Cahit Demetgül

Synthesis of the ketimine of chitosan and 4,6-diacetylresorcinol, and study of the catalase-like activity of its copper chelate

In 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 (13)C 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.

Synthesis, characterization, and biological properties of Ni(II), Co(II), and Cu(II) complexes of Schiff bases derived from 4-aminobenzylamine

New 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.

Synthesis and characterization of a Schiff base derived from 2-aminobenzylamine and its Cu(II) complex: electropolymerization of the complex on a platinum electrode

A 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.

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

In this paper, Schiff base monomers having double azomethine groups, N,N′-bis(4-hydroxybenzylidene)1,4-phenylenediamine (M1) and N,N′-bis(4-hydroxysalicylidene)1,4-phenylenediamine (M2), 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) (P1) and poly(N,N′-bis(4-hydroxysalicylidene)1,4-phenylenediamine) (P2) 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, 1H-NM, 13C-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.

Synthesis, Characterization and Thermal Properties of Oligo-N,N -bis (2,4-dihydroxybenzylidene) ethylenediamine and Its Cobalt (II) and Manganese (II) Complexes

In this study, the new oligomer Schiff base oligo-N,N′-bis (2,4-dihydroxybenzylidene) ethylenediamine (O-DHBEDA), with a double azomethine group, was synthesized by oxidative polycondensation (OP) of N,N′-bis (2,4-dihydroxybenzylidene) ethylenediamine (DHBEDA) with NaOCl as an oxidant in an aqueous alkaline medium at 90°C. About 69.3% DHBEDA was converted to O-DHBEDA. The structures of the products were studied by UV-Vis, FT-IR, 1H-NMR, 13C-NMR and elemental analysis. According to gel-permeation chromatography (GPC) analysis of O-DHBEDA, the number-average molecular weight (M n), weight-average molecular weight (M w) and PDI values were found to be 5255 g/mol, 9116 g/mol and 1.73, respectively. During the polycondensation reaction, a part of the azomethine (–CH=N–) groups oxidized to aldehyde (CHO) groups (approx. 4%). Oligomer–metal complexes of oligo-N,N′-bis (2,4-dihydroxybenzylidene) ethylenediamine (O-DHBEDA) with Co (II) and Mn (II) were synthesized and characterized by FT-IR, UV-Vis, TG-DTA and atomic absorption spectroscopy (AAS). TG/DTA analyses were shown to be stable of O-DHBEDA against thermo-oxidative decomposition. The residue values of DHBEDA, O-DHBEDA, O-DHBEDA–Co and O-DHBEDA–Mn were found to be 0%, 7.1%, 14% and 13.4%, respectively, at 1000°C.

Synthesis, Characterization and Antioxidant Activity of Chitosan-Chromone Derivatives

In this study, a new chromone-functionalized chitosan Schiff base and its cross-linked derivative were synthesized and characterized by FT-IR, UV-vis, 13C 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, 0.88mg/mL) than that of its cross-linked derivative (CSCH-TP) obtained by using terephthalaldehyde (IC50, 1.32mg/mL).