Supramolecular chemistry of chiral (1R,2S)-ephedrine confined within the AFI framework as a function of the synthesis conditions

Supramolecular chemistry controlled by packing interactions during structure-direction of nanoporous materials: Effect of the addition of methyl groups on ephedrine derivatives

“…We first analyzed the fluorescence results for the materials obtained with EPH ( Figure 5-top). As already observed in our previous work [37], an increase of the crystallization Nonetheless, aggregation of MeEPH molecules confined within the AFI materials was much weaker compared to EPH. For instance, the sample obtained with low Mg content at 180 ºC, which showed a high aggregation with EPH, in this case showed the presence of both aggregates and monomers.…”

“…MAS-NMR spectra were recorded with a Bruker AV 400 WB spectrometer, using a BL7 probe for 13 C and a BL4 probe for 31 P. 1 As in our previous works [32,37,33], the molecular structures and packing of the different ephedrine derivatives and their interactions with the AFI framework were described with the cvff forcefield [43]. The AFI structure was kept fixed during the calculations.…”

“…Based upon these grounds, we have been recently working with (1R,2S)-(-)-ephedrine ( Figure 1) as a chiral SDA for the synthesis of crystalline nanoporous aluminophosphates; this molecule directed the crystallization of the AFI framework doped with different elements [35], which is composed by 12-MR one-dimensional cylindrical channels with a diameter of 7.3 Å. Ephedrine, which is an alkaloid found in nature [36] in the Ephedra species of plants, and is commercially available at a moderate cost, was selected as SDA since it contains i) an aromatic ring which enables π-π-driven supramolecular aggregation, ii) two stereogenic centers that impart a strong asymmetric nature to the molecule, iii) H-bond donor (H(N)) and acceptor (O(H)) groups that enable a rich H-bond-driven supramolecular chemistry, and iv) positivelycharged (when protonated under the acidic pH of AlPOs synthesis) NH x + groups that would strongly-interact and spatially-direct the incorporation of the dopants. Previous works showed that (1R,2S)-(-)-ephedrine tend to form dimers when confined within the AFI channels only under particular synthesis conditions [37]. Indeed, molecularmechanics-based simulations showed that ephedrine supramolecular aggregates tend to pack within the one-dimensional channels of the AFI framework with a particular rotation angle between consecutive dimers (+30º), thus developing a long-range helicoidal, and hence chiral, supramolecular organic ordering.…”

Self-assembly of chiral (1R,2S)-ephedrine and (1S,2S)-pseudoephedrine into low-dimensional aluminophosphate materials driven by their amphiphilic nature

“…Based on this, ideal precursors of chirality (Figure 1-right) and its diastereoisomer (1S,2S)-pseudoephedrine. We have studied for some time the structure-directing behavior of these molecules in the synthesis of nanoporous aluminophosphates, [32][33][34] and we have observed a different supramolecular chemistry behavior driven by their different conformational space. 35 Ephedrine and pseudoephedrine contain two stereogenic centers, one of which has three different substituents able to develop a strong three-point interaction: i) an aromatic ring, which will promote hydrophobic and π-π interactions with other rings, ii) a hydroxyl group which will give place to localized H-bond interactions, and iii) a basic secondary amino group, which will be protonated at the acidic pH of the synthesis, and will develop strong electrostatic and H-bond interactions with the inorganic network ( Figure 1-right); indeed, H-bond interactions have been shown to be fundamental for a transfer of chirality to occur.…”

“…Our previous experience with these molecules 33 showed that high organic and low water contents tend to lead to layered materials with XRD patterns consisting of one intense peak at low angle (4-5º 2θ) corresponding to the basal space. However, no intense peaks in the middle-angle region were observed, suggesting a low ordering of the inorganic framework.…”