Theory and Applications of Aryl CH Hydrogen Bonds in Arylethynyl Receptors
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Design of selective non-covalent binding systems for chemical and biological recognition requires an intimate understanding of the factors that control the strength of each interaction. Weak interactions such as anion-Π, Π-Π, and CH-Π are understood to be important contributors to the overall binding of ligands, however, these interactions are almost purely electrostatic. Aryl CH hydrogen bond donors are a recent addition to the field and provide new possibilities by introducing a partial covalent character, which imparts greater directionality and acceptor preference. CH hydrogen bonds, and other similar weakly polarized donors, are an exciting development in supramolecular chemistry because of their ubiquity, stability and structural diversity. The use of experimental and computational techniques in this dissertation has provided us with a new understanding of the energetic factors that control CH hydrogen bond strength and selectivity for anion binding. 2,6-bis(2-anilinoethynyl) receptors with an aryl CH donor as the central arene act as anion receptors with one CH hydrogen bond and four supporting NH hydrogen bonds around a semi-preorganized pocket. The scaffold provides an efficient route to substitution para to the donor, which allows for tuning of optoelectronic properties and the measurement of linear free energy relationships (LFERs) on anion binding. Association constants with anions, Cl<sup>-</sup>, Br<sup>-</sup>, I<sup>-</sup>, NO3<sup>-</sup>, were measured by <sup>1</sup>H NMR and UV-vis spectroscopy in water saturated chloroform. The solution data was combined with calculated and empirical measurements to provide LFERs and identify an anion dependent substituent character. The importance of substituent resonance or inductive character has been further probed by measuring the isotope effect of selective monodeuteration. Solution measurement of a normal equilibrium isotope effect points to the role of covalency in this non-traditional hydrogen bond. The application of this new understanding to developing fluorescent probes for biological and environmental anions is demonstrated with a small receptor array. This dissertation includes both previously published and unpublished co-authored material.