Cobalt Coordination Complexes Research Articles

A cobalt coordination complex binds on a unique binding site between domain-I and domain-III of serum albumin

Serum albumin binding influences physiological effects and pharmacokinetics of drugs. Major binding sites in serum albumin are sudlow sites I and II, located on domains IIA and IIIA, respectively. However, groove between domain I and III as a binding site is not well studied. In this work, we studied the binding of a cobalt coordination complex (DCoP) with bovine serum albumin (BSA) using multi-spectroscopic methods and molecular docking. DCoP strongly interacts with BSA with association constant of ∼7 × 105M−1. The binding was found to significantly alter protein's conformation and unfolding pathway. Results of this study shows that DCoP binds at the groove formed between domains III and I. We conclude that the groove is a rare binding site for large molecules and coordination complexes. The knowledge of unique binding site of serum albumin enlightens the comprehensive role of protein as a carrier biomacromolecule.

Anti-Cancer Stem Cell Cobalt(III)-Polypyridyl Complexes Containing Salicylic Acid

Metal-containing compounds are an important class of chemotherapeutics used to treat various manifestations of cancer. Despite the widespread clinical use and success of metallopharmaceuticals, they are ineffective towards a sub-population of tumours called cancer stem cells (CSCs). CSCs evade current chemotherapeutic regimens (including metallopharmaceuticals) and promote cancer relapse and metastasis. Here, we report the synthesis, characterisation and anti-breast CSCs properties of a series of cobalt(III)-polypyridyl complexes with salicylic acid. The lead cobalt(III) complex 6 (containing 3,4,7,8-tetramethyl-1,10-phenanthroline) displayed low micromolar potency towards breast CSCs, significantly lower than the gold-standard anti-breast CSC agent, salinomycin, and the clinically used metallodrug, cisplatin. Mechanistic studies indicate that the cobalt(III) complex 6 induces its anti-breast CSC effect by entering breast CSCs, penetrating the nuclei, damaging nuclear DNA and triggering caspase-dependent apoptosis. The cytotoxic mechanism of action of the cobalt(III) complex 6 is also dependent on the modulation of cyclooxygenase-2 (COX-2) expression. This work highlights the anti-breast CSC properties of cobalt(III) coordination complexes with non-steroidal anti-inflammatory drugs (NSAIDs) and more widely spotlights the importance of metallopharmaceuticals in the development of new anticancer agents that can tackle chemotherapeutic-resistant sub-populations.

New cobalt(II) coordination complex for adsorption of Rhodamine B dye and its mechanistic pathway

A new mixed-ligand cobalt complex with the general formula [Co(H2O)(teaH3)(4-NBA)]·(4-NBA)·H2O (1), where (teaH3 = triethanolamine and 4-NBA = 4-nitrobenzoate), has been successfully synthesized and characterized. In this complex, triethanolamine acts as a tetradentate ligand and the 4-NBA act as monodentate ligands. The cobalt metal ion in the complex has a coordination number of 6 with a slightly distorted octahedral geometry. Furthermore, some intramolecular and intermolecular interactions have been observed in 1. Moreover, the kinetic studies on the rate of adsorption confirm that the Pseudo Second Order model accurately predicted the absorption of RhB by the complex. The higher R-squared value and the close agreement between the calculated (Qe = 207.3 mg/g) and experimental (194.4 mg/g) values indicate a satisfactory match. The hydrogen bonding interactions and other weaker electrostatic interactions between the complex and the RhB molecule enhance this adsorption.

Synthesis, Structural Analysis, Theoretical Calculations, In Silico Prediction of Antibacterial Efficacy, Toxicity Assessment, In Vitro Antioxidant Evaluation and Polymerization Activity of Cobalt(II) Coordination Complexes of Para-biphenylol

Synthesis, Structural Analysis, Theoretical Calculations, In Silico Prediction of Antibacterial Efficacy, Toxicity Assessment, In Vitro Antioxidant Evaluation and Polymerization Activity of Cobalt(II) Coordination Complexes of Para-biphenylol

Thermochromism: Theory Directed Design of a Thermochromic Thermometer

The dissolution of cobalt(II) chloride in an appropriate binary alcohol solvent yields an equilibrium mixture, consisting of the differently colored octahedral (pink in color) and tetrahedral (blue in color) cobalt(II) coordination complexes, which can exhibit a brilliant and reversible pink-to-blue color transition over a ∼10 °C window─i.e., function as a thermochromic thermometer─where the dynamic equilibrium is described by CoCl2(R1OH)4+2R2OH⇄CoCl2(R2OH)2+4R1OH. In this experiment, students are challenged to exploit the principles of equilibrium in order to exhibit control over the chemical system and design, model, and implement a thermochromic thermometer which, when correctly prepared, exhibits a specifically targeted composition and color at a unique temperature assigned to each student. By employing fundamental principles of physical chemistry in conjunction with spectrophotometric analysis, students quantify pertinent thermodynamic parameters for the chemical system, and then use them to predictively model/calculate (via Excel) the exact initial composition required to enable the specifically desired equilibrium composition and color to emerge at precisely the target temperature. Completely directed by their modeled prescriptions, students then validate their theoretical predictions by implementing the functional thermochromic thermometer in the laboratory.

Investigation of Cobalt(III) Cage Complexes as Inhibitors of the Mitochondrial Calcium Uniporter.

The mitochondrial calcium uniporter (MCU) mediates uptake of calcium ions (Ca2+) into the mitochondria, a process that is vital for maintaining normal cellular function. Inhibitors of the MCU, the most promising of which are dinuclear ruthenium coordination compounds, have found use as both therapeutic agents and tools for studying the importance of this ion channel. In this study, six Co3+ cage compounds with sarcophagine-like ligands were assessed for their abilities to inhibit MCU-mediated mitochondrial Ca2+ uptake. These complexes were synthesized and characterized according to literature procedures and then investigated in cellular systems for their MCU-inhibitory activities. Among these six compounds, [Co(sen)]3+ (3, sen = 5-(4-amino-2-azabutyl)-5-methyl-3,7-diaza-1,9-nonanediamine) was identified to be a potent MCU inhibitor, with IC50 values of inhibition of 160 and 180 nM in permeabilized HeLa and HEK293T cells, respectively. Furthermore, the cellular uptake of compound 3 was determined, revealing moderate accumulation in cells. Most notably, 3 was demonstrated to operate in intact cells as an MCU inhibitor. Collectively, this work presents the viability of using cobalt coordination complexes as MCU inhibitors, providing a new direction for researchers to investigate in future studies.

A trinuclear cobalt coordination complex constructed using novel triazine ligandsviaone-pot green synthesis: structural properties and biological evaluation

A triazine-based trinuclear cobalt complex, synthesisedviaa one-pot green synthesis process, exhibits unique structural behaviours and excellent biological activities.

Nickel and cobalt coordination complexes: Magnetic investigations and application values on acute pancreatitis combined with abdominal infection

Two novel coordination complexes, namely, [Ni2(TPT)2(H2O)2] (1) and [Co(TPT)(H2O)2]n (2), based on the 3-(tetrazol-5-yl)-5-(pyrid-2-yl)-1,2,4-triazole ligand were produced by solvothermal synthesis. Magnetic studies showed that between adjacent metal ions, anti-ferromagnetic coupling existed in complexes 1 and 2. The complexes’ application values against catecholamine vasoactive drug-induced acute pancreatitis complicated with abdominal infection was discussed. Subsequently, the mechanism was investigated. ELISA analysis was initially used to identify the inflammatory-response levels in acute pancreatitis complicated with abdominal infection after treatment with the complex. Additionally, the C-reactive protein content of plasma was tested through the immuno-projection turbidimetric approach.

Trends and progress in application of cobalt-based materials in catalytic, electrocatalytic, photocatalytic, and photoelectrocatalytic water splitting.

There has been a growing interest in water oxidation in recent two decades. Along with that, remarkable discovery of formation of a mysterious catalyst layer upon application of an anodic potential of 1.13V vs. standard hydrogen electrode (SHE) to an inert indium tin oxide electrode immersed in phosphate buffer containing Co(II) ions by Nocera et.al, has greatly attracted researchers interest. These researches have oriented in two directions; one focuses on obtaining better understanding of the reported mysterious catalyst layer, further modification, and improved performance, and the second approach is about designing coordination complexes of cobalt and investigating their properties toward the application in water splitting. Although there have been critical debates on true catalysts that are responsible for water oxidation in homogeneous systems of coordination complexes of cobalt, and the case is not totally closed, in this short review, our focus will be mainly on recent major progress and developments in the design and the application of cobalt oxide-based materials in catalytic, electrocatalytic, photocatalytic, and photoelectrocatalytic water oxidation reaction, which have been reported since pioneering report of Nocera in 2008 (Kanan Matthew and Nocera Daniel in Science 321:1072-1075, 2008).

The First Dimeric Derivatives of the Glycopeptide Antibiotic Teicoplanin.

Various dimeric derivatives of the glycopeptide antibiotic teicoplanin were prepared with the aim of increasing the activity of the parent compound against glycopeptide-resistant bacteria, primarily vancomycin-resistant enterococci. Starting from teicoplanin, four covalent dimers were prepared in two orientations, using an α,ω-bis-isothiocyanate linker. Formation of a dimeric cobalt coordination complex of an N-terminal L-histidyl derivative of teicoplanin pseudoaglycone has been detected and its antibacterial activity evaluated. The Co(III)-induced dimerization of the histidyl derivative was demonstrated by DOSY experiments. Both the covalent and the complex dimeric derivatives showed high activity against VanA teicoplanin-resistant enterococci, but their activity against other tested bacterial strains did not exceed that of the monomeric compounds.

Two state "ON-OFF" NLO switch based on coordination complexes of iron and cobalt containing isomeric ligand: a DFT study.

Coordination complexes are interesting materials for nonlinear optical (NLO) applications due to their large hyperpolarizability values. Moreover, switchable NLO response is also important in coordination complexes. Herein, we report two state ON–OFF switchable NLO contrast of coordination complexes of Fe and Co containing isomeric ligands. The optical, UV-visible, and electronic properties besides the “ON–OFF” switching effect are calculated using the CAM-B3LYP/6-31+G (d) method. The NLO responses of ligand–metal isomers are qualitatively evaluated through variation in charge transference (CT) style through TD-DFT. The higher βo in each isomeric pair is strongly dependent on the HOMO–LUMO gap. The isomer 4b with lowest HOMO–LUMO gap shows the highest NLO response. The charge transfer pattern in these complexes results in variation of their βo values. The notable βo contrast of 21.15 in isomeric pairs 3a and 3b makes these complexes a favorable material for genuine NLO switches. Hence, the outcome of the current investigation reveals that these ligand–metal isomeric complexes exhibit a two-state switch “ON–OFF” effect.

Leveraging coordination chemistry in the design of bipolar energy storage materials for redox flow batteries

A new cobalt(ii) coordination complex, with two widely separated cobalt-centred redox processes, has been prepared and investigated as an energy storage material for bipolar redox flow batteries.

Antibacterial Activity of Co(III) Complexes with Diamine Chelate Ligands against a Broad Spectrum of Bacteria with a DNA Interaction Mechanism.

Cobalt coordination complexes are very attractive compounds for their therapeutic uses as antiviral, antibacterial, antifungal, antiparasitic, or antitumor agents. Two Co(III) complexes with diamine chelate ligands ([CoCl2(dap)2]Cl (1) and [CoCl2(en)2]Cl (2)) (where dap = 1,3-diaminopropane, en = ethylenediamine) were synthesized and characterized by elemental analysis, an ATR technique, and a scan method and sequentially tested against Gram-positive and Gram-negative bacteria. The minimum inhibitory concentration results revealed that anaerobic and microaerophilic bacteria were found to be the most sensitive; the serial passages assay presented insignificant increases in bacterial resistance to both compounds after 20 passages. The synergy assay showed a significant reduction in the MIC values of nalidixic acid when combined with Compounds (1) or (2). The assessment of cell damage by the complexes was performed using scanning electron microscopy, transmission electron microscopy, and confocal microscopy, which indicated cell membrane permeability, deformation, and altered cell morphology. DNA interaction studies of the Co(III) complexes with plasmid pBR322 using spectrophotometric titration methods revealed that the interaction between Complex (1) or (2) and DNA suggested an electrostatic and intercalative mode of binding, respectively. Furthermore, the DNA cleavage ability of compounds by agarose gel electrophoresis showed nuclease activity for both complexes. The results suggest that the effect of the tested compounds against bacteria can be complex.

Iron(III), cobalt(II) and zinc(II) coordination compounds with a carboximidamide ligand: Synthesis, structures and properties

Coordination complexes of iron(III), cobalt(II) and zinc(II) with the ligand N′-{[1-(pyridin-2-yl)ethylidene]amino}pyridine-2-carboximidamide (pmhpa) have been synthesised and were structurally characterized by elemental analysis, mass spectrometry, X-ray diffraction and infrared spectroscopy. The mononuclear iron(III) complex, [Fe(pmhap)2][FeCl4], (1), adopts the orthorhombic non-centric space group P212121. The iron is present in an octahedral environment in the ion [Fe(pmhap)2]+. The crystallographically-determined formula of the cobalt(II) complex (2) is [Co2(pmhap)2Cl3]2[CoCl4].4MeOH. The compound crystallizes in the non-centric space group P4̄21c with a single cobalt ion in the asymmetric unit. The complex is dinuclear, with two cobalt ions bridged by chloride and the two nitrogen atoms of N=N of the pmhap ligand. The zinc(II) complex; [Zn2(pmhpa)3](NO3)4.2.75MeOH (3) crystallizes in the cubic space group Pa3̄ with disordered methanol molecules present. This is dinuclear with the two zinc atoms being bridged by three N=N links from the ligand to form a threefold symmetric rotor. Infrared spectroscopy confirms that coordination occurs through the azide bridge. Measurements of magnetic susceptibility for the iron(III) and cobalt(II) complexes show that they are paramagnetic between 5 and 300 K. Mössbauer spectroscopic data supports the structure of the iron(III) complex being composed of an octahedral and a tetrahedral iron atom.

Organic Salts as p-Type Dopants for Efficient LiTFSI-Free Perovskite Solar Cells.

Despite the ubiquity and importance of organic hole-transport materials in photovoltaic devices, their intrinsic low conductivity remains a drawback. Thus, chemical doping is an indispensable solution to this drawback and is essentially always required. The most widely used p-type dopant, FK209, is a cobalt coordination complex. By reducing Co(III) to Co(II), Spiro-OMeTAD becomes partially oxidized, and the film conductivity is initially increased. In order to further increase the conductivity, the hygroscopic co-dopant LiTFSI is typically needed. However, lithium salts are normally quite hygroscopic, and thus, water absorption has been suggested as a significant reason for perovskite degradation and therefore limited device stability. In this work, we report a LiTFSI-free doping process by applying organic salts in relatively high amounts. The film conductivity and morphology have been studied at different doping amounts. The resulting solar cell devices show comparable power conversion efficiencies to those based on conventional LiTFSI-doped Spiro-OMeTAD but show considerably better long-term device stability in an ambient atmosphere.

Three Functionalized Zinc(II)/Cobalt(II) Coordination Complexes Demonstrating Fluorescent Sensing Activities towards Fe3+ Ions and Photocatalytic Selectivity for Organic Dyes

Three new zinc(II)/cobalt(II) coordination complexes [Zn(HBTB)(L)0.5] (1), [Zn(HCPPA)(L)] (2), and [Co(HCPPA)(L)]·2H2O (3) [H3BTB = 1,3,5‐tri(4‐carboxylphenyl)benzene, H3CPPA = 5‐(4‐carboxyl‐phenoxy)‐isophthalic acid, L = N1,N4‐bis(3‐pyridyl)naphthaldiamide] were solvothermally synthesized. The structural characterization reveals that complex 1 represents a 3D coordination framework with a binodal 3,4‐connected {4.102}2{4.105}2 topology constructed from the 2D [Zn(HBTB)]n polymeric double‐layers and the bidentate L ligands. Complex 2 is a 1D metal‐organic chain derived from the dinuclear [Zn2(HCPPA)2] loops and [Zn2(L)2] loops. Complex 3 possesses a binodal 3,5‐connected {42.6}{43.6.84.102} topological 2D layered architecture based on the [Co2(HCPPA)2] ribbon chains and the bidentate L ligands. For 2 and 3, their adjacent chains or layers are respectively stacked into 3D supramolecular architectures via the hydrogen bonds. Moreover, the fluorescent and fluorescent sensing activities towards small solvent molecules of coordination complexes 1 and 2, the photocatalyitc properties of 1–3 towards organic dyes were studied.

Cobalt(II) coordination complex with 2,5-bis(pyridine-2-yl)-1,3,4-thiadiazole and thiocyanate as co-ligand: Synthesis, crystal structure, Hirshfeld surface analysis, spectroscopic, thermal and magnetic properties

The bis(2,5-di(pyridin-2-yl)-1,3,4-thiadiazole-κ2N,N′)-bis(thiocyanato-κ1N)cobalt(II) complex has been synthetized from the reaction of 2,5-bis(pyridin-2-yl)-1,3,4-thiadiazole (L) with metallic salt CoCl2.6H2O and thiocyanate ion (SCN−) as coligand in H2O/CH3CN at room temperature. The synthetized complex (CoL2(SCN)2) has been fully characterized by single crystal X-ray diffraction, Hirshfeld surface analysis, as well as UV–Visible, FTIR, Raman, and NMR spectroscopy. TGA analysis and magnetic measurements were also performed. CoL2(SCN)2 crystallizes in monoclinic symmetry and P 21/c space group with two independent cobalt crystallographic sites, where each cobalt atom is localized in a distorted octahedral environment CoN6, with the thiadiazole molecules (L) as bidentate ligands in equatorial sites and terminal SCN− ions in axial positions. The crystal cohesion is assured by intermolecular hydrogen bonding, C–H⋯π and π–π stacking; in addition to the N–Cu coordination bonds. This has been confirmed by the three dimensional Hirshfeld surface analysis and the two dimensional fingerprint plots that highlight the dominance of intermolecular interactions C⋯H/H⋯C and S⋯H/H⋯S. The thermal analysis of CoL2(SCN)2 reveals that this complex is thermally stable up to 200 °C. Variable-temperature magnetic susceptibility measurements on CoL2(SCN)2 complex indicated an antiferromagnetic exchange between the two non-equivalent cobalt(II) ions with a ferrimagnetic behaviour.

A Fast Transient Absorption Study of Co(AcAc)3

The study of transition metal coordination complexes has played a key role in establishing quantum chemistry concepts such as that of ligand field theory. Furthermore, the study of the dynamics of their excited states is of primary importance in determining the de-excitation path of electrons to tailor the electronic properties required for important technological applications. This work focuses on femtosecond transient absorption spectroscopy of Cobalt tris(acetylacetonate) (Co(AcAc)3) in solution. The fast transient absorption spectroscopy has been employed to study the excited state dynamics after optical excitation. Density functional theory coupled with the polarizable continuum model has been used to characterize the geometries and the electronic states of the solvated ion. The excited states have been calculated using the time dependent density functional theory formalism. The time resolved dynamics of the ligand to metal charge transfer excitation revealed a biphasic behavior with an ultrafast rise time of 0.07 ± 0.04 ps and a decay time of 1.5 ± 0.3 ps, while the ligand field excitations dynamics is characterized by a rise time of 0.07 ± 0.04 ps and a decay time of 1.8 ± 0.3 ps. Time dependent density functional theory calculations of the spin-orbit coupling suggest that the ultrafast rise time can be related to the intersystem crossing from the originally photoexcited state. The picosecond decay is faster than that of similar cobalt coordination complexes and is mainly assigned to internal conversion within the triplet state manifold. The lack of detectable long living states (>5 ps) suggests that non-radiative decay plays an important role in the dynamics of these molecules.

Synthesis, structure, photophysical properties and biological activity of a cobalt(II) coordination complex with 4,4′-bipyridine and porphyrin chelating ligands

A new bioactive material of cobalt(II) with 5,10,15,20-tetrakis[4 (benzoyloxy)phenyl] porphyrin (TPBP) and bpy ligands ([CoII(TPBP)(bpy)2] 1) has been synthesized and characterized by Single-crystal X-ray diffraction (SCXRD), spectroscopic methods and quantum-chemistry calculations. In the crystalline structures of six coordinated Co(II) [CoII(TPBP)(bpy)2] 1, linear 1D polymeric chains were observed in which all the porphyrin units are aligned parallel to each other. The crystal packing is stabilized by inter-and intramolecular C–H⋯O and C–H⋯N hydrogen bonds, and by weak C–H⋯Cg π interactions. Interestingly, NBO–Second-order perturbation theory analysis, carried out at the UB3LYP/6-31G(d)/SDD DFT level of theory, demonstrated that a two-center bond between the nitrogen atoms and the cobalt ions (Co) was not found, the Co–Npy/bp interactions are coming from an electronic delocalization between the Npy/Nbp filled orbitals to the anti-bonding LP*(4) and LP*(5) metal NBOs. Mass spectroscopy, and elemental analysis were also investigated to confirm the molecular structure. The downfield shift and the peak broadening of the axial ligand resonances observed in the 1H NMR indicated the contiguity to the paramagnetic Co(II) center. Additionally, the photophysical properties have been evaluated by UV–visible absorption, and fluorescence emission spectroscopies. Finally, bioactivity investigations revealed that free porphyrin TPBP, CoIITPBP and complex 1 could be used as potential antioxidant agents.

Metal Coordination Complexes as Redox Mediators in Regenerative Dye-Sensitized Solar Cells

Dye-sensitized solar cells (DSSCs) have attracted a substantial interest in the last 30 years for the conversion of solar power to electricity. An important component is the redox mediator effecting the transport of charge between the photoelectrode and the dark counter electrode (CE). Among the possible mediators, metal coordination complexes play a prominent role and at present are incorporated in several types of devices with a power conversion efficiency exceeding 10%. The present review, after a brief introduction to the operation of DSSCs, discusses at first the requirements for a successful mediator. Subsequently, the properties of various classes of inorganic coordination complexes functioning as mediators relevant to DSSC operation are presented and the operational characteristics of DSSC devices analyzed. Particular emphasis is paid to the two main classes of efficient redox mediators, the coordination complexes of cobalt and copper; however other less efficient but promising classes of mediators, notably complexes of iron, nickel, manganese and vanadium, are also presented.