Hierarchical dl -Glutamic Acid Microspheres from Polymer-Induced Liquid Precursors

Nanostructured organic crystals have a broad application potential as pharmaceuticals, pigments, or catalysts. The development of facile and reproducible synthetic routes and the upscaling of the process, however, still remain a challenge. Here, we describe the synthesis of macroporous hierarchically structured microspheres with nanoplatelets as building blocks of a model organic molecule— dl -glutamic acid ( dl -Glu)—via a polymer-induced liquid precursor (PILP) phase using oppositely charged polyethylene imine (PEI) as a polymeric additive. The impacts of experimental parameters such as [ dl -Glu], temperature, solvent composition, and the pH value were systematically investigated for the dl -Glu morphosynthesis process. A mechanism is suggested to explain the precipitation of dl -Glu with PEI as an additive based on a multistep process: (1) the formation, growth, and coalescence of the PILP droplets; (2) the homogeneous nucleation of nanoplatelets within PILP droplets and (3) the reorientation of nanoplatelets into hierarchical microspheres. This model system can be further extended to the precipitation of other amino acids that have a net charge opposite to that of the polyelectrolyte additive.