New insights into the molecular interactions of neonicotinoid pesticides with extracellular polymeric substances: spectroscopy analysis, molecular docking, and DFT simulations

Abstract

The widespread occurrence of neonicotinoid insecticides (NEOs) in soil environments inevitably leads to interactions with microbial extracellular polymeric substances (EPSs), triggering the formation of complexes that can alter the environmental fate of these pesticides. These interactions are complex and critically influence the behavior of NEOs in soil. However, the underlying binding mechanisms remain poorly understood. Therefore, this study combined multispectral techniques, fluorescence excitation emission matrix-parallel factor analysis (EEM-PARAFAC), two-dimensional correlation spectroscopy (2D-COS), molecular docking (MD), and density functional theory (DFT) simulations to investigate the binding characteristics between bacterial EPSs and NEOs (dinotefuran and thiamethoxam). The EEM-PARAFAC results showed that EPSs were primarily composed of protein-like substances and humic-like substances. Notably, compared to humic-like substances, protein-like substances in EPSs exhibited stronger affinity toward NEOs, with the highest quenching constants of 2.4311 × 10⁸ L mol⁻¹ for dinotefuran and 4.8663 × 10⁸ L mol⁻¹ for thiamethoxam. Furthermore, 2D-COS analysis indicated that tyrosine-like substances responded more rapidly to NEOs than tryptophan-like components. Moreover, the MD simulations and DFT simulations indicated that hydrogen bonds and hydrophobic forces were important driving forces for the binding of EPS-NEOs. These findings provide molecular-level insights into the interfacial behavior of NEOs in soil, which is crucial for accurately assessing their environmental fate and ecological risks and may inform the development of effective remediation strategies for NEO contaminated environments.