Selective Coordination of Cu and Subsequent Anion Detection Based on a Naphthalimide-Triazine-(DPA) Chemosensor.

A new fluorescent chemosensor for copper (II) and subsequent anion sensing was designed and fully characterized. The sensor consisted of a 1,8-naphthalimide core, bearing two terminal dipicolylamine (DPA) receptor units for binding metal cations, and an ethoxyethanol moiety for enhanced water solubility. The DPA units are connected to position 4 of the fluorophore via a triazine-ethylenediamine spacer. Fluorescence titration studies of the chemosensor revealed a high selectivity for Cu over other divalent ions, the emissions were strongly quenched upon binding, and a stability constant of 5.52 log units was obtained. Given the distance from DPA chelating units and the fluorophore, quenching from the Cu complexation suggests an electron transfer or an electronic energy transfer mechanism. Furthermore, the Cu-sensor complex proved to be capable of sensing anionic phosphate derivatives through the displacement of the Cu cation, which translated into a full recovery of the luminescence from the naphthalimide. Super-resolution fluorescence microscopy studies performed in HeLa cells showed there was a high intracellular uptake of the chemosensor. Incubation in Cu spiked media revealed a strong fluorescent signal from mitochondria and cell membranes, which is consistent with a high concentration of ATP at these intracellular sites.