Ionic Liquid Chiral Resolution: Methyl 2-Ammonium Chloride Propanoate on Al(854)^SSurface

Abstract

The adsorption of the chiral methyl 2-ammonium chloride propanoate ionic liquid on the chiral Al(854) S surface has been investigated by density functional calculations on periodic slab models. The results show that the molecule features an enantioselective dissociative adsorption at the surface chiral center. The low-coordination of Al atoms at kinked steps and the strong attractive forces towards molecular O atoms are the main causes of the dissociation. At the surface, 2-ammonium propanal, methoxy groups, and Cl atoms are generated, attached at different sites depending on the precursor enantiomer. The adsorption strengths reveal that the bonding of R-enantiomer is more favorable than S-enantiomer by 0.08 eV, enough for a chiral resolution process with an enantiomeric excess of ~96%, whereas adsorption on achiral Al(111) surface reveals no enantiomeric discrimination with a weak molecular adsorption and no dissociation. Enantiomeric discrimination on chiral Al(854) S surface is possible due to different semicore molecular levels binding energies and to distinct infrared vibrational fingerprints. The present results open the possibility for a rather simple way to separate these enantiomers.

Structure and Nanostructure in Ionic Liquids

“…The strong interaction between ions and metals may provide a route to separating enantiomers of chiral ILs . This was elegantly demonstrated by Jalili et al who showed enantiospecific chemisorption of ( R )- and ( S )-methyl 2-ammonium chloride propanoate on achiral Al(111) and on chiral Al(854) S surfaces via ab initio calculations. It would be interesting to test the broader applicability of this result, that is, whether it could be used to separate mixtures of chiral ions or chiral ILs dissolved in molecular solvents by exploiting the pronounced structuring of ILs at interfaces.…”

Chiral Resolution of Naptalam Using D-tartaric acid and Functionalized Multi-walled Carbon Nanotubes

“…Many commercial drugs in current use contain chiral structures and thus consist of enantiomers. The biological effects of enantiomers such as toxicity, mutagenicity, carcinogencity, and endocrine disruption activity are generally different [2][3][4][5][6][7]. Therefore, resolution of chiral herbicides has attracted wide attention.…”