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Öğe 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, CahitTwo 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.Öğe Crystal structure of an unsymmetrical Schiff base, immobilization of its cobalt and manganese complexes on a silica support, and catalytic studies(Springer, 2013) Durak, Damla; Delikanli, Anil; Demetgul, Cahit; Kani, Ibrahim; Serin, SelahattinAn unsymmetrical tetradentate Schiff base (H2L) was synthesized by the reaction of 3-methoxysalicylaldehyde, o-phenylenediamine, and salicylaldehyde in EtOH. H2L was characterized by single-crystallographic X-ray analysis. Its Co(II) and Mn(III) complexes ([CoL] and [MnLCl]) were prepared and immobilized on 3-aminopropyltriethoxysilane functionalized silica gel. The immobilized materials were found to be efficient catalysts for epoxidation of styrene in the presence of tert-BuOOH in acetonitrile at 40 A degrees C. The catalysts can be reused several times without significant loss of performance.Öğe 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, CahitIn 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.Öğe Electrochemical synthesis and characterization of polypyrrole/chitosan composite on platinum electrode: Its electrochemical and thermal behaviors(Elsevier Sci Ltd, 2010) Yalcinkaya, Sueleyman; Demetgul, Cahit; Timur, Mahir; Colak, NureddinThe electrochemical polymerization of conducting polymers is a simple and most convenient method for preparation of a film on the metal surface. The polypyrrole/chitosan composite film has been electrochemically synthesized on platinum electrode by using cyclic voltammetry (CV) technique. The synthesis solution was prepared by dissolving of pyrrole and chitosan in aqueous oxalic acid solution. The characterization of this film was done using Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM) and thermal analysis (TG-DTA) techniques. The synthesized composite film was different in aspect of morphology when compared to chitosan and polypyrrole. The TG-DTA results revealed that the composite film had better thermal stability with respect to chitosan. The electrochemical measurement has shown that the composite film is very stable and electroactive. (C) 2009 Elsevier Ltd. All rights reserved.Öğe Electropolymerization of CuII-(N,N?-bis(3-methoxysalicylidene)-2-aminobenzylamine) on platinum electrode: Application to the electrocatalytic reduction of hydrogen peroxide(Elsevier Science Sa, 2011) Deletioglu, Didem; Yalcinkaya, Suleyman; Demetgul, Cahit; Timur, Mahir; Serin, SelahattinThe complex of copper (II) with N,N'-bis(3-methoxysalicylidene)-2-aminobenzylamine (H2L) was synthesized and characterized by elemental analysis, magnetic susceptibility, UV-vis. and FT-IR spectroscopy. The results showed that the tetradentate ligand coordinated to the Cu(II) ion through the azomethine nitrogen and phenolic oxygen atoms. The prepared complex [CuL] was electropolymerized on platinum electrode surface in a 0.1 mol dm(-3) solution of lithium perchlorate in acetonitrile by cyclic voltammetry between 0 and 1.6V vs. Ag/Ag+. Cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), conductance measurements, FT-IR and SEM were used to characterize polymer film of Cu(II) complex. The reduction of hydrogen peroxide on poly[CuL] has been investigated mainly in phosphate buffer medium (pH 7.2), between 0 and -0.8 V versus Ag/Ag+ at a scan rate 0.1 V s(-1). (c) 2011 Elsevier B.V. All rights reserved.Öğe Schiff Base Polymers Obtained by Oxidative Polycondensation and Their Co(II), Mn(II) and Ru(III) Complexes: Synthesis, Characterization and Catalytic Activity in Epoxidation of Styrene(Taylor & Francis Ltd, 2012) Demetgul, Cahit; Delikanli, Anil; Saribiyik, Oguz Yunus; Karakaplan, Muruvvet; Serin, SelahattinIn this paper, Schiff base monomers having double azomethine groups, N,N'-bis(4-hydroxybenzylidene)1, 4-phenylenediamine (M-1) and N,N'-bis(4-hydroxysalicylidene)1,4-phenylenediamine (M-2), were prepared by a common condensation reaction between 4-hydroxybenzaldehyde and 4-hydroxysalicylaldehyde with 1,4-phenylenediamine, respectively. The new Schiff base polymers, poly(N,N'-bis(4-hydroxybenzylidene)1,4-phenylenediamine) (P-1) and poly(N,N'-bis(4-hydroxysalicylidene)1,4-phenylenediamine) (P-2) were synthesized from the oxidative polycondensation of monomers with NaOCl in an aqueous alkaline medium. The characterization of synthesized monomers and polymers was carried out by FT-IR, UV-Vis, H-1-NM, C-13-NMR and elemental analysis. The new polymer-metal complexes were prepared by using polymers and Co(II), Mn(II) and Ru(III) metal salts. Thermal properties of the compounds were studied by TG-DTA techniques. In addition, the catalytic properties of the polymers and their metal complexes were investigated in epoxidation reactions of styrene. The results of the catalysis studies were monitored by GC-MS. (C) Koninklijke Brill NV, Leiden, 2012Öğe Synthesis and characterization of a Schiff base derived from 2-aminobenzylamine and its Cu(II) complex: electropolymerization of the complex on a platinum electrode(Taylor & Francis Ltd, 2010) Demetgul, Cahit; Deletioglu, Didem; Karaca, Filiz; Yalcinkaya, Sueleyman; Timur, Mahir; Serin, SelahattinA precursor (H3A) was synthesized by the mono condensation of 2-aminobenzylamine with salicylaldehyde and then a tetradentade Schiff-base ligand (H2L) prepared by using H3A and 3-methoxysalicylaldehyde. The copper(II) complex of this new ligand was prepared and characterized by elemental analysis, electronic absorption, Fourier transform infrared (FT-IR), and magnetic susceptibility. For the ligand, 1H- and 13C-NMR and liquid chromatography mass spectrometry (LC-MS) spectra were obtained. The tetradentate ligand is coordinated to Cu(II) through the phenolic oxygen and azomethine nitrogen. The use of this metal complex in the preparation of a modified electrode is also described. CuL was electropolymerized on a platinum electrode surface in a 0.1 mol dm-3 solution of lithium perchlorate in acetonitrile by cyclic voltammetry between 0 and 1.6 V versus Ag/Ag+. Electrochemical properties of the electroactive polymeric film have been investigated and a surface confined polymerization mechanism was proposed.Öğe Synthesis and Metal Ion Uptake Studies of Silica Gel-Immobilized Schiff Base Derivatives and Catalytic Behaviors of their Cu(II) Complexes(Jihad Daneshgahi, 2017) Timur, Mahir; Demetgul, CahitNew silica supported Schiff base ligands were prepared by the condensation reaction of 4,6-diacetylresorcinol with silica-gel derivatives, which modified with 3-aminopropyltriethoxysilane and N-(2-aminoethyl) -3-aminopropyltrimethoxysilane. Metal ion uptake capacities of these compounds were studied towards of selected transition metal (Cd(II), Cu(II), Co(II), Mn(II), Pb(II) and Ni(II)) cations in an aqueous medium. In addition, Cu(II) complexes of these ligands were prepared by using heterogeneous reaction conditions. The synthesized compounds were characterized by using elemental analysis, FT-IR, DR-UV-vis., CP/MAS C-13-NMR, AAS, XRD and TGA techniques. Moreover, the morphological and chemical properties of these compounds were investigated by using a scanning electron microscope (SEM) coupled to an energy-dispersive X-ray spectrometer (EDX). The catalytic performances of the Cu(II) complexes were investigated on H2O2 decomposition. These complexes displayed good catalytic activities towards the decomposition of H2O2 as heterogeneous catalysts.Öğe 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, Cahit2-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.Öğe Synthesis of the ketimine of chitosan and 4,6-diacetylresorcinol, and study of the catalase-like activity of its copper chelate(Elsevier Sci Ltd, 2012) Demetgul, CahitIn this study, a new chitosan derivative (ketimine) was synthesized by condensation of chitosan with 4,6-diacetylresorcinol (DAR) at heterogeneous medium. The ketimine derivative of chitosan (DAR-chitosan) was characterized by elemental (C, H, N), spectral (DR-UV-vis and FT-IR spectroscopy), structural (powder XRD), and morphological (SEM) analyses. The degree of substitution (DS) of DAR-chitosan was evaluated by elemental analysis and C-13 CP-MAS NMR spectroscopy and found to be around 12%. The copper (II) metal complex of DAR-chitosan was prepared and characterized by FT-IR, DR-UV-vis and inductively coupled plasma-atomic emission spectroscopy (ICP-AES). Thermal behaviors of the synthesized compounds were investigated by DSC and TG-DTG-DTA analysis. The catalytic activity of copper (II) complex of chitosan derivative (DAR-chitosan-Cu) was investigated on hydrogen peroxide decomposition. The copper chelate showed high efficiency (over 80%) towards the decomposition of hydrogen peroxide as heterogeneous catalyst. (C) 2012 Elsevier Ltd. All rights reserved.Öğe Synthesis, characterization and antioxidant activity of chitosan Schiff base derivatives bearing (-)-gossypol(Elsevier Sci Ltd, 2020) Beyazit, Neslihan; Cakran, Halide Sinem; Cabir, Ali; Akiscan, Yasar; Demetgul, CahitIn this work, two new chitosan-Schiff base derivatives (HCS-GSP and LCS-GSP) were synthesized by the condensation reaction of high molecular weight chitosan (HCS) and low molecular weight chitosan (LCS) with (-)-gossypol (GSP), respectively. For this purpose, racemic gossypol was isolated from cotton seeds and it was further enantiomerically purified by diastereomeric resolution technique using L-tryptophan methyl ester hydrochloride. Then, chitosan polymers were derivatized with (-)-gossypol by the condensation reaction. The isolated and synthesized coumpounds were characterized by physical measurements and spectroscopic methods (elemental analysis C,H,N, Uv-vis, FT-IR, 1H&13C NMR and TG/DTG/DTA). The antioxidant activity of high molecular weight chitosan (HCS), low molecular weight chitosan (LCS) and their gossypol derivatives was evaluated as radical scavengers against 1,1-diphenyl-2-picrylhydrazyl radicals (DPPH). The results showed that both of the chitosan-gossypol derivatives (HCS-GSP and LCS-GSP) had a better ability to scavenging DPPH radical (IC50, 12 mu g/mL and 16 mu g/mL, respectively) than its unmodified chitosan.Öğe Synthesis, characterization and antioxidant activity of chitosan-chromone derivatives(Elsevier Sci Ltd, 2018) Demetgul, Cahit; Beyazit, NeslihanIn this study, a new chromone-functionalized chitosan Schiff base and its cross-linked derivative were synthesized and characterized by FT-IR, UV-vis, C-13 CP/MAS solid-state NMR, TGA, XRD-powder and SEM measurements and elemental analysis data. Degrees of substitution (DS) were determined from the elemental analysis by using the C/N ratios. The in vitro antioxidant activity of high molecular chitosan and its chromone derivatives was evaluated as radical scavengers against 1,1-diphenyl-2-picrylhydrazyl radicals (DPPH%). The results showed that both of the chitosan-chromone derivatives have good antioxidant potential which might be due to the phenolic group introduced after chemical modification of chitosan with a chromone derivative. Chromone-chitosan Schiff base (CSCH) had a better ability to scavenging DPPH radical (IC50, 0.88 mg/mL) than that of its cross-linked derivative (CSCH-TP) obtained by using terephthalaldehyde (IC50, 1.32 mg/mL).Öğe Synthesis, characterization and catecholase-like activity of new Schiff base metal complexes derived from visnagin: Theoretical and experimental study(Elsevier, 2016) Beyazit, Neslihan; Catikkas, Berna; Bayraktar, Sahin; Demetgul, CahitA new tetradentate, unsymmetrical Schiff base ligand (H2L) containing a donor set of N2O2 and its mononuclear Cu(II) and Fe(II) complexes ([CuL] and [FeL]), were synthesized and characterized on the basis of their elemental analysis, FT-IR, Raman, H-1 and C-13 NMR spectra, electronic and mass spectra, molar conductivity and magnetic susceptibility measurements. Density functional theory (DFT) calculations were performed in order to clarify molecular structures, 1H NMR and 13C NMR chemical shift values, frontier molecular orbitals (FMOs), nonlinear optical properties and map of molecular electrostatic potential (MEP) of the title molecules. In agreement with trials, the results provide a full explanation of the highest efficiency observed for the compounds in relation to the electronic and the structural characteristics. The catecholase-like activity of the complexes toward the oxidation of 3,5-ditert-butylcatechol (3,5-DTBC) to the corresponding quinone showed that both complexes have moderate catalytic activity. [FeL] shows higher activity (k(cat) = 26.4 h(-1)) than that of [CuL] (k(cat) = 23.4 h(-1)). (c) 2016 Elsevier B.V. All rights reserved.Öğe Synthesis, characterization, and biological properties of Ni(II), Co(II), and Cu(II) complexes of Schiff bases derived from 4-aminobenzylamine(Taylor & Francis Ltd, 2009) Demetgul, Cahit; Karakaplan, Mueruevvet; Serin, Selahattin; Digrak, MetinNew Schiff bases, N,N'-bis(salicylidene)-4-aminobenzylamine (H2L1), N,N'-bis(3-methoxysalicylidene)-4-aminobenzylamine (H2L2), and N,N'-bis(4-hydroxysalicylidene)-4-aminobenzylamine (H2L3), with their nickel(II), cobalt(II), and copper(II) complexes have been synthesized and characterized by elemental analyses, electronic absorption, FT-IR, magnetic susceptibility, and conductance measurements. For the ligands, 1H and 13C NMR and mass spectra were obtained. The tetradentate ligands coordinate to the metal ions through the phenolic oxygen and azomethine nitrogens. The keto-enol tautomeric forms of the Schiff bases H2L1, H2L2, and H2L3 have been investigated in polar and apolar solvents. All compounds were non-electrolytes in DMSO (10-3 M) according to the conductance measurements. Antimicrobial activities of the Schiff bases and their complexes have been tested against Acinobacter baumannii, Pseudomonas aeruginosa, Micrococcus luteus, Bacillus megaterium, Corynebacterium xerosis, Staphylococcus aureus, Escherichia coli, Candida albicans, Rhodotorula rubra, and Kluyveromyces marxianus by the disc diffusion method; biological activity increases on complexation.
