Exploring the Chelating Potential of an Easily Synthesized Schiff Base for Copper Sensing

The present study deals with the investigation of Cu²⁺, Ni²⁺ and Pd²⁺ chelating potential of the Schiff base, (E)-N-(2-((2-hydroxybenzylidene)amino)benzyl)-4-methylbenzenesulfonamide (H₂SB). Crystal structures of Ni(HSB)₂, Pd(HSB)₂ and Cu(HSB)₂ have been elucidated from single crystal X-ray diffraction data. NMR spectroscopy showed the presence of two conformers of Pd(HSB)₂ in solution, both with an E configuration of the ligand. The determination of binding constants by fluorescence quenching showed that affinity of H₂SB to Cu²⁺ in solution is higher than for Ni²⁺ and Pd²⁺. Since there is a high demand for selective, sensitive, rapid and simple methods to detect copper in aqueous samples (both as Cu²⁺ ions and as CuO NPs), we have explored H₂SB as an optical chemosensor. H₂SB interacts with increasing concentrations of Cu²⁺ ions, giving rise to a linear increase in the absorbance of a band centered at about 392 nm. H₂SB displays a high selectivity toward Cu²⁺, even in the presence of the most common metal ions in water (Ca²⁺, Mg²⁺, Na⁺, K⁺, Al³⁺ and Fe³⁺), and some heavy transition metal ions such as the soft acids Pd²⁺ and Cd²⁺. H₂SB also interacts with increasing concentrations of CuO NPs, which gives rise to a linear decrease in its fluorescence intensity (λ_em = 500 nm, λ_ex = 390 nm). Quenching has occurred as a result of the formation of a non-fluorescent ground-state surface complex H₂SB–CuO NPs. The limits of detection and quantification of CuO NPs were 9.8 mg/L and 32.6 mg/L, respectively. The presence of TiO₂, Ag and Au NPs does not interfere with the determination of CuO NPs. View Full-Text