Discerning subtle high-pressure phase transitions in glyphosate

Cameron J.G. Wilson, Peter A. Wood, Simon Parsons*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

Abstract / Description of output

The common garden herbicide glyphosate, N-(phosphonomethyl)glycine, has been studied between ambient pressure and 5.17 GPa using single crystal X-ray diffraction. Glyphosate forms a structure composed of layers parallel to the (1 0 −2) planes. Hydrogen bonds form along the stacking direction, which are very incompressible so that the effects of pressure are accommodated mostly within the layers. This study has confirmed two high pressure phase transitions previously observed by Raman spectroscopy, enabling the structural signatures of the transitions to be identified. Both transitions are very subtle and second order, involving changes to the way the structure responds to pressure rather than changes to the structure. The first transition occurs between 0.93-1.21 GPa and corresponds to the onset of greater compressibility within the layers. The second transition between 3.78-4.23 GPa is an intramolecular feature signalling a deformation of the molecular backbone. In the absence of a first order phase transition, the packing remains in a compressed form of its ambient pressure form up until the highest pressure measured. A reconstructive phase transition occurs at 5.98 GPa forming a polycrystalline high-pressure phase.

Original languageEnglish
JournalCrystEngComm
Early online date11 Jan 2023
DOIs
Publication statusE-pub ahead of print - 11 Jan 2023

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