Synthesis, cadmium sensing ability and biological activities of a pyrrole-based macrocyclic Schiff base fluorescent ligand: DFT studies

A novel turn-on fluorescent sensor was designed for cadmium detection and synthesized by the condensation reaction of a prepared dialdehyde with diethylenetriamine, and characterized by FT-IR, UV–visible, 1HNMR, Mass spectra, and elemental analyses. According to the fluorescent findings, an approximately 3-fold enhancement of the emission intensity of L toward Cd2+ ions was observed at 430 nm, while 18 other metal ions did not make significant changes (LOD=2.7×10−9 M). DFT calculations confirmed the experimental results. Lowering the band gap (Eg) and increasing the electrophilicity index (ω) indicated that charge transfer is responsible for the enhancement of emission intensity of L when binding to Cd2+. The sensor (L) and its complexes exhibited significant antioxidant potency. Furthermore, [CdL] demonstrated much more extensive antibacterial activity against Staphylococcus aureus, Pseudomonas aeruginosa, and Escherichia coli, among other evaluated compounds.