Formation of Racemic Phases of Amino Acids by Liquid-Assisted Resonant Acoustic Mixing Monitored by Solid-State NMR Spectroscopy.

Mechanochemistry has become a fundamental method in various sciences including biology and chemistry. Despite its popularity, the mechanisms behind mechanochemically induced reactions are not very well understood. In previous work, we investigated molecular-recognition processes of molecules capable of forming racemic phases in ball mill devices. Solid-state nuclear magnetic resonance (solid-state NMR) was used as the key technique to analyze such events. We now extended this study and focused on mechanochemically induced racemic-phase formations of two representative amino acids, alanine and serine, in a resonant acoustic mixer. The data reveal the importance of adding small amounts of solvents (here water) to facilitate the underlying solid-state molecular-recognition processes. The role of water therein is further studied by deuterium magic-angle spinning (MAS) NMR experiments, also revealing that resonant acoustic mixing (RAM) enables efficient hydrogen to deuterium exchange in enantiopure serine, paving the way to deuterate organic compounds in the RAM device.