Browsing by Subject "UV-Vis spectroscopy"

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    Current Analysis of Color Separation of Chiral Enantiomers via Pyrogallol Red Indicator and UV-Vis Spectrophotometry and Future Applications for Chiral Identification
    (2023-04-24) Reyes, Sabrina
    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.
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    The development of optical methods for rapid asymmetric reaction screening : characterizing enantiomeric excess, diastereomeric excess and reaction yield
    (2019-09-13) Herrera, Brenden Tate; Anslyn, Eric V., 1960-; Korgel, Brian A; Que, Emily; Martin, Stephen F; Keatinge-Clay, Adrian
    In the past twenty years, optical methods for asymmetric reaction characterization have had much success. Optical protocols allow for the determination of enantiomeric excess (ee) and reaction yield of transformations that are amenable to high-throughput experimentation. Chapter 1 highlights the advances of optical methods for determining ee and reaction yield. Despite the extensive success of these methods, few reports of optical assays for both enantiomers and diastereomers have been demonstrated. Such methods could be applied to an asymmetric reaction that sets two stereocenters in the same transformation, where the ee, diastereomeric excess (de) and reaction yield would be needed for complete asymmetric reaction characterization. Chapter 2 discusses the derivation of a mathematical relationship for relating the enantiomeric ratios of two individual stereocenters within a single chiral molecule to the diastereomeric ratio. Further, mathematical relationships are given for determining complete stereoisomer speciation with the knowledge of individual stereocenter ee values and a de value. Chapter 3 describes the first example of the use of optical methods for determining the ee, de, and total concentration of 2-aminocyclohexanol, where the complete stereoisomeric speciation was accomplished with an average absolute error of 4%. The procedure presented would allow for the total speciation of approximately 100 reactions in 30 minutes using a high-throughput experimentation routine. Chapter 4 details the progress made towards screening a stereodivergent biocatalytic transformation catalyzed by ketoreductases using optical methods. Chapter 5 describes workflows that have been developed for characterizing the success of transformations that set a single stereocenter, specifically a metalloenzyme-catalyzed aziridination and a ketoreductase-mediated reduction.