Fluorescent-colorimetric selective and sensitive detection of sulfide anions by salicylaldehyde-2,4-dinitrophenylhydrazone: biological, environmental and logic gate application

Abstract

Herein, salicylaldehyde-2,4-dinitrophenylhydrazone (L) has been reported and characterised by the usual spectroscopic techniques, X-ray single crystal analysis and DFT studies. In a 1 : 1 methanol–water medium (v/v), the receptor L detected S²⁻ ions with a color change from light yellow to orange and with turn-off fluorescence enhancement through a de-protonation mechanism. UV-vis spectroscopy, fluorescence titration, FTIR, ESI-MS and ¹H-NMR titrations have been used to analyse the response mechanisms of fluorescent colorimetric sensing. The other interfering anions (F⁻, Cl⁻, Br⁻, HSO₃⁻, N₃⁻, PO₄³⁻, NO₃⁻, OAc⁻, CO₃²⁻ and CN⁻) showed very negligible interference for detection of the sulfide ion. The colorimetric sensitivity for S²⁻ is 2.40 × 10⁻⁷ M and the fluorometric sensitivity is 0.93 × 10⁻⁷ M; both values are sufficiently below the WHO permissible limits in aqueous solution. From the Job plot measurements and the ESI-MS spectrum, 1 : 1 stoichiometric complexation between L and S²⁻ has been established. Receptor L shows remarkable detection ability in a wide pH range and can be successfully applied for the detection and quantification of S²⁻ ions in environmental and biological samples. L may also be used in building INHIBIT type molecular logic gates. Molecular docking studies further revealed favorable binding interactions of the ligand with the KIT receptor tyrosine kinase (PDB ID: 3G0E), supporting its potential as a modulator of cancer-associated targets.