Selective chromogenic detection of cyanide in aqueous solution – Spectral, electrochemical and theoretical studies

Add time:08/02/2019    Source:sciencedirect.com

A bisimidazole ensemble (R) possessing naphthoquinone as signaling unit is synthesized and characterized using 1H and 13C NMR and LC-MS spectral techniques. Anion sensing behaviour of the receptor has been investigated using electronic and fluorescence spectral techniques. The receptor exhibits a striking colour change from yellow to brown selectively with cyanide in aqueous HEPES buffer-DMSO (1:1 v/v) medium with a detection limit of 1 μM. Job's continuous variation method suggests that the stoichiometry of the interaction is 1:2 (R:CN−). The binding constant for receptor-cyanide complex was found to be 8.7 × 102 M−1. The mechanism of detection of cyanide occurs via deprotonation of imidazole N-H protons, which is well supported by electrochemical study. DFT based theoretical calculations shows that the energy gap between HOMO and LUMO decreases from 3.3086 (in R) to 1.7799 eV (in R + CN−), which is responsible for the red-shift observed in the UV–Vis spectrum of R upon addition of cyanide ions. The present quinone-bisimidazole based receptor shows few advantages over similar bisimidazoles reported elsewhere.

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