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    Chromone-based Schiff base metal complexes as catalysts for catechol oxidation: Synthesis, kinetics and electrochemical studies
    (Pergamon-Elsevier Science Ltd, 2017) Beyazit, Neslihan; Cakmak, Didem; Demetgul, Cahit
    Two new Schiff base ligands with chromone moiety and their transition metal complexes were synthesized and characterized by elemental analyses, magnetic susceptibility, molar conductance and TGA analyses, FT IR, UV-Vis, NMR and mass spectroscopy. All the complexes synthesized have been investigated as functional models for catechol oxidase (catecholase) activity by employing 3,5-di-tert-butylcatechol as a model substrate. The two mononuclear copper(II) and two mononuclear iron(II) complexes show catecholase activity with turnover (k(cat)) numbers lying in the range 27.2-1328.4 h(-1). According to the kinetic measurement results, the rate of catechol oxidation follows first order kinetics and iron(II) complexes were found to have higher catalytic activity than those of copper(II) complexes. Electron donating substituent on Schiff base ligand enhanced the catalytic activity of metal complexes while the electron-withdrawing substituent led to a decrease in activity. The electrochemical properties of two Schiff bases and their metal complexes were also investigated by Cyclic Voltammetry (CV) using glassy carbon electrode (GCE) at various scan rates. Electrochemical processes of all the compounds were observed as irreversible. (C) 2017 Elsevier Ltd. All rights reserved.
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    Electrochemical synthesis and characterization of poly (o-amino benzyl alcohol) and poly (o-amino benzyl alcohol-co-o-anisidine)
    (Wiley, 2021) Yalcinkaya, Suleyman; Cakmak, Didem; Seymen, Kubra; Demetgul, Cahit
    In this study; poly (o-amino benzyl alcohol) and poly (o-amino benzyl alcohol-co-o-anisidine) copolymer films were electrochemically synthesized by cyclic voltammetry technique on the platinum electrode. The synthesis of copolymer films was achieved in various monomers feed ratio (o-amino benzyl alcohol: o-anisidine; 8:2, 1:1, 2:8) of o-amino benzyl alcohol and o-anisidine. Different solution types were tested in aqueous and non-aqueous media, especially during the synthesis process, as the electrolyte medium. As a result of the experiments, it was determined that sulfuric acid solution was the most suitable solution for both homopolymer and copolymer film growth. Homopolymer and copolymer samples were characterized by FT-IR, cyclic voltammetry (CV), SEM, digital images and TGA/DTA techniques. The CV, SEM and digital images results indicated that the solution which has high ratio of monomer is more effective in copolymer film synthesis mechanism. TGA results showed that the 1:1 copolymer film had higher thermal stability than the films at other monomer ratios. Also, electrochemical studies exhibited that the copolymer film in 1:1 ratio is partially more electrochemically stable than other copolymer films.
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    Electrochemical synthesis of poly(pyrrole-co-o-anisidine)/chitosan composite films
    (Elsevier Science Bv, 2017) Yalcinkaya, Suleyman; Cakmak, Didem
    In this study, poly(pyrrole-co-o-anisidine)/chitosan composite films were electrochemically synthesized in various monomers feed ratio (pyrrole: o-anisidine; 9:1, 7:3,1:1, 3:7 and 1:9) of pyrrole and o-anisidine on the platinum electrode. Electrochemical synthesis of the composite films was carried out via cyclic voltammetry technique. They were characterized by FT-IR, cyclic voltammetry, SEM micrographs, digital images, TGA and DSC techniques. The SEM results indicated that the particle size of the composite decreased with increasing o-anisidine ratio and the films became more likely to be smooth morphology. The TGA results proved that the film of the composite with 1:1 ratio showed highest final degradation temperature and lowest weight loss (83%) compared to copolymer and 9:1 1:9 composite films. The 1:1 composite film had higher thermal stability than copolymer and the other composite films (9:1 1:9). Meanwhile, electrochemical studies exhibited that the 1/9 composite film had good electrochemical stability as well. (C) 2017 Elsevier B.V. All rights reserved.
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    Immobilization of Co II-(N,N?-bis(salicylidene)-2-aminobenzylamine) on Poly(pyrrole-co-o-anisidine)/Chitosan Composite Films: Application to Electrocatalytic Oxidation of Catechol
    (Wiley-V C H Verlag Gmbh, 2021) Yalcinkaya, Suleyman; Cakmak, Didem
    In this study, poly (pyrrole-co-o-anisidine)/chitosan composite (Cs) films were prepared by cyclic voltammetry technique on platinum electrode using different pyrrole and o-anisidine mole ratios. Immobilization process was accomplished in Co-II-(N,N '-bis(salicylidene)-2-aminobenzylamine)(CoL) dissolved 0.15 M acetonitrile-LiClO4 solution by cyclic voltammetry technique at 0.2-2.0 V potential range. Three electrode methods were applied in all electrochemical studies. After immobilization process, the characterizations of the electro catalytic surfaces (Cs-CoL-Pt) were carried out by cyclic voltammetry and SEM images. The SEM images clearly indicated that the [CoL] complex is immobilized onto composite films. The electrocatalytic activity of the modified electrodes on the catechol was investigated using buffer solutions of different pH values. The results of catalytic studies revealed that, pH=10 buffer solution was the optimal solution and 1 : 1 Cs-CoL-Pt electrode was the best electrode for catechol oxidation. In square wave voltammetry measurements using this electrode, two linear working ranges were determined. The linear response ranges for catechol determination were found as 3.0 mu M-6.0 mu M and 16 mu M-80 mu M for the first and the second linear working ranges, respectively, with 1.1 mu M detection limit.
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    Synthesis of salen-type Schiff base metal complexes, electropolymerization on graphite electrode surface and investigation of electrocatalytic effects
    (Elsevier Science Sa, 2018) Cakmak, Didem; Cakran, Sinem; Yalcinkaya, Suleyman; Demetgul, Cahit
    2-Aminobenzylamine-based unsymmetrical salen-type Schiff base and its Cu (II), Ni (II), Co (II) and Fe (III) metal complexes were synthesized and their structures were investigated by various spectroscopic methods. The electropolymerization of the synthesized metal complexes were achieved on the graphite electrode. The electropolymerization process was conducted by cyclic voltammetry (CV) in a 0.15 M LiClO4/Acetonitrile as supporting electrolyte medium. Characterization of the polymer coated electrodes were carried out by CV, SEM, EDX and UV-Vis techniques. The electrocatalytic activities of graphite electrodes modified with Schiff-base metal complex were investigated in the determination of compounds such as Dopamine (DA), Catechol (CC), Cysteine (Cys) and Uric Acid (UA). These studies showed that the salen-type Schiff base-Ni(II)-modified graphite electrode gave the best result in the determination of catechol and dopamine. Square wave voltammetry showed a linear response in the range of 0.09-0.35 mu M and 0.22-0.58 mu M with LoD of 0.03 mu M and 0.06 mu M for CC and DA, respectively.