Pyridine-2,6-dicarboxamide-based fluorescent sensor for detection of Fe3+ and Hg2+

Novel and efficient fluorescent probes having N2, N6-bis(5-Mercapto-1,3,4-thiadiazol-2-yl)pyridine-2,6-dicarboxamide (TPDC) are synthesized by the condensation reaction between pyridine-2,6-dicarboxylic acid and amino derivatives of thiadiazoles. The novel fluorescent probe TPDC exhibits a highly sensitive and selective response to Fe3+ and Hg2+ ions in HEPES buffer solution showing the detection limit to be 0.49 micromole and 0.0066 micromole, respectively. The binding stoichiometry of TPDC with Fe3+ and Hg2+ have been estimated by Jobs plot and found to be 1:1. These have been confirmed by MS spectra.  The stability constant of the fluorescent probe with Fe3+ and Hg2+ has been determined by the Benesi–Hildebrand equation.  The binding constant for Fe3+ and Hg2+ ions are 2.54 × 101 M−1 and 0.18 × 102 M−1, respectively. The crystallinity of compounds have also been calculated by XRD spectra and found to be 66.37%.