Supramolecular Chemistry Controlled by Conformational Space during Structure Direction of Nanoporous Materials: Self-Assembly of Ephedrine and Pseudoephedrine

In an attempt to produce chiral solids, where chirality arises from an asymmetric ordering of the spatial distribution of dopants, we have studied the supramolecular aggregation of π–π-type interactions between aromatic rings of two closely related diastereoisomers, (1R,2S)-ephedrine and (1S,2S)-pseudoephedrine, during structure direction of the microporous AFI large-pore aluminophosphate framework. Despite their very similar molecular structures, differing only in the stereochemistry of the hydroxyl substituent, fluorescence spectroscopy clearly shows completely different aggregation behaviors of the two isomers, with ephedrine displaying a much stronger aggregation trend than pseudoephedrine in aqueous solution; interestingly, this supramolecular behavior is reproduced when the molecules are occluded within the AFI framework during crystallization. A molecular mechanics study of the conformational behavior of the two chiral flexible molecules, both in a vacuum and in aqueous solution, revealed that the ...