Fluorescence Response and Self-Assembly of a Tweezer-Type Synthetic Receptor Triggered by Complexation with Heme and Its Catabolites.

There is increasing interest in the development and applications of synthetic receptors that recognize target biomolecules in aqueous media. We have developed a new tweezer-type synthetic receptor that gives a significant fluorescence response upon complexation with heme in aqueous solution at pH 7.4. The synthetic receptor consists of a tweezer-type heme recognition site and sulfo-Cy5 as a hydrophilic fluorophore. The receptor-heme complex exhibits a supramolecular amphiphilic character that facilitates the formation of self-assembled aggregates, and both the tweezer moiety and the sulfo-Cy5 moiety are important for this property. The synthetic receptor also exhibits significant fluorescence responses to biliverdin and bilirubin, but shows very weak fluorescence responses to flavin mononucleotide, folic acid, and nicotinamide adenine dinucleotide, which contain smaller pi-scaffolds.