Very Strong Binding for a Neutral Calixpyrrole Receptor Displaying Positive Allosteric Binding
Publikation: Bidrag til tidsskrift › Tidsskriftartikel › Forskning › peer review
The dual-analyte responsive behavior of tetraTTF-calixpyrrole receptor 1 has shown to complex electron-deficient planar guests in a 2:1 fashion in the so-called 1,3-alternate conformation. However, stronger 1:1 complexes have been demonstrated with tetraalkylammonium halide salts that defer receptor 1 to its so-called cone conformation. Herein, we report the complexation of an electron-deficient planar guest, namely 1,4,5,8-naphthalene-tetracarboxylic dianhydride (NTCDA, 2), that champions the complexation with 1 resulting in a very high association constant Ka = 3 × 1010 M−2. The tetrathiafulvalene (TTF) subunits in the tetraTTF-calixpyrrole receptor 1 present a nearly perfect shape and electronic complementarity to the NTCDA guest, which was confirmed by X-ray crystal structure analysis, DFT calculations, and electron density surface mapping. The complexation results in formation of a charge transfer complex (22⊆1), that is visualized as a color change from yellow to brown.