Polymer-induced alignment of DL-alanine nanocrystals to crystalline mesostructures.

Crystallization of DL-alanine by cooling of a supersaturated solution in the presence of a chiral double-hydrophilic block copolymer poly(ethylene glycol)-block-poly(ethylene imine)-S-isobutyric acid (PEG4700-PEI1200-S-iBAc) yields crystal superstructures with an astonishing morphology. Although analysis by light microscopy reveals these crystals to be apparently well facetted, electron microscopy shows that they consist of three-dimensionally, well-aligned nanocrystals that are scaffolded to a so-called mesocrystal. This mesocrystal is formed by polymer-mediated structuration, and provides evidence for the importance of mesoscopic events in a typical crystallization process.