Gökhan Ceyhan

Antioxidant, electrochemical, thermal, antimicrobial and alkane oxidation properties of tridentate Schiff base ligands and their metal complexes

In this study, two Schiff base ligands (HL(1) and HL(2)) and their Cu(II), Co(II), Ni(II), Pd(II) and Ru(III) metal complexes were synthesized and characterized by the analytical and spectroscopic methods. Alkane oxidation activities of the metal complexes were studied on cyclohexane as substrate. The ligands and their metal complexes were evaluated for their antimicrobial activity against Corynebacterium xerosis, Bacillus brevis, Bacillus megaterium, Bacillus cereus, Mycobacterium smegmatis, Staphylococcus aureus, Micrococcus luteus and Enterococcus faecalis (as gram-positive bacteria) and Pseudomonas aeruginosa, Klebsiella pneumoniae, Escherichia coli, Yersinia enterocolitica, Klebsiella fragilis, Saccharomyces cerevisiae, and Candida albicans (as gram-negative bacteria). The antioxidant properties of the Schiff base ligands were evaluated in a series of in vitro tests: 1,1-diphenyl-2-picrylhydrazyl (DPPH) free radical scavenging and reducing power activity of superoxide anion radical generated non-enzymatic systems. Electrochemical and thermal properties of the compounds were investigated.

Tetradentate Schiff base ligands and their complexes: synthesis, structural characterization, thermal, electrochemical and alkane oxidation.

Three Schiff base ligands (H(2)L(1)-H(2)L(3)) with N(2)O(2) donor sites were synthesized by condensation of 1,5-diaminonapthalene with benzaldehyde derivatives. A series of Cu(II), Co(II), Ni(II), Mn(II) and Cr(III) complexes were prepared and characterized by spectroscopic and analytical methods. Thermal, electrochemical and alkane oxidation reactions of the ligands and their metal complexes were investigated. Extensive application of 1D ((1)H, (13)C NMR) and 2D (COSY, HETCOR, HMBC and TOSCY) NMR techniques were used to characterize the structures of the ligands and establish the (1)H and (13)C resonance assignments of the three ligands. Ligands H(2)L(1) and H(2)L(3) were obtained as single crystals from THF solution and characterized by X-ray diffraction. Both molecules are centrosymmetric and asymmetric unit contains one half of the molecule. Catalytic alkane oxidation reactions with the transition metal complexes investigated using cyclohexane and cyclooctane as substrates. The Cu(II) and Cr(III) complexes showed good catalytic activity in the oxidation of cyclohexane and cyclooctane to desired oxidized products. Electrochemical and thermal properties of the compounds were also investigated.

Chemically Modified Silica-Gel With an Azo-Schiff Ligand and Its Metal Complexes With Cu(II), Co(II), Ni(II) and Mn(II): Applications as Catalysts on the Oxidation of Cyclohexane Under Microwave Power

A novel 2-hydroxy-5-((2-hydroxyphenyl)diazenyl)benzal- dehyde (L1: HPDB) ligand was synthesized and bound to silica gel, which was activated with 3-aminopropyltriethoxysilane. Cu(II), Co(II), Ni(II), and Mn(II) complexes of silica-supported ligand (L2: MDPMP) were synthesized. A buffer (pH = 12) was used for a coupling reaction of diazonium electrophile to salicylaldehyde. The ligand and its complexes were characterized by using NMR, FT-MIR/FAR, elemental analysis, ICP-OES, TGA, and scanning electron microscopy. Catalytic properties of the complexes were investigated for the selective oxidation of cyclohexane under microwave power. Silica-supported L2-Cu(II) complex showed well selective catalytic activity for the oxidation of cyclohexane to cyclohexanol and cyclohexanone with 8.40% and 3.77% yields with 48.43% conversion.

Polydentate Schiff Base Ligands and Their La(III) Complexes: Synthesis, Characterization, Antibacterial, Thermal, and Electrochemical Properties

We synthesized the Schiff base ligands H2L1–H2L4 and their La(III) complexes and characterized them by the analytical and spectroscopic methods. We investigated their electrochemical and antimicrobial activity properties. The electrochemical properties of the ligands H2L1–H2L4 and their La(III) complexes were studied at the different scan rates (100 and 200 mV), different pH ranges (pH=2−12), and in the different solvents. The electrooxidation of the Schiff base ligands involves a reversible transfer of two electrons and two protons in solutions of pH up to 5.5, in agreement with the one-step two-electron mechanism. In solutions of pH higher than 5.5, the process of electrooxidation reaction of the Schiff base ligands and their La(III) complexes follows an ECi mechanism. The antimicrobial activities of the ligands and their complexes were studied. The thermal properties of the metal complexes were studied under nitrogen atmosphere in the range of temperature 20–1000°C.

A novel Schiff base: Synthesis, structural characterisation and comparative sensor studies for metal ion detections.

A novel Schiff base ligand was synthesized by the condensation reaction of 2,6-diformylpyridine and 4-aminoantipyrine in MeOH and characterised by its melting point, elemental analysis, FT-IR, (1)H, (13)C NMR and mass spectroscopic studies. Molecular structure of the ligand was determined by single crystal X-ray diffraction technique. The electrochemical properties of the Schiff base ligand were studied in different solvents at various scan rates. Sensor ability of the Schiff base ligand was investigated by colorimetric and fluorometric methods. Visual colour change of the ligand was investigated in MeOH solvent in presence of various metal ions Na(+), Mg(2+), Al(3+), K(+), Cr(3+), Mn(2+), Fe(3+), Co(2+), Ni(2+), Cu(2+), Zn(2+), Cd(2+), Hg(2+) and Pb(2+). Upon addition of Al(3+) ion into a MeOH solution of the ligand, an orange colour developed which is detectable by naked eye. Fluorescence emission studies showed that the ligand showed single emission band at 630-665nm upon excitation at 560nm. Addition of metal ions Na(+), Mg(2+), K(+), Cr(3+), Mn(2+), Fe(3+), Co(2+), Ni(2+), Cu(2+), Zn(2+), Cd(2+), Hg(2+) and Pb(2+) (1:1M ratio) cause fluorescence quenching, however addition of Al(+3) resulted in an increase in fluorescence intensity. No significant variation was observed in the fluorescence intensity caused by Al(3+) in presence of other metal ions. Therefore, the Schiff base ligand can be used for selective detection of Al(3+) ions in the presence of the other metal ions studied.

Synthesis, characterization and non-linear optical properties of two mononuclear Cu(II) complexes of 2,6-bis(1-butylbenzimidazol-2-yl)pyridine

Abstract Two copper(II) complexes, [Cu(L)(N3)2]·MeOH and [Cu(L)(NCS)2]·MeOH, were prepared and characterized by spectroscopic, analytical, and quantum chemical studies, where L is 2,6-bis(1-butylbenzimidazol-2-yl)pyridine. X-ray quality crystals of [Cu(L)(N3)2]·MeOH were obtained by slow evaporation of MeOH solution of the complex. Molecular structure of [Cu(L)(N3)2]·MeOH was determined by X-ray crystallography. The asymmetric unit contains one [Cu(L)(N3)2] and one MeOH molecule. Cu(II) in [Cu(L)(N3)2]·MeOH is five-coordinate, bonded to five nitrogens (three from L and two from two azide anions). Coordination geometry around Cu(II) center is distorted square-pyramidal with τ value of 0.065. Optimized geometries, IR spectra, and non-linear optical properties of the complexes were obtained by computational studies based on density functional theory (DFT) with M062X method. NLO properties of these complexes were investigated computationally and both complexes exhibit better NLO properties than urea.

Novel Cobalt(II), Zinc(II) Phthalocyanines Bearing Discrete Substituents: Synthesis, Characterization, Aggregation Behavior, Electrochemical Properties, and Antioxidant Activity

A new phthalonitrile derivative bearing 3,4,5-trimethoxy- benzyloxy and chloro-substituents at peripheral position was prepared by a nucleophilic displacement reaction. Cyclotetramerization of phthalonitrile derivative in dimethylsulfoxide (DMSO) gave the metallophthalocyanines. Novel Co(II), Zn(II) phthalocyanines (Pcs) were obtained from the reaction 4-[(3,4,5-trimethoxybenzyloxy]-5-chlorophthalonitrile and metal salts. The novel compounds have been characterized by using elemental analysis, UV-Vis, FTIR, 1H-NMR spectral data. The aggregation behaviors of Co(II), Zn(II) Pcs were also investigated. These metallophthalocyanines do not show any aggregation behavior between 1.2 × 10−5 and 4.0 × 10−6 M concentration range in DMF. The antioxidant activities of Pcs were investigated antioxidant assays such as free radical scavenging ability of 1,1-diphenyl-2-picryl-hydrazyl (DPPH) and ferrous ion chelating ability. Furthermore, the redox properties of the Pcs complexes were investigated by using cyclic voltammetry.

Antiproliferative, antioxidant, computational and electrochemical studies of new azo-containing Schiff base ruthenium(II) complexes

A new series of ruthenium(II) complexes 7–11 containing the –NN– group are synthesized and characterized via elemental analysis, and IR, UV-visible and 1H–13C NMR spectroscopy. The solid-state structures of 2, 6 and 9 are determined by single crystal X-ray diffraction studies. The antiproliferative activities of the Schiff base ligands and their ruthenium(II) complexes are investigated in vitro against non-small cell lung cancer cells (H2126), prostate adenocarcinoma cells (PC3) and breast cancer cells (MCF7). The cell proliferation tests are performed as dose-dependent assays at eight concentrations, and 5-fluorouracil is used as the positive control. Compounds 4 and 5 show higher antiproliferative activities against PC3 cells than the other synthesized compounds. Furthermore, the antioxidant capacities of the Schiff base ligands and their ruthenium(II) complexes are investigated in vitro via ferric reduction power, DPPH free radical, and ABTS cation radical scavenging activity tests. The radical scavenging activities of complexes 7–11 are found to be higher than BHT, BHA, and Trolox, which are used as positive controls. The antioxidant activity of the complexes is found to be 30–150 fold higher than the ligands. According to obtained results, the ruthenium complexes in this study may be used as antioxidant agents in the food, drug and cosmetic industries.

Structural characterisation and photoluminescence of a pyridine–diimine compound

A pyridine–diimine compound N,N′-[pyridine-2,6-diyldi(E)methylylidene]bis(4-chloroaniline) is synthesised by a Schiff base condensation of 2,6-diformylpyridine with 4-chloroaniline in methanol and characterised by spectroscopic and analytical techniques. The molecular structure of the compound is determined by the single crystal X-ray diffraction study. The compound crystallizes in the monoclinic crystal system, I2/c space group with unit cell parameters a = 7.0843(12) Å, b = 6.1909(11) Å, c = 36.262(6) Å, β = 91.576(3)°, V = 1589.8(5) Å3 and Z = 4. There is an intermolecular hydrogen bonding in the molecule resulting in a 1D hydrogen bonding chain and these hydrogen bonding chains are linked by Cl…HC(aromatic) interactions forming a 2D network. Crystal packing of the compound is determined by Cl…HC and π–π interactions. In the fluorescence emission spectra in CH3CN, DMF, DMSO and EtOH, the compound shows only one emission maximum.