High pressure Raman spectra and DFT calculation of glyphosate.

ABSTRACT

Glyphosate, N-(phosphonomethyl)glycine, (C3H8NO5P), was obtained through the method of slow evaporation method from aqueous solution and its structure analyzed through X-ray diffraction and the Rietveld method. The normal modes of the crystal were investigated using Raman spectroscopy and Density Functional Theory to obtain the assignment of most of the normal modes in the spectral range between 3070 and 45 cm-1. The crystal was compressed to high pressure through a diamond anvil cell, up to 6.2 GPa. From the behavior of the modes corresponding to both internal modes and lattice modes it was possible to discovery two phase transitions undergone by glyphosate, one between 0.97 and 1.5 GPa and other in the pressure interval 4.29-4.63 GPa. The analysis of the Raman spectra also indicates a certain disorder and conformational changes of the molecules in the unit cell at high pressure. Additionally, the phase transitions revealed to be reversible, with no cracking of the sample in the compression - decompression run.