Binding thermodynamics of synthetic dye Allura Red with bovine serum albumin

• Allura Red bound to warfarin site on bovine serum albumin (BSA).
• Allura Red–BSA binding was entropically driven by fluorescence spectroscopy.
• Allura Red–BSA binding was entropically and enthalpically driven by calorimetry.
• Surface tension at equilibrium provided Allura Red–BSA stoichiometry.
• Allura Red diffusion coefficient indicated Allura Red–BSA interaction.

The interaction between Allura Red and bovine serum albumin (BSA) was studied in vitro at pH 7.4. The fluorescence quenching was classified as static quenching due to the formation of AR–BSA complex, with binding constant (K) ranging from 3.26 ± 0.09 to 8.08 ± 0.06 104 L.mol−1, at the warfarin binding site of BSA. This complex formation was driven by increasing entropy. Isothermal titration calorimetric measurements also showed an enthalpic contribution. The Allura Red diffusion coefficient determined by the Taylor-Aris technique corroborated these results because it reduced with increasing BSA concentration. Interfacial tension measurements showed that the AR–BSA complex presented surface activity, since interfacial tension of the water-air interface decreased as the colorant concentration increased. This technique also provided a complexation stoichiometry similar to those obtained by fluorimetric experiments. This work contributes to the knowledge of interactions between BSA and azo colorants under physiological conditions.