Search Results (203)

Countries like Saudi Arabia receive abundant sunshine with exceptionally high solar irradiance. High temperatures in desert regions and the sunray angle dependence of solar modules are some of the key challenges of conventional solar cells. Dye-sensitized solar cells present a compelling alternative with the simple cell design and use of non-toxic materials without angle dependence, but their performance hinges on the solid redox mediators used for dye regeneration. These mediators must have an electrical conductivity (σ_25°C) of more than 10⁻⁴ S cm⁻¹ with an activation energy of less than 0.3 eV for device application. Our work focused on novel solid Co(II/III) redox mediators using cobalt complexes and LiClO₄ in different matrices: pure PEO (an abbreviation for poly(ethylene oxide) with its redox mediator as M1), a [PEO–SN] blend (M2A and M2B with ethylene oxide to lithium ions molar ratio of 112.9 and 225.8, respectively), and pure SN (an abbreviation for succinonitrile with its redox mediator as M3). Impedance spectroscopy was the key technique, showing M1 and M2 behave like a mediator explainable with an (R₁–C)-type circuit, while M3 is explainable with an (R₁ − [R₂‖C])-type circuit. M3 achieved the highest value of σ_25°C with 2 × 10⁻³ S cm⁻¹, while M1 had the lowest σ_25°C, 3 × 10⁻⁵ S cm⁻¹. M2 achieved an optimal balance with σ_25°C of 4 × 10⁻⁴ S cm⁻¹ (M2A) and 1.5 × 10⁻⁴ S cm⁻¹ (M2B). M2 exhibited a remarkably low pseudo-activation energy of 0.042 eV and a Vogel–Tammann–Fulcher behavior ideal for consistent performance across temperatures. In contrast, M1 and M3 showed higher Arrhenius-type activation energies (>0.74 eV) in their solid states. These results correlated with those of the XRD, FT-IR spectroscopy, XPS, SEM, DSC, and TGA analyses. Ultimately, the [PEO–SN] blend emerges as a robust matrix, enabling the combination of high conductivity and low activation energy needed for a durable device in harsh environments. Full article

The urgent need for effective therapies against cancer and antimicrobial-resistant pathogens motivates the development of novel metal-based complexes. Herein, we report the synthesis and characterization of four novel cobalt(II) complexes with biologically relevant β-diketo ester ligands. The complexes were characterized via UV-Vis, FTIR, mass spectrometry, and elemental analysis. Their biological activities were evaluated through antimicrobial and cytotoxic assays. Complex B1 exhibited the strongest antimicrobial activity, with minimum inhibitory concentrations (MICs) of 0.23 mg/mL against Staphylococcus aureus and Proteus mirabilis, and 0.01 mg/mL against Mucor mucedo, exceeding the performance of ketoconazole. Cytotoxicity studies on SW480 colorectal cancer cells and HaCaT normal keratinocytes identified B3 as the most potent anticancer agent (IC₅₀ = 11.49 µM), selectively targeting tumor cells. Morphological analysis indicated apoptosis as the primary mode of cell death. Mechanistic studies were performed to elucidate interactions with biomolecules. UV-Vis and fluorescence spectroscopy, viscosity measurements, and molecular docking revealed that B3 binds strongly to calf thymus DNA via hydrophobic interactions and groove binding, and exhibits selective binding to bovine serum albumin (site II, subdomain IIIA). These results highlight the potential of cobalt(II) complexes as multifunctional agents with significant antimicrobial and antitumor activities and provide detailed insight into their molecular interactions with DNA and serum proteins. Full article

This study investigates the synthesis and potential applications of the coordination compound cobalt(III) complex tris[N-(prop-2-en-1-yl)hydrazinecarbothioamide]-cobalt(III) chloride ([Co(Tsc)₃]Cl₃). The complex has been synthesized via the reaction of cobalt(II) chloride hexahydrate with N-(prop-2-en-1-yl)hydrazinecarbothioamide in ethanol. Its antioxidant activity has been evaluated using 2,2′-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid (ABTS) assay, demonstrating a significant effect with an IC₅₀ of 7.3 µmol/L. Toxicity evaluations using Daphnia magna showed a low half maximal inhibitory concentration (LC₅₀) of 56.3 µmol/L. Experimental results have showed that [Co(Tsc)₃]Cl₃ significantly elevated the total antioxidant status (TAS) of the hemolymph of honeybees and larvae, increasing it by 5 and 8 times, respectively. The IC₅₀ values for antioxidant activity were 2.5 mg/mL in bee hemolymph and 1.3 mg/mL in larval hemolymph, notably lower than control values of 13.6 mg/mL and 10.0 mg/mL. The stimulatory effect of the coordination compound [Co(Tsc)₃]Cl₃ on TAS was five times higher than that of vitamin C. Additionally, [Co(Tsc)₃]Cl₃ exhibited acaricidal properties, effectively inhibiting Varroa destructor with an lethal concentration (LC₅₀) of 0.2 µmol/L. These findings indicate that this cobalt complex could serve both a natural antioxidant and an effective acaricide, offering a promising approach to improv bee health and sustainability in apiculture. Full article

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). Full article

The reaction of CoCl₂ · 6H₂O with 6-chloro-2-hydroxypyridine (Hchp) and 1,10-phenanthroline (phen) afforded the complex [Co(chp)₂(phen)] (1). Although this complex has been previously reported, it was obtained in this work under mild conditions (in acetonitrile at room temperature) and characterized for the first time by single-crystal X-ray diffraction. The use of Co(F₃CCOO)₂ · 4H₂O under similar conditions yielded a new trinuclear molecular complex [Co₃(chp)₂(F₃CCOO)₄(phen)₂] (2). According to X-ray diffraction data, the cobalt(II) ions in complexes 1 and 2 are located in an octahedral environment (coordination number CN_Co = 6). As an ambidentate ligand, Hchp exhibits different types of coordination modes in the resulting complexes 1 and 2. Additional stabilization of molecules in the crystal is achieved by π-π stacking between aromatic systems of coordinated phen ligands. The cytotoxic activity of 1 and [CoCl₂(phen)₂] · 1.5MeCN (3) against a panel of human cancer cell lines (SKBR3, HCT116, A549) and normal dermal fibroblasts (HDF) was evaluated using the MTT assay. Complex 3 demonstrated cytotoxic activity against the HCT116 cell line comparable to that of cisplatin, indicating its potential as a promising antitumor agent. Full article

Laminated polymer composites have emerged as a promising class of materials that provide exceptional mechanical and functional properties owing to multilayered architectures. In addition, additive manufacturing (AM) offers boundless opportunities to fabricate complex and intricate geometries with a wide variety of materials. Utilizing AM processes for producing laminated polymer composites can open new pathways for producing these intricate structures with fine control over geometry, layer thickness, and material distribution. In this study, we demonstrate the use of the stereolithography (SLA) process to fabricate laminated polymer composites to overcome the limitations of extrusion-based AM processes, i.e., challenges in high precision, strong interlayer bonding and uniform particle distribution. Photocurable polymer composites were prepared by adding different reinforcing particles, i.e., cobalt iron oxide (CoFe₂O₄), graphene (G), magnesium (Mg) and iron (II,III) oxide (Fe₃O₄), into the photocurable resin. Ultrasonication and mechanical mixing processes were used to prepare stable photocurable composites suitable for the SLA process. SLA process was also optimized, varying the process parameters (exposure time, bottom exposure time and bottom layer count) to achieve optimum dimensional accuracy and surface quality. Microscopic analysis confirmed the distinct and well-adhered composite layer sandwiched between the unfilled resin, validating the structural integrity of the multilayer design. Mechanical testing revealed significant improvement in the tensile properties of the laminated composites compared to pure resin, with resin/CoFe₂O₄ exhibiting 35.6% and 50.1% improvement in tensile strength and Young’s modulus compared to the pure resin, respectively. These results highlight the feasibility of SLA for producing multilayered polymer composites with improved mechanical performance and controlled architecture, broadening its potential for advanced engineering and biomedical applications. Full article

A series of five cobalt(II) complexes, dichloro-bis(1-benzyl-benzimidazole)-cobalt(II) (1a), dichloro-bis[1-(4-fluorobenzyl)-benzimidazole]-cobalt(II) (1b), dichloro-bis((Z)-1-styryl-benzimidazole)-cobalt(II) (1c), dichloro-bis[(Z)-1-(2-fluorostyryl)-benzimidazole]-cobalt(II) (1d) and dichloro-bis(1-cinnamyl-benzimidazole)-cobalt(II) (1e), were evaluated in ethylene dimerization. Four of these complexes were described for the first time and fully characterized by IR, elemental analysis, mass and NMR spectroscopy. In the solid state, the cobalt atom exhibited a typical tetrahedral geometry and was found to be coordinated to two chlorine atoms and two benzimidazole rings. In the presence of 20 bar of ethylene and diethylaluminium chloride as a co-catalyst, the complex with styryl substituents on the benzimidazole rings, complex 1c, exhibited the highest activity with a turnover frequency of 3430 mol(ethylene)·mol(Co)⁻¹·h⁻¹. Full article

The reaction of 4′–bromo-fenamic acid, a bromo-derivative of fenamic acid (the scaffold of the fenamate non-steroidal anti-inflammatory drugs), with Co(II) in the absence or presence of various nitrogen-donor ligands yielded nine novel, neutral mononuclear Co(II) complexes. These complexes were characterized by physicochemical and spectroscopic techniques and single-crystal X-ray crystallography. The biological evaluation of the compounds focused on their antioxidant and antimicrobial efficacy, as well as their interaction with calf-thymus DNA, pBR322 plasmid DNA (in the absence or presence of diverse irradiations) and serum albumins. The complexes have shown significant antioxidant activity since they can scavenge 2,2′-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid) radicals (up to 96.48 ± 0.07%) and reduce H₂O₂ (up to 96.93 ± 0.53%). Antimicrobial testing revealed that the complexes were more active than free 4′-bromo-fenamic acid with four of them classified as bactericidal agents against selected bacterial strains. The compounds can interact with calf-thymus DNA via intercalation, and the calculated DNA-binding constants are on the 10⁶ M⁻¹ order. The plasmid DNA-cleavage ability of the compounds is strongly enhanced under UVA irradiation (photocleavage > 90%). In addition, the compounds can bind tightly and reversibly to serum albumins with binding constants in the 10⁵ M⁻¹ range. Full article

This research prepared and characterised novel mixed coordination complexes derived from escitalopram with eugenol and curcumin to form (L₁) and (L₂), respectively. The complexes were prepared via Williamson ether synthesis and analysed by FTIR, UV–Vis, ¹H-NMR spectroscopy, elemental analysis, molar conductivity, and magnetic susceptibility. The results confirmed their octahedral geometries. Magnetic investigation reported high-spin configurations for Mn(II), Co(II), and Ni(II) complexes, whereas Cu(II) exhibited a distorted octahedral arrangement with characteristic d–d transitions. In addition, the calculation of Density functional theory (DFT) provided more insight into the detailed structural and electronic properties of the new ligand and its complexes. Antimicrobial compounds were evaluated against Escherichia coli, Staphylococcus aureus, and Candida albicans through the agar well diffusion method. The reported results revealed that Cobalt complexes showed antimicrobial activity followed by Copper (Cu), Nickel (Ni) and Manganese(Mn) complexes, respectively, due to an increase in Co-lipophilicity, which leads to improved diffusion through microbial cell membranes. The research findings confirmed that escitalopram-based mixed ligands coordinate with transition metals and could have significant biological applications. Full article

A series of cobalt(II) dicyanamide (dca⁻) coordination polymers with substituted pyrazines (pyz) and pyrimidines (pym) as auxiliary ligands have been synthesized and structurally characterized to investigate the influence of the type and substitution pattern of the auxiliary ligand on the dimensionality and topology of the resulting frameworks. As a result of our studies, 13 novel heteroleptic cobalt(II) dicyanamide coordination polymers were obtained, and their crystal structures were determined by single-crystal X-ray diffraction. Eight of the investigated compounds exhibit a single-chain structure composed of [Co(L_pyz/_pym)₂]²⁺ units bridged via double μ_1,5–dca ligands. In two complexes, neutral triple-chain topologies were observed, in which double μ_1,5– and single μ_1,3,5–dca bridges connect two crystallographically independent cobalt(II) ions, both being six-coordinate in tetragonally elongated octahedral environments. Two- and three-dimensional architectures were confirmed only in the case of Co(II) compounds with 2,6–Me₂pyz and 4-NH₂-pym co-ligand, respectively The cobalt(II) complexes described herein have also been compared with dicyanamide-based cobalt(II) systems incorporating pyrazine- and pyrimidine-like ligands. These structural relationships are of high significance for the rational design and synthesis of heteroleptic cobalt(II) dicyanamide systems. Full article

The aim of this paper is to obtain ethyl (2-(methylcarbamoyl)phenyl)carbamate and its metal complexes as promising antimicrobial agents. The title compound was synthesized using the ring-opening of isatoic anhydride with methylamine and further acylation with ethyl chloroformate. All metal complexes were successfully obtained after mixing the ligand dissolved in DMSO and water solutions of the corresponding metal salts and sodium hydroxide, in a metal-to-ligand-to base ratio 1:2:2. As a result, mixed ligand complexes of ethyl 2-(methylcarbamoyl)phenyl)carbamate and 3-methylquinazoline-2,4(1H,3H)-dione were obtained. The obtained complexes were characterized by their melting points, FTIR, NMR spectroscopy, and MP-AES. Then, the antimicrobial effect of the compounds against both Gram-negative and Gram-positive bacteria, yeasts, and fungi was studied. Only the Co(II) complex showed antimicrobial activity against almost all Gram-positive and Gram-negative bacteria. The cobalt complex exhibited promising antimicrobial activity against Gram-positive Micrococcus luteus with inhibition zones of 20 mm, Listeria monocytogenes (15 mm), Staphylococcus aureus (13 mm), as well as Gram-negative Klebsiella pneumoniae (13 mm) and Proteus vulgaris (13 mm). Given the potential of metal complexes as antimicrobial agents, understanding their cytotoxic effects is crucial for evaluating their therapeutic safety. To assess the in vitro biocompatibility of the experimental compounds, a range of cell viability assays was conducted using human malignant leukemic cell lines (LAMA-84, K-562) and normal murine fibroblast cells (CCL-1). The Ni(II) complex shows IC₅₀ = 105.1 µM against human malignant leukemic cell lines LAMA-84. Based on the reported results, it may be concluded that the mixed cobalt complex of 2-(methylcarbamoyl)phenyl)carbamate and 3-methylquinazoline-2,4(1H,3H)-dione can be attributed as a promising antimicrobial agent. Future in vivo tests will contribute to establishing the antimicrobial properties of this complex. Full article

The ability of earth-abundant metals to serve as catalysts for the oxygen reduction reaction is of increasing importance given the prominence of this reaction in several emerging technologies. It is now recognized that both the primary and secondary coordination environments of these catalysts can be modulated to optimize their performance. In this present work, we describe two Co^II complexes [Co^II(PaPy₂Q)](OTf) (1) and [Co^II(PaPy₂N)](OTf) (2) that catalyze chemical and electrochemical dioxygen reduction. Both 1 and 2 contain Co^II centers in a N₅⁻ coordination environment, but 2 has a naphthyridine group that places a nitrogen atom in the secondary coordination sphere. Solid-state X-ray crystallography and solution-state spectroscopic measurements reveal that, apart from this second-sphere nitrogen in 2, complexes 1 and 2 have essentially identical properties. Despite these similarities, 2 performs the chemical reduction of dioxygen ~10-fold more rapidly than 1. In addition, 2 has an enhanced performance in the electrochemical reduction of dioxygen compared to 1. Both complexes yield a significant amount of H₂O₂ in the chemical reduction of dioxygen (>25%). The enhanced catalytic performance of 2 is attributed to the presence of the second-sphere nitrogen atom, which might enable the efficient protonation of cobalt–oxygen intermediates formed during turnover. Full article

We report an investigation on the cobalt(II) chelation mechanism by a modified α-maltoside ligand 9 decorated with two iminodiacetate (IDA) residues on C6,C6′ positions. Herein we uncovered the capacity of this biodegradable ligand to chelate cobalt(II), an ionic metal contaminant in the environment that is used, in particular, in lithium-ion batteries. The interactions between cobalt(II) and synthesized ligand 9 were systematically studied using different analytical methods such as ¹H and ¹³C NMR, potentiometry, spectrophotometry, ITC, and ICP-AES. We observed a high affinity for the 1:1 complex, one cobalt(II) associated with two iminodiacetate groups, which is 10-fold higher than the 2:1 complex, where each of the two IDA groups interacts alone with a cobalt(II). Taking into account the log β_CoL value obtained (≈12.3) with the stoichiometry 1:1, the strength of this complexation with cobalt(II) can be ranked as follows for the most common ligands: IDA < MIDA < NTA < 9 < EDTA < TTHA < DTPA. We further completed a preliminary remediation test with water contaminated with cobalt(II) and recovered cobalt(II) metal using Chelex^® resin, which allowed a recycling of the synthetic ligand for future recovering experiments. The results shed light on the great potential of using this synthetic ligand as an effective and green remediation tool. Full article

The development of metallic coatings as Ni-Co alloys, with particular emphasis on their homogeneity, processability, and sustainability, is of the utmost significance. To address these challenges, the utilization of phenylsalicylimines (PSIs) as additives within deep eutectic solvents (DES) was investigated, assessing their influence on the electrodeposition process of these metals at an intermediate temperature of 60 °C, while circumventing aqueous reaction conditions. The findings demonstrated that the incorporation of PSIs markedly enhances coating uniformity, resulting in an optimal cobalt content of 37% and an average thickness of 24 µm. Electrochemical evaluations revealed improvements in charge and mass transfer, thereby optimizing process efficiency. Moreover, computational studies confirmed that PSIs form stable complexes with Co (II), modulating the electrochemical characteristics of the system through the introduction of the diethylamino electron-donating group, which significantly stabilizes the coordinated forms with both components of the DES. Additionally, the coatings displayed exceptional corrosion resistance, with a rate of 0.781 µm per year, and achieved an optimal hardness of 38 N HRC, conforming to ASTM B994 standards. This research contributes to the development of electroplating bath designs for metallic coating deposition and lays the groundwork for the advancement of sophisticated technologies in functional coatings that augment corrosion resistance and mechanical properties. Full article

In this study, 3-chlorothiophene-2-carboxylic acid (HL) was used as a main ligand to successfully synthesize four novel complexes: [Cu(L)₂(Py)₂(OH₂)₂] (1), [Co(L)₂(Py)₂(OH₂)₂] (2) (Py = pyridine), [{Ni(L)₂(OH₂)₄}₂{Ni(L)(OH₂)₅}]L•5H₂O (3), and [{Co(L)₂(OH₂)₄}₂{Co(L)(OH₂)₅}]L•5H₂O (4). All four compounds were identified by elemental analysis and ESI mass spectrometry, and subsequently characterized by IR spectroscopy, UV-visible diffuse reflectance spectroscopy, electron paramagnetic resonance spectroscopy, thermogravimetric analysis, single-crystal X-ray crystallography, and cyclic voltammetry. X-ray analyses revealed that complexes 1 and 2 exhibit a centrosymmetric pseudo-octahedral coordination geometry; the copper (II) and cobalt (II) metal ions, respectively, are located at the crystallographic center of inversion. The coordination sphere of the copper (II) complex is axially elongated in accordance with the Jahn–Teller effect. Intriguingly, for charge neutrality, compounds 3 and 4 crystallized as three independent mononuclear octahedrally coordinated metal centers, which are two $\left[\mathrm{M}{\mathrm{L}}_2{\left({\mathrm{O}\mathrm{H}}_2\right)}_4\right]$ complex molecules and one ${\left[\mathrm{M}\mathrm{L}{\left({\mathrm{O}\mathrm{H}}_2\right)}_5\right]}^{+}$ complex cation (M = ${\mathrm{N}\mathrm{i}}^{\mathrm{I}\mathrm{I}}$ and ${\mathrm{C}\mathrm{o}}^{\mathrm{I}\mathrm{I}}$, respectively), with the ligand anion ${\mathrm{L}}^{-}$ serving as the counter ion. The anticancer activities of these complexes were systematically assessed on human leukemia K562 cells, lung cancer A549 cells, liver cancer HepG2 cells, breast cancer MDA-MB-231 cells, and colon cancer SW480 cells. Among them, complex 4 shows significant inhibitory effects on leukemia K562 cells and colon cancer SW480 cells. Full article