Thermodynamic and kinetic characterization of pH-dependent interactions between bovine serum albumin and ibuprofen in 2D and 3D systems

• Design of BSA-IBU NPs was carried out by the results of several 2D and 3D experiments.
• The pH-induced structural changes of BSA were proven in 2D and 3D systems.
• Quantitative data of the BSA-IBU interactions were presented at different pH.
• Kinetic constants and thermodynamic state functions were determined by SPR and ITC.
• The pH-induced ibuprofen release of the nanosized composite particles was confirmed.

The interactions between bovine serum albumin (BSA) and ibuprofen (IBU) were investigated at pH 3.0 and pH 7.4 by several two-(2D) and three-(3D) dimensional techniques to provide quantitative, kinetic and thermodynamic data on the BSA-IBU binding. Based on the results, the preparation of BSA-IBU composite nanoparticles (NPs) were successfully carried out for controlled drug release. The high resolution transmission electron microscopy (HRTEM), dynamic light scattering (DLS) and small angle x-ray scattering (SAXS) studies confirm the formation of nearly monodisperse NPs with daverage = 10–13 nm depending on the protein concentrations and IBU contents. The kinetics of pH-induced drug release was studied by a vertical diffusion cell at pH 7.4 at 25 °C. The pH-dependent changes in the secondary structure of BSA were proven by SAXS, DLS and surface plasmon resonance (SPR) investigations. Depending on the protein conformations, the SPR results suggest that the bonded amounts of the drug molecule are 1239 mg IBU/g BSA and 174 mg IBU/g BSA at acidic and neutral pH, respectively. Besides quantification of the interactions, the rate of association (ka) and dissociation (kd), the KA and KD standard equilibrium constants and the binding free energy (ΔG°) were also calculated on the basic of SPR measurements. The ΔG° = − 21.5 ± 0.2 kJ mol−1 obtained by SPR in 2D system is in good agreement with the ΔG° = − 17.38 ± 0.54 kJ mol−1 determined by isotherm titration calorimetry (ITC) in solution (3D).

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