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    Towards Responsive Squaramides: Anion Recognition, Sensing, and Transport

    Marchetti, Luke A. (2022) Towards Responsive Squaramides: Anion Recognition, Sensing, and Transport. PhD thesis, National University of Ireland Maynooth.

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    Anions play a crucial role in both biological and environmental contexts to such an extent where the absence or the overabundance of anions can lead to severe health implications and environmental concerns. The recognition of the universal significance of anions has led to an explosion of research in the field of supramolecular chemistry, resulting in a solid foundation of the principles of synthetic anion receptors and transporters. Indeed, synthetic anion transporters show particular promise in medicinal chemistry where they are being developed as new approaches for anti-cancer agents, anti-microbials and as novel Cystic Fibrosis treatments. This thesis focuses on the use of squaramides as an anion binding motif, where novel recognition motifs, stimuli responsive transport, and selective anion sensing is explored. The thesis commences with a literature review and introductory chapter that outlines the aims and objectives of the research. Chapter 2 details the design and synthesis of squaramides featuring an N-acyl linkage, termed ‘amido- squaramides’. These novel compounds were investigated as potential anion binding units via a combination of experimental and computational techniques where it was shown that the amido-squaramides exist in the anti/syn conformation due to the presence of an intramolecular H-bond. The receptors’ anion binding abilities were assessed and were shown to selectively bind to Cl- via H-bond formation in a 1:1 binding mode. Finally, the receptors were found not to display anionophoric activity at pH 7.20, but at pH 4.20, anion transport was observed to ‘switch on’. This established amido-squaramides as pH-switchable anion transport units. The 3rd Chapter details attempts to synthesise tertiary squaramides, featuring enzyme- and fluoride- responsive triggers. This chapter reports four novel secondary amines, featuring a nitrobenzyl moiety, and triisopropylsilyl ether moiety and also outlines several synthesis optimisation studies to obtain the tertiary squaramides. Synthetic problems were encountered during the experimental work that prevented successful synthesis of the target molecules, however, it is envisaged that future work may focus on the use of metal-based catalysis to generate the desired stimuli-responsive anion transporters. The 4th Chapter outlines the development and application of a squaramide based chemosensor. A small family of squaramidoquinoxalines were synthesised via a one-step synthesis. X-ray crystallographic analysis demonstrated the tendency of the squaramidoquinoxalines to participate in a number of intermolecular interactions and displayed selective sensing of F- over other halide anions, resulting in visible to the naked-eye colour change from pink-red to green to yellow. Experimental and theoretical results suggest that the colourimetric change is brought about by two distinct deprotonation events. The squaramidoquinoxalines were also incorporated into test strips that allowed for the rapid and naked-eye detection of F- in aqueous media.

    Item Type: Thesis (PhD)
    Keywords: Responsive Squaramides; Anion Recognition; Sensing; Transport;
    Academic Unit: Faculty of Science and Engineering > Chemistry
    Item ID: 16495
    Depositing User: IR eTheses
    Date Deposited: 08 Sep 2022 14:52
      Use Licence: This item is available under a Creative Commons Attribution Non Commercial Share Alike Licence (CC BY-NC-SA). Details of this licence are available here

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