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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., (Copyright © 2019 Elsevier B.V. All rights reserved.)

Determine the thermodynamic and kinetic parameters of interaction between micellar casein (MC) and curcumin (CUR) is useful for the application of MC-CUR systems in food products. We used surface plasmon resonance (SPR) and ultraviolet-visible spectrophotometry (UV-vis) to study the complex formation between MC obtained from skimmed milk and CUR, MC carrying capacity, and thermal protection for CUR at a pH of 6.6. An MC could carry about 18,000 molecules of CUR. SPR suggested an enthalpy-driven process (∆H° = -64.63 kJ∙mol -1 and T∆S° ranging from -42.45 to -44.46 kJ∙mol -1 ). Temperature increased reduced the rate of MC-CUR complex formation and increased its dissociation rate. The activation energy for the formation of MC-CUR activated complexes was negative for association of free MC and CUR molecules (-62.8 kJ mol -1 ) and positive for dissociation of the thermodynamically stable complexes (1.80 kJ mol -1 ). MC protected the CUR against its thermal degradation when it was subjected to different temperatures (30, 40, 50, and 60 °C for 5.5 h). This study shows the importance of characterizing MC-small molecules interactions for better application of MC as a nanocarrier., (Copyright © 2019. Published by Elsevier B.V.)

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]

The complexation between protein and polyphenol affects their biological functions. A complete understanding of such interactions requires comprehensive thermodynamic and kinetic characterizations. Surface plasmon resonance (SPR) and fluorescence spectroscopy (FS) described similarly the thermodynamic of interaction between bovine lactoferrin (bLF) and epigallocatechin-3-gallate (EGCG). The formation of the bLF-EGCG complex is spontaneous (Δ G S P R o ≈ -29.00 kJ mol−1, Δ G F S o ≈ -26.00 kJ mol−1) and entropically driven (Δ H S P R o = 14.26, Δ H F S o = 10.20 kJ mol−1 and T Δ S S P R o ≈ 43.00, T Δ S F S o ≈ 36.00 kJ mol−1). The kinetic parameters obtained by SPR showed that the reaction occurs through an activated complex, whose energetic formation parameters from the association of free molecules ( E a c t (a) = 49.5 kJ mol−1, Δ H a ‡ = 47.0 kJ mol−1, and T Δ S a ‡ = −2.10 kJ mol−1) were higher than those in the opposite direction (namely the dissociation of the stable complex, E a c t (d) = 17.4 kJ mol−1, Δ H d ‡ = 32.8 kJ mol−1, and T Δ S d ‡ = −45.10 kJ mol−1), except for Δ G ‡ (Δ G a ‡ = 49.1 kJ mol−1 and Δ G d ‡ = 77.9 kJ mol−1). This study provides useful information for optimizing the use of bLF – EGCG complex as a bioactive compound in different systems, such as medical, food, cosmetic, and pharmaceutical formulations. Image 1 • Epigallocatechin-3-gallate (EGCG) and bovine lactoferrin (bLF) form a stable complex. • bLF – EGCG complex formation was driven by enthalpic and entropic interactions. • bLF – EGCG complex formation proceeded through an intermediate complex. • Intermediate formation from free EGCG and bLF was accompanied by an entropy decrease. • Fluorescence spectroscopy supported SPR thermodynamic binding parameters. [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]

Ponceau 4R (P4R) and bovine serum albumin (BSA) may interact changing food properties. We compared fluorescence spectroscopy and surface plasmon resonance (SPR) for studying, in vitro , the interactions between BSA and P4R at pH 7.4 and 3.5 in different temperatures. Fluorescence data pointed to the formation of a complex where P4R was bound on site I or II of BSA, with a stoichiometry around one and a binding constant (K b ) ranging from 1.37 × 10 5 to 20.15 × 10 6 L mol −1 . The complex formation at both pH was enthalpically driven (standard enthalpy change, ΔH° F = −60.69 and −63.06 kJ mol −1 , for pH 7.4 and 3.5, respectively). Using SPR, we also found the formation of 1:1 BSA-P4R complexes, but the calculated K b values were much smaller, on the order of 10 3 L mol −1 . Again, we found that the formation of BSA-P4R complex was driven by enthalpy decreasing; however the standard enthalpy change was less negative than that found by fluorescence (ΔH° SPR = −15.05 and −40.55 kJ mol −1 , at pH 7.4 and 3.5, respectively). Our results show that these distinct techniques provided different thermodynamic binding parameters for the BSA-P4R interaction, especially regarding ΔH° values, indicating that BSA-P4R binding was a multisite phenomenon, and that sites far from tryptophan residues were the main responsible by electrostatic interaction. Thus, this work clearly shows the importance of using complementary techniques for a complete thermodynamic characterization of complexes formed between azo-colorants and proteins; which is directly related to physicochemical properties of systems containing both molecules together. [ABSTRACT FROM AUTHOR]

[Display omitted] • Thermodynamically stable complexes are formed through activated complexes. • The water molecules of the desolvation layer influence the association. • The interaction causes a conformational change at the beta-lactoglobulin site. • At the low temperature (285.15 K) the hydrophobic interaction prevails. • At high temperatures (301.15 K), hydrophilic interactions are dominant. Despite some thermodynamics studies about β-lactoglobulin (βLG) and resveratrol (RES) interactions, there is a gap regarding kinetics data about βLG-RES complex formation. Here, we determined the kinetic and thermodynamic parameters of βLG-RES interactions by using surface plasmon resonance (SPR). The kinetic association parameters were dependent on the 3D water structure present on the solvation shell of both interacting molecules. At lower temperature (285.15 K), all activation energies were positive (E a c t a ‡ = 82.86 kJ.mol−1, T Δ S a ‡ = 32.26 kJ.mol−1, and Δ C p a ‡ = 4.15 kJ.mol−1K−1) due to the higher water structuration on the RES and βLG solvation shell. All these energetic barriers become mainly from the energetic cost for the desolvation process of RES and βLG. At higher temperature (301.15 K), the solvation water structure decreases and all the above activation energies become negative (E a c t a ‡ = - 121.58 kJ.mol−1, T Δ S a ‡ = - 173.59 kJ.mol−1, and Δ C p a ‡ = - 29.92 kJ.mol−1K−1) because the direct interaction between desolvated RES and βLG molecules released more energy than it is absorbed by desolvation process. However, kinetic dissociation parameters were not dependent on the hydrogen bond density of the water solvation shell as showed by the temperature independence of dissociation energetic parameters. This non-dependence of the dissociation process from the desolvation step probably is because the water molecules interacting with the βLG-RES complex is not concentrated around/inside the protein site of interaction. The association of free molecules was 1.5 times faster than the dissociation of the thermodynamically stable complex (Δ G (a) ‡ ≅ 48.15 kJ.mol−1, Δ G (d) ‡ ≅ 73.10 kJ.mol−1). The lower free energy barrier observed for the association came from an isokinetic process where entropic and enthalpic parameters compensated for each other. The ΔG° values indicate that the thermodynamically stable complex predominates over free molecules. At low temperature (285.15 K), the hydrophobic interaction (Δ H° = 73.06 kJ.mol−1; T Δ S° = 99.60 kJ.mol−1) drove the βLG-RES complex formation while at high temperature (301.15 K), hydrophilic interactions became dominant (Δ H° = −142.50 kJ.mol−1; T Δ S° = −118.18 kJ.mol−1). [ABSTRACT FROM AUTHOR]

• Peanut proteins (ARA or CON) interact with Congo red (CR) to form stable complexes. • CON has a higher binding affinity toward CR than does ARA. • Hydrophilic interactions were the main driving forces for [ A R A - C R ] 0 formation process. • The formation of [ C O N - C R ] 0 was enthalpically and entropically driven. • Transition complexes had a more structured conformation than their stable form. The thermodynamics and kinetics of arachin-Congo red (ARA - C R) and conarachin-Congo red (CON - C R) interactions were studied using surface plasmon resonance. KCl led to a reduction of up to 55% in the values of the associated kinetic constants, but it had less influence on the dissociation rates (less than 12%). The change in ionic strength had little effect on the thermodynamic stability of the complexes, but it did reduce their affinities (K b ( 25 ° C) [ A R A - C R ] 0 from 3.52 to 2.44 × 103 M−1 and K b (25 ° C) [ C O N - C R ] 0 from 15.1 to 12.5 × 103 M−1). The shielding of the electrical double layer favored ARA - C R hydrophilic interactions (Δ H [ A R A - C R ] 0 0 decreased from −30.60 to −42.98 kJ mol−1). On the other hand, hydrophobic interactions came to dominate during the formation of [ C O N - C R ] 0 (Δ H [ C O N - C R ] 0 0 increased from −11.21 to 28.34 kJ mol−1 and T Δ S 25 ° C [ C O N - C R ] 0 0 increased from 12.64 to 51.73 kJ.mol−1). The data presented here improve our understanding of plant-based protein nanocarriers of small bioactive molecules. [ABSTRACT FROM AUTHOR]

[Display omitted] β-Carotene (β C A R) is a pro-vitamin A carotenoid with powerful antioxidant properties. However, it has low aqueous solubility, light and heat stability, and bioavailability. An interesting strategy to improve β C A R incorporation in food matrices while preserving its properties is the use of proteins as nanocarriers. Lysozyme (LYS) is a protein capable of carrying bioactive molecules and has antitumor, antiviral, and antimicrobial activities. To enable the use of LYS with β C A R , it is important to understand the dynamics of LYS - β C A R binding. Here, a thermodynamic and kinetic investigation of LYS - β C A R ° complex formation at physiological pH was carried out using fluorescence spectroscopy (FS), differential scanning nanocalorimetry (nanoDSC), molecular docking, and surface plasmon resonance (SPR). The binding constants were found to be on the order of 105 to 103 L mol−1 by FS and SPR, respectively, revealing that the interaction between LYS and β C A R is entropically driven. In addition, kinetic parameters related to intermediate complex formation were obtained, and we found that the rate of intermediate complex formation was higher on the free molecules association than on the LYS - β C A R ° dissociation based on the lower Δ G a ‡ values than Δ G d ‡. In addition, the occurrence of an isokinetic relationship indicates that intermediate complex formation results in changes in LYS binding sites, and both desolvation of the free molecules and conformational changes are temperature dependent. Thus, we have elucidated the dynamics of LYS - β C A R ° complex formation and provided important evidence that LYS can be used to carry β C A R , which will improve its application and functionality in food. [ABSTRACT FROM AUTHOR]

The formation of nanocomplexes between lutein (Lut) and lysozyme (Lys) is an alternative method of transporting Lut and improving its chemical stability. To optimize the formation of the Lut-Lys complex, binding assays were performed in the temperature range of 12–28 °C using real-time label-free surface plasmon resonance (SPR). Kinetics analysis showed that about 2000 Lut-Lys complexes are formed per second, of which 36% dissociate per second. The speed of formation of the activated complex was not affected by temperature because the Gibbs free energy barriers were almost constant (∆ ‡ G a 0 ≅ 53 and ∆ ‡ G d 0 ≅ 74 kJ.mol−1). There was a critical temperature (T ≅ 18.36 °C), below it the hydrophobic forces dominated (∆ ‡ H a 0 and ∆ ‡ H d 0 > 0) and above it hydrophilic interactions (∆ ‡ H a 0 and ∆ ‡ H d 0 < 0), such as van der Waals and hydrogen bonds, determined the activated complex formation. The stability of the thermodynamic complex was temperature-independent (∆G 0 ≅ − 21 kJ mol−1); however, the relative hydrophobic/hydrophilic contributions to the enthalpy and entropy change for the formation of this complex were dependent on the temperature (∆H 0 = 11.72 to − 36.71 kJ.mol−1 and T∆S 0 = 32.11 to − 15.54 kJ.mol−1). The SPR data provide useful insight for the discovery of potential lutein-protein nanocarriers. Unlabelled Image • Lutein (Lut) and Lysozyme (Lys) formed a stable complex via activated complex (AC). • The Gibbs free energy barrier of the AC formation is temperature independent. • Lut-Lys AC formation promoted the entropy system reduction. • Lut-Lys stable complex occurred through enthalpic-entropic compensation. • The Lut-Lys hydrophobic/hydrophilic interaction balance is temperature dependent. [ABSTRACT FROM AUTHOR]

The incorporation of bioactive molecules is important to improve food functionality. Despite the low solubility of some bioactive molecules, e.g., flavonoids, their binding with proteins contribute to their incorporation. There are some studies regarding globular proteins as flavonoid nanocarriers, but binding between flavonoids and βCN monomers, which are flexible proteins, is less reported. Here, the thermodynamics and kinetics of naringin–β-casein (NR–βCN) binding were determined by fluorescence spectroscopy (FS) and surface plasmon resonance (SPR). FS indicated that NR binds with βCN close to Trp 143 with K b 24 ° C = 2.71 × 104 m −1 and a key role of desolvation. SPR revealed that NR also binds far from Trp 143 (K b 24 ° C = 7.01 × 103 m −1) with small enthalpic and entropic temperature dependencies. We also present the kinetic parameters related to an intermediate complex formation, which was formed with minimal conformation and desolvation changes. Our results demonstrate βCN monomers as potential nanocarriers for NR. [ABSTRACT FROM AUTHOR]

The thermodynamics of curcumin (CUR) binding with bovine lactoferrin (bLF) was investigated by employing fluorescence spectroscopy (FS) and surface plasmon resonance (SPR) and comparing the results. Moreover, the kinetics of bLF-CUR binding was studied using SPR. FS data showed that with an increase in temperature (from 293.15 to 306.15 K), more complexes were formed (K b ranged from 2.07 × 104 to 6.68 × 104 M−1) owing to an increase in the entropy (Δ H ° = 66.70 kJ mol−1; T Δ S ° ranged from 90.93 to 94.98 kJ mol−1), demonstrating the role of hydrophobic interactions. However, the bLF-CUR complex formation detected through the SPR technique was entropically and enthalpically driven below and above 293.75 K, respectively. SPR also demonstrated that an enthalpy increase is compensated by an entropy increase for both stable and activated complex formation, characterizing enthalpy-entropy compensation and iso-kinetic compensation, respectively. These results are helpful to better understand the dynamics of complex formation between proteins and small bioactive molecules. Image 1 • Curcumin (CUR) and bovine lactoferrin (bLF) formed a stable complex. • SPR showed that bLF has more sites for CUR binding than those close to tryptophan. • The stable bLF-CUR complex formation passes through an intermediate state. • The bLF-CUR interaction occurred with enthalpy-entropy compensation. • bLF-CUR binding is driven mainly by the conformational and desolvation processes. [ABSTRACT FROM AUTHOR]

• Resveratrol (RES) and its analog RESAn1 form complexes with human serum albumin (HSA). • Polyphenol structure influenced the thermodynamic and kinetic binding parameters. • RESAn1 has a higher binding affinity toward HSA than does RES. • The RES-HSA and RESAn1-HSA complex formation was entropically driven. • Formation of the activated complex from the association was faster than dissociation. The thermodynamics and kinetics of binding between human serum albumin (HSA) and resveratrol (RES) or its analog (RESAn1) were investigated by surface plasmon resonance (SPR). The binding constant and the kinetic constants of association and dissociation indicated that RESAn1 has higher affinity toward HSA than does RES. The formation of these complexes was entropically driven ( T Δ S 0 HSA - R E S ≅ 33.8 , T Δ S 0 HSA - R E S A n 1 ≅ 56.4 KJ mol−1). However, for both polyphenols, the activation energy (E act ) of association (a) of free molecules was higher than that for dissociation (d) of the stable complex (E a c t a H S A - R E S = 11.37 , E a c t d H S A - R E S = - 3.06 , E a c t a H S A - R E S A n 1 = 30.76 , E a c t d H S A - R E S A n 1 = - 5.24 KJ mol−1), and the rate of association was faster than that of dissociation since the activation Gibbs free energy ( Δ G ‡) was lower for the former (Δ G aHSA - R E S ‡ ≅ 54.73 , Δ G dHSA - R E S ‡ ≅ 73.83 , Δ G aHSA - R E S A n 1 ‡ ≅ 54.14 , Δ G dHSA - R E S A n 1 ‡ ≅ 73.97 KJ mol−1). This study showed that small differences in the structure of polyphenols such as RES and RESAn1 influenced the thermodynamics and kinetics of the complex formation with HSA. [ABSTRACT FROM AUTHOR]