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

Abstract

A polypyridyl ligand functionalized with a long alkyl chain (L^C10) was prepared. The reaction of L^C10 with selected iron salts of different stoichiometries formed two metal complexes: [Fe(L^C10)(Cl)₃] (1) and [Fe(L^C10)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 (K_b) 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 > L^C10, which demonstrates the enhanced effect of iron when coordinated to the bioinspired ligand.