title: Study of the stepwise deprotonation reactions of glyphosate and the corresponding pKa values in aqueous solution.
abstract: Glyphosate (N-(phosphonomethyl)glycine) (Gph) is a herbicide that is broadly used in several countries. Its application to eliminate weeds may have the undesired effect of diminishing the metallic cations found in the soil (e.g., Ni(2+) and Zn(2+)), due to a complexation reaction that depends on the soil's pH. To better understand the molecular structures of glyphosate that are involved in such a complexation reaction, we have studied all possible glyphosate conformations in aqueous solution that may be involved in deprotonation reactions in the pH range from 2 to 11 using the polarizable continuum method (PCM). We have also compared direct (or absolute) methods to calculate pKa values, the cluster-continuum model and the proton-exchange scheme, using different thermodynamic cycles. The best result was achieved when using a proton-exchange scheme, which was able to properly reproduce three glyphosate experimental pKa values predicted for the glyphosate structures and conformations previously determined.
authors: Departamento de Química-ICE, Universidade Federal Rural do Rio de Janeiro, Rodovia BR465, km 47, Seropédica - RJ, 23897-000, Brazil.
authors: Miqueias M
authors: MM
authors: Peixoto
authors: Departamento de Química-ICE, Universidade Federal Rural do Rio de Janeiro, Rodovia BR465, km 47, Seropédica - RJ, 23897-000, Brazil.
authors: Glauco F
authors: GF
authors: Bauerfeldt
authors: Departamento de Química-ICE, Universidade Federal Rural do Rio de Janeiro, Rodovia BR465, km 47, Seropédica - RJ, 23897-000, Brazil.
authors: Marcelo H
authors: MH
authors: Herbst
authors: Departamento de Química-ICE, Universidade Federal Rural do Rio de Janeiro, Rodovia BR465, km 47, Seropédica - RJ, 23897-000, Brazil.
authors: Marcio S
authors: MS
authors: Pereira
authors: Departamento de Química-ICE, Universidade Federal Rural do Rio de Janeiro, Rodovia BR465, km 47, Seropédica - RJ, 23897-000, Brazil.
authors: Clarissa O
authors: CO
authors: da Silva
mesh_terms: D002412:Cations / Q000737:chemistry; D005740:Gases / Q000737:chemistry; D005998:Glycine / Q000031:analogs & derivatives* / Q000737:chemistry; D006540:Herbicides / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D008956:Models, Chemical; D015394:Molecular Structure; D011522:Protons; D012987:Soil / Q000737:chemistry; D012996:Solutions; D055672:Static Electricity; D013816:Thermodynamics; D014867:Water / Q000737:chemistry*; D000097797:Glyphosate
chemical_list: D002412:Cations; D005740:Gases; D005998:Glycine; D006540:Herbicides; D011522:Protons; D012987:Soil; D012996:Solutions; D014867:Water; D000097797:Glyphosate