Amplification of a small enantiomeric excess by preferential co-adsorption. A study of adsorption of N-acetyl Amino acids onto Zeolite NaY by Solid State NMR, Thermogravimetric Analysis (TGA) and Differential Scanning Calorimetry (DSC)
Authors:Jessica Cardenas, Hyeran Choi, Lauren Que, Julia Stearns
- Deniz Cizmeciyan, Professor of Physical Sciences, Mount St. Mary's College
- Robert Senter, Professor of Physical Sciences, Mount St. Mary's College
Chemistry of life depends on chiral molecules. How this chirality originated is a fascinating question. The separation of one enantiomer from the other is very important in medicine today because the incorrect enantiomer is either useless or may cause detrimental side effects. Zeolite lattices do not prefer one enantiomer over the other, and adsorb the enantiomers equally well. However, if the D and L enantiomers adsorb together as a heterodimer, we can use that tendency to remove equal amounts of enantiomers, leave only the excess enantiomer in the solution. We used NMR, TGA, DSC 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 illustrated the same results as the racemic mixture of N-acetyl DL Leucine. Thus, N-acetyl DL Leucine forms a conglomerate crystal of pure microcrystals of pure D and L. The racemic mixture displays the same spectrum when adsorbed in Zeolite NaY indicating that they are adsorbed as homodimers. In contrast the 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 -Carbon peak at 51 ppm. Similarly, the 13C spectrum of D- and L-N-Acetyl methionine exhibit peaks at 170, 55 and 30ppm for the carbonyl, and carbons respectively, while the racemic mixture shows a second peak for the carbonyl group at 165 ppm implying that the latter crystallizes as a racemic compound giving reason to speculate an increased tendency for heterodimer adsorption onto the zeolite. Preliminary TGA data for all compounds exhibits 4-8% adsorption of the amino acids, whereas pure NaY shows 34 % water adsorption. Exothermic decomposition of the samples occurs as seen with DSC.