Current Analysis of Color Separation of Chiral Enantiomers via Pyrogallol Red Indicator and UV-Vis Spectrophotometry and Future Applications for Chiral Identification

Chiral substances are extremely important in many pharmaceutical drugs and in a variety of fields; therefore, the reliable identification of chiral enantiomers is equally as important. Unfortunately, the identification of enantiomers from a racemic mixture is challenging as there are many problems with current methods. To help address these issues, the main project objective was to develop efficient methods for identifying the chirality of enantiomers in solution of Pyrogallol Red (PR) indicator, 2-FormylPhenylBoronic Acid (FPBA), and (S)-(-)-1-Phenylethylamine (amine) by using UV-vis spectroscopy analysis. The structure of FPBA allows for rapid formation of both imines and boronate esters with reaction intermediates of amines and vicinal diols respectively. However, FPBA is an achiral sensor and therefore is not sensitive to chiral objects. Bindings between FPBA and PR lead to changes in color and absorbance, and based on the standard that the amine intermediate would transform into an imine, the chirality of the beginning amine can impact the equilibria between the boronic acid, competing indicator, and vicinal diols of the saturated solution. By introducing color and chirality to the system, equilibria between the species in the saturated solution can be exploited to determine enantiomeric excess of a sample via the monitoring of absorbance changes across solution composition/enantiomeric excess. Overall, the data gathered from this project indicates that the saturation point between FPBA and PR has not yet been reached and therefore it is not yet possible to exploit substance equilibria for color discrimination of enantiomers. However, initial data is promising as absorbance and equivalence data did differ across each trial, indicating that the expected reactions are occurring and giving promise that these reactions can continue to be exploited for chiral color analysis.