF-AZA binding thermodynamic parameters (ΔG AZA o = −30.50 and ΔH AZA o = 10.8 (kJ·mol−1)) were higher in magnitude than those of the BLF-MB systems (ΔG MB o = −27.3 and ΔH MB o = 5.72 (kJ·mol−1)). To increase the systems' entropy (TΔS AZA o = 41.3 and TΔS MB o = 33.0 (kJ·mol−1)), the hydrophobic interactions must outweigh the electrostatic repulsion, thereby promoting BLF-dye binding. The activation complex formation (E ac , a MB = 33, E ac , a AZA = 32, ∆H a, MB ‡ = 31, ∆H a, AZA ‡ = 30, ∆G a, MB ‡ = 51.84, ∆G a, AZA ‡ = 50.7, T∆S a, MB ‡ = −21, T∆S a, AZA ‡ = −21 (kJ·mol−1)), owing to free BLF and MB (or AZA) associations, was not affected by the dye chemical structure, while for the thermodynamically stable BLF-dye complex dissociation, the same energetic parameters (E ac , d MB = 16, E ac , d AZA = 6.4, ∆H d, MB ‡ = 14, ∆H d, AZA ‡ = 3.9, ∆G d, MB ‡ = 81.4, ∆G d, AZA ‡ = 74.93, T∆S d, MB ‡ = −68, T∆S d, AZA ‡ = −71.0 (kJ·mol−1)) were considerably affected by the number of methyl groups. Our results may be very useful to determine binding processes controlled by kinetic parameters, as well as to optimize the application of these photosensitive dyes in biological systems. Unlabelled Image • Lactoferrin interacts with methylene blue or azure A dyes. • Kinetic and thermodynamic binding parameters are dye chemical structure dependent. • Entropic factors were the driving forces for apo-BLF/phenothiazine dye interaction. • Holo-BLF/phenothiazine dye interaction was enthalpy driven. • Dye (-CH 3) groups number decrease make BLF/phenothiazine dye interaction stronger. [ABSTRACT FROM AUTHOR]

Understanding nonionic surfactant-protein interactions is fundamental from both technological and scientific points of view. However, there is a complete absence of kinetic data for such interactions. We employed surface plasmon resonance (SPR) to determine the kinetic and thermodynamic parameters of bovine lactoferrin-Brij58 interactions at various temperatures under physiological conditions (pH 7.4). The adsorption process was accelerated with increasing temperature, while the desorption rate decreased, resulting in a more thermodynamically stable complex. The kinetic energetic parameters obtained for the formation of the activated complex, [bLF-Brij58]‡, indicated that the potential energy barrier for [bLF-Brij58]‡ formation arises primarily from the reduction in system entropy. [bLF-Brij58]○ formation was entropically driven, indicating that hydrophobic interactions play a fundamental role in bLF interactions with Brij58. [Display omitted] • Lactoferrin-Brij58 interaction form a entropically driven complex, [bLF-Brij58]○. • Stability of [bLF-Brij58]○ increases at elevated temperatures. • [bLF-Brij58]○ is formed via the transition state intermediate [bLF-Brij58]‡. • [bLF-Brij58]‡.enthalpic barrier is higher in the adsorption step. • Transition state entropic barrier is dominated by conformation change. [ABSTRACT FROM AUTHOR]

• β-casein and quercetin form supramolecular complexes driven by an entropic increase • Increase in temperature favored the thermodynamically stable complex formation • The interaction process was equally affected by both studied Hofmeister ions • KCl or KSCN increased the stability of the β-casein/quercetin complexes Characterizing the energetics and molecular dynamics of binding between proteins and bioactive compounds is strategic. Using surface plasmon resonance, we demonstrated that β-casein (β-cas) and quercetin (Qct) form supramolecular complexes driven by an increase in entropy (ΔH° = 25.86 and TΔS° =53.49 kJ∙mol-1 at 25 °C). It was possible to infer that the β-cas/Qct complex was formed via an activated complex synthesized by an entropic reduction (TΔS‡ (a) = -15.31 kJ mol-1 and TΔS‡ (d) = -68.80 kJ mol-1 at 25 °C) and an enthalpic increase (ΔH‡ (a) = 30.87 and ΔH‡ (d) =5.0 kJ∙mol-1 at 25 °C). Independent of the nature of the Hofmeister ions, the salts KCl or KSCN increased complex stability by decreasing both the kinetic and thermodynamic enthalpy values, through shielding of the electrostatic interactions at the electric double layer of the interacting molecules. An increase in temperature favored both the association of the free interacting molecules and the dissociation of the thermodynamically stable β-cas/Qct complexes. These results provide insights into the β-cas/Qct interaction process and contribute to the understanding of how Hofmeister ions can modulate intermolecular interactions between proteins and small molecules. [ABSTRACT FROM AUTHOR]

This study examines the kinetics and thermodynamics of the inclusion complex (IC) formation between sodium dodecylbenzenesulfonate (SDBS) and amine-modified β-cyclodextrin (βCD-NH 2 ) using surface plasmon resonance (SPR) and theoretical analysis. We determined a binding constant of 10 3 L mol -1 for the thermodynamically stable complex ([βCD-NH 2 /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 10 2 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-NH 2 /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-NH 2 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.