Thermodynamics, conformation and active sites of the binding of Zn-Nd hetero-bimetallic Schiff base to bovine serum albumin.

The interactions between N,N'-di(2-hydroxy-3-methyoxy-phenyl-1-methylene)-o-phenyldiamine-mone Zn(II), Nd(III) nitrate (2LZnNd) and bovine serum albumin (BSA) was investigated by various spectroscopic techniques under physiological conditions. It was proved that the fluorescence quenching of BSA by 2LZnNb was a result of the formation of a non-fluorescent complex with the binding constants of 3.15 x 10(5); 2.72 x 10(5) and 2.44 x 10(5) M(-1) at 298 K, 304 K and 310 K, respectively. A marked increase in the fluorescence anisotropy in the proteinous environments indicates that BSA introduces motional restriction on the drug molecule. The corresponding thermodynamics parameters DeltaH and DeltaS were calculated to be -16.36 kJ mol(-1) and 43.48 J mol(-1) K(-1) via van't Hoff equation. Moreover, the competitive probes experiment revealed that the binding location of 2LZnNb to BSA is in the hydrophobic pocket of site II. The effect of 2LZnNb on the conformation of BSA has been analyzed by means of CD spectrum and three-dimensional fluorescence spectra. The results indicate that the conformation of BSA molecules was changed in the presence of 2LZnNb Schiff base.