pH dependence of the binding interactions between humic acids and bisphenol A - A thermodynamic perspective

• Published in: Environmental pollution (1987) Vol. 255; no. Pt 2; p. 113292
• Main Authors: Gan, Li-hong, Yan, Zi-run, Ma, You-fei, Zhu, Yu-ying, Li, Xiu-yan, Xu, Juan, Zhang, Wei
• Format: Journal Article
• Language: English
• Published: England Elsevier Ltd 01.12.2019
• Subjects: Benzhydryl Compounds - chemistry; Bisphenol A; Calorimetry; Humic acids; Humic Substances - analysis; Hydrogen Bonding; Hydrogen-Ion Concentration; Hydrophobic and Hydrophilic Interactions; Interaction; Models, Chemical; Phenols - chemistry; Thermodynamic mechanism; Thermodynamics; Water Pollutants, Chemical - chemistry; pH; Bisphenol A; Humic acids; Thermodynamic mechanism; Interaction
• ISSN: 0269-7491; 1873-6424
• DOI: 10.1016/j.envpol.2019.113292

The wide application of bisphenol A (BPA) leads to the emergence of BPA residuals in natural water environments. Dissolved organic matter (DOM) existed in water can bind with BPA, hence influencing the migration and transformation of BPA in aquatic environments. pH is a crucial factor governing the binding interactions between DOM and BPA. However, the mechanisms driven the binding process under different pH conditions are still unclear. In this study, the interactions between BPA and humic acids (HA), a primary component of DOM, are investigated over a wide pH range of 3–12 by integrating fluorescence quenching, dynamic light scattering and microcalorimetry. pH dependence of the binding interactions between HA and BPA are interpreted from a thermodynamic perspective. The results indicate that HA can spontaneously interact with BPA to form a stable HA-BPA complex. With the increasing pH, the binding interactions change from entropy driven to entropy-enthalpy co-driven. Hydrophobic force dominate the binding interactions under acidic condition. The synergy of hydrophobic force and hydrogen bond promotes the binding process under neutral condition. Under alkaline conditions, electrostatic repulsion participates the binding process in addition to hydrophobic force and hydrogen bond, weakening the binding strength. Therefore, neutral pH is favorable for HA to bind with BPA, consequently enhancing the dissolution of BPA in natural water bodies. The results are beneficial to better understand the pH dependent distribution of BPA in aquatic environments. [Display omitted] •HA interacts with BPA to form a stable HA-BPA complex in a wide pH range.•Driven mechanisms change from entropy to entropy-enthalpy with increasing pH.•Neutral pH is favorable for the binding interactions between HA and BPA.•HA enhances the dissolution of BPA in natural water environments. Hydrophobic force and hydrogen bond promote the binding interactions between HA and BPA under neutral condition from the thermodynamic perspective.