Multimode selective detection of mercury by chiroptical fluorescent sensors based on methionine/cysteine

Two multimode Hg(II) sensors, L‐MethBQA and L‐CysBQA, were obtained by fusing methionine or S ‐methyl cysteine, into a bis‐quinolyl amine‐based chiral podand scaffold. Quinolyl groups serve as the fluorophore and possess nitrogen lone pairs capable of chelating metal ions. On exposure to Hg 2+ or Zn 2+ , these sensors show signal enhancement in fluorescence. However, Cu 2+ quenches their fluorescence in 30:70 acetontrile/water. L‐CysBQA complexes with Hg 2+ , producing an exciton‐coupled circular dichroism spectrum with the opposite sign to the one that is produced by Cu 2+ or Zn 2+ complexation. L‐CysBQA binds Hg 2+ more strongly than Zn 2+ and is shown to differentiate Hg 2+ from other metal ions, such as Zn 2+ , Cu 2+ , Ni 2+ , and Pb 2+ , exceptionally well. The synergistic use of relatively soft sulfur, quinoline‐based chiral ligands and chiroptically enhanced fluorescence detection results in high sensitivity and selectivity for Hg 2+ . Chirality, 2011. © 2011 Wiley‐Liss, Inc.