Experimental and Computational Studies on the Interaction of a Dansyl-Based Fluorescent Schiff Base Ligand with Cu 2+ Ions and CuO NPs.

We studied the interaction of Cu 2+ ions and CuO nanoparticles with the fluorescent Schiff base ligand H 3 L, which derives from the condensation of 4-formyl-3-hydroxybenzoic acid with N -(2-aminobenzyl)-5-(dimethylamino)naphthalene-1-sulfonamide (DsA). A detailed assignment of the most significant bands of the electronic and infrared spectra of H 3 L and DsA was performed using DFT methods, based on both crystal structures. The affinity of H 3 L to react with Cu 2+ ions in solution (K B = 9.01 10 3 L mol -1 ) is similar to that found for the Cu 2+ ions present on the surface of CuO NPs (K B = 9.84 10 3 L mol -1 ). Fluorescence spectroscopic measurements suggest five binding sites for H 3 L on the surface of the CuO NPs used. The µ-XRF analysis indicates that a polycrystalline sample of CuO-H 3 L NPs contains 15:1 Cu:S molar ratio (CuO:H 3 L). ATR-FTIR spectroscopy, supported by DFT calculations, showed that the HL 2- (as a phenolate and sulfonamide anion) is coordinated to superficial Cu 2+ ions of the CuO NPs through their azomethine, sulphonamide, and phenolic groups. A solution of H 3 L (126 ppb) shows sensitive responses to CuO NPs, with a limit of detection (LOD) of 330 ppb. The working range for detection of CuO NPs with [H 3 L] = 126 ppb was 1.1-9.5 ppm. Common metal ions in water, such as Na + , K + , Mg 2+ , Ca 2+ , Fe 3+ , and Al 3+ species, do not interfere significantly with the detection of CuO NPs.