Design and synthesis of acyclic bis-triazole ligands: Complexation with metal ions, DFT calculations, and biological activity

Triazole-derived heterocyclic compounds have significant biological activities and pharmaceutical stability. A new series of acyclic bis-triazole ligands 16–20 with ester end groups were designed. The synthesized ligands were evaluated for their complexation ability with transition metals (Cu 2+, Hg 2+, Pb 2+, and Zn 2+ ). The molar conductivity of bis-1,2,3-triazole ligand-metal complexes was measured in acetonitrile at a temperature range 288.15–308.15 K. Furthermore, the thermodynamic quantities (∆H°, ∆S°, and ∆G°) were determined using the van't Hoff equation and the computational stability constants of the resulting 1:1 complexes were determined based on 1:1 stoichiometry. Meanwhile, the optimized geometry of ligands and ligand-metal complexes was computationally calculated using density fraction theory (DFT). Moreover, the antioxidant potential, in DPPH and ABTS assays, as well as the antibacterial activity of the bis-1,2,3-triazole ligands were evaluated. Ligands 16, 19, and 20 complexed with Hg 2+ as well as ligand 17 with Cu 2+, Hg 2+, and Pb 2+ showed a continuous decrease in molar conductivity on complexation, however, ligand 18 complexed with Cu 2+, Hg 2+, Pb 2+, and Zn 2+ begins to level off at a mole ratio of 1:1 (ligand:metal) indicating the formation of stable complexes. Noteworthy, ligand 17 formed a 1:2 and 2:1 ligand-to-metal ratio with Hg 2+ and Pb +2 cations, respectively. The formation reactions of all ligand-metal complexes were exothermic and spontaneous indicating a strong triazole-metal interaction based on ∆H° and ∆G° values. Bis-triazole ligands 16–20 revealed antioxidant activity with IC 50 values ranging from 89.0 to 156.1 µg/ml in DPPH and 91.3–167.2 µg/ml in ABTS assays. Ligands 16–19 exhibited antibacterial activity against the Gram-positive Bacillus cereus with MICs ranging from 150 to 250 µg/ml. The synthesized bis-triazole ligands have a potential application in the pharmaceutical and food industries. Moreover, the selectivity of ligands 16, 19, and 20 to Hg 2+ could be useful for removing such a metal from industrial wastewater containing a variety of toxic heavy metals and ISE construct.