Abstract:
Anions are abundant throughout our environmental and biological systems. These negatively charged and weakly coordinating species play crucial roles as ingredients in soil fertilizers and regulators of cellular processes. Supramolecular interactions, like anion-π, weak-σ, and hydrogen bonding, offer a convenient method to identify and quantify a variety of anions. However, we struggle to design selective molecular receptors due to the inherently complex thermodynamic and kinetic processes involved in host-guest interactions.
2,6-bis(anilinoethynyl) receptors and the mono(anilinoethynyl) derivatives offer an easily modified scaffold for studying the influence of supporting secondary interactions on anion selectivity. Two mono-urea receptors with the ability to bind anions via anion-pi, aryl CH-hydrogen bonds, or weak-sigma interactions were synthesized. Association constants with halide anions Cl-, Br-, and I-, were measured by 1H NMR spectroscopy and UV-Vis spectroscopy titrations. The receptors aggregated to form a 2-to-1 host-guest complex, with a different mechanism of complexation based on the supporting interaction of the aromatic core. Three additional bis-urea receptors with different secondary-binding motifs were synthesized and found to bind three disparate oxoanions at similarly high-affinities in non-polar solvents. In polar solvents, however, the receptors bound each oxoanion in a predictable manner based on the acidity of the conjugate acid of the guest. This understanding is applied through an array of differentially substituted receptors for anions of environmental and biological interests.
This dissertation contains previously published and unpublished co-authored material.
