In silico evaluation of the stability and antibacterial activity of some cobalt complexes

The novel octahedral cobalt(III) complexes [Co(HL)BrL']ClO4 have been prepared by the reaction of (E,E)-3,9-dimethyl-5,7-di-oxa-4,8-diaza-3,8-undecadi-ene-2,10-dione dioxime (H2L) and CoBr2·6H2O. The complexes of H2L have a metal : ligand ratio of 1:1 and the ligand coordinates through the N atoms, as in most oximes, with axial ligation by substitued pyridines (L1) and bromide ion. The cobalt complexes have been characterized by 1H NMR, IR, MS spectral and elemental analysis data.

Four and six-coordinated cobalt complexes based on thiosemicarbazone. Formation, experimental and theoretical characterization

New cobalt complexes, Co1 and Co2, were synthesized starting from acetylacetone‐S‐methylthiosemicarbazone. The square planar cobalt(II) and octahedral cobalt(III) complexes were characterized by FT‐IR, UV–visible, 1H NMR, and X‐ray diffraction spectroscopies and mass spectrometry. Frontier orbitals of the complexes were theoretically obtained to better understand the complex structures and intermolecular interactions. The electrochemical behaviors of Co1 and Co2 were investigated and the results were evaluated by comparing with each other and with similar published compounds to determine their possible usage in various electrochemical technologies, such as energy storage devices, electrocatalysts, and electrosensors. Metal‐based oxidation at around 0 V and metal‐based reduction at around −1.0 V indicated that these complexes are valuable for the proposed applications. By determining the trolox equivalent antioxidant capacity and the radical scavenging activity of the cobalt complexes, the compatibility between the antioxidant qualification, redox, and theoretical calculation results was discussed.

A detailed infrared and far-infrared spectral investigation of the alkyl- and (non-alkyl)cobalt(III) complexes of 3,8-dimethyl-5,6-benzo-4,7-diazadeca-3,7-diene-2,9-dione dioxime and a study of ground state trans-effect in tetragonally distorted octahedral cobalt(III) complexes by far-infrared and electronic absorption spectroscopy

A new end-off type acyclic ligand with four hydroxyethyl arms, 2,6-bis[bis(2-hydroxyethyl)aminomethyl]-4-methylphenol [H(bhmp)], formed dinuclear cobalt(II) complexes [Co(2)(bhmp)(OAc)(2)]BPh(4) (1) and [Co(2)(bhmp)(OBz)(2)]BPh(4) (2). The complex 1.2.5CH(3)CN (C(50)H(62.5)BCo(2)N(4.5)O(9)) crystallizes in the monoclinic space group C2/c with dimensions a = 25.424(5) A, b = 13.376(2) A, c = 29.913(6) A, beta = 105.930(3) degrees, and V = 9781(3) A(3) and with Z = 8. X-ray diffraction analysis revealed a mu-phenoxo-bis(mu-acetato)dicobalt(II) core structure containing two octahedral cobalt(II) ions. Electronic spectra were investigated for 1 and 2 in the range 400-1800 nm, and the data were typical for the octahedral high-spin cobalt(II) complexes. Magnetic susceptibility was measured for 1 and 2 over the temperature range 4.5-300 K, and the data were analyzed well using our theoretical method. The best fitting parameters were kappa = 0.77, lambda = -116 cm(-1), Delta = 572 cm(-1), and J = -0.44 cm(-1) for complex 1 and kappa = 0.96, lambda = -93 cm(-1), Delta = 616 cm(-1), and J = -0.33 cm(-1) for complex 2.

The use of molecular docking to predict interactions between drug candidates and biological targets has evolved a new perspective in medicine. Understanding mechanisms of action, both experimentally and in silico, is important in drug development. Based on this, new Schiff base cobalt(II) complexes containing aminophenol moiety; bis(2-((E)-(4-methoxy benzylidene)amino) phenoxy) cobalt (complex(1), bis(2-((E)-(4-chloro benzylidene) amino) phenoxy)cobalt (complex(2) and bis(2-((E)-(4 nitro benzylidene) amino) phenoxy )cobalt (complex(3) was evaluated for its drug properties against B-DNA. Molecular docking was carried out to establish the interactions of B-DNA and cobalt complexes, evaluate drug-likeness, and toxicity profile. The results obtained were compared with the experimental DNA report. The result showed that all the cobalt complexes exhibited one or more hydrogen bonding interactions with residue B-DNA, as the cobalt complexes revealed binding of the minor groove of Adenine-Thymine rich DNA segments. Van der Waals and hydrogen bonding interactions were observed, which is consistent with the experimental DNA results. From the inhibition of kinases and proteases, the bioactivity scores of the cobalt complexes suggest a moderate interaction with drug targets. Our study also revealed that all cobalt complexes are non-inhibitors of the human ether-a-go-go related gene and are not mutagenic except the nitro-substituted complex 3. Evidently, complex 1 exhibited the highest bioactivity, and this can be developed as a drug candidate. KEY WORDS: Cobalt complex, DNA, Drug-likeness, In-silico, Toxicity Bull. Chem. Soc. Ethiop. 2026, 40(2), 413-428 DOI: https://dx.doi.org/10.4314/bcse.v40i2.11

Metal complexes of 2,5-dicarboxamidopyrroles and 2,5-dicarbothioamidopyrroles have been structurally characterised for the first time, complementing the significant amount of work that has been reported for the analogous pyridine ligands. N,N'-Bis(3,5-dinitrophenyl)-3,4-diphenyl-1H-pyrrole-2,5-dicarboxamide forms octahedral bis(tridentate) complexes with cobalt(III) and nickel(II), where the ligands are bound to the metal centres through deprotonated pyrrole and amide N atoms. N,N'-Dibutyl-3,4-diphenyl-1H-pyrrole-2,5-dicarboxthioamide and N,N'-diphenyl-3,4-diphenyl-1H-pyrrole-2,5-dicarboxthioamide also form bis(tridentate) cobalt complexes but are only deprotonated at the pyrrole N atom, the remainder of the coordination sphere comprising the thioamide S atoms. The dibutyl derivative was isolated as a Co(II) complex, whereas the diphenyl system deposited a Co(III) complex. In contrast, N,N'-dibutyl-3,4-dichloro-1H-pyrrole-2,5-dicarboxamide was found to act as a bidentate ligand, in an octahedral cobalt(II) complex comprising of two bidentate pyrrole ligands, and two aqua ligands. Synthesis of N,N-bis(pyridin-2-ylmethyl)-3,4-diphenyl-1H-pyrrole-2,5-carboxamide gave a pyrrole ligand with increased denticity. Reaction with cobalt(II) chloride resulted in the isolation of a dinuclear helicate complex. The ligand was found to have undergone addition of a methoxy group to one of the linking methylene carbons, presumably as a result of the oxidative addition of solvent methanol.

DFT modelling of cobalt and nickel complexes with dithiophosphinic acid

Two new octahedral cobalt(III) and nickel(II) complexes, [CoL2]·ClO4 (1) and [NiL2]·H2O·NO3 (2) containing the potentially tridentate Schiff base like hydrazone ligand, N′-[1-(pyridin-2-yl)ethylidene]acetohydrazide (L) (1:1 condensation product of acetichydrazide and 2-acetylpyridine) were synthesized and characterized by spectral a well as thermal analysis and single crystal X-ray diffractometry. Structural investigation shows that in both complexes, the central Co or Ni atom belongs into N4O2 coordination sphere, developed with the NNO donor sets of two independently hydrazone units. The corresponding M–N(pyridine) bonds being significantly longer than the M–N(imino) bonds, Co1–N1 and Co1–N4 [1.934(3) and 1.926(3) A] for 1 and Ni1–N1 and Ni1–N4 [2.076(3) and 2.085(3) A] for 2, Co1–N2 and Co1–N5 [1.846(3) and 1.854(3) A] for 1 and Ni1–N2 and Ni1–N5 [2.001(3) and 1.972(3) A] for 2 respectively. Two new octahedral cobalt(III) and nickel(II) complexes containing the potentially tridentate hydrazone ligand, N’-[1-(pyridin-2-yl)ethylidene]acetohydrazide (L) were synthesized and characterized by IR and UV–Vis spectra as well as thermal analysis and single crystal X-ray diffractometry.

An octahedral cobalt(iii) complex based on cheap 1,2-phenylenediamine operates as an efficient bifunctional hydrogen bond donor catalyst in cycloaddition of epoxides with CO2 under ambient conditions and solvent- and co-catalyst-free conditions.

Guanine-rich sequences of DNA are known to readily fold into tetra-stranded helical structures known as G-quadruplexes (G4). Due to their biological relevance, G4s are potential anticancer drug targets and therefore there is significant interest in molecules with high affinity for these structures. Most G4 binders are polyaromatic planar compounds which π-π stack on the G4's guanine tetrad. However, many of these compounds are not very selective since they can also intercalate into duplex DNA. Herein we report a new class of binder based on an octahedral cobalt(III) complex that binds to G4 via a different mode involving hydrogen bonding, electrostatic interactions and π-π stacking. We show that this new compound binds selectivity to G4 over duplex DNA (particularly to the G-rich sequence of the c-myc promoter). This new octahedral complex also has the ability to template the formation of G4 DNA from the unfolded sequence. Finally, we show that upon binding to G4, the complex prevents helicase Pif1-p from unfolding the c-myc G4 structure.

The Schiff base ligands in their deprotonated forms have been utilized to synthesize thermodynamically and kinetically stabilized Cobalt(II) complexes. In the complexes, cobalt ion present is in distorted octahedral arrangement and is coordinated by four tridentate ligands in complexes. The synthesized Schiff base ligands coordinate with Cobalt (II) ion through four azomethine nitrogen atoms and two sulfur atoms developing a 6- membered chelate ring. Synthesized Cobalt(II) complexes via hexadentate ligands have been characterized thoroughly through various spectroscopic techniques like FT-IR, UV-Vis, 1HNMR, TGA, TEM, SEM, Particle size, Elemental analysis (C, H, N, Co, S) and conductivity measurements. All Cobalt(II) complexes have been evaluated for in vitro antimicrobial activity against isolated bacterial strains of E. coli (MTCC-1687), E. faecalis (MTCC-439), S. aureus (MTCC-737) and MR S. aureus (Indigenous). All Cobalt complexes show mild to moderate antibacterial activity. The MIC ranged from 50 µg/ mL to 3.125 µg/ mL. All Cobalt(II) complexes displayed in-vitro antibacterial activity against both gram-positive and gram-negative bacterial strains. It may be proved that the antibacterial activity of the complexes is related to the cell wall structure of the tested bacteria. In-vitro toxicity tests explained the Cobalt complexes were less cytotoxic than the Vancomycin drug on A431 cancer cell lines and the results explain that synthesized Cobalt complexes can act as potent antimicrobial agents and can be considered as a good drug candidate for medicinal chemistry researchers.

The replacement, by hydroxide ion, of the co-ordinated chloride in the chloropentamminecobalt(III) cation in aqueous solution has been studied over a wide range of alkali concentrations. The kinetics were done with excess of hydroxide ion at a constant ionic strength so that pseudo-first-order rate constants were obtained in all the runs. The rate constants are non-linear in hydroxide concentration, and this kinetic dependence may be explained on the basis of the ion-pair mechanism, according to which the reaction between the cobalt(III) cation and the hydroxide ion proceeds by a pre-equilibrium formation of an “intimate” ion-pair between the two ions, followed by a rate-determining rearrangement within the ion-pair. The above investigations are extended to other similar complexes, where it is shown that, when four ammonia groups in the chloropentamminecobalt(III) cation are changed to two ethylenediamine ligands, and thereafter to one triethylenetetramine ligand, the nonlinearity in the dependence of observed first-order rate constants on hydroxide concentration becomes less and less noticeable. This observation constitutes evidence against the conjugate-base mechanism for the base hydrolysis of octahedral cobalt(III) complexes in aqueous solutions.

Synthesis, characterization, solution equilibria, DFT study, DNA binding affinity and cytotoxic properties of a cobalt(II) complex with a 5-pyrazolone ligand

Although CH…O hydrogen bonds are generally very weak, here investigated CH…O interactions of coordinated 1,10-phenanthroline (phen) are very frequent and quite strong. In the crystal structures from the Cambridge Structural Database, 8344 CH…O interactions between coordinated phen and water molecule in the second coordination sphere were found. We calculated all possible types of CH…O interaction energies at DLPNO-CCSDT/CBS level for non-coordinated and coordinated phen with a water molecule. The data for non-coordinated phen exhibited the weakest interactions, from −2.09 to −2.94 kcal/mol. Upon coordination of phen, interactions become stronger. In octahedral cobalt(II) complexes, interaction energies are from −3.37 to −4.35 kcal/mol. With the decrease in the complex coordination number, interaction energies become stronger, the strongest are for square planar palladium(II) complexes from −3.91 to −4.94 kcal/mol. There is a linear correlation between interaction energies and electrostatic potential values at the interacting hydrogen atom, with a correlation coefficient of 0.97. For all studied systems, the weakest is always a linear interaction, and the strongest is a bifurcated interaction. The strongest calculated CH…O interactions of coordinated phen with water in the second coordination sphere (−4.94 kcal/mol) are as strong as the hydrogen bond between two water molecules (−5.0 kcal/mol).