Fluorescence Regeneration as a Signaling Principle for Choline and Carnitine Binding: A Refined Supramolecular Sensor System Based on a Fluorescent Azoalkane


  • This work was supported by the International University Bremen and the Swiss National Science Foundation Program within the NRP 47 “Supramolecular Functional Materials”.


The fluorescent azoalkane, 2,3-diazabicyclo[2.2.2]oct-2-ene (DBO), forms inclusion complexes with p-sulfonatocalix[4]arene (CX4). The binding constants are on the order of 103 M–1 in water. The addition of CX4 to DBO solutions results in an efficient fluorescence quenching (up to 90 %). This supramolecular system can be used as a truly water-soluble sensor system to signal the binding of organic ammonium ions over a large pH range. Addition of choline and carnitine derivatives and tetraalkylammonium ions results in regeneration of this fluorescence, from which the binding constants (KC = 103–105 M–1) are calculated by means of a competitive complexation model. Electrostatic effects are observed, namely, a more-than-one order of magnitude weaker binding of the carnitines in neutral solution.