Synthesis, characterization and antibacterial activity of FeIII, CoII, CuII and ZnII complexes probed by transmission electron microscopy

We synthesized iron(III), cobalt(II), copper(II) and zinc(II) complexes [FeIII(HBPClNOL)Cl2]·H2O (1), [CoII(H2BPClNOL)Cl2] (2), [CuII(H2BPClNOL)Cl]Cl·H2O (3), and [ZnII(HBPClNOL)Cl] (4), where H2BPClNOL is the ligand (N-(2-hydroxybenzyl)-N-(2-pyridylmethyl)[(3-chloro)(2-hydroxy)]propylamine). The complexes obtained were characterized by elemental analysis, IR and UV–visible spectroscopies, electrospray ionization mass spectrometry (ESI-MS), tandem mass spectrometry (MS/MS), and cyclic voltammetry. X-ray diffraction studies were performed for complexes (3) and (4) revealing the presence of mononuclear and dinuclear structures in solid state for (3). However, the zinc complex is mononuclear in solid state. Biological studies of complexes (1)–(4) were carried out in vitro for antimicrobial activity against nine Gram-positive bacteria (Staphylococcus aureus strains RN 6390B, COL, ATCC 25923, Smith Diffuse, Wood 46, enterotoxigenic S. aureus FRI-100 (SEA+), FRI S-6 (SEB+) and SEC FRI-361) and animal strain S. aureus LSA 88 (SEC/SED/TSST-1+). The following sequence of inhibition promoted by the complexes was observed: (4) > (2) > (3) > (1), showing the effect of the metal on the biological activity. To directly observe the morphological changes of the internal structure of bacterial cells after the treatment, transmission electron microscopy (TEM) was employed. For the most active complex [ZnII(HBPClNOL)Cl] (4), granulation deposits around the genetic material and internal material leaking were clearly detected.

Graphical AbstractWe report the synthesis and characterization of: [FeIII(HBPClNOL)Cl2]·H2O (1), [CoII(H2BPClNOL)Cl2] (2), [CuII(H2BPClNOL)Cl]Cl·H2O (3), and [ZnII(HBPClNOL)Cl] (4) (H2BPClNOL = (N-(2-hydroxybenzyl)-N-(2-pyridylmethyl)[(3-chloro)(2-hydroxy)]propylamine)). Biological studies were carried out for antimicrobial activity against nine strains of S. aureus, revealing complexes (2) and (4) showed higher inhibitory activities. TEM was employed to investigate any structural changes.Figure optionsDownload as PowerPoint slide