A dansyl-appended N-heterocycle for Cu2+ and S2- recognition via a displacement mode.

A novel l-proline based heterocycle 3 of C2 symmetry has been designed and synthesized for cation and anion recognition in aqueous solution. Ligand 3 shows a strong affinity to Cu2+ ion, and their interaction induces a remarkable fluorescence quenching in DMSO:H2O=9:1 (HEPES buffer, 0.01M, pH7.4) among various metal ions. Both the in-situ generated and isolated 3-Cu2+ complex exhibit specific fluorescence recovery upon addition of S2-, even in the presence of S2O32-, L-histidine, and thiol-containing amino acids. For this dual functional switch, a combination of 1H NMR titration, ESI mass and FT-IR spectra suggest that its sensing behavior is via a displacement mode. Sequential "on-off-on" fluorescence bio-imaging of the heterocycle 3 to Cu2+ and S2- was carried out in HeLa cells.