In the past years we studied zeolites as a possible medium for enriching the enantiomeric excess of solutions. Zeolite lattices being achiral, do not prefer one enantiomer over the other, and adsorb both enantiomers equally well. However, if the D- and L- enantiomers adsorb together as a heterodimer, the enantiomeric excess of the solution they leave behind is augmented. We used NMR to explore the adsorption behaviors of D-, L-, and DL- N-acetyl Leucine, Alanine and Methionine into Zeolite NaY. The solid state NMR spectra of the pure D- and L- acetyl Leucine showed the same results as the racemic mixture of N-acetyl-DL-Leucine, indicating a preference to form microcrystals of pure D and L forms. In contrast differences in the solid state NMR spectra are observed for N-Acetyl -DL- Methionine and N-acetyl-DL -Alanine from their pure enantiomers. This implied that both form a mixed crystal. However when adsorbed onto the zeolite, N-Acetyl Methionine and N-acetyl-Alanine exhibit the same behavior as its Leucine counterpart indicating that they are adsorbed as homodimers. NMR line widths of all compounds show a 10 fold increase when adsorbed in NaY indicating restricted molecular motion. Recently, in order to investigate this behavior further we decided to study the same set of systems with molecular modelling. We will present the results of computer simulations regarding the dynamics and energetics of the enantiomer-zeolite interactions.

Enantiomeric interactions of amino acids adsorbed in zeolites: An investigation using solid-state NMR and molecular modelling

251st National Meeting (2016)

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