Photoluminescent tetrahedral d 10 -metal Schiff base complexes exhibiting highly ordered mesomorphism

4-[(E)-2-(1-Pyrenyl)Vinyl]Pyridine Complexes: How to Modulate the Toxicity of Heavy Metal Ions to Target Microbial Infections

Pyrene derivatives are regularly proposed for use in biochemistry as dyes due to their photochemical characteristics. Their antibacterial properties are, however, much less well understood. New complexes based on 4-[(E)-2-(1-pyrenyl)vinyl]pyridine (PyPe) have been synthesized with metal ions that are known to possess antimicrobial properties, such as zinc(II), cadmium(II), and mercury(II). The metal ion salts, free ligand, combinations thereof, and the coordination compounds themselves were tested for their antibacterial properties through microdilution assays. We found that the ligand is able to modulate the antibacterial properties of transition metal ions, depending on the complex stability, the distance between the ligand and the metal ions, and the metal ions themselves. The coordination by the ligand weakened the antibacterial properties of heavy metal ions (Cd(II), Hg(II), Bi(III)), allowing the bacteria to survive higher concentrations thereof. Mixing the ligand and the metal ion salts without forming the complex beforehand enhanced the antibacterial properties of the cations. Being non-cytotoxic itself, the ligand therefore balances the biological consequences of heavy metal ions between toxicity and therapeutic weapons, depending on its use as a coordinating ligand or simple adjuvant.

The synthesis of a Cu(ii) Schiff base complex using a bidentate N2O2 donor ligand: crystal structure, photophysical properties, and antibacterial activities

In this paper, a new mononuclear Cu(ii) complex was synthesized by using a bidentate N₂O₂ Schiff base ligand, (E)-2-bromo-4-chloro-6-[(2,6-dimethylphenylimino)methyl]phenol (HL), with a copper(ii) salt in a methanol solvent. The structures of the HL ligand and the complex were characterized by Fourier transform infrared (FTIR) spectroscopy, single crystal X-ray diffraction (SCXD), and elemental analysis (EA). The Cu(ii) center in the complex is four-coordinated by a bidentate N₂O₂ donor ligand, forming slightly distorted square planar geometry. The detailed studies of their photophysical properties such as UV-Vis and fluorescence were done and the X-ray diffraction (XRD) patterns were investigated in the powder forms. Density functional theory calculations were carried out on both the HL ligand and the Cu(ii) complex to investigate the changes in the structural parameters and energies of the HOMO and LUMO. The results demonstrated that the HOMO and LUMO were effectively separated with the benzene ring of 2,6-dimethylbenzenamine as the donor unit and the benzene ring of 3-bromo-5-chlorosalicylaldehyde as well as the chelate ring as the acceptor unit. The effective HOMO–LUMO separation helps induce intramolecular charge transfer from the HOMO to the LUMO. The HOMO–LUMO energy gap become smaller when the Schiff base ligand coordinated with Cu(ii) ions, which was most likely due to the Cu(ii) perturbation effect. These theoretical calculations supported the experimentally observed results. The antibacterial activities of the HL ligand and the Cu(ii) complex were studied on Staphylococcus aureus, Pseudomonas aeruginosa, and Escherichia coli. The obtained data confirmed their potent antimicrobial activity and the Cu(ii) complex had the MIC value of 1.25 mmol L⁻¹ against Escherichia coli.

Reaction of a symmetric compartmental Schiff base ligand (HL) with copper(ii) salt in 2 : 1 M ratio in methanol gave rise to a mononuclear copper(ii) complex, which was characterized by single crystal X-ray diffraction studies.