ITC and NMR spectroscopy binding studies of meso- octamethyl-calixpyrrole and its derivatives
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This dissertation reports on the recent discovery that calixpyrrole not only functions as an anion receptor, but also has the ability to act as an ion pair receptor. It was discovered that in the solid state large diffuse cations, such as Cs+ and imidazolium, will occupy the electron-rich cone-like cavity that is formed upon anion binding to the NH region of the calixpyrrole core. Also discussed are efforts devoted to improving the anion binding ability of calixpyrroles and fine-tuning their inherent selectivity. This has been probed through a variety of structural modifications. One of the most attractive of the modification strategies currently being explored involves expansion of the central binding cavity by using higher order β-fluorinated calix[n]pyrroles; n = 5, 6, and 8. An advantage of β-fluorinated calixpyrrole is that it shows enhanced anion binding affinities toward several anions compared to the parent calixpyrrole. Fluorinated calixpyrroles have also shown an ability to extract anions from aqueous environments into organic media. An alternative strategy has been to attach “straps” resulting in bicyclic systems, which further define the binding cavity achieving higher affinity and anion selectivity. The binding interactions of calixpyrrole and it derivative have been quantified using analytical techniques, such as nuclear magnetic resonance spectroscopy and isothermal titration calorimetry. The results of these latter studies will be discussed herein.