Fluorescence quenching study on the interaction of some Schiff base complexes with bovine serum albumin

The interaction of Schiff base ligand A and its three metal complexes [A-Fe(II), A-Cu(II), and A-Zn(11)] with bovine serum albumin (BSA) was investigated using a tryptophan fluorescence quenching method. The Schiff base ligand A and its three metal complexes all showed quenching of BSA fluorescence in a Tris-HCl buffer. Quenching constants were determined for quenching BSA by the Schiff base ligand A and its metal complexes in a Tris-HCl buffer (pH=7.4) at different temperatures. The experimental results show that the dynamic quenching constant (K-SV) was increased with increasing temperature, whereas the association constant (K) was decreased with the increase of temperature. The thermodynamic parameters Delta H, Delta G and AS at different temperatures were calculated. The ionic strength of the Tris-HCl buffer had a great influence on the wavelength of maximum emission of BSA. Under low ionic strength, the emission spectra of BSA influenced by A-Zn(II) had a small blue shift. Compared to A-Zn(II), the emission spectra of BSA in the presence of the Schiff base ligand A and A-Cu(II) had no significant A,m shift. At high ionic strength, the emission spectra of BSA upon addition of the Schiff base A, A-Fe(II), and A-Zn(II) all had a red shift, but the emission spectra of BSA had A,m shift neither at low ionic strength, nor at high ionic strength in the presence of A-Cu(II). Furthermore, the temperature did not affect the A,m shift of BSA emission spectra.