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

A bisimidazole ensemble (R) possessing naphthoquinone as signaling unit is synthesized and characterized using H-1 and C-13 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 fromyellowto brown selectively with cyanide in aqueous HEPES buffer-DMSO (1: 1 v/v) medium with a detection limit of 1 mu M. 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 x 10(2) 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 spectrumof R upon addition of cyanide ions. The present quinone-bisimidazole based receptor shows fewadvantages over similar bisimidazoles reported elsewhere. (C) 2019 Elsevier B.V. All rights reserved.