On the Degradation Pathway of Glyphosate and Glycine

Glyphosate is a systemic and non-selective herbicide consisting of a glycine and a phosphonomethyl group [1]. The use of glyphosate-based herbicides (GBHs) has increased significantly as to be worthy of attention in the health areas, both environmental and human health [2]. In case of treatment, e.g. water depollution, it is important to know the details of molecular degradation mechanism. Computation models open the possibility of studying such process in silico. In processes that occur in liquid phase solvent plays an important rule. One alternative to include solvent effects in quantum chemical calculations is the solvent implicit model. There are several models and they have proved to be very useful to take into account macroscopic effects but they are poor in describing microscopic detail, such as bond-breaking process. Another alternative is to include solvent explicitly, by means of addition of solvent molecules, i.e. microsolvation. We studied the degradation mechanism of glyphosate and glycine, sketched in Scheme 1. All calculations were performed using the GAUSSIAN 09 package [3]. We performed geometry optimizations and intrinsic coordinate reaction (IRC) [4] calculation using aug-cc-pVDZ basis set [5] and M062X [6] functional. Solvent effects were included by means of both microsolvation and the polarizable continuum solvation model IEF-PCM [7]. We found two degradation pathways of glycine and glyphosate. Both routes lead to a decarboxylation of the molecule. In the case of glyphosate the product formed was the aminomethylphosphonic acid (AMPA), which is one of the degradation product already reported [4].