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 Hg2+ or Zn2+, these sensors show signal enhancement in fluorescence. However, Cu2+ quenches their fluorescence in 30:70 acetontrile/water. L-CysBQA complexes with Hg2+, producing an exciton-coupled circular dichroism spectrum with the opposite sign to the one that is produced by Cu2+ or Zn2+ complexation. L-CysBQA binds Hg2+ more strongly than Zn2+ and is shown to differentiate Hg2+ from other metal ions, such as Zn2+, Cu2+, Ni2+, and Pb2+, 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 Hg2+. Chirality 23:916-920, 2011. (C) 2011 Wiley-Liss, Inc.