Polypyridyl iron(III) complexes containing long alkyl chains: synthesis, characterization, DFT calculations and biological activity

A polypyridyl ligand functionalized with a long alkyl chain (LC10) was prepared. The reaction of LC10 with selected iron salts of different stoichiometries formed two metal complexes: [Fe(LC10)(Cl)3] (1) and [Fe(LC10)2](ClO4)3·5H2O (2), which were fully characterized by a suite of physicochemical methods in which 1 had its crystal structure determined by XRD. The structural and spectroscopic data were tightly supported by DFT and TD-DFT calculations. The interaction between these two iron complexes and salmon sperm DNA was monitored spectrophotometrically in the UV region and binding constants (Kb) were estimated and docking studies were performed using the PatchDock® server. Both complexes had their biocide activity confirmed against selected microorganisms: Gram-positive (S. aureus) and Gram-negative (E. coli) bacteria, A. fumigatus and S. cerevisiae with good values of MBC and IC50. Finally, the cytotoxic activities of 1 and 2 were probed against the erythroleukemia K562 cell line after 24, 48 and 72 h of incubation. For all biological studies, the magnitude of the activity followed the order: 2 > 1 > LC10, which demonstrates the enhanced effect of iron when coordinated to the bioinspired ligand.