Interaction between the anti-cancer drug diacetyl maslinic acid and bovine serum albumin: A biophysical study

Steady-state and time-resolved fluorescence, as well as Fourier transform-infrared (FT-IR) spectroscopy studies were made to understand the interaction between diacetyl maslinic acid (DMA) and bovine serum albumin (BSA) at pH 7.4. A decrease in fluorescence intensity and a blue shift of the emission peak were observed in the DMA-BSA complex, which were attributed to changes in the microenvironment of the protein fluorophores. Spectroscopic analysis revealed that the fluorescence-quenching mechanism between DMA and BSA was a static procedure. Displacement experiments with site markers indicated that DMA binds to BSA at Sudlow's site I (subdomain IIA). Binding constants for the protein-drug interaction were determined at three different temperatures (298, 305, and 310 K). Enthalpy (Delta H-0) and entropy (Delta S-0) changes indicated that hydrophobic interactions were the dominant intermolecular forces in the binding of DMA to BSA. The interaction appears to be entropy-driven, and the process spontaneous and endothermic. Enthalpy-entropy compensation suggests that reorganization of water molecules plays an important role. Anisotropy and FT-IR experiments revealed that BSA loses its structure in the presence of DMA. The secondary structure compositions of free BSA and DMA-BSA complex were determined by FT-IR. The binding distance and transfer efficiency for DMA-BSA complex were calculated according to the Foster theory of non-radiative energy transfer. (C) 2015 Elsevier B.V. All rights reserved.