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

Abstract

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 Cterminal
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.