Exploiting Co(III)-Cyclopentadienyl Complexes To Develop Anticancer Agents

In recent years, organometallic complexes have attracted much attention as anticancer therapeutics aiming at overcoming the limitations of platinum drugs that are currently marketed. Still, the development of half-sandwich organometallic cobalt complexes remains scarcely explored. Four new cobalt(III)-cyclopentadienyl complexes containing N,N-heteroaromatic bidentate, and phosphane ligands were synthesized and fully characterized by elemental analysis, spectroscopic techniques, and DFT methods. The cytotoxicity of all complexes was determined in vitro by the MTS assay in colorectal (HCT116), ovarian (A2780), and breast (MDA-MB-231 and MCF-7) human cancer cell lines and in a healthy human cell line (fibroblasts). The complexes showed high cytotoxicity in cancer cell lines, mostly due to ROS production, apoptosis, autophagy induction, and disruption of the mitochondrial membrane. Also, these complexes were shown to be nontoxic in vivo in an ex ovo chick embryo yolk sac membrane (YSM) assay.

A novel triruthenium nitrosyl bearing a quinolinic ligand: a comparison of its spectroscopic behavior with its pyridine analogues

A comparative analysis of ruthenium nitrosyl spectroscopic data helps unravel the electronic character of the unit {RuNO}6[RuIIIRuIIIO].

Novel Ferrocene-Appended β-Ketoimines and Related BF2 Derivatives with Significant Aggregation-Induced Emission and Second-Order Nonlinear Optical Properties

A series of new β-ketoimines containing a ferrocene moiety and their BF₂ complexes have been synthesized and structurally characterized. The solvatochromism of the β-ketoimines was studied, putting in evidence a redshift with increasing solvent polarity. This positive solvatochromism can be attributed to a more polarized excited state compared with the ground state, due to intramolecular charge transfer (ICT) transitions. The β-ketoimines exhibited weak emission, attributable to the excited-state intramolecular proton transfer (ESIPT) phenomenon. This ESIPT effect is suppressed upon restriction of the keto-enamine tautomerism, induced upon addition of BF₃ ⋅OEt₂ , which afforded the related BF₂ complexes, characterized by an enhancement of the fluorescence through the ICT effect. Both the β-ketoimines and BF₂ complexes exhibited significant aggregation-induced emission behavior in mixtures of CH₃ CN/H₂ O, due to restriction of intramolecular rotation in the aggregated state. The frontier molecular orbital levels, ground- and excited-state dipole moments (μ_g and μ_e ), and the origin of electronic absorption spectra were studied by time-dependent DFT calculations. The second-order nonlinear optical (NLO) properties were determined by the electric-field-induced second-harmonic generation technique. The μβ₁₉₀₇ values of the β-ketoimines increased upon the formation of the related BF₂ complexes, mainly due to an enhancement of the ground-state dipole moment. The results presented here reveal that some of these novel compounds are excellent multifunctional candidates for NLO and luminescence applications.

Syntheses and electronic, electrochemical, and theoretical studies of a series of μ-oxo-triruthenium carboxylates bearing orthometalated phenazines

This work reports a series of five-acetate triruthenium clusters [Ru₃O(OAc)₅(L)(py)₂]PF₆, where L = dppn (benzo[i]dipyrido[3,2-a:2',3'-c]phenazine, 1); dppz (dipyrido[3,2-a:2',3'-c]phenazine, 2); CH₃-dppz (7-methyldipyrido [3,2-a:2',3'-c] phenazine, 3); Cl-dppz (7-chlorodipyrido [3,2-a:2',3'-c] phenazine, 4); and phen (1,10-phenanthroline, 5). The EPR spectra collected at 10 K displayed one isotropic signal without a hyperfine structure and with g values of ∼2.0, which showed that the five-acetate triruthenium clusters are paramagnetic, and that their electronic delocalization resembled the electronic delocalization of the parent hexa-acetate complexes. ¹H NMR analysis showed that the orthometalated phenazines lowered the symmetry of the compounds significantly. Inductive effects from the carbanion and ring current effects outweighed the effect of paramagnetic anisotropy and dominated the spectra. This resulted in a lack of typical correlations with ligand parameters such as pK_a that are observed for the parent hexa-acetate compounds. DFT calculations allowed for a discussion of those parameters in terms of the optimized geometry of compound 2. Natural bond orbital (NBO) results, in turn, aided the rationalization of the orthometalation reaction. The intra-cluster transitions (IC) at ∼690 nm consistently shifted to higher energies, and the redox pair [Ru₃O]^0/+1 also shifted to more positive E_1/2 values. Again, the shifts were small and produced poor correlations with phenazine basicity. Overall, the substitution of one acetate bridge caused poor π-interactions between the delocalized [Ru₃O] unit and the phenazine electron cloud. fsTA experiments, performed for the first time for such systems, showed that an ²IC excited state decayed very fast on the picosecond timescale.

Crystal structure, electrochemical and spectroscopic investigation of mer-tris-[2-(1H-imidazol-2-yl-κN3)pyrimidine-κN1]ruthenium(II) bis-(hexa-fluorido-phosphate) trihydrate

The crystal structure of the title compound, [Ru(C7H6N4)3](PF6)2·3H2O, a novel RuII complex with the bidentate ligand 2-(1H-imidazol-2-yl)pyrimidine, comprises a complex cation in the meridional form exclusively, with a distorted octa-hedral geometry about the ruthenium(II) cation. The Ru-N bonds involving imidazole N atoms are comparatively shorter than the Ru-N bonds from pyrimidine because of the stronger basicity of the imidazole moiety. The three-dimensional hydrogen-bonded network involves all species in the lattice with water mol-ecules inter-acting with both counter-ions and NH hydrogen atoms from the complex. The supra-molecular structure of the crystal also shows that two units of the complex bind strongly through a mutual N-H⋯N bond. The electronic absorption spectrum of the complex displays an asymmetric band at 421 nm, which might point to the presence of two metal-to-ligand charge-transfer (MLCT) bands. Electrochemical measurements show a quasi-reversible peak referring to the RuIII/RuII reduction at 0.87 V versus Ag/AgCl.

New uses for old complexes: The very first report on the trypanocidal activity of symmetric trinuclear ruthenium complexes

This work reports on the trypanocidal activity of a series of symmetric triruthenium complexes combined with azanaphthalene ligands of general formula [Ru₃O(CH₃COO)₆(L)₃]PF₆ (L=(1) quinazoline (qui), (2) 5-nitroisoquinoline (5-nitroiq), (3) 5-bromoisoquinoline (5-briq), (4) isoquinoline (iq), (5) 5-aminoisoquinoline (5-amiq), and (6) 5,6,7,8-tetrahydroisoquinoline (thiq)). All complexes within the series presented in vitro trypanocidal activity against both the trypomastigote and amastigote forms of T. cruzi. The IC₅₀ values obtained for complexes 1-6 ranged from 1.39 to 165.9μM for the trypomastigote form and from 1.06 to 53.16μM for the amastigote form. These values were lower than the values observed for the metallic core [Ru₃O(CH₃COO)₆(CH₃OH)₃]⁺ itself and for the free ligands in all cases. Remarkably, complex 6 displayed lower IC₅₀ values than the reference drug (benznidazole) for the acute (trypomastigote form) and chronic (amastigote form) phases of Chagas disease. These findings, combined with the low toxicity against healthy cells (LLK-MK₂ strain) and a high SI value (Selectivity Index >10) make complex 6 an excellent candidate for in vivo tests.