Multi-signaling thiocarbohydrazide based colorimetric sensors for the selective recognition of heavy metal ions in an aqueous medium.

A series of colorimetric chemosensors R1-R6 have been developed from thiocarbohydrazide derivatives, for the selective detection of heavy metal ions. The structures of the receptors R1-R6 were well characterized by standard spectroscopic techniques like FT-IR, 1H NMR, and ESI-MS. The solid structure of receptor R1 and R2 were derived by single crystal X-ray diffraction (SC-XRD). The cation reorganization abilities of receptors R1-R6 were studied by UV-Vis spectroscopy. The receptors R1, R3 and R4 acts as a tremendous sensitive probe for heavy metal ions (Hg2+, Cd2+ and Pb2+) with the μM detection (R1 for Hg2+, 2.72, R3 for Cd2+, 3.22, R4 for Hg2+, Cd2+ & Pb2+, 0.70, 0.20 & 0.30μM) and the receptors R2, R5 &R6 are sensitive towards Cu2+ ions with the μM detection (3.34, 0.90 & 1.20μM) in an aqueous medium among all other tested cations. The receptor R4 shows a multi-color response towards Hg2+, Cu2+, Cd2+ and Pb2+ ions. The recognition mechanism, stoichiometric binding ratio and detection limit (DL) have been examined by UV-Visible spectroscopic titration experiments and Benesi-Hildebrand (B-H) plot, receptor R1-R6 sowed 1:1 binding ratio with good binding constant range of 103 to 105M-1 with Hg2+, Cu2+, Cd2+ and Pb2+ ions metal ions.