title: Mechanisms of Bond Cleavage during Manganese Oxide and UV Degradation of Glyphosate: Results from Phosphate Oxygen Isotopes and Molecular Simulations.
abstract: Degradation of glyphosate in the presence of manganese oxide and UV light was analyzed using phosphate oxygen isotope ratios and density function theory (DFT). The preference of C-P or C-N bond cleavage was found to vary with changing glyphosate/manganese oxide ratios, indicating the potential role of sorption-induced conformational changes on the composition of intermediate degradation products. Isotope data confirmed that one oxygen atom derived solely from water was incorporated into the released phosphate during glyphosate degradation, and this might suggest similar nucleophilic substitution at P centers and C-P bond cleavage both in manganese oxide- and UV light-mediated degradation. The DFT results reveal that the C-P bond could be cleaved by water, OH-or•OH, with the energy barrier opposing bond dissociation being lowest in the presence of the radical species, and that C-N bond cleavage is favored by the formation of both nitrogen- and carbon-centered radicals. Overall, these results highlight the factors controlling the dominance of C-P or C-N bond cleavage that determines the composition of intermediate/final products and ultimately the degradation pathway.
authors: Department of Plant and Soil Sciences , University of Delaware, Newark, Delaware 19716, United States.
authors: Deb P
authors: DP
authors: Jaisi
authors: Department of Plant and Soil Sciences , University of Delaware, Newark, Delaware 19716, United States.
authors: Hui
authors: H
authors: Li
authors: Department of Geological Sciences , University of Delaware, Newark, Delaware 19716, United States.
authors: Adam F
authors: AF
authors: Wallace
authors: Department of Plant and Soil Sciences , University of Delaware, Newark, Delaware 19716, United States.
authors: Prajwal
authors: P
authors: Paudel
authors: Department of Plant and Soil Sciences , University of Delaware, Newark, Delaware 19716, United States.
authors: Mingjing
authors: M
authors: Sun
authors: Department of Plant and Soil Sciences , University of Delaware, Newark, Delaware 19716, United States.
authors: Avula
authors: A
authors: Balakrishna
authors: USDA-ARS , Cropping Systems and Water Quality Research Unit, Columbia, Missouri 65211, United States.
authors: Robert N
authors: RN
authors: Lerch
mesh_terms: D055598:Chemical Phenomena / Q000528:radiation effects*; D005998:Glycine / Q000031:analogs & derivatives* / Q000737:chemistry; D017895:Manganese Compounds / Q000737:chemistry*; D015394:Molecular Structure; D010087:Oxides / Q000737:chemistry*; D010103:Oxygen Isotopes / Q000737:chemistry*; D010710:Phosphates / Q000737:chemistry*; D014466:Ultraviolet Rays; D000097797:Glyphosate
chemical_list: D005998:Glycine; D017895:Manganese Compounds; D010087:Oxides; D010103:Oxygen Isotopes; D010710:Phosphates; D000097797:Glyphosate; C027424:manganese oxide
keywords: C−P and C−N bond cleavage; DFT; degradation; glyphosate; manganese oxide; phosphate isotopes