Green Synthesis of Triazole-Based Chemosensors and their Efficacy Towards Mercury Sensing

Abstract

Background: The synthesis of small organic molecules based Hg2+ ions receptors have gained considerable attention because it is one of the most prevalent toxic metals which is continuously discharged into the environment by different natural and industrial activities. 1,4-Disubstituted 1,2,3-triazoles have been reported as good chemosensors for the detection of various metal ions including Hg2+ ions. Methods: The synthesis of 1,2,3-triazoles (4a-4c) was achieved by Cu(I)-catalyzed azide-alkyne cycloaddition, and their binding affinity towards various metal ions and anions were studied by UVVisible titration experiments. The perchlorate salts of metal ions and tetrabutylammonium salts of anions were utilized for the UV-Visible experiments. DFT studies were performed to understand the binding and mechanism on the sensing of 4a toward Hg2+ using the B3LYP/6-311G(d,p) method for 4a and B3LYP/LANL2DZ for 4a-Hg2+ species on the Gaussian 09W program. Results: The UV-visible experiments indicated that the compounds 4a-4c show a selective response towards Hg2+ ion in UV-Visible spectra, while other ions did not display such changes in the absorption spectra. The binding stoichiometry was evaluated by Job’s plot which indicated the 1:1 binding stoichiometry between receptors (4a-4c) and Hg2+ ion. The detection limit of 4a, 4b and 4c for the Hg2+ ions was found to be 29.1 nM, 3.5 μM and 1.34 μM, respectively. Conclusion: Some 1,2,3-triazole derivatives were synthesized (4a-4c) exhibiting high selectively and sensitivity towards Hg2+ ions in preference to other ions. Compound 4a has a low detection limit of 29.1 nM and the binding constant of 2.3×106 M-1. Similarly, 4b and 4c also showed selective sensing towards Hg2+ ions in the μM range. The observed experimental results were corroborated by density functional theory (DFT) calculations.