Synthesis, structure, anion binding, and sensing by calix 4 pyrrole isomers

  • Nishiyabu R
  • Palacios M
  • Dehaen W
 et al. 
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The synthesis, structure, and anion binding properties of chromogenic octamethylcalix[4] pyrroles (OMCPs) and their N-confused octamethylcalix[4] pyrrole isomers (NC-OMCPs) containing an inverted pyrrole ring connected via alpha'- and beta-positions are described. X-ray diffraction analyses proved the structures of two synthesized isomeric pairs of OMCPs and NC-OMCPs. The addition of anions to solutions of chromogenic OMCPs and NC-OMCPs resulted in different colors suggesting different anion-binding behaviors. The chromogenic NC-OMCPs showed significantly stronger anion-induced color changes compared to the corresponding chromogenic OMCP, and the absorption spectroscopy titrations indicated that chromogenic OMCPs and NC-OMCPs also possess different anion binding selectivity. Detailed NMR studies revealed that this rather unusual feature stems from a different anion-binding mode in OMCPs and NC-OMCPs, one where the beta-pyrrole C-H of the inverted pyrrole moiety participates in the hydrogen-bonded anion-NC-OMCP complex. Preliminary colorimetric microassays using synthesized chromogenic calixpyrroles embedded in partially hydrophilic polyurethane matrices allow for observation of analyte-specific changes in color when the anions are administered in the form of their aqueous solutions and in the presence of weakly competing anions.

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  • R Nishiyabu

  • M A Palacios

  • W Dehaen

  • P Anzenbacher

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