Molecular Pockets Derived from Cholic Acid as Chemosensors for Metal Ions

Molecular pockets in the form of a tripod made of cholic acid were found to be able to solubilize pyrene in polar media as a result of the facial amphiphilicity of bile acids. The trimer containing 1,2,3-triazole groups Call complex with heavy metal ions, as clearly shown by electron paramagnetic resonance spectroscopy. Both the metal cation and the pyrene molecule can be brought close together in the cavity formed by the cholic acid trimer, resulting ill significantly improved efficiency for fluorescence quenching of pyrene. The decrease of fluorescence intensity can be used for the detection of heavy metal ions, and the detection limit is about 1 mu M in water, suggesting the usefulness of such molecules as chemosensors for such metal ions. A different trimer without the coordinating triazole groups is shown to shield pyrene away from metal ions, causing a much reduced fluorescence quenching.