A Path to Bootstrap from a Small Enantiomeric Excess to Enantiomeric Purity. A study of Adsorption of D, L, and DL N-acetyl Leucine in Zeolite NaY
Authors:Hyeran Choi, Erika Martinez, Julia Stearns, Jasmine Wills
- Deniz Cizmeciyan, Professor of Physical Sci. & Mathematics, Mount St. Mary's College
- Robert Senter, Instructor of Physical Sci. & Mathematics, Mount St. Mary's College
Biochemistry crucially depends on asymmetric (chiral) molecules that can exist as two versions that are mirror images of each other (enantiomers). The answer to the important question of how enantiomeric purity was achieved in a prebiotic world is still unknown. Enantiomeric purity is also very important in the pharmaceutical industry, since the wrong enantiomer is often useless or harmful. Achiral zeolites do not adsorb preferentially one enantiomer over the other. However, adsorbing enantiomers at a 1:1 ratio will increase the enantiomeric excess of a solution that already had an enantiomeric imbalance. This is only achieved when the D- and L-enantiomers are adsorbed as a heterodimer. The adsorption behavior of D, L, and DL N-acetyl Leucine into Zeolite NaY was investigated using solid state NMR, thermogravimetric analysis (TGA), Differential Scanning Calorimetry (DSC) and X-ray diffraction. The solid state NMR spectra of pure D-, L-, as well as the racemic mixture N-acetyl-DL-Leucine generated identical NMR spectra in the absence of Zeolite NaY. This indicates that N-acetyl-DL-Leucine crystallizes as a racemic conglomerate where the powder consists of microcrystals of pure D or L enantiomers, rather than a racemic compound where the unit cell of the crystals contain a 1:1 ratio of D- and L-enantiomers. According to our latest results the racemic mixture displays the same spectrum when adsorbed in Zeolite NaY indicating that they are adsorbed as homodimers. Preliminary Thermogravimetric Analysis (TGA) data indicated that approximately 8 percent of the enantiomers are adsorbed. DSC shows exothermic decomposition of the sample at 290 ºC. X-Ray diffraction techniques will be analyzed to further elucidate the microenvironments of free and adsorbed amino acids.