Study on the interaction characteristics of dexamethasone sodium phosphate with bovine serum albumin by spectroscopic technique

The interaction of dexamethasone sodium phosphate (DEX-P) with bovine serum albumin (BSA) was studied by fluorescence quenching in combination with UV-Vis spectroscopic method under near physiological conditions. Fluorescence quenching rate constants and binding constants for BSA–DEX-P system were determined at different temperatures. The fluorescence quenching of BSA by DEX-P was due to static quenching and energy transfer. The results of thermodynamic parameters, ΔH (−161.0 kJ mol−1), ΔS (−468.0 J mol−1 K−1) and ΔG (−21.54 to −16.86 kJ mol−1), indicated that van der Waals interaction and hydrogen bonding played a major role in DEX-P–BSA association. Competitive experiments demonstrated that the primary binding site of DEX-P on BSA was located at site III in sub-domain IIIA of BSA. The distance between BSA and DEX-P was estimated to be 1.23 nm based on the Forster resonance energy transfer theory. The binding constant (Ka) of BSA–DEX-P at 298 K was 2.239 × 104 L mol−1. Circular dichroism spectra, synchronous fluorescence and three-dimensional fluorescence studies showed that the presence of DEX-P could change the conformation of BSA during the binding process.