Effect of pressure on methylated glycine derivatives: relative roles of hydrogen bonds and steric repulsion of methyl groups

Phase transitions with fragmentation of the single crystals into fine powder were observed for partially methylated N-methyl and N,N-dimethylglycine, whereas the structural changes in N,N,N-trimethylglycine were continuous with some peculiar features in the 1.4–2.0 GPa pressure range, and accompanied by splitting of the crystals into several large fragments. Structural rearrangements in N-methylglycine and N,N,N-trimethylglycine were strongly dependent on the rate of pressure variation: the higher the rate of increasing pressure, the lower the pressure at which the phase transition occurred.