The synthesis, structure, and anion binding properties of chromogenic octamethylcalix pyrroles (OMCPs) and their N-confused octamethylcalix 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.
Nishiyabu, Ryuhei; Palacios, Manuel A.; Dehaen, Wim; and Anzenbacher, Pavel Jr., "Synthesis, Structure, Anion Binding, And Sensing By Calix Pyrrole Isomers" (2006). Chemistry Faculty Publications. 74.
Journal Of The American Chemical Society