Boronic acid and guanidinium based synthetic receptors: new applications in differential sensing
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In the field of supramolecular chemistry a common goal is to design a receptor that is highly selective for a targeted analyte. While this is a worthwhile goal, many of these synthetic receptors are less selective than their natural counterparts such as enzymes or antibodies. Many aspects of the work shown herein demonstrate that these less selective synthetic receptors are still useful chemosensors. Just as Nature utilizes differential receptors in our sense of taste and smell, synthetic sensor arrays can be developed to achieve similar results. Chapter 1 is an overview of the development of a sensor. It begins with the aspects of binding carboxylates and diols, specifically by guanidiniums and boronic acids. Next, signaling motifs of a sensor are discussed, leading to the advantages of using an indicator displacement assay. Finally, differential sensors are discussed, introducing the idea of incorporating non-selective synthetic sensors for the detection of multiple analytes with the use of pattern recognition. Chapter 2 discusses the use of non-selective synthetic receptors in a number of sensing schemes. First a receptor was used to bind a class of age related analytes found in scotch whiskies. A correlation was found between the age of the scotch and the sensing ensemble’s response to the beverage. In another sensing application, a high degree of selectivity was achieved by using two receptors and two indicators together in solution. Due to the differential response of the receptors to the indicators and the guests, the simultaneous quantification of tartrate and malate was achieved with the aid of pattern recognition. Finally, initial efforts were put forth for incorporating the receptor into a differential sensing array by immobilizing the receptor on a solid support. The selectivity of the receptor was investigated, showing that the receptor still had a higher affinity for tartrate over malate. Chapter 3 investigated the thermodynamics of guanidiniums and boronic acids binding carboxylates and diols, respectively. Four hosts were investigated with a variety of guests. The association constants were determined through UV/vis analysis, while the entropy and enthalpy were determined with isothermal titration calorimetry. The binding of boronic acids to more than just aliphatic diols was also investigated. Chapter 4 discussed the development of new sensor for catechol containing analytes. The sensor’s design is based on iron binding siderophores. The iron is both the binding site and the signaling motif for the sensor. Upon addition of catechol guests, a signal modulation did occur.