Synthesis, physicochemical characterization, DFT calculation and biological activities of Fe(III) and Co(II)–omeprazole complexes. Potential application in the Helicobacter pylori eradication

• The interaction between omeprazole (OMZ) and Fe(III) and Co(II) was studied.
• Fe(III)–OMZ and Co(II)–OMZ complexes were characterized by solid state techniques.
• The most favorable conformation for the complexes was obtained by DFT calculations.
• The compounds show antibacterial activities against Helicobacter pylori.
• Co(II)–OMZ shows a promising potential use for the treatment of gastric pathologies.

The reaction between the antiulcer agent omeprazole (OMZ) with Fe(III) and Co(II) ions was studied, observing a high ability to form metal complexes. The isolated microcrystalline solid complexes were characterized by elemental analysis, X-ray powder diffraction (XRPD), Scanning Electron Microscopy (SEM), magnetic measurements, thermal study, FTIR, UV–Visible, Mössbauer, electronic paramagnetic resonance (EPR), and DFT calculations. The metal–ligand ratio for both complexes was 1:2 determined by elemental and thermal analysis. FTIR spectroscopy showed that OMZ acts as a neutral bidentate ligand through the pyridinic nitrogen of the benzimidazole ring and the oxygen atom of the sulfoxide group, forming a five-membered ring chelate. Electronic, Mössbauer, and EPR spectra together with magnetic measurements indicate a distorted octahedral geometry around the metal ions, where the coordination sphere is completed by two water molecules. SEM and XRPD were used to characterize the morphology and the crystal nature of the complexes. The most favorable conformation for the Fe(III)–OMZ and Co(II)–OMZ complexes was obtained by DFT calculations by using B3LYP/6-31G(d)&LanL2DZ//B3LYP/3-21G(d)&LanL2DZ basis set. Studies of solubility along with the antibacterial activity against Helicobacter pylori for OMZ and its Co(II) and Fe(III) complexes are also reported. Free OMZ and both metal complexes showed antibacterial activity against H. pylori. Co(II)–OMZ presented a minimal inhibitory concentration ∼32 times lower than that of OMZ and ∼65 lower than Fe(III)–OMZ, revealing its promising potential use for the treatment of gastric pathologies associated with the Gram negative bacteria. The morphological changes observed in the cell membrane of the bacteria after the incubation with the metal-complexes were also analyzed by SEM microscopy. The antimicrobial activity of the complexes was proved by the viability test.