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• 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]

To optimize the therapeutic applications of Congo red (CR), a potential inhibitor of protein aggregation, the kinetics and thermodynamics of the interactions between CR and a model protein need to be understood. We used surface plasmon resonance (SPR) and fluorescence techniques to determine the dynamics and thermodynamic parameters for the formation of complexes between CR and bovine serum albumin (BSA). CR interacts with BSA through a transition complex; the activation energy for association (E act(a) ) was determined to be 35.88 kJ mol −1 , while the activation enthalpy (ΔH ‡ ), entropy (ΔS ‡ ), and Gibbs free energy (ΔG ‡ ) are 33.41 kJ mol −1 , 0.18 J mol −1 K −1 , and 33.35 kJ mol −1 , respectively. When this intermediate transforms into the final CR-BSA complex, the entropy of the system increases and part of the absorbed energy is released; this process is associated with a reverse activation energy (E act(d) ) of 20.17 kJ mol −1 , and values of ΔH ‡ , ΔS ‡ , and ΔG ‡ of 17.69 kJ mol −1 , −162.86 J mol −1 K −1 , and 66.25 kJ mol −1 , respectively. A comparison of the SPR and fluorescence results suggests that there is more than one site where BSA interacts with CR. [ABSTRACT FROM AUTHOR]