Pressure turns graphite to diamond and glyphosate to...
20 Feb 2024
- Orla Fernie



Professor Simon Parsons and PhD student Cameron Wilson from The Chemistry department at the University of Edinburgh visited PEARL to study phase behaviour in glyphosate.


​​​​​​​​​Known by most as the main ingredient in weed killer, glyphosate has been used to observe the impact of pressure on molecular structure.​​​​


Glyphosate is known by most as the main ingredient in commercially available weedkiller, but it is also a prime example for observing the effects of pressure on molecular structure. It can be used as a representative system for testing how hydrogen bonds and organic crystal structures respond to pressure, providing fundamental information about interaction between molecules. This information helps build understanding of why crystal structures form in the first place, and how we can control solid-state phase behaviour. 

Phase behaviour can be studied by managing external temperature and pressure. By applying pressure to glyphosate, it directly compresses the molecular interactions. An understanding of what interactions are compressed first can help researchers learn fundamental information about the molecules structure. 

Previously, glyphosate has been studied by Raman vibrational spectroscopy, which showed jumps that were interpreted as a phase change. There are two types of phase changes: first order transitions which are major transitions, like the change from graphite to diamond, and second order transitions, which are a change in the way a structure compresses. Raman spectroscopy is very sensitive to second order phase changes. 

One member of the team, Cameron Wilson developed a software for detecting subtle transitions, to show that this change seen in glyphosate is not a gross change. When a molecule is compressed, it is not the molecule itself that compresses, but, initially, the interstitial spaces, then, the hydrogen bonds and other interactions. 

The team previously confirmed this with X-rays, but they also saw some first order transitions. This is what they are studying at ISIS. At ~5Gpa, glyphosate becomes polycrystalline, which signifies a major transition. This was found by chance, when the team significantly increased the pressure on the sample at a very fast rate. They also studied the sample in varying media and again, observed different phase transitions. Now, they want to observe these conditions in a more systematic and controlled way on PEARL. The team want to see if the same phase transitions previously observed will also happen when the experimental conditions are altered systematically, or if it was dependent on what they did previously. 

The findings from this work will be important in increasing the understanding of crystal structures, which is relevant across a variety of areas. In the pharmaceutical industry, knowledge is drawn from research such as these and millions is spent on solid-from screening for the optimal formulation of drugs. ​​

Contact: Fernie, Orla (STFC,RAL,ISIS)