Spectroscopic studies on the binding of bromocresol purple to different serum albumins and its bilirubin displacing action

The interaction between bromocresol purple (BCP) and bovine serum albumin (BSA)/porcine serum albumin (PSA) was investigated both in the absence and presence of bilirubin (BR) using absorption/absorption difference spectroscopy. A significant red shift in the absorption maxima of BCP accompanied by a decrease in absorbance was indicative of BCP binding to albumin. The titration of BSA and PSA with BCP using absorption difference spectroscopy and analysis of results by Benesi–Hildebrand equation yielded the values of association constant, K as 9.9 ± 0.9 × 104 L mol−1 and 4.1 ± 0.3 × 104 L mol−1 for BSA and PSA, respectively. The differential extinction coefficient (Δε) of 34,484 M−1 cm−1 at 615 nm and 41,870 M−1 cm−1 at 619 nm were estimated for BSA and PSA, respectively. Decrease in (ΔAbs.)615 nm of BCP–BSA complex with the increase in ionic strength suggested the role of hydrophobic interactions in the binding phenomenon. A significant blue shift in the absorption maxima and change in (ΔAbs.)λmax(ΔAbs.)λmax values of BR–albumin complexes upon addition of increasing concentrations of BCP revealed the BR displacing action of BCP on albumin molecule.