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    Öğe
    3D Polyoxometalate-Functionalized Graphene Quantum Dots with Mono-Metallic and Bi-Metallic Nanoparticles for Application in Direct Methanol Fuel Cells
    (Electrochemical Soc Inc, 2016) Colak, Alper Tolga; Eren, Tanju; Yola, Mehmet Lutfi; Besli, Erdem; Sahin, Onur; Atar, Necip
    A fuel cell is an electrochemical cell that converts a source fuel into an electrical current. It generates electricity inside a cell through reactions between a fuel and an oxidant, triggered in the presence of an electrolyte. Fuel cells have been attracting more and more attention in recent decades due to high-energy demands, fossil fuel depletions, and environmental pollution throughoutworld. Afacile and cost-effective catalysts have been developed on polyoxometalate (NaPWO) functionalized graphene quantum dots (GQDs) with several mono-metallic and bi-metallic nanoparticles such as platinum nanoparticles (PtNPs), palladium nanoparticles (PdNPs) and platinum-palladium nanoparticles (Pt-PdNPs). The successful synthesis of nanomaterials and the prepared glassy carbon electrode (GCE) surfaces were confirmed by transmission electron microscope (TEM), X-ray photo electron spectroscopy (XPS), scanning electron microscope (SEM), electrochemical impedance spectroscopy (EIS) and X-ray diffraction (XRD) method. According to TEM images, the average particle sizes of PtNPs and PdNPs were found to be approximately 20-30 nm. The Pt-PdNPs/NaPWO/GQDs also exhibited a higher peak current for methanol oxidation than those of comparable PdNPs/NaPWO/GQDs and PtNPs/NaPWO/GQDs, thus providing evidence for its higher electro-catalytic activity. (C) 2016 The Electrochemical Society. All rights reserved.
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    Öğe
    A novel 1D borotungstate polymer: Structure and biologic activity
    (Elsevier, 2026) Cakar, Afife Banu; Cakir, Mucahit Suleyman; Besli, Erdem; Colak, Ferdag; Ica, Tuba; Sahin, Onur; Dikim, Selinsu
    In this study, a novel boron-containing polyoxometalate (BPOM) coordination polymer, Na5[trea]3[BW12O40]& sdot; 3H2O (Compound 1; trea = triethylamine), with a molecular weight of 3329.57 g/mol, was synthesized and comprehensively characterized by elemental analysis, single-crystal X-ray diffraction, NMR and FT-IR spectroscopy. Antimicrobial assays demonstrated that Compound 1 exhibited MIC values ranging from 62.5-1000 mu g/mL (1.88x10-5-3.00x10-4 M) for Gram-positive strains and 3.9-62.5 mu g/mL (1.17x10-6-1.88x10-5 M) for Gram-negative strains. The strongest inhibition was observed against Arcobacter butzleri AB5 with a MIC of 3.9 mu g/mL (1.17x10-6 M) and MBC of 7.18 mu g/mL (2.15x10-6 M). For Staphylococcus aureus ATCC 29213, MIC and MBC were 62.5 mu g/mL (1.88x10-5 M) and 250 mu g/mL (7.51x10-5 M), respectively. For Listeria monocytogenes, MIC values were 250-1000 mu g/mL (7.51x10-5-3.00x10-4 M). Antibiofilm testing using a virulent Escherichia coli wild-type strain revealed a concentration-dependent inhibition, with 72% biofilm reduction at 1000 mu g/mL (3.00x10-4 M) and 60%, 56%, 48%, 37%, and 21% reduction at 500, 250, 125, 62.5 and 31.2 mu g/mL, respectively. Haemolysis assays showed 0% erythrocyte lysis up to 1000 mu g/mL, indicating non-toxic behavior toward red blood cells. DNA interaction experiments using pBR322 plasmid DNA demonstrated no conversion of supercoiled Form Ito nicked (Form II) or linear DNA (Form III) at 1000 mu g/mL (3.00x10-4 M) or 500 mu g/mL (1.50x10-4 M) after 4 h incubation at 37 degrees C, indicating absence of DNA cleavage activity. These data position boron-substituted polyoxometalates as promising antimicrobial and antibiofilm candidates with clearly defined quantitative performance parameters.
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    Öğe
    Sodium salt of boron-substituted first keggin-type polyoxometalate; synthesis, crystal structure and investigation of antimicrobial activities
    (Pergamon-Elsevier Science Ltd, 2025) Besli, Erdem; Colak, Ferdag; Sahin, Onur; Dikim, Selinsu; Colak, Alper Tolga
    This study aims to investigate the antimicrobial activity of the boron-containing polyoxometalate (BPOM) Na7[H1.5BW12O40]center dot 6en (1), synthesized as a single crystal. The structural and thermal properties of this novel BPOM were thoroughly analyzed using FT-IR, TGA, and X-ray diffraction (XRD) techniques. The incorporation of boron into these structures is believed to enhance their antimicrobial properties. The antimicrobial activity of the compound was evaluated against two Gram-positive bacteria (Staphylococcus aureus, Bacillus cereus), three Gramnegative bacteria (Escherichia coli, Legionella spp., Legionella pneumophila sg 2-15), and a yeast (Candida albicans) using disc diffusion and tube dilution (Minimal Inhibition Concentration) methods. The results demonstrated that the synthesized compound exhibited significant antimicrobial activity, particularly against Bacillus cereus (Gram-positive) and Legionella spp. and Legionella pneumophila sg 2-15 (Gram-negative).