A simple oxindole-based colorimetric HSO 4 ¯ sensor: Naked-eye detection and spectroscopic analysis

Abstract

Detection of hydrogen sulfate from an aqueous organic solvent systems medium attracts to lots of interest because of could be in most environmental and biological systems. In this study, the simple receptors 5 and 6 containing oxindole core were synthesized, and the anion sensing properties were studied using colorimetric, fluorometric detection and 1 H-NMR spectroscopy. The research indicated that the specific ligand affinity for hydrogen sulfate ions results in drastic color and spectral changes. According to the data obtained, a new peak at 371 nm in the absorption spectrum of 5 and an increase in fluorescence intensity of 5 were observed in the presence of HSO 4 ¯ ions. The binding ratio of 5 to HSO 4 ¯ was calculated to be 1:1 according to Job's plot experiments. The Ks value was found to be 1.21×10 5 M −1 using the Benesi-Hildebrand equation. The LOD value was calculated with value as low as 8.9 μM for HSO 4 ¯ . Moreover, DFT calculations confirmed the nonplanar structures or propeller structures. As a result of all these studies, it can be said that 5 which is non-toxic, may be a useful and selective candidate turn-on sensor for HSO 4 ¯ sensing in the industrial wastewaters. © 2019 Elsevier B.V.