Adsorption of glyphosate on montmorillonite: A comparison of theoretical calculations at interlayer surfaces and edges

LORENA TRIBE; GEORGE A. KHOURY; BAO PHUNG TRUONG; TODD GEHRIS; MARÍA DOS SANTOS AFONSO

San Francisco, California

Congreso; The 232nd ACS National Meeting; 2006

American Chemical Society

Glyphosate (N-phosphonomethylglycine) is the most popular herbicide in the world. Glyphosate is rapidly adsorbed and tightly bound to mostsoils through constituents such as clay minerals, metallic oxides, organic materials and humic substances. Glyphosate can be adsorbed onclay silicates like montmorillonite or bound to octahedral cations, specifically iron and aluminum, exposed on the edges of the mineralsurface. Glyphosate also penetrates into the interlayer space, which expands in aqueous solution. As the exact binding mechanism is notfully understood we develop and implement a theoretical structural model of these interactions using the molecular modeling and quantummechanical calculations. This model reproduces the expansion of the interlayer in presence of water adequately and allows for estimationsof the adsorption energies of the glyphosate molecule through its phosphonate and amino moieties, both to silicates in the interlayer spacesand to octahedral aluminum atoms at the edges of the mineral.