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

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