In recent years the availability of circular dichroism (CD) as a method for determining the enantiomeric excess (ee) of chiral solutions has been extremely useful in both quantitatively and qualitatively identifying enantiomers. This process is done by finding the difference between the absorption of left and right circularly polarized light, and is most importantly sensitive to the absolution configuration and conformational features that are often obscured in the ordinary absorption spectrum. A problem often encountered with chiral analytes is they produce small CD signals in solution due to the small amount of light they can affect, but this can be overcome by first incorporating the chiral analyte of interest into a metal complex with large CD signals more in the visible region. An organometallic complex with large steric ligands can produce a chiral molecule and large optical activity. Since the ligands have a favorable locking position due to their steric hindrance, the chirality of the desired chiral analyte will determine the chirality and optical activity of the bound organometallic complex where the ligands are forced to lock in the most stable conformer. Herein, the synthesis of two chiral standards was performed with the explicit purpose of binding them to a CD-active metal complex in order to generate calibration curves that correlate eeand magnitude in CD signal. Next, biocatalytic transformations were screened with the eebeing determined via CD spectroscopy. First, a chiral alcohol was created through a biocatalytic process where 3-(2-Hydroxyphenyl)-1-phenyl-1-propanone was treated with isopropanol and NADH cofactor in a solution of water and acetonitrile. This successfully created a defined enantiomer of 2-Hydroxy-α-phenylbenzenepropanol where the leftover starting materials were filtered out before attaching the chiral alcohol molecule to the metal complex to perform CD measurements. A chiral aziridination was also screened with the aziridine created through a biocatalytic process by reacting styrene with tosyl-azide before removing the excess. This product was then treated with sodium metal and naphthalene to form the desired chiral 2-phenylaziridine before being filtered and bound to the metal complex for CD analysis.

Determination of chiral analytes through bound metal complexes by circular dichroism

2019 Spring National Meeting

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