The investigation of the interaction between piracetam and bovine serum albumin by spectroscopic methods

The interaction between piracetam (OPA) with bovine serum albumin (BSA) has been thoroughly studied by fluorescence quenching technique in combination with UV–vis absorption, Fourier transform infrared (FT-IR), and circular dichroism (CD) spectroscopies under the simulative physiological conditions. The quenching of BSA fluorescence by OPA was found to be a static quenching process. The binding constants (Ka) are 3.014, 2.926, and 2.503 × 103 M−1 at 292, 298, and 309 K, respectively. According to the van’t Hoff equation, the thermodynamic functions standard enthalpy (ΔH) and standard entropy (ΔS) for the reaction were calculated to be −74.560 kJ mol−1 and −159.380 J mol−1 K−1, which indicated that OPA binds to BSA mainly by hydrogen bonds and van der Waals interactions. The binding distance between BSA and OPA was calculated to be 4.10 nm according to the theory of FÖrster’s non-radiation energy transfer. The displacement experiments confirmed that OPA could bind to the site I of BSA. Furthermore, the effects of pH and some common ions on the binding constant were also examined. And the alterations of protein secondary structure in the presence of OPA were observed by the CD and FT-IR spectra.