β-lactoglobulin and resveratrol nanocomplex formation is driven by solvation water release

Abstract

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 (Eacta‡= 82.86 kJ.mol−1,TΔSa‡= 32.26 kJ.mol−1, and ΔCpa‡= 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 (Eacta‡=-121.58 kJ.mol−1,TΔSa‡=-173.59 kJ.mol−1, and ΔCpa‡=-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 (ΔG(a)‡ ≅ 48.15 kJ.mol−1, ΔG(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 (ΔH° = 73.06 kJ.mol−1; TΔS° = 99.60 kJ.mol−1) drove the βLG-RES complex formation while at high temperature (301.15 K), hydrophilic interactions became dominant (ΔH° = −142.50 kJ.mol−1; TΔS° = −118.18 kJ.mol−1).