posted on 2005-03-16, 00:00authored byMichael Kruppa, Christian Mandl, Stefan Miltschitzky, Burkhard König
Crown ethers of suitable size are the perfect artificial host compounds for ammonium ion binding,
but the rather low affinity in aqueous solution prevents their use at physiological conditions. We report
here the synthesis and properties of a luminescent benzo crown ether with a pendant copper imidodiacetic
acid complex, which coordinates with high affinity to histidine. The emission intensity of the benzo crown
ether increases significantly in the presence of ammonium ions in methanol. At physiological conditions in
buffered water at pH 7.5 these interactions are too weak to be detected. If an ammonium ion and an
imidazole moiety are present in the analyte, such as in His-Lys-OMe or His-OMe, high binding affinity in
aqueous solution is restored. The binding event is signaled by an increase in emission intensity, which can
even be observed with the naked eye. This allows the selective detection of small peptides containing
N-terminal histidine or histidine among all other amino acids at physiological conditions.