Fluorescent sensors for the detection of analytes in solution

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Best, Michael Douglas

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This dissertation describes work aimed at the development of fluorescent sensors for various analytes in solution. In chapter 1, an introduction to molecular recognition and sensing is presented to provide background information pertaining to research discussed in the later chapters. Here, topics such as molecular interactions in solution, single-analyte sensing using preorganized scaffolds, installation of signaling groups for detection of binding, analytical techniques for complexation and sensing using multiple component sensing ensembles are reviewed. Chapter 2 describes a project to develop a molecular sensor with a Noxide-bipyridine complex as a binding site and for signaling the association. The project progressed through the synthesis towards three different sensor designs, until 2.60 was obtained containing a bis-bipyridine-tetra-N-oxide europium complex and two ammonium groups as binding sites. Binding studies were performed using a target guest, 2,3- bisphosphoglycerate (2.1), a glycolytic intermediate involved in oxygen transport regulation. A 1:1 host-guest complex was observed in 50% methanol / acetonitrile solution with a Ka of 6.70 x 105 M-1. Related glycolytic intermediates lacking a second phosphate (2.2, 2.3, 2.63), however, showed 2:1 guest to 2.60 binding. Phenylphosphate bound 1:1 with a Ka of 2.0 x 105 M-1. Finally, all compounds showed 2:1 guest to host binding with model host 2.61, which lacks the ammonium groups. The data shows that of similar glycolytic intermediates, only 2.1 undergoes 1:1 binding with 2.60 and indicates the importance of the second phosphate on the guest and the host ammoniums in forming this complex. In chapter 3, work towards the development of multiple differential sensors for small metal cations is presented. Approaches included random derivitization of resin beads with fluorophores and azacrown ethers and two attempts at synthesizing resin bound azacrown ethers and cryptands with covalently attached coumarins. Finally, in chapter 4, work concerning the construction of a Brønsted plot using compounds which could potentially form low-barrier hydrogen bonds is presented. Determination of the kinetics and acidity of a series of compounds with varying electronics at hydrogen bonding locations is discussed.