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Caffeine is a molecule with bioactive properties related to increased mental performance. Its use in food products is limited by its bitterness and self-association behavior. The complex formed by β-lactoglobulin and caffeine was characterized by fluorescence spectroscopy, isothermal titration calorimetry, and molecular docking. Fluorescence spectroscopy revealed that β-lactoglobulin interacted with caffeine to form a 1:1 stoichiometric complex. Isothermal titration calorimetry characterization of β-lactoglobulin-caffeine binding revealed a different stoichiometry (1:3). Molecular docking analysis confirmed the information obtained by the two thermodynamic evaluation techniques, showing that the best interaction occurred in the hydrophobic cavity of β-lactoglobulin. The effect of protein conformation was also evaluated by fluorescence spectroscopy. The complex stoichiometry and binding constants were from the same order as those obtained for native β-lactoglobulin. However, in contrast to the complex formation with native protein, the flexibility increase observed in the thermal unfolded protein promoted a great temperature effect on the standard enthalpy and entropy changes of interaction, indicating the presence of a balance between hydrophobic and hydrophilic forces. • β-lactoglobulin complex with caffeine in its native or denatured form. • β-lactoglobulin conformation influences in the thermodynamics of interaction with caffeine. • Caffeine binds predominantly on β-lactoglobulin hydrophobic cavity for both conformations. [ABSTRACT FROM AUTHOR]

Abstract: The partitioning behavior of the [Fe(CN)5(NO)]2− and [Fe(CN)6]3− anions were studied in aqueous two-phase systems (ATPS) formed by potassium phosphate and macromolecules—poly(ethylene oxide) (1500gmol−1) and triblock copolymers, PEO–PPO–PEO, where PEO and PPO are poly(ethylene oxide) and poly(propylene oxide), respectively. Two copolymers with different hydrophobicity were used, L35 (50% EO and 1900gmol−1) and F68 (80% EO and 8400gmol−1). The partition coefficient for the [Fe(CN)5(NO)]2− and [Fe(CN)6]3− anions in each ATPS were investigated as a function of the temperature, tie-line length and phases hydrophobicity. The relative order of the partition coefficient is L35

Abstract: The extraction behavior of the ions Ni(II), Fe(III), Cd(II), Co(II), Zn(II) and Cu(II) was studied as a function of the amount of extractant added, in aqueous two-phase systems (ATPS) formed mostly by water and without the use of any organic solvent. The others ATPS components were a triblock copolymer (L35) and Na2SO4. Two types of water-soluble extractants (thiocyanate, iodide) and one slightly water-soluble extractant [1-nitroso-2-naphthol (1N2N)] were studied separately. It must be emphasized that this is the first study using a slightly water-soluble complexant for the metallic partition in ATPS, which was not a restrictive factor to the technique as believed. The extraction to the L35 rich-phase of all suited metal ions was insignificant without extractant addition. However, the effectiveness of SCN− in extracting metal ions in the system could be observed in the following sequence: Zn(II)≅Co(II)>Cd(II)>Cu(II)>Fe(III)>Ni(II), with Zn(II), Co(II) and Cd(II) quantitatively extracted and Cu(II) enriched by almost 80%. In the case of the I− extractant, all metal ions, except Cd(II) and Cu(II), remained in the salt-rich phase, providing favorable conditions to the selective separation of Ni(II), Co(II) and Fe(III) ions from Cd(II). The results show that, at pH 7.2, L35/Na2SO4/H2O ATPS can be used with 1N2N as extractant, to separate Co(II) from a complex mixture containing Fe(III), Zn(II) and Cd(II). It was observed, when using 1N2N, that a significant increase in metal extraction takes place as the pH increases, except for Cd(II) and Zn(II). [Copyright &y& Elsevier]

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]

• 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]

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. • Micellar casein (MC) of 180 nm can carry about 18,000 molecules of curcumin (CUR). • SPR measurements showed that the MC-CUR complex formation was exothermic. • Temperature increasing reduced MC-CUR association but increased its dissociation rate. • MC exhibited thermal protection for CUR. [ABSTRACT FROM AUTHOR]

Highlights • Polydiacetylene (PDA)/triblock copolymer (TC)/surfactant (SDS) formed nanosensor. • Enrofloxacin (ENRO) induced a colorimetric transition (CT) in the PDA/TC/SDS sensor. • Energy released by ENRO–SDS interaction was the driving force for PDA color change. • Limit of detection of sensor to ENRO was five times smaller than the allowed by EU. • PDA/TC/SDS sensor shows potential to be applied for detecting ENRO in foods. Abstract Colorimetric nanosensors formed of polydiacetylene (PDA), triblock copolymer (L64 or F68), and sodium dodecyl sulfate (SDS), so-called nanoblends, were developed to detect enrofloxacin (ENRO) in aqueous media. The nanosensors show hydrodynamic diameter ranging from 234.2 ± 3.5 to 801.6 ± 17.8 nm for SDS concentrations of 13.0–21.0 mM, respectively. The lowest limit of detection was 0.054 µM, which is five times smaller than the maximum limit allowed by the European Union. The response surfaces showed that both the SDS and ENRO concentrations influenced the colorimetric response (p < 0.05), and kinetic rate of colorimetric transition (R CT). SDS concentration between 11.0 and 14.0 mM in the nanoblend yielded the most sensitive nanosensors for detecting ENRO. When L64 was replaced by F68, the colorimetric response of the nanoblends was similar, but PDA/F68/SDS showed a slower R CT than PDA/L64/SDS. The developed nanosensor is a sensitive and simple device for the fast detection of ENRO. [ABSTRACT FROM AUTHOR]

Here, investigation was made of the interaction between lactoferrin (Lf) and the anionic surfactants sodium dodecyl sulfate (SDS), sodium dodecylbenzene sulfonate (SDBS), and sodium decyl sulfate (DSS), using isothermal titration calorimetry, Nano differential scanning calorimetry (NanoDSC), and fluorescence spectroscopy. The Lf-surfactant interaction was enthalpically favorable (the integral enthalpy change ranged from −5.99 kJ mol −1 , for SDS at pH 3.0, to −0.61 kJ mol −1 , for DSS at pH 12.0) and promoted denaturation of the protein. The Lf denaturation efficiency followed the order DSS < SDS < SDBS. The adsorption capacity of the protein with respect to surfactant strongly depended on pH and the surfactant structure, reaching a maximum value of 505 SDBS molecules per gram of Lf at pH 3.0. The different efficiencies of the surfactants in denaturing Lf were attributed to the balance of hydrophobic and electrostatic interactions, which also depended on pH and the surfactant structure, highlighting the SDBS-tryptophan residue specific interaction, where SDBS acted as a quencher of fluorescence. Interestingly, the NanoDSC and fluorescence measurements showed that the ferric ion bound to Lf increased its stability against denaturation induced by the surfactants. The results have important implications for understanding the influence of surfactants on structural changes in metalloproteins. [ABSTRACT FROM AUTHOR]

Bovine serum albumin (BSA)/curcumin binding and dye photodegradation stability were evaluated. BSA/curcumin complex showed 1:1 stoichiometry, but the thermodynamic binding parameters depended on the technique used and BSA conformation. The binding constant was of the order of 10 5 L·mol −1 by fluorescence and microcalorimetric, and 10 3 and 10 4 L·mol −1 by surface plasmon resonance (steady-state equilibrium and kinetic experiments, respectively). For native BSA/curcumin, fluorescence indicated an enthalpic and entropic driven process based on the standard enthalpy change (ΔH ○ F = −8.67 kJ·mol −1 ), while microcalorimetry showed an entropic driven binding process (ΔH ○ cal = 29.11 kJ·mol −1 ). For the unfolded BSA/curcumin complex, it was found thatp ΔH ○ F = −16.12 kJ·mol −1 and ΔH ○ cal = −42.63 kJ·mol −1 . BSA (mainly native) increased the curcumin photodegradation stability. This work proved the importance of using different techniques to characterize the protein-ligand binding. [ABSTRACT FROM AUTHOR]

Polydiacetylene (PDA) vesicles have been applied as optical sensors in different areas, although there are difficulties in controlling their responses. In this study, we prepared nanoblends of PDA with triblock copolymers (TC) as a better sensor system for detecting temperature change. The influences of diacetylene (DA) monomer, and the TC chemical structure and concentration on the colorimetric response (CR) were examined. The TC/PDA nanoblend was remarkably more sensitive to temperature change, than classical vesicles. A higher L64 concentration of 12.0% (w/w) reduced the chromatic transition temperature (T tr ) to as low as 24 °C. When using different TCs, the T tr values can be ordered as L35 < F68< L64 < F127

Cinnamic acid (CA) and methyl cinnamate (MC) have attracted interest of researchers because of their broad therapeutic functions. Here, we investigated the interaction of CA and MC with bovine serum albumin (BSA) at pH 3.5, 5.0, and 7.4 using fluorescence spectroscopy, differential scanning nanocalorimetry, and measurements of interfacial tension, size, and zeta potential. BSA formed a complex with the ligands with stoichiometry of approximately 1.0. At pH 7.4, CA-BSA complex formation was entropically driven. The interaction between MC and BSA was more favorable than with CA and was enthalpically driven under the same conditions. The pH played an important role in BSA conformation, which altered the manner in which it interacts with the ligands. Interestingly, both CA and MC had no effect on the surface tension of BSA/air interfaces. These data contribute to the knowledge of CA/MC-BSA interactions and provide important data for application in the food industry. [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]

The interaction between Allura Red and bovine serum albumin (BSA) was studied in vitro at pH 7.4. The fluorescence quenching was classified as static quenching due to the formation of AR–BSA complex, with binding constant (K) ranging from 3.26 ± 0.09 to 8.08 ± 0.06 10 4 L.mol −1 , at the warfarin binding site of BSA. This complex formation was driven by increasing entropy. Isothermal titration calorimetric measurements also showed an enthalpic contribution. The Allura Red diffusion coefficient determined by the Taylor-Aris technique corroborated these results because it reduced with increasing BSA concentration. Interfacial tension measurements showed that the AR–BSA complex presented surface activity, since interfacial tension of the water-air interface decreased as the colorant concentration increased. This technique also provided a complexation stoichiometry similar to those obtained by fluorimetric experiments. This work contributes to the knowledge of interactions between BSA and azo colorants under physiological conditions. [ABSTRACT FROM AUTHOR]

Polydiacetylene (PDA) and triblock copolymer nanoblends were synthesized to detect micellar casein (MC), the main milk protein and an indicator of milk quality. UV–Vis spectrum showed that MC induced blue-to-red transition in nanoblends. When nanoblends and MC were separated by dialysis membrane colorimetric response (CR) was similar, whereas a remarkable CR reduction was noticed after addition of dialyzed-MC, suggesting that small molecules present in MC (salts) caused PDA color change. Interaction enthalpy variation between nanoblends and MC showed an abrupt increase that coincided with MC concentration when colorimetric transition occurred. Copolymer hydrophobic/hydrophilic balance and presence of other molecules in the system affected nanoblends CR. MC salts were found to interact with nanoblends leading to color changes. MC concentration, MC salt release, copolymer hydrophobic/hydrophilic balance, and presence of other molecules in the system affected responses of the sensors. These results contribute to future applications of PDA/copolymer nanosensors to dairy models. [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]

Partitioning behavior of the whey proteins a-lactalbumin (α-la) and β-lactoglobulin (β-lg) in aqueous two-phase systems prepared with poly ethylene glycol (PEG) and sodium polyacrilate (NaPA) was investigated as a function of pH and polymer concentrations. It was observed that α-la concentrated in the PEG phase while β-lg concentrated in the NaPA phase. Response surface methodology was applied to optimize protein partitioning and to achieve the best conditions for their fractionation. Thermodynamic analysis based on isothermal titration microcalorimetry indicated that the partitioning of α-la was accompanied by endothermic heat and was entropically driven, while β-lg partitioning was accompanied by exothermic heat and was enthalpically driven at low polymer concentrations and entropically driven at high polymer concentrations. Purification and yield parameters were determined using fresh whey and the results allowed for conclusion of the great applicability of this new system for α-la and β-lg fractionation. [ABSTRACT FROM AUTHOR]

Abstract: In the present study, a thermodynamic analysis was performed using an isothermal titration microcalorimeter to measure changes in the enthalpy of mixing (ΔmixH) of water in microemulsion systems formed by soybean lecithin, isooctane and butanol. These energies were important to determine the driving forces associated with the formation of reverse micelles. It was observed that the titration curves of water in pure isooctane and in isooctane with soybean lecithin present values of ΔmixH equal to −9.46×10−3 kJ/mol and −5.68×10−3 kJ/mol, respectively. This shows that water does not form intermolecular interactions with these components. Exothermic behavior, with values of ΔmixH ranging from +2.17kJ/mol to −1.63×10−2 kJ/mol, was observed from the titration curve of water in systems formed by soybean lecithin, isooctane and butanol. These values were associated with the water dissolution process, where the formation of reverse micelles had been observed in the evaluated systems. Differences in behavior of ΔmixH for the water curves were observed in systems formed by butanol and soybean lecithin, only pure butanol and butanol with isooctane. The curve of the system containing soybean lecithin, butanol and isooctane clearly shows that the formation of aggregates occurred in this system (reverse micelles). Finally, it was also noted that soybean lecithin did not suffer any degradation process, since the energy involved in the process of water titration in the systems containing the same substance was considered low. Thus, soybean lecithin may be used without problems in this type of system. [Copyright &y& Elsevier]

Abstract: The phase diagrams of PEO1500+sodium tartrate+water, PPO400+sodium tartrate+water, PEO1500+sodium succinate+water, PPO400+sodium succinate+water, PEO1500+sodium citrate+water, PPO400+sodium citrate+water and PPO400+sodium acetate+water aqueous two-phase systems were determined at (283.15, 298.15, and 313.15)K. Both equilibrium phases composition were analyzed by conductimetry and refractive index. In this paper, the influences of polymer hydrophobicity, salt nature and temperature on the phase diagram were analyzed. The phase separation processes was endothermic and the hydrophobic increase make easier the phase splitting, while the electrolyte capacity to induce phase separation follow the order: citrate>tartrate>succinate. The consistency of the tie-line data was ascertained by applying the Othmer–Tobias correlation. The experimental data were correlated with the NRTL model for the activity coefficient, with estimation of new interaction energy parameters. The results, analyzed in terms of root mean square deviations between experimental and calculated compositions, were considered satisfactory. [Copyright &y& Elsevier]

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]