Binding of rare earth metal complexes with an ofloxacin derivative to bovine serum albumin and its effect on the conformation of protein

The water-soluble Pr (Ⅲ) and Nd (Ⅲ) complexes with an ofloxacin derivative have been prepared and characterized. The single-crystal X-ray diffraction showed that the Pr (III) and Nd (III) complexes have the similar molecular structure. Under physiological pH condition, the effects of [PrL(NO3)2(CH3OH)](NO3) and [NdL(NO3)2(CH3OH)](NO3) on bovine serum albumin (BSA) were examined using fluorescence spectroscopy in combination with UV–vis absorbance and circular dichroism (CD) spectra. The result reveals that the quenching mechanism of fluorescence of BSA by two complexes is a static quenching process and the number of binding sites is about 1 for both. The thermodynamic parameters (ΔH=−14.52 kJ mol−1, ΔS=56.54 J mol−1 K−1 for [PrL(NO3)2(CH3OH)](NO3) and ΔH=−24.63 kJ mol−1, ΔS=22.07 J mol−1 K−1 for [NdL(NO3)2(CH3OH)](NO3)) indicate that hydrophobic and electrostatic interactions are the main binding force in the complexes–BSA system. The binding average distance between complexes and BSA was obtained on the basis of Försterʹs theory. In addition, it was proved by the CD spectra that the BSA secondary structure was changed in the presence of complexes in an aqueous solution.