Sensing of Antipyretic Carboxylates by Simple Chromogenic Calix[4]pyrroles

We present a simple, two- or three-step method for the synthesis of chromogenic octamethylcalix[4]pyrrole-based (OMCP) sensors for anions. Electrophilic aromatic substitution allows for converting the pyrrole moieties of OMCP into a dye. The formation of a sensor−anion complex results in partial charge transfer and a dramatic change in color. The absorption (UV−vis) and NMR titration experiments show that the chromogenic OMCPs sense anions administered as aqueous solutions, even at high ionic strength (∼0.1 M NaCl), while displaying selectivity for pyrophosphate and carboxylate anions. The experiments with polyurethane sensor films show a strong response for aqueous carboxylates, such as antipyretics naproxen ≈ ibuprofen > salicylate, without being biased by bicarbonate or carboxy termini of blood plasma proteins.