Synthesis and characterization of Schiff base metal complexes: their antimicrobial, genotoxicity and electrochemical properties

Synthesis, spectral characterization, computational studies, antifungal, DNA interaction, antioxidant and fluorescence property of novel Schiff base ligand and its metal chelates

Cobalt, Copper, Nickel and Zinc coordinated metal complexes were synthesized by novel thiazole Schiff base ligand 2-ethoxy-4-((5-methylthiazol-2-ylimino)methyl) phenol derived from 3-ethoxy-4-hydroxybenzaldehyde and 2-amino- 5-methylthiazol. The synthesized compounds were spectrochemically characterized by elemental analysis, molar conductance, FT-IR, UV-Vis, Mass spectral analysis, Powdered-XRD and cyclic voltammetry. The thermal stability of synthesized complexes were investigated by using thermogravimetric analysis (TGA). Theoretical computational study were performed for all the synthesized compounds utilizing the DFT/B3LYP method at the 6-31G basic set for Schiff base ligand whereas LANL2DZ basis set for metal complexes. Molecular Electrostatic Potential (MEP), HOMO-LUMO, Mulliken charges and global reactivity descriptors, including chemical potential (μ), global softness (S), chemical hardness (η), and electrophilicity index (ω) were measured and correlated with antimicrobial activity. The synthesized thiazole Schiff base ligand and its coordinated metal complexes shows good antifungal agreement against Fusarium Oxysporum and Aspergillus Niger species. These compounds also exhibit DNA binding, DNA cleaving and antioxidant activity. All the synthesized molecules indicate potential fluorescence property.

Synthesis, Characterization, Theoretical and Experimental Anticancer Evaluation of Novel Cocrystals of 5-Fluorouracil and Schiff Bases against SW480 Colorectal Carcinoma

The chemotherapeutic agent known as 5-fluorouracil (5-FU) is an artificial fluoropyrimidine antimetabolite that has been widely used for its antineoplastic properties. Cocrystals of 5-fluorouracil (5-FU) with five different Schiff bases (benzylidene-urea (BU), benzylidene-aniline (BA), salicylidene-aniline (SA), salicylidene-phenylhydrazine (SPH), and para-hydroxy benzylideneaniline (HBA)) are reported in this study. The newly synthesized cocrystals were analyzed by FTIR and PXRD. In this study, we investigated the antitumor efficacy of 5-FU derivatives in SW480 colon cancer cells via MTT assay at varying dose concentrations. Molecular docking was performed to predict the binding mechanism of TS with various 5-FU complexes. FTIR revealed the presence of respective functional groups in the prepared cocrystals. The frequencies (v) of N-H (3220.24 cm^-1) and carbonyl groups (1662.38 cm^-1) in the spectrum of 5-FU shifted considerably in all derivative cocrystal new interactions. There was a noticeable transformation in the PXRD peak of 5-FU at 2θ = 28.37° in all derivatives. The novelty of the present study lies in the fact that 5-FU-BA showed an anticancer potential IC₅₀ (6.4731) far higher than that of 5-FU (12.116), almost comparable to that of the reference drug doxorubicin (3.3159), against SW480 cancel cell lines, followed by 5-Fu-HBA (10.2174). The inhibition rates of 5-FU-BA and 5-FU-HBA were highest among the derivatives (99.85% and 99.37%, respectively) in comparison with doxorubicin (97.103%). The results revealed that the synthesized 5-FU cocrystals have promising antitumor efficacy compared with previously reported 5-FU and 5-FU. The activities of the cocrystals were rationalized by a molecular modeling approach to envisage binding modes with the target cancer protein.

Orto-hydroxy bioactive schiff base compounds: Design, comprehensive characterization, photophysical properties and elucidation of antimicrobial and mutagenic potentials

Preparation and comprehensive characterization of three Schiff base ligands; with trimethoxy substitution (1E,1'E)-N,N'-(naphthalene-1,5-diyl)bis(1-(3,4,5-trimethoxyphenyl)methanimine, 1, with ortho-hydroxy substitution 6,6'-((1E,1'E)-(naphthalene-1,5-diylbis(azaneylylidene))bis(methaneylylidene))bis(2-methoxyphenol), 2 and 3,4-bis(((E)-2-hydroxy-3-methoxy benzylidene)amino)benzoicacid, 3 and their Ni(II), Cu(II), Co(II), Zn(II), Fe(II), Mn(II) complexes have been reported. Their spectral properties were studied in solution and solid-state by a combination of different analytical techniques; FT-IR spectroscopy, ¹H NMR and ¹³C NMR spectroscopy, elemental analysis and thermal analysis. Diamagnetic and paramagnetic natures of the complexes were also determined by magnetic susceptibility measurements in solid-state. Promising photophysical properties were observed as; A_max. were recorded at 226 nm for 2; at 795 nm for 2-Ni, at 782 nm for 2-Cu, at 784 nm for 2-Co, at 702 nm for 2-Zn, at 784 nm for 2-Fe, at 702 nm for 2-Mn and at 289 nm for 3, at 786 nm for 3-Ni, at 797 nm for 3-Cu, at 746 nm for 3-Co, at 794 nm for 3-Zn, at 699 nm for 3-Fe, at 781 nm for 3-Mn ; and I_max were also recorded at; 380, 490, 725 nm for 2 and 2-Metal; 375 nm, 510 nm, 725 nm for 3 and 3-Metal when excitated at 220 nm. Antibacterial activities against different microorganisms; Escherichia coli ATCC 25922, Pseudomonas aeruginosa ATCC 27853, Klebsiella pneumoniae ATCC 70603, Staphylococcus aureus ATCC 43,300 (MRSA), Salmonella enteritidis ATTC 13076, Sarcina lutea ATCC 9341, Bacillus cereus ATTC 11778, and antifungal activities against Candida albicans NRRL Y-417 of the compounds 1, 2, 3, 2-Cu, 2-Fe, 3-Zn, 3-Fe were determined. Mutagenic properties of the compounds were also studied and according to the results 2-Cu and 3 have been found non-mutagenic in Ames test but also they have strong antimicrobial potential against pathogen microorganisms. For 2-Cu MIC values were ranging between 0.39 and 0.024 mg/ml and the lowest minimum inhibitory concentration (0.024 mg/ml) was determined against E. coli. The 3 numbered compound revealed strong antimicrobial activity at doses of ranging between 0.39 and 0.097 mg/ml and E. coli was the most sensitive bacterium against this chemical.

Efficient Catalytic Reduction of 4-Nitrophenol Using Copper(II) Complexes with N,O-Chelating Schiff Base Ligands

The reduction of 4-nitrophenol to 4-aminophenol by sodium borohydride was used as a model to test the catalytic activity of copper(II) complexes containing N,O-chelating Schiff base ligands. In this study, a series of copper(II) complexes containing respective Schiff base ligands, N'-salicylidene-2-aminophenol (1), N'-salicylidene-2-aminothiazole (2), and N,N'-bis(salicylidene)-o-phenylenediamine (3), were synthesized and characterized by elemental analysis, Fourier transform infrared (FT-IR), UV-Visible (UV-Vis) and electron paramagnetic resonance (EPR) spectroscopies. The results from the 4-nitrophenol reduction showed that 3 has the highest catalytic activities with 97.5% conversion, followed by 2 and 1 with 95.2% and 90.8% conversions, respectively. The optimization of the catalyst amount revealed that 1.0 mol% of the catalyst was the most optimized amount with the highest conversion compared to the other doses, 0.5 mol% and 1.5 mol%. Recyclability and reproducibility tests confirmed that all three complexes were active, efficient, and possess excellent reproducibility with consistent catalytic performances and could be used again without a major decrease in the catalytic activity.

Design of New Schiff-Base Copper(II) Complexes: Synthesis, Crystal Structures, DFT Study, and Binding Potency toward Cytochrome P450 3A4

We report the synthesis and crystal structures of three new copper(II) Schiff-base complexes. The complexes have been characterized by elemental analysis and Fourier transform infrared (FT-IR) and UV-visible spectroscopies. The X-ray diffraction (XRD) analysis reveals that complexes 1 and 3 crystallize in a monoclinic space group C2/c and 2 in a triclinic space group P1̅, each adopting a square planar geometry around the metal center. We use a density functional theory method to explore the quantum chemical properties of these complexes. The calculation proceeds with the three-dimensional (3D) crystal structure characterization of the complexes in which the calculated IR and UV-vis values are comparable to the experimental results. Charge distribution and molecular orbital analyses enabled quantum chemical property prediction of these complexes. We study the drug-likeness properties and binding potentials of the synthesized complexes. The in silico outcome showed that they could serve as permeability-glycoprotein (P-gp) and different cytochrome P450 substrates. Our calculations showed that the complexes significantly bind to cytochrome P450 3A4.

Crystal structure of bis(2-hydroxy-6-((phenylimino)methyl)phenolato-κ2N,O)copper(II), C26H20CuN2O4

C26H20CuN2O4, triclinic, P1̄ (no. 2), a = 5.8633(1) Å, b = 12.2597(2) Å, c = 14.5517(3) Å, α = 82.960(1)°, β = 85.058(2)°, γ = 86.436(4)°, V = 1032.85(3) Å3, Z = 2, Rgt(F) = 0.0264, wRref(F2) = 0.0732, T = 100(2) K.

Metal complexes driven from Schiff bases and semicarbazones for biomedical and allied applications: a review

Schiff bases are versatile organic compounds which are widely used and synthesized by condensation reaction of different amino compound with aldehydes or ketones known as imine. Schiff base ligands are considered as privileged ligands as they are simply synthesized by condensation. They show broad range of application in medicine, pharmacy, coordination chemistry, biological activities, industries, food packages, dyes, and polymer and also used as an O2 detector. Semicarbazone is an imine derivative which is derived from condensation of semicarbazide and suitable aldehyde and ketone. Imine ligand-containing transition metal complexes such as copper, zinc, and cadmium have shown to be excellent precursors for synthesis of metal or metal chalcogenide nanoparticles. In recent years, the researchers have attracted enormous attention toward Schiff bases, semicarbazones, thiosemicarbazones, and their metal complexes owing to numerous applications in pharmacology such as antiviral, antifungal, antimicrobial, antimalarial, antituberculosis, anticancer, anti-HIV, catalytic application in oxidation of organic compounds, and nanotechnology. In this review, we summarize the synthesis, structural, biological, and catalytic application of Schiff bases as well as their metal complexes.

Preparation, characterization and comparison of biological potency in two new Zn(II) and Pd(II) complexes of butanedione monoxime derivatives

A novel Schiff base ligand (2-iminothiophenol-2,3-butanedione monoxime, ITBM) and its complexes with Pd(II) and Zn(II) metal ions ([M(ITBM)₂]Cl₂) were synthesized and characterized in the present study. The formulated complexes were evaluated for in vitro antioxidant activity as radical scavengers against 1,1-diphenyl-2-picrylhydrazyl radicals (DPPH^•). According to the results, antioxidant activity of Pd complex (IC₅₀=36 mg L^-1) was more effective than that of Zn(II) complex (IC₅₀=72 mg L^-1). Biophysical techniques along with computational modeling were employed to examine the binding of these complexes with human serum albumin (HSA) as the model protein. The trial findings revealed an interaction between Schiff base complexes and HSA with a modest binding affinity [K_b=6.31(±0.11)×10⁴ M^-1 for Zn(II) complex and 0.71(±0.05)×10⁴ M^-1 for Pd(II) complex at 310 K]. An intense fluorescence quenching of protein through a static quenching mechanism was occurred due to the binding of both complexes to HSA. Hydrogen bonds and van der Waals forces in both examined systems were the main stabilizing forces in the development of drug-protein complex. Based on far-UV-CD observations, the content of α-helical structure in the protein was reduced through induction by both complexes. Analysis of protein-ligand docking demonstrated binding of the two Schiff base complexes to residues placed in the IIA subdomain of HSA. In addition, Zn complex with HSA showed a stronger binding ability than that of Pd complex.Communicated by Ramaswamy H. Sarma.

Syntheses, crystal structure, Hirshfeld surfaces, fluorescence properties, and DFT analysis of benzoic acid hydrazone Schiff bases

Two hydrazone Schiff base analogues, namely, (E)-N'-(4-hydroxy-3-methoxybenzylidene)benzohydrazide (3a) and (E)-N'-(4-methoxybenzylidene)benzohydrazide (3b), were synthesized using a mild, efficient method and characterized by (1)H NMR, mass spectrometry, elemental analysis, and single-crystal X-ray diffraction. X-ray analysis of a single crystal of 3a revealed a tetragonal, space group I4(1)/a structure, with an E-configuration around the azomethine (C8N2) double bond. In this structure, the NH and OH groups act as proton donors and the >CO and N groups as proton acceptors, and these facilitate hydrogen bond formation in the crystal state. Plausible intermolecular interactions were studied using 3D Hirshfeld surfaces and related 2D fingerprint plots. The optimized geometry, vibrational frequencies, Mulliken charge distribution, molecular electrostatic potential (MEP) maps, frontier molecular orbitals (FMOs), and associated energies of the ground state and the first single excited state were calculated using density functional theory (DFT) and time-dependant DFT calculations using the B3LYP/6-311G method. Vibrational frequencies calculated in the gaseous phase compared with experimental values measured in the solid state and showed good agreement with each other. The chemical reactivities of 3a and 3b were predicted by mapping MEP surface over optimized geometries and comparing these with MEP map generated over crystal structures. Mulliken charge distribution analysis and MEP map of 3a and 3b revealed that N(1), O(1), O(2) and O(3) atoms could act as electron donors and coordinate with metals and that these represented the most suitable sites for electrophilic attack. In fluorescence spectra, the absorption and emission spectra of 3a and 3b were similar in different polar solvents with few exceptions. In addition, both compounds exhibited dual emission spectra in acetone due to keto-enol tautomerism induced by photoexcitation.

Anticancer, photoluminescence and electrochemical properties of structurally characterized two imine derivatives

Two imine compounds, 4-[(E)-(2-methoxybenzylidene)amino]phenol (L(1)) and 4-[(E)-(3,4-dimethoxybenzylidene)amino]phenol (L(2)) were synthesized and characterized by the analytical and spectroscopic methods. The electrochemical and photoluminescence properties of the imine compounds L(1) and L(2) were investigated in different solvents. The compounds L(1) and L(2) show different redox processes at some potentials. The molecular structures of two Schiff base compounds are broadly similar, differing principally in the position, the number of methoxy (-OCH3) groups and dihedral angles between aromatic rings. While the compound L(1) has only one methoxy group located on the o-position with respect to the imine bond (C=N), the L(2) contains two methoxy groups on the p-m-positions with respect to the imine bond. The imine compounds show two or three emission bands in the 619-832 nm range in organic solvents. In the 1.0×10(-3) M concentration, the compounds have the highest excitation and emission bands. The imine compounds L(1) and L(2) were screened for their in vitro cytotoxicity on HeLa cell lines using the xCELLigence system (Real Time Cell Analyzer).

Synthesis, characterization and antibacterial activity of a tridentate Schiff base derived from cephalothin and sulfadiazine, and its transition metal complexes

Metal(II) coordination compounds of a cephalothin Schiff base (H2L) derived from the condensation of cephalothin antibiotic with sulfadiazine were synthesized. The Schiff base ligand, mononuclear [ML(H2O)3] (M(II)=Mn,Co,Ni,Zn) complexes and magnetically diluted dinuclear copper(II) complex [CuL(H2O)3]2 were characterized by several techniques, including elemental and thermal analysis, molar conductance and magnetic susceptibility measurements, electronic, FT-IR, EPR and (1)H NMR spectral studies. The cephalothin Schiff base ligand H2L behaves as a dianionic tridentate NOO chelating agent. The biological applications of complexes have been studied on two bacteria strains (Escherichia coli and Staphylococcus aureus) by agar diffusion disc method.

Electroactive and bioactive films of random copolymers containing terthiophene, carboxyl and Schiff base functionalities in the main chain

Copolymers made of a bis-thienyl monomer with preformed azomethine linkages and terthiophene are promising functional biomaterials.

Preparation of multi-functional cellulose containing huge conjugated system and its UV-protective and antibacterial property

A novel Schiff base containing huge azo conjugated system and reactive groups, 3,5-bis{2-hydroxyphenyl-5-[(2-sulfate-4-sulfatoethylsulfonyl-azobenzol)methylene amino]}benzoic acid (BHSABA) was applied to modify cellulose. Exhaustion and grafting reactive rate, and grafting quantity of BHSABA on cellulose were calculated. The chemical structure of the modified cellulose was characterized and thermal degradation and morphology were also investigated. The UV protection and antibacterial properties were measured. With increasing the concentration of BHSABA, grafting quantity of BHSABA on cellulose increased from 1.52 × 10(-2)mmol/g to 5.08 × 10(-2)mmol/g. The multi-functional cellulose fabrics had excellent UV-protective property, which possessed very high UPF value and very low ultraviolet transmittance. The UPF values exceeded 50 and the ultraviolet transmittances were all less than 1%. They also exhibited moderate activity against Staphylococcus aureus and after 10 times washing still maintained antibacterial activity. The onsets of degradation slightly decreased. With increasing the grafting quantity of BHSABA on cellulose, mass loss yields of the residues increased. The morphological structure had no noticeable change.

Synthesis, characterization and antibacterial activity of a Schiff base derived from cephalexin and sulphathiazole and its transition metal complexes

Metal(II) coordination compounds of a cephalexin Schiff base (HL) derived from the condensation of cephalexin antibiotic with sulphathiazole were synthesized. The Schiff base ligand, mononuclear [ML(OAc)(H2O)2] (M(II)=Mn, Co, Ni, Zn) complexes and magnetically diluted trinuclear copper(II) complex [Cu3L(OH)5] were characterized by several techniques, including elemental and thermal analysis, molar conductance and magnetic susceptibility measurements, electronic, FT-IR, EPR and (1)H NMR spectral studies. The analytical and molar conductance values indicated that the acetate ions coordinate to the metal ions. The Schiff base ligand HL behaves as a monoanionic tridentate NNO and tetradentate NNOO chelating agent in the mono and trinuclear complexes respectively.

Synthesis, magnetic and spectroscopic studies of a Schiff base derived from cephaclor and 1,2-diaminobenzene and its transition metal complexes

M(II) coordination compounds of Mn, Fe, Co and Ni with a Schiff base (HL) derived from the condensation of cephaclor antibiotic with 1,2-diaminobenzene were synthesized and characterized by several techniques, including elemental and thermal analysis, molar conductance and magnetic susceptibility measurements, electronic, FT-IR, EPR and (1)H NMR spectral studies. The analytical and molar conductance values indicated that the chloride ions coordinate to the metal ions. Based on these studies, the general formulae [M(L)Cl(H2O)] (M(II)=Mn, Fe, Co, Ni) are proposed for the complexes. The ligand HL behaves as a monoanionic tetradentate NNNO chelating agent.

Synthesis, evaluation of antioxidant activity and crystal structure of 2,4-dimethylbenzoylhydrazones

2,4-Dimethylbenzoylhydrazones 1-30 were synthesized by condensation reactions of 2,4-dimethylbenzoylhydrazide with various aromatic aldehydes and characterized. The assigned structures of compounds 10, 15 and 22 were further supported by single-crystal X-ray diffraction data. The synthesized compounds were evaluated for their in vitro DPPH radical scavenging activity. They exerted varying degree of scavenging activity toward DPPH radical with IC₅₀ values between 25.6-190 µM. Compounds 1, 4, 2, 3, 7, and 6 have IC₅₀ values of 25.6, 28.1, 29.3, 29.8, 30.0 and 30.1 µM respectively, showing better activity than an n-propyl gallate standard (IC₅₀ value = 30.30 µM). For super oxide anion scavenging activity compounds 1, 2 and 3 with IC₅₀ values of 98.3, 102.6, and 105.6, respectively, also showed better activity than the n-propyl gallate standard (IC₅₀ value = 106.34 µM).

Organic cadmium complexes as proteasome inhibitors and apoptosis inducers in human breast cancer cells

Although cadmium (Cd) is a widespread environmental contaminant and human carcinogen, our studies indicate an organic Cd complex to be a potent inhibitor of proteasomal chymotrypsin-like (CT-like) activity, further capable of inducing apoptosis in a cancer cell-specific manner. It has been reported that the ligands indole-3-butyric acid (L1) and indole-3-propionic acid (L2) have cancer-fighting effects when tested in a rat carcinoma model. In addition, 3, 5-diaminobenzoic acid o-vanillin Schiff bases (L3) have high antimicrobial activity and a large number of Schiff base complexes have been reported to have proteasome-inhibitory activity. We therefore hypothesized that synthetic forms of Cd in combination with L1, L2 and L3 may have proteasome-inhibitory and apoptosis-inducing activities, which would be cancer cell-specific. To test this hypothesis, we have synthesized three novel Cd-containing complexes: [Cd2(C12H12O2N)4(H2O)2]·2H2O (Cd1), [Cd2(C11H10O2N)4(H2O)2]·2H2O (Cd2) and [Cd(C7H4N2O2)(C8H6O2)2]·2H2O (Cd3), by using these three ligands. We sought out to characterize and assess the proteasome-inhibitory and anti-proliferative properties of these three Cd complexes in human breast cancer cells. Cd1, Cd2 and Cd3 were found to effectively inhibit the chymotrypsin-like activity of purified 20S proteasome with IC50 values of 2.6, 3.0 and 3.3 μΜ, respectively. Moreover, inhibition of cancer cell proliferation also correlated with this effect. As a result of proteasomal shutdown, the accumulation of ubiquitinated proteins and the proteasome target IκB-α protein as well as induction of apoptosis were observed. To account for the cancer specificity of this effect, immortalized, non-tumorigenic breast MCF10A cells were used under the same experimental conditions. Our results indicate that MCF10A cells are much less sensitive to the Cd1, Cd2 and Cd3 complexes when compared to MDA MB 231 breast cancer cells. Therefore, our study suggests that these Cd organic complexes are capable of inhibiting tumor cellular proteasome activity and consequently induce cancer cell-specific apoptotic death.

Synthesis, Spectroscopic, and Magnetic Studies of Mono- and Polynuclear Schiff Base Metal Complexes Containing Salicylidene-Cefotaxime Ligand

Metal complexes of a Schiff base ligand derived from cefotaxime and salicylaldehyde were prepared. The salicilydene-cefotaxime ligand (H2L) and mononuclear [M(L)] (M(II) = Co, Ni and Cu), dinuclear [Ag2(L)(OAc)2], and tetranuclear metal complexes [M4(L)(OH)6] (M(II) = Ni, Cu) were characterized on the basis of analytical, thermal, magnetic, and spectral studies (IR, UV-visible, 1H NMR, 13C NMR, and EPR). The electronic spectra of the complexes and their magnetic moments suggesttetrahedral geometry for the isolated complexes. The complexes are nonelectrolytes and insoluble in water and common organic solvents but soluble in DMSO.

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.

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.