Understanding the stability, phase transitions, and oligomerization of amino acids under high-pressure conditions is important due to their practical applications in pharmaceuticals and their role in complex biomolecules formation. Several theories have recently been put forth that suggest pressure may have had a dominant role in life’s origin. These hypotheses have sparked new efforts to understand the role of pressure in biology and more fundamentally the effects of high pressure on the structure and chemistry of amino acids and peptides. We investigated the effects of hydrostatic pressure on α-glycylglycine using a combined experimental and theoretical approach. First principles evolutionary structure search performed with USPEX predicts a structural transformation to an α’-digly conformer at 11.4 GPa and is energetically competitive at lower pressures. The calculated structure of α’-digly involves a slight conformational change of the molecule and a change in the hydrogen bonding network from the ambient phase concomitant with a change in the compressibility of the c-axis. Powder X-ray diffraction show a dramatic change in compressibility of the c-axis at ~6.8 GPa. A noticeable change in the Raman spectra at this pressure further supports the predicted structural modification. Such combined experiment and modelling provide atomic level insight into conformational changes occurring as hydrogen bonding is affected by pressure.

This work was performed under the auspices of the U. S. Department of Energy by Lawrence Livermore National Security, LLC under Contract DE-AC52-07NA27344. Thanks to the Laboratory Directed Research and Development Program at LLNL for supporting this study under 18-LW-036.