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Wang, Caihong, et al. Journal of Environmental Sciences (2025).
Benzalkonium chloride (BAC), a widely used quaternary ammonium biocide, has recently gained attention not only as an environmental contaminant but also as a key modulator of bacterial susceptibility to antibiotics. This case study highlights a scientifically significant application: the use of BAC to enhance the antibacterial efficacy of polymyxin B (PB) against Pseudomonas aeruginosa, a clinically challenging Gram-negative pathogen.
Evidence from controlled time-killing assays demonstrates that the BAC-PB combination produces a pronounced synergistic bactericidal effect, marked by substantial reductions in viable cell counts. Multi-instrument characterization-including scanning electron microscopy, zeta potential analysis, hydrophobicity profiling, and membrane potential fluorescence assays-shows that BAC markedly facilitates PB activity by intensifying cell envelope damage. The combined treatment disrupts membrane integrity, collapses membrane potential, and increases cell surface destabilization.
At the molecular level, transcriptomic profiling reveals extensive downregulation of genes responsible for lipid A modification, outer membrane assembly, and cell envelope biosynthesis, such as phoPQ, pmrAB, bamABCDE, lptABCDEG, lolB, yidC, and murJ. The combination also induces oxidative stress through elevated reactive oxygen species and impairs ATP generation, collectively weakening cellular metabolic resilience.
These findings underscore a critical application of benzalkonium chloride: its use as an adjuvant agent to potentiate last-line antibiotics. This synergistic strategy provides fresh insight into biocide-antibiotic interactions and offers promising therapeutic value for external treatment of Pseudomonas-infected wounds and burns, while contributing to antibiotic-resistance mitigation efforts.
Yang, Jing, et al. "The overlooked role of benzalkonium chlorides in enhancing chlorination of organic contaminants." Journal of Environmental Sciences (2025).
Benzalkonium chloride (BAC), a widely applied quaternary ammonium disinfectant, plays an underrecognized yet critical role in chlorination chemistry within wastewater treatment systems. This case study examines the mechanistic contribution of BAC to the enhanced formation of chlorinated disinfectant byproducts (DBPs), particularly in hospital effluents where BAC concentrations are elevated.
Recent research demonstrates that BAC markedly accelerates the chlorination of phenolic compounds, resulting in increased yields of hazardous chlorophenols. The key mechanistic driver is the oxidation of BAC by free chlorine, generating highly electrophilic R₃N⁺-Cl intermediates. These species exhibit strong chlorinating ability, thereby promoting the rapid formation of 2,4-dichlorophenol and 2,4,6-trichlorophenol. Notably, shorter-chain homologues such as C12-BAC display stronger enhancement effects than longer-chain variants (C14, C16), a trend associated with higher aqueous solubility and diffusion efficiency.
Further oxidation of 2,4,6-trichlorophenol leads to the formation of trichloro-hydroxy-cyclopentene-dione, a DBP with substantial toxicological concern. Density functional theory calculations reveal that while BAC-derived chloramine intermediates share similar electronic structures, mass transport limitations reduce reactivity in longer-chain BACs.
This case underscores a significant environmental application of benzalkonium chloride: its unintended role in promoting toxic DBP formation during chlorination. These findings highlight the necessity of monitoring BAC concentrations in wastewater treatment processes and evaluating their influence on DBP generation, particularly in healthcare-associated waste streams.
Andreeva, N. A., Abuelela, A. M., Alkhalifah, M. A., Bedair, M. A., & Chaban, V. V. (2025). Journal of Molecular Liquids, 128583.
Benzalkonium chloride (BAC), a quaternary ammonium surfactant widely employed as a corrosion inhibitor in oilfield operations, plays a pivotal role in mitigating material degradation in aqueous and saline environments. This case study highlights a density functional theory (DFT)-based investigation that elucidates the molecular interactions governing BAC's selective inhibition behavior toward key corrosive species encountered in oil and gas infrastructure.
Computational simulations reveal that BAC exhibits strong thermodynamic affinity toward FeCl₂ (ΔG = -18.88 kJ/mol), driven by notable π-cation stabilization within the BAC-Fe²⁺ complex. Moderate interactions with NaCl and NaHCO₃ (ΔG = +14.39 and +22.21 kJ/mol, respectively) further support its capacity to mitigate chloride- and bicarbonate-induced corrosion. In contrast, interactions with acetic acid, dissolved CO₂, and CaCl₂ are energetically unfavorable, with CaCl₂ showing the weakest binding (ΔG = +62.50 kJ/mol), indicating limited inhibitory effects under high-calcium conditions.
Electronic structure analyses-including HOMO-LUMO evaluation and NBO calculations-confirm that BAC's inhibition strength is strongly correlated with its electron-donating capability and the formation of stable charge-transfer complexes. These insights provide a mechanistic understanding of how BAC selectively interacts with corrosive species at the molecular level.
This study demonstrates the value of Benzalkonium chloride as a targeted corrosion inhibitor and underscores the potential of integrating BAC with complementary chemistries to achieve broader-spectrum protection. The findings offer a predictive framework for designing advanced corrosion control strategies for oilfield pipelines, storage systems, and production facilities.
