Development of Hydrazone-Derived Lanthanide Complexes and Materials Aiming Dual Biological Applications

The constant evolution of bacteria makes the search for new and effective bactericidal agents essential. In this context, developing antibacterial compounds with luminescent properties offers a promising strategy to investigate intracellular biochemical processes while simultaneously assessing the drug's effects. In the present work, coordination polymers of composition [{M(L1)2}{M(L1)(H2O)2}]n (M = Sm3+, Gd3+, and Yb3+) were obtained from reactions of their respective lanthanide salts with 1.5 equivalent of the ligand 1,2-diphenylethane-1,2-diylidene)diisonicotinohydrazide (H2L1). The techniques used for characterization of the compounds included FTIR, UV-visible spectroscopy, high-resolution mass spectrometry and single-crystal X-ray diffraction. In addition, emission spectra were obtained at room temperature and at 77 K, along with emission spectra in the presence of oxygen or argon. The antibacterial activity of the compounds was evaluated against Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus and their clinical resistant strains - MRSA (methicillin-resistant Staphylococcus aureus). It was observed that, upon complexation, there was a general increase in the activity, particularly with a more pronounced percentage of inhibition against bacterial biofilms. Additionally, the complex [{Yb(L1)2}{Yb(L1)(H2O)2}]n was used for functionalization of Bi2O3/Bi2S3 nanoparticles, however, a fluorescence suppression was observed for the Yb-containing nanoparticles. Finally, cellular internalization studies demonstrated that the Ln³⁺ polymers alone could be detected inside Vero cells through their luminescence properties. Altogether, these lanthanide complexes present potential for dual-modality biological performance, combining significant antibacterial activity with the ability for intracellular detection.