Solvation effects on glyphosate protonation and deprotonation states evaluated by mass spectrometry and explicit solvation simulations

Author:

Obeid Guilherme1ORCID,Moraes Gustavo O.1,Penna Tatiana C.1ORCID,Schenberg Leonardo A.1ORCID,Ducati Lucas C.1ORCID,Correra Thiago C.1ORCID

Affiliation:

1. Department of Fundamental Chemistry, Institute of Chemistry–University of São Paulo , Av. Prof. Lineu Prestes, 748, Cidade Universitária, São Paulo, SP, Brazil

Abstract

Glyphosate is a widely used herbicide, and its protonation and deprotonation sites are fundamental to understanding its properties. In this work, the sodiated, protonated, and deprotonated glyphosate were evaluated in the gas phase by infrared multiple photon dissociation spectroscopy to determine the exact nature of these coordination, protonation, and deprotonation states in the gas phase. In this context, Natural Bond Orbital analyses were carried out to unravel interactions that govern glyphosate (de)protonation states in the gas phase. The solvent effect on the protonation/deprotonation equilibria was also investigated by implicit (Solvation Model Based on Density and polarizable continuum models) and explicit solvation models (Monte Carlo and Molecular Dynamics simulations). These results show that glyphosate is protonated in the phosphonate group in the gas phase because of the strong hydrogen bond between the carboxylic oxygen (O7) and the protonated phosphonate group (O8–H19), while the most stable species in water is protonated at the amino group because of the preferential interaction of the NH2+ group and the solvent water molecules. Similarly, deprotonated glyphosate [Glyp−H]− was shown to be deprotonated at the phosphonate group in the gas phase but not in solution, also because of the preferential solvation of the NH2+ group present in the other deprotomers. Therefore, these results show that the stabilization of the protonated amino group by the solvent molecules is the governing factor of the (de)protonation equilibrium of glyphosate in water.

Funder

Fundação de Amparo à Pesquisa do Estado de São Paulo

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior

Ministério da Ciência, Tecnologia e Inovação

Conselho Nacional de Desenvolvimento Científico e Tecnológico

Publisher

AIP Publishing

Subject

Physical and Theoretical Chemistry,General Physics and Astronomy

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