Fluorescence enhancement detection of underivatized amino acids using a trifluoroacetophenone-based tripodal fluoroionophore

A tripodal fluoroionophore based on a hexasubstituted benzene unit having two trifluoroacetophenone groups and a pyrenyl moiety was synthesized, and its characteristics as fluorogenic reagent or component of an ISE or optode membrane towards several underivatized amino acids were examined. In a solid-liquid extraction experiment in acetonitrile, the fluorescence enhancement response was observed in the order of Phe, Cys, and Gly. On the other hand, the PVC-based polymeric membrane applied in ISE showed Phe selectivity with a monoanionic Nernstian response, supporting the assumption that the ionophore binds Phe in its anionic form. It is demonstrated that the optode membrane based on this fluoroionophore shows fluorescence enhancement response towards Phe or Cys in a flow-system.