Spectroscopic studies on the interaction between disperse blue SBL and bovine serum albumin

The interaction of disperse blue SBL (DBSBL) with bovine serum albumin (BSA) was investigated using fluorescence, UV–visible and far-UV circular dichroism (CD) spectroscopy. The results showed that the fluorescence of BSA was quenched by DBSBL through static quenching after correcting for the inner filter effects (IFE). The binding constant Kb of DBSBL with BSA at 288, 298 and 303 K were 0.116×106, 3.18×106 and 12.3×106 L mol−1, respectively. The thermodynamic parameters, standard enthalpy change (ΔH0) and standard entropy change (ΔS0), for the reaction were evaluated to be 227.2 kJ mol−1 and 886 J mol−1 K−1 according to the van’t Hoff equation. The above data suggested that the forces acting between DBSBL and BSA were predominantly hydrophobic interactions. The results of UV–visible absorption and far-UV CD spectroscopy also revealed that the conformation and microenvironment of BSA molecule were changed after DBSBL binding to BSA. At 288 K one binding site was present but at higher temperatures a second binding site was detected between DBSBL and the BSA molecule. The lower bound for the distance between the bound dye and the Trp residue is 2.35 nm as calculated from Forster energy transfer.