Anion Sensing in Polar Media by Fluorecent Small Molecule Receptors via Halogen Bonding
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Date
2022-10-26
Authors
Bates, Hannah
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Publisher
University of Oregon
Abstract
Anions are a ubiquitous class of molecule which play critical roles in many of the environments with which humans concern themselves. From our physiology to nuclear waste to our water supply, anions have been the focus of much of the host- guest chemistry to have emerged within the last five decades. Host-guest chemists have used supramolecular tools, including halogen and hydrogen bonding, along with many others, to reversibly binding these and many other analytes. The purposes of binding are as wide ranging as real-time molecular recognition, catalysis, mechanically interlocked molecules, purification, and many others. Due to the many factors that can contribute to the efficacy of host-guest systems, including solvent effects, pocket size, molecular geometry, pH and others, most systems must be fined tuned for their particular application. One frequently encountered challenge is the competitive nature of any polar solvents, especially water, in solution state binding. Halogen bonding has recently come onto the scene as a potential answer to this problem, often demonstrating higher binding affinities than comparable hydrogen bonding molecules in polar environments. Despite its promise, much remains to be learned about how to best deploy halogen bonding motifs. This lacuna motivates the work covered in this thesis, which explores the design principles behind incorporating halogen bond donors effectively in a variety of arylethynyl; systems which were inspired by similar hydrogen bonding scaffolds published by the Johnson and Haley groups. After examining the successes and pitfalls of these halogen bond receptors in Chapter 3, Chapters 4 and 5 go on to report on the use of halogen bond and hydrogen bond systems in tandem, which are shown to bind the chloride anion notably well in appreciably polar organic solvents. These studies, suggest that the accepted definition of a halogen bond, as presented by IUPAC and discussed in Chapter 1, biases chemists to place undue importance on ensuring that the location of a polarizing group is as close as possible to the halogen-bond donor. Finally, future studies that can help flush out the ideas established in this thesis are reviewed in Chapter 6.
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Keywords
Anion Sensing, Halogen Bonding, Host Guest Chemistry, Hydrogen Bonding, Physical Organic Chemistry, Supramolecular Forces