American Chemical Society
ja034921w_si_005.cif (18.98 kB)

Slow Anion Exchange, Conformational Equilibria, and Fluorescent Sensing in Venus Flytrap Aminopyridinium-Based Anion Hosts

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posted on 2003-07-17, 00:00 authored by Karl J. Wallace, Warwick J. Belcher, David R. Turner, Kauser F. Syed, Jonathan W. Steed
The synthesis, anion binding, and conformational properties of a series of 3-aminopyridinium-based, tripodal, tricationic hosts for anions are described. Slow anion and conformational exchange on the 1H NMR time scale at low temperature, coupled with NMR titration, results in a high level of understanding of the anion-binding properties of the compounds, particularly with respect to significant conformational change resulting from induced fit complexation. Peak selectivity for halides, particularly Cl-, is observed. The approach has been extended to dipodal and tripodal podands based on 3-aminopyridinium “arms” containing photoactive anthracenyl moieties. The 1,3,5-tripodal host shows a remarkable selectivity for acetate over other anions, in contrast to the analogous unsubstituted tris(3-aminopyridinium) analogue, despite the fact that low-temperature 1H NMR experiments reveal a total of four acetate-binding conformations. Photodimerization of anthracene units results in the formation of potential fluorescent anion sensors.