Chelation Therapy-inspired Design of a Water-stable Fluorescent Probe for Effectual Monitoring of Copper(II) ions in Real Water

Abstract

This work introduces a thought-provoking design to develop a water-soluble chemical probe, sodium 4-hydroxy-3-((E)-((E)-((2-hydroxynaphthalen-1yl)methylene)hydrazono)methyl) benzenesulfonate (SW2) and it's analytical characterization for efficient detection and monitor of Cu2+ ions in a matrix of s-, d-, and f- metal ions in pure water. The water-stable molecular probe, SW2 in the presence of Cu2+ salts in pure water exhibits a fluorescence turn-off characteristic with a high detection limit, 3.8 µM, and irresistibly, holds a 4-cycle reversibility in the presence of sulphide ion without any significant loss of chemosensing efficiency. Spectroscopic and computational studies ensure the 1:1 complexation between SW2 and Cu2+ ions leading to the formation of SW2-Cu2+ chelate, inducing the dynamic quenching in the emission property for SW2 which subsequently reverts by the addition of S2- ion in water. Additionally, SW2-Cu2+ chelate was isolated in microcrystalline powder and the complexation was compelled with mass spectrometry and EPR analysis. Computational analysis reveals the remarkable reduction of the S0-S1 energy level for SW2-Cu2+ complex attributing the drastic quenching in the fluorescence intensity. Furthermore, SW2 is successfully applied to the detection of Cu2+ ions in tap and pond water. Interestingly, the probe is also effective for the determination of Cu2+ ions in the aqueous solution of a Cu-based fungicide (copper oxychloride), commercially available as Blitox in India evaluating the effectiveness of SW2 for real sample analysis.