Multi-spectroscopic study on interaction of bovine serum albumin with lomefloxacin–copper(II) complex

The binding reactions of lomefloxacin–copper(II) complex (LMF–Cu) or LMF to bovine serum albumin (BSA) in physiological solution were investigated by multi-spectroscopy. The binding constant, the number of binding sites and the binding distance between LMF–Cu or LMF and BSA were obtained by a fluorescence quenching method and according to the mechanism of Forster-type dipole–dipole non-radioactive energy-transfer, respectively. Enthalpy and entropy changes for two systems were calculated to be −7.970 kJ mol−1 and 47.438 J mol−1 K−1 for LMF–BSA, −12.469 kJ mol−1 and 33.542 J mol−1 K−1 for LMF–Cu–BSA, respectively. The highly positive values observed for the entropy give evidence for a strong interaction. The values of ΔH and ΔS in two systems are similar, indicating that electrostatic interactions in two systems play major role. The effect of LMF–Cu or LMF on the conformation of BSA was also analyzed by synchronous fluorescence, three-dimensional fluorescence and circular dichroism spectra. The results showed that the presence of Cu ion in LMF–Cu can affect the conformation of BSA to some degree. All the results revealed that the addition of copper ion promotes the interaction of lomefloxacin with bovine serum albumin.