Molecular Insights into Glyphosate Adsorption to Goethite Gained from ATR-FTIR, Two-Dimensional Correlation Spectroscopy, and DFT Study.
Wei YanChuanyong JingPublished in: Environmental science & technology (2018)
Glyphosate (PMG) complexation on iron (hydr)oxides impacts its fate and transport in the environment. To decipher the molecular-level interfacial configuration and reaction mechanism of PMG on iron (hydr)oxides, the PMG protonation process, which influences the chemical and physical properties of PMG, was first determined using ATR-FTIR spectroscopy. The FTIR results reveal that the deprotonation occurs at carboxylate oxygen when pKa1< pH < pKa2, at phosphonate oxygen when pKa2< pH < pKa3, and at amino nitrogen when pH > pKa3. PMG complexation on goethite was investigated using in situ flow-cell ATR-FTIR, two-dimensional correlation spectroscopy (2D-COS), and density functional theory (DFT) calculations. The results indicate that the phosphonate group on PMG interacts with goethite to form inner-sphere complexes with multiple configurations depending on pH: binuclear bidentate (BB) and mononuclear bidentate (MB) without proton under acidic conditions (pH 5), mononuclear monodentate (MM) with proton and BB without proton at pH 6-8, and MM without proton under alkaline conditions (pH 9). Phosphate competition significantly impacted the PMG adsorption capacity and its interfacial configurations. As a result, the stability of the adsorbed PMG was impaired, as evidenced by its elevated leachability. These results improve our understanding of PMG-mineral interactions at the molecular level and have significant implications for risk assessment for PMG and structural analog pollutants.
Keyphrases
- density functional theory
- single molecule
- risk assessment
- molecular dynamics
- high resolution
- electron transfer
- molecular dynamics simulations
- growth factor
- single cell
- peripheral blood
- dna damage response
- heavy metals
- mental health
- mesenchymal stem cells
- molecular docking
- stem cells
- climate change
- dna repair
- iron deficiency