Figure 7: Hot-stage polarizing microscope pictures of L-P crystals at different temperatures on heating (1–4) and subsequent cooling (5–8); crystals move at ∼69°C on heating and ∼55°C on cooling. By hot-stage optical microscopy, significant changes to crystals of L-P were seen on both heating and cooling through the R T β transition. Specifically, some crystals, especially larger ones, jumped around the glass slide holding the samples, as shown by the sequence of micrographs on heating (1–4) and subsequent cooling (5–8). Starting with six crystals in the field of view at 30°C and 68°C, three of these disappeared on increasing the temperature to 69°C, and a further one disappeared on holding at 69°C. On subsequent cooling, one of the two remaining crystals jumped out of the field of vision at 55°C, and the other one also disappeared on holding at 55°C.
Figure 8: (Top) Corresponding DSC trace showing α to β and α to α’ phase transitions for pyroglutamic acid. (Bottom) Standalone optical DSC450 setup and close-up of sample and reference crucibles with quartz windows enabling imaging.
