(1 R,2 S)-ephedrine: A new self-assembling chiral template for the synthesis of aluminophosphate frameworks

Abstract

(1R,2S)-(-)-Ephedrine is used as a new structure-directing agent for the synthesis of nanoporous aluminophosphates. This molecule is selected based on the self-aggregating behavior through π-π type interactions between the aromatic rings and the presence of H-bond-forming groups. Additionally, this molecule possesses two chiral centers, which could enhance a potential transfer of chirality to the inorganic framework. Synthesis results showed that (1R,2S)-(-)-ephedrine is very efficient in directing the crystallization of the AFI-type structure in the presence of several catalytically active dopants. A combination of fluorescence spectroscopy and molecular mechanics simulations shows that ephedrine displays a great trend to self-assemble in water solution, establishing not only π-π type interactions between the aromatic rings but also intermolecular H-bonds between NH2 and OH moieties which compete with the formation of H-bonds with water. These molecules are invariably incorporated as aggregates within the AFI structure, regardless of the dopant introduced, showing a very strong trend to self-assemble within nanoporous frameworks as well. The stability of this supramolecular arrangement within the framework is due to a molecular recognition phenomenon based on the establishment of two H-bonds between the H atoms of the amino group and the O atoms of the hydroxyl group of the consecutive dimer, leading to an infinite supramolecular π-π H-bonded chainlike arrangement within the AFI channels.