A Multiscale Modeling Approach to Understand the Degradation of Glyphosate under Dark and Light Conditions

Glyphosate is an organophosphate herbicide that has been
used for
decades in agriculture. Its potential to cause carcinogenic effects
and many other neurological diseases in humans has been well reported.
Due to its significant environmental impact, considerable attention
has been given to the removal of glyphosate from soil. A promising
route is the degradation of glyphosate induced by titanium dioxide
surfaces. Even though a number of experimental and theoretical studies
have already addressed this topic, the exact mechanistic pathways
of the degradation process, depending on the environmental conditions,
are still unknown. In this work we use a multiscale approach based
on classical and ab initio molecular dynamics combined
with ground-state and excited-state electronic-structure simulations
to unravel the degradation pathways under dark and light conditions.
A detailed chemical bond analysis of the most predominant adsorption
configuration of glyphosate on TiO2 is used to discuss
the molecular degradation in terms of molecular strain, charge transfer,
and occupation of antibonding orbitals upon adsorption. Transition-state
analyses of competitive degradation pathways suggest that aminomethylphosphonic
acid and sarcosine are the main initial degradation products under
dark and light conditions, respectively.