Antenna effect of luminescent levofloxacin-lanthanide complexes in biological medium

The resistance to antibiotics and the appearance of super-resistant bacteria have become a serious public health problem all around the world. Antibiotics repositioning through the development of metal-antibiotic complexes could be a solution because they improve antibiotic therapeutic activity by increasing its electronic delocalization and lipophilic nature, easing its access into cells and improving interactions with biomolecules. An example of a commonly used antibiotic is levofloxacin (Levo), a third-generation quinolone which has been coordinated with different metal ions to enhance its antibacterial and anti-tumor properties. This work presents the synthesis, crystallography, and photophysical characterization of three coordination compounds based on Levo with Zn(II), Tb(III) and Eu(III), alongside their physicochemical properties under biological media. The most relevant result of this work is that Levo coordinates with Eu(III) and Tb(III) showing the so-called antenna effect through energy transfer from the drug as a ligand to the lanthanide ions in biological medium. This result opens new avenues for exploring its localization in cells and enabling future therapeutic applications in biomedicine, where the drug could act as an antenna ligand. Furthermore, experimental absorption and emission spectra were obtained, and Density Functional Theory (DFT) and Time-Dependent Density Functional Theory (TD-DFT) calculations were carried out to characterize their electronic and photophysical properties and confirm the sensitization of the lanthanide ions by the Levo drug.