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