Lanthanide coordination compounds with benzimidazole-based ligands. luminescence and EPR

Study on the host-guest complex of dicyclohexanocucurbit[6]uril and 2-phenylbenzimidazole, and its recognition effect toward Fe3

This paper has selected dicyclohexanocucurbit[6]uril (CyH2Q[6]) as the host and 2-phenylbenzimidazole (G) as the guest to investigate the host-guest interaction mode between CyH2Q[6] and G. Under acidic conditions, the complex was characterized using nuclear magnetic resonance, ultraviolet and fluorescence spectroscopy. The results show that the molecular ratio of CyH2Q[6] to G is 2 : 1. The crystals were cultured with ZnCl2 as a structural inducer under acidic conditions and single crystal X-ray diffraction showed that the molecular ratio of CyH2Q[6] to G is 1 : 3. The G@CyH2Q[6] was used as a fluorescent probe to identify metal cations. The probe exhibits a good selective recognition effect toward Fe3+ ions, which involves a reduced fluorescence intensity with a limit of detection of 1.321 × 10-6 mol l-1.

Synthesis, biological evaluation and model membrane studies on metal complexes containing aromatic N,O-chelate ligands

Novel lanthanide (Ln) compounds [Ln(L)₂]Cl^.xH₂O (Ln = La³⁺, Ce³⁺, Sm³⁺) containing aromatic N,O-chelate ligands [HL1 = 4-amino-2-(1H-benzimidazol-2-yl)phenol; HL2 = 5-amino-2-(1H-benzimidazol-2-yl)phenol] have been synthesized and structurally characterized by elemental analysis, NMR and IR spectroscopy, molar conductance measurements, and mass spectrometry (MS). The spectroscopic data suggested that the benzimidazolyl-phenol ligands act as N,O-chelate ligands through the iminic nitrogen and phenolic oxygen atoms. Elemental analysis indicated that lanthanide compounds were formed in a 1:2 stoichiometry (metal:ligand). In vitro biological evaluation was carried out using these complexes, exhibiting moderate cytotoxicity against six different human tumor cell lines (U251, human glioblastoma; HCT-15, colorectal carcinoma; MCF-7, breast epithelial adenocarcinoma; PC-3, prostate cancer; K562, myelogenous leukemia; SKLU-1, lung carcinoma) and lower toxicity against a non-cancerous cell line (COS-7, primate kidney). In addition, the antibacterial activity of the compounds was assessed against two gram-positive strains (Staphylococcus aureus ATCC 25923, Listeria monocytogenes ATCC 19115) and two gram-negative strains (Escherichia coli ATCC 25922, Pseudomonas aeruginosa ATCC 27583) using the microdilution method. The results obtained show that the metal complexes exhibit higher biological activity than the free ligands, confirming a synergistic effect. Further benzimidazolyl-phenol derivatives were explored for the detection of bacteria using fluorescence imaging studies. Interestingly, the fluorescent properties of these compounds make them potential candidates to monitor the morphology of bacteria at different compound concentrations. Hence, the interaction of the ligand and complexes with model membranes mimicking those of bacteria was studied by using differential scanning calorimetry (DSC) and molecular dynamics (MD), showing that both compounds decreased the enthalpy of transition in two model membranes as the concentration of the compounds increased. In addition, the main transition temperature was slightly reduced as a result of these interactions.

Complexes containing benzimidazolyl-phenol ligands and Ln(III) ions: Synthesis, spectroscopic studies and preliminary cytotoxicity evaluation

Fourteen new complexes were obtained from Ln(III)(NO₃)₃∙n-H₂O and the chromophores 2-(1H-benzo[d]imidazol-2-yl)-phenol (Bzp1) or 2-(5-methyl-1H-benzo[d]imidazol-2-yl)-phenol (Bzp2). The complete characterization allowed us to assign unequivocally the structures of all the complexes. The techniques used for this purpose were Ultraviolet-Visible (UV-Vis) and Fourier-Transform Infrared (FT-IR) spectroscopies, High-Resolution Mass Spectrometry (HRMS), Magnetic Susceptibility (MS), Elemental Analysis (EA) and Molar Conductivity (MC). HRMS allowed us to find the molecular ion and its isotopic pattern. The FT-IR spectral data suggested that benzimidazolyl-phenol ligands coordinate with Ln(III) ions through iminic nitrogen and phenolic oxygen. Thermogravimetric Analysis (TGA) studies of NdBzp1 and GdBzp2 complexes indicate the presence of lattice water along with three nitrates and two benzimidazolyl-phenol ligands; the thermal decomposition was consistent with the minimal formula suggested by EA. The coordination type of the benzimidazolyl-phenol ligands, the geometry and the structural organization of these coordination complexes have been interpreted by Density Functional Theory (DFT) calculations, and they coincided with the physicochemical data suggesting a coordination number eight for the Ln(III) ions. The cytotoxicity of the chromophores and their coordination complexes was tested against a cancer cell line (HeLa), as compared with structure/support cells (NIH-3T3) and defense cells (J774A.1), revealing that three coordination complexes showed moderate cytotoxicity against the cell lines studied.

Solid-state luminescence properties, Hirshfeld surface analysis and DFT calculations of mononuclear lanthanide complexes (Ln = EuIII, GdIII, TbIII, DyIII) containing 4'-phenyl-2,2':6',2″-terpyridine

Four mononuclear lanthanide complexes containing 4'-phenyl-2,2':6',2″-terpyridine (ptpy), [Ln(NO₃)₃(ptpy) (H₂O)] (Ln = Eu (1), Gd (2), Tb (3), Dy (4)), were solvothermally synthesized and characterized via elemental analysis, infrared spectroscopy, thermogravimetric analysis, single-crystal X-ray diffraction, and powder X-ray diffraction. Hirshfeld surfaces and the solid-state luminescence properties of the complexes were investigated. The 3-D Hirshfeld surface and 2-D fingerprint plots show that the main interactions are the O H/H O intermolecular interactions in 1-4. Solid-state luminescence investigation reveals that Gd^III complex 2 displays a ligand-centered emission and the Eu^III, Tb^III and Dy^III complexes 1, 3 and 4 show the characteristic lanthanide-centered luminescence upon UV excitations. The Eu^III and Tb^III complexes exhibit red (CIE: 0.6549, 0.3447) and green (CIE: 0.3760, 0.5412) luminescence in the solid state with quantum yields of 16.8% and 0.8% and lifetimes of 0.545 and 0.043 ms, respectively. Density functional theory (DFT) calculations were conducted to unravel the HOMO-LUMO energy gaps of the structures of ptpy and complexes 1 and 3.