Development of cross-reactive receptors based on serum albumin
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In recent years, differential sensing has become an increasingly popular approach to molecular recognition. Mimicking the mammalian senses of taste and smell, arrays of semi-selective sensors generate a fingerprint for each analyte. Pattern recognition algorithms allow these arrays to be used for discriminating analytes and for predicting the identity of unknowns. Arrays of cross-reactive receptors have found use in a variety of sensing applications, including the differentiation of biologically-relevant analytes (Chapter 1). Serum albumin has previously been used in an array format for the discrimination of hydrophobic analytes such as terpenes, plasticizers, and fatty acids. This protein is a versatile cross-reactive receptor because of its ability to bind hydrophobic analytes with different affinities and in different modes. In Chapter 2, the use of serum albumin to pattern hydrophobic analytes was further expanded to include glycerides. Glycerides are challenging analytes because they are structurally similar to one another. Due to difficulties in identifying the regio- and stereochemistry of the unsaturated glycerides, a sample pretreatment consisting of olefin cross metathesis was used prior to array analysis. Using the array, twenty glycerides were discriminated, including stereo- and regioisomeric pairs. Further, glycerides in mixtures were quantitated. Due to the success with using serum albumins as receptors for hydrophobic analytes, it was hypothesized that serum albumin could be used in a different way to develop receptors for other types of analytes. The serum albumin functions as a scaffold onto which species dynamically assemble through hydrophobic interactions. In Chapter 3, the use of fatty acid-appended recognition units was explored as a way of building such receptors. While these conjugates did not bind to the protein as well as expected, an alternative strategy was explored in Chapter 4 with squaraines and thiols. As a starting point toward this goal, a series of squaraines were synthesized, and their reactivity to thiols and affinity for serum albumin were investigated. Finally, in Chapter 5, the reversible covalent attachment of recognition units to serum albumin with thia-Michael chemistry was explored. A bifunctional conjugate acceptor was used to reversibly label proteins with thiols as well as to generate resin-bound dynamic combinatorial libraries.