Drug molecules are often chiral, where only one of the mirror images is useful. We are investigating the selectivity of Zeolite NaY in enhancing the relative abundance of one enantiomer over the other in the adsorption of D, L, and DL amino acids and their N-acetyl derivatives. Being achiral, zeolites cannot favor one enantiomer over the other. However, any tendency for the mixed dimer (DL) adsorption, by removing a 1:1 ratio of enantiomers, would lead to enantiomeric enrichment of the remaining solution. We are using solid-state 13C NMR to probe the microenvironment of the adsorbed solutes. D- and L-Cysteine exhibit 13C NMR peaks at 175, 54 and 35ppm for the carbonyl, a and b carbons respectively while the racemic DL mixture shows a second peak for each chemical group, implying strong interactions and conformational differences between the enantiomers. The spectra for the D- and L-alanine differ from the racemate DL, which shows changes when adsorbed, verifying that the microenvironment of the adsorbed molecules impacts the NMR signals. Spectra of pure enantiomers of N-acetyl-Alanine change significantly upon adsorption while their racemate's one carbonyl peak at 175 ppm is replaced with three when adsorbed, as is the a-Carbon peak at 51 ppm. The interactions occurring inside the zeolite will be further investigated by Thermal Gravimetric Analysis and X-Ray Crystallography. A new avenue to enantiomeric enrichment in zeolites is important for pharmaceutical industry and also as a possible explanation for the prebiotic development of enantiomeric purity.

Identification of enantiomeric interactions in zeolites by solid state NMR, X-ray, and TGA

243rd National Meeting (2012)

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