Glyphosate, the most widely used herbicide in the world, degrades in the environment<b> </b>through microbial and abiotic processes. Due to the potential ecological risks and health hazards associated with herbicides, it is imperative to understand the fate of glyphosate and its degradation products in soil . We developed a ReaxFF reactive empirical force field to investigate the potential abiotic degradation pathways of glyphosate using molecular dynamics. Beginning with an existing ReaxFF force field for glycine, we fitted additional parameters against a density functional theory (DFT) based training set that included energies corresponding to variations in the C-P bond length, C-P-O angles, and C-P-O-H dihedral angles. The force field has been validated through static energy calculations and molecular dynamics simulations of glyphosate in water. Energies obtained using the force field closely match the DFT values. Glyphosate remains stable during long (&gt;1 ns) molecular dynamics simulations. The statistical average of the three P-O bond lengths in the phosphonate group are 1.53 Å, 1.42 Å, and 1.42 Å, respectively, and the C-P bond length is 1.75 Å, in close agreement with the experimental values. The other bond lengths, e.g., C-C, C-N and C-O, are also reproduced accurately. Molecular dynamics simulations are being performed to obtain the free energy landscapes for C-P and C-N bond dissociation using umbrella sampling.

Development of a ReaxFF force field for glyphosate

ACS Spring Meeting 2021

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