Activated Complex Approach to Describe Bovine Serum Albumin-Azure A and Bovine Serum Albumin-Azure B Intermolecular Interactions

Azure A (AZA) and azure B (AZB) phenothiazine dyes are used for clinical and medical purposes, and their functions can be altered via interactions with proteins. However, no kinetics information on the interactions between phenothiazine dyes and bovine serum albumin (BSA) is available. Surface plasmon resonance was used to determine the energetic and dynamic of the BSA-AZA and BSA-AZB complexes formation at pH 7.4. At temperature ≤ 16 °C, the formation of activated (DH‡a,12°C,AZA= -310.57 kJ mol-1 and DH‡a,12 °C,AZB= -256.37 kJ mol-1) and thermodynamically stable (DH°12°C,AZA= -314.56 kJ mol-1 and DH°12°C,AZB= -265.73 kJ mol-1) complexes was driven by enthalpy, while at temperature ≥ 20 °C, by entropy, (TDS‡a,28°C,AZA= 207.49 and TDS‡a,28°C,AZB= 190.69; TDS°28°C,AZA= 277.50 and TDS°28°C,AZB= 257.26 kJ mol-1). Hydrophobic interactions were fundamental to the complex stability and the increase in number of -CH3 groups in the dyes do not affect kinetic and thermodynamic parameters. Our results could help optimize the medical and pharmaceutical applications of phenothiazine dyes.