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.

Azure A（AZA）与Azure B（AZB）吩噻嗪（phenothiazine）染料可应用于临床与医学场景，其生物功能可通过与蛋白质的相互作用发生改变。然而目前尚无关于吩噻嗪染料与牛血清白蛋白（bovine serum albumin，BSA）之间相互作用的动力学数据公开报道。本研究采用表面等离子体共振（surface plasmon resonance，SPR）技术，测定了pH 7.4条件下BSA与AZA、BSA与AZB复合物形成过程的热力学与动力学特性。当温度≤16℃时，活化复合物（12℃下，AZA的活化焓ΔH‡a,12℃,AZA = -310.57 kJ·mol⁻¹，AZB的ΔH‡a,12℃,AZB = -256.37 kJ·mol⁻¹）及热力学稳定复合物（12℃下，AZA的标准焓变ΔH°12℃,AZA = -314.56 kJ·mol⁻¹，AZB的ΔH°12℃,AZB = -265.73 kJ·mol⁻¹）的形成由焓驱动；而当温度≥20℃时，复合物形成则由熵驱动，相关参数为：28℃下，AZA的活化TΔS‡a,28℃,AZA=207.49、AZB的TΔS‡a,28℃,AZB=190.69；AZA的标准TΔS°28℃,AZA=277.50、AZB的TΔS°28℃,AZB=257.26 kJ·mol⁻¹。疏水相互作用是维持复合物稳定性的关键因素，且染料中甲基（-CH3）数量的增加不会对其动力学与热力学参数产生影响。本研究结果可为吩噻嗪染料的医疗与药学应用优化提供理论参考。