On glyphosate–kaolinite surface interactions. A molecular dynamic study

Abstract

Glyphosate is an important and widely used herbicide, its environmental behaviour being of scientific and public interest. Computational models of clay minerals and their interactions with small organic molecules are valuable in studying adsorption processes at an atomistic resolution. We analysed the adsorption process of glyphosate on kaolinite, a clay mineral with a high abundance in several types of soils (e.g., of subtropical or tropical origin), in terms of the adsorption strength. The molecular interactions are characterized by monitoring the occurrence of hydrogen bonds, the orientation of the molecular dipole relative to the interface and the interaction energy. Two different ionic forms of glyphosate were considered: neutral and anionic (−1). It was shown that the main mechanism of the binding of both glyphosate forms to the aluminol surface of kaolinite is through multiple hydrogen bonds. The standard free energy of adsorption of neutral glyphosate from water solution to the basal octahedral surface of kaolinite was computed at −5 kJ mol −1 , whereas for the anionic form this quantity amounted to −14 kJ mol −1 . Our finding showed that kaolinite has an important contribution to overall adsorption capacity of soils for glyphosate, specifically in its anionic form. Highlights• The adsorption free energy of glyphosate on a kaolinite surface is quantified • Interactions are computed by quantum mechanics and by classical force field • Molecular interactions are characterized in terms of hydrogen bonds and orientations • The effect of polarization of the medium on the calculations is analysed K E Y W O R D S adsorption free energy, clay mineral interface, herbicide, molecular modeling, polarization | INTRODUCTIONGlyphosate (N-(phosphonomethyl)-glycine) is a nonselective herbicide for weed elimination, which has been widely used in recent history (Duke, 2018;Duke & Powles, 2008). Specifically, no-till agricultural management systems often rely on glyphosate for weed control. In some countries, it contributes more than 50% of all herbicide applications (Okada, Costa, & Bedmar, 2019). It seems that glyphosate remains in soil for longer time

On the Adsorption Mechanism of Humic Substances on Kaolinite and Their Microscopic Structure

“…For the modeling of organo-mineral aggregates, we used a pore space model with the mineral phase represented by a periodic kaolinite layer. The kaolinite layer consisted of 16 × 16 unit cells (8.3 × 14.3 nm 2 ; in the a and b unit cell directions) from the bulk structure derived by Bish [42] parallel to the xy-plane, similar to that used in our previous works [40,41,43,44]. The kaolinite layer is formed from an octahedral AlOOH sheet and a tetrahedral SiO sheet; thus, two different basal surfaces exist-the aluminol basal surface [001] and the siloxane basal surface [001].…”

“…The kaolinite was described by the ClayFF force field [46,47] and the water molecules by the simple point charge (SPC) model [48]. In previous works [40,41,43,44], the CLAYFF and the GROMOS54a7 have exhibited compatibility. This behavior is expected as both force fields are based on the SPC water model.…”

Electronic-Level Insight into the Adsorption and Surface Diffusion Kinetics of a Simplified Glyphosate Model on a Goethite Surface

“…Adsorption of phosphonate moieties has been frequently investigated by experimental methodologies 3,4 and occasionally by theoretical approaches. 5,6 However, to the best of our knowledge, neither experiments nor theoretical calculations have been applied so far to study their surface diffusion.…”

“…As it occurs with many chemicals, the environmental mobility of phosphonates is controlled by adsorption processes and surface diffusion on mineral surfaces. Adsorption of phosphonate moieties has been frequently investigated by experimental methodologies , and occasionally by theoretical approaches. , However, to the best of our knowledge, neither experiments nor theoretical calculations have been applied so far to study their surface diffusion.…”

Adsorption of Pharmaceuticals onto Smectite Clay Minerals: A Combined Experimental and Theoretical Study

“…Theoretical calculations are useful tools to understand further the adsorption of organic compounds onto clay surfaces, and they have already shown their ability to provide a precise image of the molecular interactions at play in the adsorption mechanism [25][26][27][28]. For example, modeling the adsorption of two glyphosate ionic forms on kaolinite surface [29] showed a larger adsorption free energy for the anionic form. Another study coupling X-ray diffraction (XRD), infrared and nuclear magnetic resonance spectroscopies, and molecular dynamics (MD) simulations provided a detailed description of oxytetracycline interactions with sodium-montmorillonite [30].…”