A tailored graphene supramolecular gel for pharmaceutical crystallization.

A graphene-based supramolecular gel was designed and prepared to control the crystallization process and polymorphism of pharmaceuticals. The gelators were modified at the end segments with pyrene moieties, which spontaneously interact with the graphene surface by aromatic stacking interaction resulting in a graphene-incorporated supramolecular gel linked by noncovalent interactions between urea groups. When graphene was included into the gel, the critical gel concentration and system rigidity changed significantly, fluorescence spectroscopy determined the close π-π stacking interaction between the gelator and graphene, and the material was confirmed as a true nanocomposite gel system by electron microscopy. Further the graphene was oxidatively modified to obtain hydroxylated graphene (Gr-OH), which was successfully incorporated into the gel system to serve as a medium for pharmaceutical crystallization. Glycine (GLY), caffeine (CAF) and aripiprazole (APZ) were selected as model drugs for gel surface crystallization and gel phase crystallization by Gr-OH hybrid gels. Incorporation of Gr-OH in the gel allowed close interaction by hydrogen bonding with drug molecules, resulting in different polymorphs of GLY, CAF and APZ compared to solution crystallization and shorter induction time of CAF compared to the native gel.