Synthesis of dl-Alanine Mesocrystals with a Hollow Morphology

The crystallization of dl-alanine from water/alcohol supersaturated solutions results in the precipitation of a racemic compound displaying a needlelike hollow morphology, in contrast to the needlelike crystals grown from pure aqueous solutions. This unusual morphology is explained by assuming that the supersaturated solutions crystallized rapidly to create dl-alanine nanocrystals that assemble to give mesoscale crystals. The resulting dl-alanine crystals are characterized by a range of techniques such as X-ray diffraction, scanning electron microscopy, micro-Raman, and differential scanning calorimetry. The kinetics was studied by light scattering and ion-solution conductivity. These measurements revealed that these superstructures of dl-alanine mesocrystals consist of three-dimensional dl-alanine nanocrystals. Finally, a mechanism for the formation of dl-alanine mesocrystals with a hollow morphology is proposed.