Year of Award

2018

Document Type

Dissertation

Degree Type

Doctor of Philosophy (PhD)

Degree Name

Chemistry (Organic Option)

Other Degree Name/Area of Focus

Organic and Supramolecular Chemistry

Department or School/College

Department of Chemistry and Biochemistry

Committee Chair

Christopher P. Palmer

Commitee Members

Orion B. Berryman, Nigel D. Priestley, Earle R. Adams, Mark L. Grimes

Keywords

Anion helicates, Anions, Halogen bonding, Kinetics, Self-assembly, Supramolecular chemistry

Publisher

University of Montana

Abstract

The form and function of biopolymers depend on the precise folding and organization of vast arrays of chemical groups. Hence, the simple yet elegant helix is one of the most pervasive structural elements in nature. Moreover, given the ubiquity and importance of anions, anion-interfacing helical structures hold promise as useful, stimuli-responsive supramolecules. Like metals, anions can powerfully coordinate organic ligands and promote helical self-assembly. However, anion coordination is far less understood than that of metals. Halide ions are an especially challenging target due to their small size, low charge, and variable coordination number/geometry. This work presents a new strategy that leverages the linearity of halogen bonding to form high-fidelity, iodide- and bromide-encapsulating triple helicates in solution and the solid state. These triplexes proved kinetically stable, and their ligands exchanged slowly on the seconds timescale. In contrast, intrachannel anion exchange was rapid, on the millisecond-or-faster timescale. Taken together, these findings offer a tractable strategy to create anion-responsive and kinetically stable helical secondary structure.

Chapter 1 provides an introduction to anion helicates/foldamers and situates these supramolecules within their larger framework. This chapter will be augmented and submitted as a review article. Chapter 2 introduces preliminary work with a halogen-bonding m-arylene-ethynylene three-mer. Before synthesizing and studying the eventual nonameric target, the three-mer was screened for halide-ion and perrhenate affinity. Interestingly, this trimeric precursor formed stable complexes with perrhenate in solution and the solid state. This chapter includes work that was published in Chemical Communications (2015, 51, 1417–1420). Chapter 3 presents the design and synthesis of the helicate-forming, nonameric target. The first iodide-encapsulating triple helicate was fully characterized using 1H 1D and 2D NMR spectroscopy and single-crystal X-ray diffraction. This chapter includes work that was published in Angewandte Chemie International Edition (2016, 55, 12398–12402). Chapter 4 presents the first kinetic studies of an anion helicate. Additionally, the first bromide-encapsulating triple helicate was characterized in solution and the solid-state. This chapter includes work that was published in Angewandte Chemie International Edition (2018, published online). Chapter 5 touches on preliminary work and future directions for the project.

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© Copyright 2018 Casey John Massena