Study of peptides under simultaneous application of high pressure and shear*

There is a renewed interest in the role of non-hydrostatic mechanical stress, or shear stress, as a driver for reactions. Combining high pressure with mechanical shearing can significantly alter reaction mechanisms and lead to a decrease in the onset pressure of structural transformations. Such conditions can be achieved with a rotational diamond anvil cell (RDAC). We will discuss the study of simple amino acids and peptides subjected to high-pressure, high-shear conditions using an RDAC. Amino acids have been studied extensively under static compression due to their significance in the fields of chemistry and biology. We compare amino acid behavior under high shear to that in a conventional DAC. μ-Raman spectroscopy and X-ray diffraction are used to probe the phase transitions and amino acid condensation. Theoretical calculations are also performed using USPEX, metadynamics, and quantum molecular dynamics to predict novel phases and reaction barriers under compressive shear.