Azomethine Compounds Research Articles

Antitubercular activity of some new Azomethine compounds

Antitubercular activity of some new Azomethine compounds

Effect of temperature and hydrodynamic conditions on corrosion inhibition of an azomethine compounds for mild steel in 1 M HCl solution

Abstract This work studies the influence of temperature (25–55 °C) and hydrodynamic conditions (0–2000 rpm) on corrosion inhibition of a azomethine compounds: PhN N C (COCH3) = NC6H4Y {Y = OCH3 (SB1), CH3 (SB2), H (SB3), Br (SB4) and Y = Cl (SB5)} on mild steel in a 1 M HCl. Potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) techniques were employed. The results of electrochemical measurements show that the inhibition efficiency increased with increasing compound concentration and decreasing with temperature and hydrodynamic condition. The adsorption process on mild steel surface obeyed Langmuir isotherm. The associated activation parameters and thermodynamic data of adsorption were evaluated and discussed. The inhibition mechanism was determined by potential of zero charge (PZC) measurements. Corrosion attack morphologies were observed at stagnant and hydrodynamic conditions to verify qualitatively the results obtained by electrochemical methods.

The influence of methoxy side groups and halogen nature on the mesomorphic and optical properties of symmetrical azomethines

ABSTRACTThe preparation, characterisation, thermotropic and optical properties of low-molecular azomethines with or without methoxy side group are described in this paper. The azomethine compounds were synthesised by condensation reaction of o-dianisidine/benzidine with para-halogen substituted benzaldehyde. Their properties were analysed by differential scanning calorimetry, thermogravimetry analysis, polarised optical microscopy, X-ray diffraction and optical spectroscopy. The azomethines present liquid crystalline behaviour with large mesophase range and high thermal stability. The compounds without lateral methoxy groups showed smectic A phase, while those with methoxy groups exhibited only nematic phase. The effect of methoxy group and different terminal substituents on the mesomorphic behaviour, molecular and optical properties was estimated in terms of parameters such as molecular polarisability, dipole moment, interdigitation parameter and axial ratio.

Corrosion inhibition efficiency and adsorption behavior of azomethine compounds at mild steel/hydrochloric acid interface

The adsorption and inhibition effect of azomethine compounds: PhN = NAC (COCH3) = NC6H4Y {Y = OCH3 (SB1), CH3 (SB2), H (SB3), Br (SB4) and Y = Cl (SB5)} on mild steel in 1 M HCl at 25 °C were studied using gravimetric measurements, cyclic voltammetry, UV–visible Spectrophotométrique and scanning electron microscope (SEM) methods. Inhibition efficiency was found to increase with the increase in azomethine SB1-SB5 concentration. The adsorption of each inhibitor on mild steel surface obeys Langmuir adsorption isotherm. The results of cyclic voltammetry showed that the presence of azomethine compound decreases the charge density in the transpassive region. The UV–visible absorption spectra of the solution containing the inhibitor after the immersion of mild steel specimen indicate the formation of a (SB1-SB5)-Fe complex. SEM and EDX observations confirmed the existence of protective inhibitor film on a metal surface.

In vitro antibacterial, radical scavenging and solvato-chromism properties of some 4-((4-R-phenyldiazenyl-2-(pyridin-2-ylimino)methyl) phenols

The 4-((4-R-phenyldiazenyl-2-(pyridin-2-ylimino) methyl) phenols were synthesized from the reaction of 5-((4-R-phenyl)diazenyl)-2-hydroxybenzaldehyde with aminopyridines in absolute ethanol and characterized by elemental analysis, mass, FT-IR, UV and NMR spectroscopy. The absorption maxima of synthesized compounds show bathochromic shift in various solvents. The nature of substitutions, solvent environment, hydrogen bonds, temperature, pH and dipole moment of the molecules are the key factors in deciding the solvato-chromism of azo–azomethine dyes. Antibacterial activity was studied by disk diffusion and broth microdilution methods. Diphenylpicrylhydrazyl assay was used to determine the radical scavenging properties. Compounds having electron donating groups in the aryl azo component showed significant antibacterial activity against Bacillus cereus, Staphylococcus aureus, Escherichia coli and Klebsiella pneumonia. Derivative 2-((E)-(pyridin-4-ylimino) methyl)-4-((E)-p-tolyldiazenyl) phenol (2h) with excellent antibacterial activity showed the highest scavenging effect, while the minimum antibacterial and scavenging activity was observed by 4-((E)-(4-chlorophenyl)diazenyl)-2-((E)-(pyridin-2-ylimino)methyl) phenol (2f) having electron withdrawing Cl substituent in the aryl azo component. The antibacterial and scavenging activity of synthesized derivatives are affected by the nature and position of the substituent groups and position of the nitrogen atoms in the pyridine ring. The aminopyridine-based azo–azomethine compounds have been synthesized by condensation reaction of 5-((4-R-phenyl)diazenyl)-2-hydroxybenzaldehyde with n-aminopyridine. The spectra indicated positive solvato-chromism in prepared substances which is dependent on the solvent, substitution, pH and temperature. All the synthesized azo Schiff bases except 2f showed significant antibacterial activity.

Structural characterization and thermal behaviour of some azomethine compounds derived from pyridoxal and 4-aminoantipyrine

Eight azomethine-type compounds (1–8) derived from pyridoxal (3-hydroxy-5-(hydroxymethyl)-2-methylpyridine-4-carbaldehyde) and 4-aminoantipyrine, respectively, were prepared and thoroughly characterized from structural and thermal perspective. The structures of the compounds were studied based on IR, 1H and 13C NMR spectroscopy and electrospray ionization mass spectrometry. The formation of the azomethine derivatives is confirmed by the occurence of signals typical for the imine bond. Compounds 6 and 8 feature a high crystallinity, and their structures were resolved by single-crystal X-ray diffraction. The thermal behaviour of all the compounds was studied by non-isothermal chemiluminescence in static air atmosphere at different heating rates. The pattern of the oxidation process is described. Moreover, thermo-gravimetric and differential scanning calorimetry experiments were conducted in order to assess the thermal oxidation stability. The onset oxidation temperatures show a high thermal stability for all the tested azomethine compounds. The crystallinity degree was comparatively evaluated on the basis of melting enthalpy values and discussed in connection with the molecular structure. Compounds 6–8 show the higher thermal stability and crystallinity degree.

Metal complexes of azomethine compounds bearing an azo group in the amine fragment: Syntheses, structures, and properties

New complexes of Cu(II), Co(II), Ni(II), and Zn(II) with 1-phenyl-3-methyl-4-(4-phenylazophenylaminomethylene)pyrazol-5-one (HL1) and 1-phenyl-3-methyl-4-[4-methyl-2-(4-methylphenylazo)phenylaminomethylene]pyrazol-5-one (HL2) are synthesized using chemical and electrochemical methods and characterized by IR spectroscopy, 1H NMR spectroscopy, X-ray absorption spectroscopy, X-ray diffraction analysis, and magnetic measurements. All complexes are mononuclear. The structures of HL2 and related cobalt complex are determined by X-ray diffraction analysis (CIF files CCDC nos. 1028957 and 1035847, respectively).

Electrochemical and quantum chemical studies of some azomethine compounds as corrosion inhibitors for mild steel in 1 M hydrochloric acid

The corrosion inhibition effect of new azomethine compounds: PhNNC (COCH3)NC6H4Y {Y=OCH3 (SB1), CH3 (SB2), H (SB3), Br (SB4) and Y=Cl (SB5)} on mild steel in 1M HCl, was investigated using potentiodynamic polarization, electrochemical impedance spectroscopy (EIS) and quantum chemistry analysis. It has been found that the inhibition efficiency increased with increasing inhibitor concentration. The polarization curves showed that these Schiff bases function as mixed inhibitors. The adsorption of studied compounds on mild steel surface was found to follow the Langmuir isotherm. Molecular modeling was used to correlate corrosion inhibition properties and calculated quantum chemical parameters.

Synthesis and ultraviolet‐visible spectroscopic and electrochemical analyses of dyes derived from 2‐aminobenzothiazole, and study of their adsorption on titanium dioxide

A series of Schiff bases with hydroxyl anchoring group/s in various positions were synthesised. Their visible light absorption and electrochemical and physicochemical adsorption properties were investigated. Results show that the studied compounds have adequate highest-occupied-molecular-orbital and lowest-unoccupied-molecular-orbital levels that match with the conduction band of titanium dioxide and the redox potential of the electrolyte. Adsorption of azomethine compounds with hydroxyl group/s on titanium dioxide was studied. Experimental data show that the introduction of two β-hydroxyethyl groups can greatly enhance the adsorption efficiency of the studied Schiff base on titanium dioxide. Sorption kinetics was measured for di-(β-hydroxyethyl)aminobenzyliden-2-aminobenzothiazol. Results show rapid initial sorption (<30 min), followed by a slower rate of increasing uptake between 0.5 and 6 h. Kinetic data were modelled using pseudo-first-order, pseudo-second-order, and intraparticle diffusion kinetics equations. These results indicate that the pseudo-second-order equation and intraparticle diffusion model can better describe the adsorption kinetics of di-(β-hydroxyethyl)aminobenzyliden-2-aminobenzothiazol onto titanium dioxide.

Computational study and antimicrobial activity of few Dapsone Schiff base derivatives

Condensation of 4,4-diaminodiphenyl sulfone (Dapsone) with aliphatic and aromatic aldehydes yielded a few Schiff base derivatives in good yields. The optimized structural parameters (bond lengths and bond angles) of three azomethine compounds have been obtained by using the GAUSSIAN 09 program package. Conformer of compound 1 has the highest energy, which has less stability than compounds 2 and 3 at the same model. The synthesized compounds were screened for antibacterial activity against Staphylococcus aureus , Escherichia coli , Bacillus subtilis and fungicidal activity against Aspergillus niger and Candida albicans . All compounds exhibited potent antibacterial and antifungal activity with the reference standard ciprofloxacin and Amphotericin B, respectively.

New 1,2,4-triazole-based azo–azomethine dye. Part III: Synthesis, characterization, thermal property, spectrophotometric and computational studies

A new 1,2,4-triazole-based azo–azomethine compound, H2L, has been prepared by condensation reaction of 1-(3-formyl-4-hydroxyphenylazo)-4-ethylbenzene with prepared triazole-based diamine. The structure of H2L was characterized by using FT-IR, UV–Vis and 1H NMR spectroscopic methods as well as elemental analysis. Hard model chemometrics method has been used to determine the formation constants of zinc(II), copper(II), nickel(II) and cobalt(II) complexes of H2L in DMSO by UV–Vis spectrophotometric method. Solvatochromic behavior of the dye has been also investigated in some organic solvents with different polarities. Thermal properties of the prepared dye was examined by thermogravimetric analysis. Results indicated that the framework of the dye was stable up to 245°C. Furthermore,1H chemical shifts and UV–Vis of H2L were studied by the gauge independent atomic orbital (GIAO), continuous set of gauge transformations (CSGT) and time-dependent density functional theory (TD-DFT) methods respectively at the level of density functional theory using B3LYP/6-311+G(d) basis sets in DMSO. The computational data are in reasonably good agreement with the experimental data.

Spectroscopy and solvatochromism studies along with antioxidant and antibacterial activities investigation of azo–azomethine compounds 2-(2-hydroxyphenylimino)methyl)-4-phenyldiazenyl)phenol

The azo–azomethine compounds 2-(2-hydroxyphenylimino)methyl)-4-phenyldiazenyl)phenol (2a–d) were prepared from the reaction of 2-aminophenol with 2-hydroxy-5-(aryldiazenyl)benzaldehyde (1a–d). The structures of all compounds were then characterized by elemental analysis, mass, infrared, UV–vis, 1H and 13C NMR spectroscopy. The electronic absorption spectra indicated enol–keto tautomeric and positive solvatochromism in compounds (2a–d), which is dependent on the substitution, nature of solvent, pH and environment temperature. The compounds (2a–d) were also evaluated for antibiotic activities by disc diffusion method. Compounds 2a and 2b exhibited antibacterial activities against Staphylococcus aureus and Bacillus cereus, but 2c and 2d were found to have no remarkable antibacterial activity. All the compounds (2a–d) also showed antioxidant activity as determined by 1,1-diphenyl-2-picryl-hydrazyl (DPPH) method.

Relaxation processes in the polymer structure of an azomethine base

The results of studying the isothermal polarization of thin polymer films of an azomethine compound (Schiff base) with varying polarization field intensity are described. Intense relaxation processes induced by space-charge accumulation in the metal-polymer near-contact zone are revealed in the studied samples. Experimental data are analyzed in terms of the relay mechanism of charge transfer in the conduction band involving deep local levels. Values of the microparameters characterizing the observed relaxation phenomena are determined.

Đánh giá khả năng ức chế ăn mòn thép và nhôm của một số dãy hợp chất azometin

The corrosion inhibition efficiencies of 39 Schiff’s bases of series from aniline, ethylendiamine, cyclohexylamine and 4,4-benzidine in the 1M and 2M HCl solutions on the steel (CT-3) and aluminium (D16) have been studied. It seems that the azomethine compounds with aldehyde moieties of 3-indolyl group (B8, C8 and H8) strongly inhibited the corrosion on aluminium but the corrosion inhibition effects on steel are relatively low. The azomethine compounds with aldehyde moieties of p-nitrophenyl group (B1, C1 and H1) inhibited highly the corrosion of both steel and aluminium in HCl solution. The bis-(4-nitrobenzylidene) diethylamine (B1) compound can be used as a good corrosion inhibitor for low carbon steel and aluminium in HCl acid solution.

Resistance Monitoring and Assessment of Resistance Risk to Pymetrozine in &lt;I&gt;Laodelphax striatellus&lt;/I&gt; (Hemiptera: Delphacidae)

Laodelphax striatellus (Fallén) is a major pest of cultivated rice. Pymetrozine, a pyridine azomethine compound, represents a novel insecticide with a selective activity against sucking pests. The resistance of L. striatellus to thiamethoxam, nitenpyram, chlorpyrifos, and pymetrozine in five field populations, collected from Jiangsu, Anhui, and Zhejiang in China, was monitored from 2009 to 2011 in laboratory. All the populations kept susceptible to minor resistance to thiamethoxam and nitenpyram in the 3 yr (0.6- to 2.2-fold and 0.8- to 3.8-fold, respectively), while the insects developed low to high level resistance to chlorpyrifos (9.7- to 76.1-fold). Three populations were all susceptible to pymetrozine (1.1- to 2.1-fold) in 2009, but the Wuxi and Yancheng populations developed low level resistance to pymetrozine (5.5-fold and 5.3-fold, respectively) in 2011. Meanwhile, the resistance level of the selected strain reared in laboratory increased by 1.0-fold after 12-generation selection with pymetrozine. The realized heritability (h2) of resistance at different selection stages was estimated as 0.0470 (F1 to F13) and 0.2070 (F5 to F13) by using threshold trait analysis. It suggested that L. striatellus had the definite risk of resistance to pymetrozine.

Synthesis and genotoxicity of Schiff base transition metal complexes

A new ONNO-type azomethine ligand, 2,2′-(ethane-1,2-diylidenedinitrilo)dibenzoic acid, (YLH2) (1) has been prepared by the condensation of 2-aminobenzoic acid and glyoxal. The coordination compounds [Ni(YL)] (2), [Co(YL)] (3), [Cu(YL)(H2O)] (4), [Zn(YL)] (5), and [Cd(YL)] (6) of the YLH2 ligand with five transition metal ions, Ni(II) Co(II), Cu(II), Zn(II), and Cd(II) have been prepared. The structures of these new azomethine compounds are proposed on the basis of the elemental analyses, proton nuclear magnetic resonance, infrared, ultraviolet–visible spectroscopy, and X-ray powder diffraction patterns. Elemental analyses indicate a ligand metal ratio of 1:1 in the coordination compounds. X-ray powder diffraction parameters for [Cu(YL)(H2O)] and [Cd(YL)] compounds correspond to orthorhombic and monoclinic structures, respectively. The ligand acts as a tetradentate ligand bending through oxygen atoms of the hydroxyl groups of benzoic acid and nitrogen atoms of the azomethine groups. In addition, the ligand and its metal complexes have been studied for their possible genotoxic potential. © 2011 Wiley Periodicals, Inc. Heteroatom Chem 22:119–130, 2011; View this article online at wileyonlinelibrary.com. DOI 10.1002/hc.20665

Conjugated Fluorenes Prepared From Azomethines Connections-II: The Effect of Alternating Fluorenones and Fluorenes on the Spectroscopic and Electrochemical Properties

The photophysics and electrochemistry of fluorene and fluorenone azomethine derivatives were examined in order to understand the deactivation pathways responsible for the quenched fluorescence of these compounds, which should otherwise be fluorescent. Steady-state fluorescence showed that the fluorene singlet excited state is quenched both by fluorenone (1) and a model aliphatic azomethine compound (14) with k(q) approximately 10(10) M(-1) s(-1). The quencher concentration required to deactivate 95% of the excited singlets formed was 8.4 mM for fluorenone and 34 mM for 14. Intramolecular photoinduced electron transfer (PET) from fluorene to both 1 and 14 was found as the principle deactivation mode of the fluorene's excited state. The high degree of conjugation of the azomethines promotes intersystem crossing to the triplet manifold by narrowing the singlet-triplet energy gap, which is also in part responsible for the reduced fluorescence observed for the fluorenone azomethine derivatives 5-11. Fluorescence quenching by PET was corroborated from the electrochemical and spectroscopic data by applying the Rehm-Weller equation. Meanwhile, the inherent fluorene fluorescence can be restored by protonating the azomethine, resulting from suppressed PET. Although PET is exergonically favorable (-242 kJ/mol for 1 and -96 kJ/mol for 14), intersystem crossing still occurs. The resulting fluorene triplet state is efficiently quenched by both 1 (k(q) = 7 x 10(9) M(-1) s(-1)) and 14 (k(q) = 5 x 10(9) M(-1) s(-1)) confirming that the absence of triplet signal by laser flash photolysis is a result of rapid intramolecular energy transfer to the two quencher sites. A concentration-dependent second emission was observed for the fluorenone containing azomethines assigned to the formation of excimers.

FTIR investigations of phase transitions in an asymmetric azomethine liquid crystal

The liquid crystalline (LC) behavior of a literature-reported asymmetric azomethine compound (4-[4-(n-butyloxy)-benzylideneimino]-chlorobenzene, Cl.O4) was investigated by using optical polarized light microscopy, differential scanning calorimetry and medium-wide angle X-ray diffraction. FTIR in attenuated total internal reflection configuration was employed to study the microstructural changes occurring during phase transitions of the azomethine. Spectral modifications, associated with molecular conformation rearrangements, allowing the change of the molecular shape from a LC organization to another, have been found. The spectral analysis gave significant evidences for the different phase transitions, thus proving the efficiency of such method for investigating LC materials.

Kinetics of the nematic phase growth across the isotropic-nematic phase transition in polymer-dispersed liquid crystals

Polymer-dispersed liquid crystals (PDLCs) composed of poly(dimethyl siloxane), cured poly(dimethyl siloxane) and polysulfone (as matrices), and an azomethine compound (as an embedded mesogen varying in weight from 5 to 80%) were prepared via solvent-induced phase separation. After preparation, they were heated to the melt and then cooled; phase transitions upon both heating and cooling were detected with a differential scanning calorimeter and a polarising optical microscope (POM). The nematic droplets appearing in the POM images across the isotropic-nematic phase transition were treated statistically and described with principles of irreversible thermodynamics. Furthermore, kinetics of the nematic phase growth across this phase transition was studied and described analytically with the universal law for cluster growth. Both flexibility of the polymer matrix and the mesogen content in PDLCs were shown to influence the processes studied.

Synthesis of Some Biologically Important Hydrazono and Azomethine Compounds.

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