Luminescent Hybrids Combining a Metal Complex and a Crown Ether - Receptors for Peptidic Ammonium Phosphates

Hybrid compounds combining a luminescent aza crown ether and 1,4,7,10-tetraazacyclododecane (cyclene) or bis(pyridin-2-ylmethylamine) (bpa) metal complexes were prepared. These synthetic receptors signal the presence of peptidic ammonium phosphates in buffered aqueous solution by changes in their emission intensity. Reversible phosphate ion coordination to the metal complex binding sites decreases the emission intensity of the phthalic ester fluorophore. Structurally suitable ammonium phosphates, such as the C-terminal domain of RNA polymerase II or the protein kinase G target sequence, bind to the synthetic receptors by an additional intramolecular interaction between the ammonium ion and the aza crown ether. The binding of the ammonium ion to the aza crown ether increases the emission intensity of the fluorophore. In aqueous solution, this weak interaction can only occur within aggregates of phosphates and metal complex receptors of matching geometry;therefore, it allows the distinction of structurally related phosphorylated peptides in buffered aqueous solution.