Benzimidazole-acid hydrazide Schiff–Mannich combo ligands enable the nano-molar detection of Zn2+ in semi-aqueous media, HuH-7 cells, and plants via a fluorescence turn-on mode

Abstract

In this study, we synthesized two unsymmetrical and dipodal Schiff–Mannich combo ligands, namely benzoic acid (3-benzoimidazol-1-ylmethyl-2-hydroxy-5-methyl-benzylidene)-hydrazide (H₂BBH) and the hydroxyl analogue 2-hydroxy-benzoic acid (3-benzoimidazol-1-ylmethyl-2-hydroxy-5-methyl-benzylidene)-hydrazide (H₃BSH), for the selective detection of Zn²⁺ in semi-aqueous media. Both the probes selectively depict a turn-on response to Zn²⁺ as a result of the combined effect of chelation-induced enhanced fluorescence (CHEF) and photo-induced electron transfer (PET). Detailed experimental studies reveal that H₂BBH and H₃BSH can detect Zn²⁺ in solutions with limit of detections of 27 nM and 46 nM, respectively. The structures of probe-Zn²⁺ ensembles were proposed as [(HBBH)₂Zn] and [(H₂BSH)₂Zn] by ESI-MS, FT-IR spectroscopy, ¹H NMR titration and DFT/TD-DFT methods. Moreover, both the probes were successfully employed in the detection of Zn²⁺ in HuH-7 cells, seedlings of chickpea and mung beans, and paper strips.