Heterocyclic Schiff Base Research Articles

Synthesis of new chiral heterocyclic Schiff base modulated Cu(II)/Zn(II) complexes: Their comparative binding studies with CT-DNA, mononucleotides and cleavage activity

New Schiff base ligand L derived from the condensation reaction of 2-amino-3-formylchromone with (R)-2-amino-2-phenylethanol was synthesized and characterized which involves combination element of ammine functionality and naturally occurring heterocyclic chromone, 4H-benzopyran-4-one. Subsequently, their complexes 1 and 2 with Cu(NO 3) 2 and Zn(NO 3) 2, respectively were prepared. The DNA binding studies of the ligand L and complexes 1 and 2 with CT-DNA as compared to classical anticancer drug cisplatin were carried out by employing different optical methods viz, UV–vis, fluorescence, circular dichroism and viscosity measurements. Furthermore, the absorption studies, 1H and 31P with mononucleotides were also monitored to examine the base specific interactions of the transition metal complexes which revealed a higher propensity of copper(II) complex 1 for 5′-GMP while for zinc(II) complex 2 towards 5′-TMP involving groove binding mechanism of the complexes towards DNA. The complex 1 exhibits a remarkable DNA cleavage activity with pBR322 DNA in presence of different activators and cleavage reaction involves various oxygen species suggesting the involvement of active oxygen species for the DNA scission.

Synthesis, characterization and crystal structure of some bidentate heterocyclic Schiff base ligands of 4-toluoyl pyrazolones and its mononuclear Cu(II) complexes

We depict the synthesis of a new set of six bidentate heterocyclic Schiff base ligands, formed by the condensation of three different 4-toluoyl pyrazolones with various aromatic amines in ethanolic medium. All of these ligands have been characterized on the basis of elemental analysis, IR, 1H NMR, 13C NMR and Mass spectral data. The molecular geometries of three of these ligands have been determined by single crystal X-ray study. It reveals that these ligands exist in amine-one tautomeric form in the solid state. The reaction of these ligands with copper(II) resulted in the formation of mononuclear complexes having the general composition [CuL 2(H 2O) 2] with two water molecules at axial positions. These complexes have been characterized on the basis of elemental analysis, Cu-estimation, molar conductivity, magnetic measurements, IR, UV–Visible, FAB–Mass, TG–DTA–DSC data, cyclic voltametric measurements and ESR spectral studies. ESR spectra and magnetic susceptibility measurements indicates distorted octahedral stereochemistry of Cu(II) complexes, while non-electrolytic behaviour of complexes indicates the absence of counter ion.

The Asymmetric Transfer Hydrogenation of Benzoylpyridine: Preparation and Crystal Structure of Chiral Heterocyclic Schiff Base Ligands

Two optically active heterocyclic imine ligands 3 (3a and 3b) have been synthesised for the iridium catalysed asymmetric transfer hydrogenation of 4-benzoylpyridine. 3b was characterised by single crystal X-ray diffraction analysis. The two ligands (3a and 3b) were applied to Ir-catalysed asymmetric transfer hydrogenation of 4-benzoylpyridine using 2-propanol as a source of hydrogen. The results showed that the corresponding chiral alcohol could be obtained with moderate yield and enantioselectivity at an optimum temperature.

Synthesis, characterization, antifungal, antibacterial and DNA cleavage studies of some heterocyclic Schiff base metal complexes

Co(II), Ni(II), Cu(II) and Zn(II) complexes of the Schiff base derived from indole-3-carboxaldehyde and m-aminobenzoic acid were synthesized and characterized by elemental analysis, molar conductance, IR, UV–Vis, magnetic moment, powder XRD and SEM. The IR results demonstrate the bidentate binding mode of the ligand involving azomethine nitrogen and carboxylato oxygen atoms. The electronic spectral and magnetic moment results indicate that Co(II) and Ni(II) complexes have tetrahedral geometry, while Cu(II) complex is square planar. Powder XRD and SEM indicate the crystalline state and surface morphology studies of the complexes. The antimicrobial activity of the synthesized ligand and its complexes were screened by disc diffusion method. The results show that the metal complexes were found to be more active than the ligand. The nuclease activity of the ligand and its complexes were assayed on CT DNA using gel electrophoresis in the presence of H2O2. The Cu(II) complex showed increased nuclease activity in the presence of an oxidant when compared to the ligand and other complexes.

Preparation and Characterization of New Heterocyclic SchiffBase Complexes

Metal complexes of general formula [M(L)2]Cl2 and [Fe(L)2Cl2] where M is Mn(II), Co(II), Ni(II), Cu(II) and Zn(II) and L is the Schiff base, 2-(pyrimidin-2-yliminomethyl) furan (FAP) are prepared. The complexes were characterized by analytical as well as spectroscopic, magnetic and conductance measurements. The infrared spectra of the complexes agree with coordination to the central metal atom through the nitrogen of the azomethine group and oxygen of the furan ring. Magnetic susceptibility data coupled with electronic spectra suggest a distorted octahedral structure for the Fe(II) complex, a tetrahedral geometry for the Mn(II), Co(II) and Zn(II) complexes, and a square planar for the Ni(II) and Cu(II) complexes. Conductance measurements suggest the 1 :2 electrolytic nature of the complexes with the exception of the Fe(II) complex as of a non-electrolytic nature.

Spectroscopic, magnetic and thermal studies of Co(II), Ni(II), Cu(II) and Zn(II) complexes of 3-acetylcoumarin–isonicotinoylhydrazone and their antimicrobial and anti-tubercular activity evaluation

Co(II), Ni(II), Cu(II) and Zn(II) complexes with a new heterocyclic Schiff base derived by the condensation of isonicotinoylhydrazide and 3-acetylcoumarin have been synthesized. 1H, 13C and 2D HETCOR NMR analyses confirm the formation of title compound and existence of the same in two isomeric forms. The metal complexes were characterized on the basis of various spectroscopic techniques like electronic, EPR, IR, 1H and 13C NMR studies, elemental analysis, magnetic properties and thermogravimetric analysis, and also by the aid of molar conductivity measurements. It is found that the Schiff base behaves as a monobasic tridentate ligand coordinating in the imidol form with 1:1 metal to ligand stoichiometry. Trigonal bipyramidal geometry has been assigned for Ni(II) and Cu(II) complexes, while tetrahedral for Co(II) and Zn(II) complexes. The compounds were subjected to antimicrobial and anti-tubercular activity screening using serial broth dilution method and Minimum Inhibitory Concentration (MIC) is determined. Zn(II) complex has shown significant antifungal activity with an MIC of 6.25 μg/mL while Cu(II) complex is noticeable for antibacterial activity at the same concentration. Anti-TB activity of the ligand has enhanced on complexation with Co(II) and Ni(II) ions.

Spectral, magnetic, biocidal screening, DNA binding and photocleavage studies of mononuclear Cu(II) and Zn(II) metal complexes of tricoordinate heterocyclic Schiff base ligands of pyrazolone and semicarbazide/thiosemicarbazide based derivatives

We depict the synthesis and characterization of copper(II) and zinc(II) coordination compounds of 4-(3',4'-dimethoxybenzaldehydene)2-3-dimethyl-1-phenyl-3-pyrazolin-5-semicarbazone (1a), 4-(3',4'-dimethoxybenzaldehydene)2-3-dimethyl-1-phenyl-3-pyrazolin-5-thiosemicarbazone (1b), 4-(3'-hydroxy-4'-nitrobenzaldehydene)2-3-dimeth yl-1-phenyl-3-pyrazolin-5-semicarbazone (1c) and 4-(3'-hydroxy-4'-nitrobenzal dehydene)2-3-dimethyl-1-phenyl-3-pyrazolin-5-thiosemicarbazone (1d). All the remote compounds have the general composition [ML(2)] (M=Cu(II) and Zn(II)); L=Schiff base (1a-1d). All the complexes were characterized by elemental analysis, molar conductivity, IR, (1)H NMR, UV-vis, ESI-Mass, magnetic susceptibility measurements, cyclic voltammetric measurements, and EPR spectral studies. It has been originated that the Schiff bases with Cu(II) and Zn(II) ions form mononuclear complexes on 1:2 (metal:ligand) stoichiometry. Distorted octahedral environment is suggested for the metal complexes. The conductivity data confirm the non-electrolytic nature of the complexes. The interaction of CuL(2)(1a-1d) complexes with CT DNA was investigated by spectroscopic, electrochemical and viscosity measurements. Results suggest that the copper complexes bind to DNA via an intercalative mode. Moreover, the complexes have been found to promote the photocleavage of plasmid DNA pBR322 under irradiation at 365 nm. The Schiff bases and their metal complexes were screened for their antifungal and antibacterial activities against different species of pathogenic fungi and bacteria and their biopotency has been discussed.

Synthesis, Spectroscopic Characterization, Thermal Investigation and Antimicrobial Activity of S, O and N-Donor Heterocyclic Schiff Base Ligands and their Co(II), Cd(II), Hg(II), Fe(III) and UO2(II) Metal Complexes

Synthesis, Spectroscopic Characterization, Thermal Investigation and Antimicrobial Activity of S, O and N-Donor Heterocyclic Schiff Base Ligands and their Co(II), Cd(II), Hg(II), Fe(III) and UO2(II) Metal Complexes

Synthesis and Antimicrobial Activity of Some New Heterocyclic Schiff Bases Derived from 2-Amino-3-formylchromone

Some new hydrazone derivatives 3a–e have been obtained from 2-amino-3-formylchromone (1). Heterocyclization of thiocarbohydrazone derivative 3e via reaction with some electrophilic reagents afforded 1,2,4-triazoles 6–8 and 1,2,4-triazines 9–13. Condensation reactions of aldehyde 1 with o-aminoaldehydes and/or ketones afforded some new isolated and condensed heterocyclic systems 17, 19, and 20. The newly synthesized compounds were screened for their antimicrobial activity.

Corrosion inhibition of mild steel in hydrochloric acid solution by Schiff base furoin thiosemicarbazone

A heterocyclic Schiff base furoin thiosemicarbazone was tested for its corrosion inhibition towards mild steel in 1 M HCl solution using weight loss, Tafel polarization and electrochemical impedance spectroscopy techniques. Furoin thiosemicarbazone revealed good corrosion inhibition efficiency even at low concentrations towards mild steel in HCl medium. Comparison of corrosion inhibition efficiency of Schiff base and its parent amine and effect of temperature on inhibition efficiency were also investigated. The adsorption of furoin thiosemicarbazone on mild steel surface obeys Langmuir isotherm.

Synthesis and characterization of heterocyclic Schiff base and its complexes with Cu(II), Ni(II), Co(II), Zn(II), and Cd(II)

A new Schiff base, {1-[(2-hydroxy-naphthalen-1-ylmethylene)-amino]-4-phenyl-2-thioxo-1, 2-dihydro-pyrimidin-5-yl}-phenyl-methanone, has been synthesized from N-amino pyrimidine-2-thione and 2-hydroxynaphthaldehyde. Metal complexes of the Schiff base were prepared from acetate/chloride salts of Cu(II), Co(II), Ni(II), Zn(II), and Cd(II) in methanol. The chemical structures of the Schiff-base ligand and its metal complexes were confirmed by elemental analyses, IR, 13C-NMR, 1H-NMR, API-ES, UV-Visible spectroscopy, magnetic susceptibility, and thermogravimetric analyses. The electronic spectral data and magnetic moment measurements suggest mononuclear octahedral and mononuclear or binuclear square planar structures for the metal complexes. In light of these results, it was suggested that this ligand coordinates to each metal atom by hydroxyl oxygen, azomethine nitrogen, and thione sulfur to form octahedral complexes with Cd(II) and Zn(II).

Synthesis and characterization of new heterocyclic Schiff base palladacycles: Ring activation through N-oxide formation

Reaction of the Schiff base ligand derived from 4-pyridinecarboxaldehyde NC 5H 4C(H) N[2′,4′,6′-(CH 3)C 6H 2], ( 1), with palladium(II) acetate in toluene at 60 °C for 24 h gave [Pd{NC 5H 4C(H) N[2′,4′,6′-(CH 3)C 6H 2]} 2(OCOCH 3) 2], ( 2), with two ligands coordinated through the pyridine nitrogen. Treatment of the Schiff base ligand derived from 4-pyridinecarboxaldehyde N-oxide, 4-(O)NC 5H 4C(H) N[2′,4′,6′-(CH 3)C 6H 2], ( 4), with palladium(II) acetate in toluene at 75 °C gave the dinuclear acetato-bridged complex [Pd{4-(O)NC 5H 3C(H) N[2′,4′,6′-(CH 3)C 6H 2]}(OCOCH 3)] 2, ( 5) with metallation of an aromatic phenyl carbon. Reaction of complex 5 with sodium chloride or lithium bromide gave the dinuclear halogen-bridged complexes [Pd{4-(O)NC 5H 3C(H) N[2′,4′,6′-(CH 3)C 6H 2]}(Cl)] 2, ( 6) and [Pd{4-(O)NC 5H 3C(H) N[2′,4′,6′-(CH 3)C 6H 2]}(Br)] 2, ( 7), after the metathesis reaction. Reaction of 6 and 7 with triphenylphosphine gave the mononuclear species [Pd{4-(O)NC 5H 3C(H) N[2′,4′,6′-(CH 3)C 6H 2]}(Cl)(PPh 3)], ( 8) and [Pd{4-(O)NC 5H 3C(H) N[2′,4′,6′-(CH 3)C 6H 2]}-(Br)(PPh 3)], ( 9), as air stable solids. Treatment of 6 and 7 with Ph 2P(CH 2) 2PPh 2 (dppe) in a complex/diphosphine 1:2 molar ratio gave the mononuclear complexes [Pd{4-(O)NC 5H 3C(H) N[2′,4′,6′-(CH 3)C 6H 2]}(PPh 2(CH 2) 2PPh 2)][Cl], ( 10), and [Pd{4-(O)NC 5H 3C(H) N[2′,4′,6′-(CH 3)C 6H 2]}(PPh 2(CH 2) 2PPh 2)][PF 6], ( 11), with a chelating diphosphine. The molecular structure of complex 9 was determined by X-ray single crystal diffraction analysis.

Microwave Assisted Synthesis, Spectroscopic, Thermal and Biological Studies of Some Lanthanide(III) Chloride Complexes with a Heterocyclic Schiff Base

Microwave assisted condensation of salicylaldehyde with 2-amino-3-carboxyethyl-4,5-dimethylthiophene in the absence of solvent was efficiently performed to form a potentially tridentate Schiff base viz., 2-(N-salicylideneamino)-3-carboxyethyl-4,5-dimethylthiophene (HSAT). This compound is versatile in forming well defined complexes with lanthanide(III) chlorides under microwave irradiation in solid state. The spectral data showed that the ligand acted as neutral tridentate with ONO donor sequence towards the lanthanide(III) ions, forming complexes of the type [Ln(HSAT) 2 Cl 3 ] where Ln = La(III), Ce(III), Pr(III), Nd(III), Sm(III), Eu(III) and Gd(III). The complexes possessed 1:2 metal-ligand ratio. X-ray diffraction studies on the ligand and [La(HSAT) 2 Cl 3 ] showed that the ligand exists in tetragonal and the complex in orthorhombic crystalline forms. Thermal decomposition study of lanthanum(III) complex was carried out. The complex [La(HSAT) 2 Cl 3 ] underwent facile transesterification. The ligand and the complexes were screened for their antibacterial activities.

Ni(II) and Ru(II) Schiff base complexes as catalysts for the reduction of benzene

Two new complexes, [M II(L)(Cl)(H 2O) 2]·H 2O (where M = Ni or Ru and L = heterocyclic Schiff base, 3-hydroxyquinoxaline-2-carboxalidene-4-aminoantipyrine), have been synthesized and characterized by elemental analysis, FT-IR, UV–vis diffuse reflectance spectroscopy, FAB-MASS, TG–DTA, AAS, cyclic voltammetry, conductance and magnetic susceptibility measurements. The complexes have a distorted octahedral structure and were found to be effective catalysts for the hydrogenation of benzene. The influence of several reaction parameters such as reaction time, temperature, hydrogen pressure, concentration of the catalyst and concentration of benzene was tested. A turnover frequency of 5372 h −1 has been found in the case of ruthenium complex for the reduction of benzene at 80 °C with 3.64 × 10 −6 mol catalyst, 0.34 mol benzene and at a hydrogen pressure of 50 bar. In the case of the nickel complex, a turnover frequency of 1718 h −1 has been found for the same reaction with 3.95 × 10 −6 mol catalyst under similar experimental conditions. The nickel complex shows more selectivity for the formation of cyclohexene while the ruthenium complex is more selective for the formation of cyclohexane.

Lanthanum(III) chloride complexes with heterocyclic Schiff bases

Condensation of 2-amino-3-carboxyethyl-4,5,6,7-tetrahydrobenzo[b]thiophene with carbonyl compounds such as isatin, o-hydroxyacetophenone or benzoin in 1:1 ratio in ethanol medium yielded three distinctly different heterocyclic Schiff bases viz. 2-(N-indole-2-one)amino-3-carboxyethyl-4,5,6,7-tetrahydrobenzo[b]thiophene (ISAT), 2-(N-o-hydroxyacetophenone)amino- 3-carboxyethyl-4,5,6,7-tetrahydro-benzo[b]thiophene (HAAT) or 2-(N-benzoin)amino-3-carboxyethyl-4,5,6,7-tetrahydrobenzo[b]thiophene (HBAT) respectively. These ligands formed well defined complexes with lanthanum(III) chloride under suitable conditions.

Complexation of 4-amino-1,3 dimethyl-2,6 pyrimidine-dione derivatives with cobalt(II) and nickel(II) ions: synthesis, spectral, thermal and antimicrobial studies

Four heterocyclic Schiff-base ligands derived from condensation of 4-amino-1,3 dimethyl-2,6 pyrimidine-dione with 2-hydroxybenzaldehyde, 2-methoxybenzaldehyde, 4-hydroxy-3-methoxybenzaldehyde and 4-(dimethylamino) benzaldehyde, (HL1, L2, HL3and L4), respectively, and their Co(II) and Ni(II) complexes have been prepared and characterized via elemental analysis, molar conductance, magnetic moment, thermal and XRPD analysis as well as spectral data (IR, 1H-NMR, mass and solid reflectance). IR data reveal that the ligands are bidentate neutral ligands except HL1, which is monobasic tridentate with coordination sites azomethine (N), carbonyl (O) and phenolic (O). Conductance data suggest that all complexes are non-electrolytes, except cobalt(II) complexes of L2and HL3are 1 : 1 electrolytes. The mass spectra confirm the proposed structure of the ligands and their complexes. The solid reflectance spectral data and magnetic moment measurements suggest octahedral, tetrahedral and square planar geometrical structures for the metal complexes. The spectral data were utilized to compute the important ligand field parameters B, β and Dq; LFSE also was calculated. The thermal behavior is also studied. Antibacterial and antifungal properties of the ligands and their complexes show broad-spectrum activities and the metal complexes show higher activity than the free ligands.

Polymerization of isoprene catalyzed by neodymium heterocyclic Schiff base complex

Neodymium-based heterocyclic Schiff base complex was prepared and applied for the coordination polymerization of isoprene. This complex polymerized isoprene to afford products featuring high cis-1,4 stereo specificity (ca. 95%) and high molecular weight (ca. 10 5) in the presence of the tri-isobutyl aluminium (AliBu 3) as cocatalyst. The microstructure of obtained polyisoprene was investigated by FTIR, 1H NMR. Two different kinds of active centers in the catalyst system were examined by GPC method.

HETEROCYCLIC SCHIFF BASE NEODYMIUM COMPLEX AS CATALYST FOR RING-OPENING POLYMERIZATION OF ε-CAPROLACTONE

An aromatic heterocyclic Schiff base neodymium complex bearing thiazole was synthesized and its activity in the ring-opening polymerization of e-caprolactone (CL) was examined. The conditions of the CL/Nd molar ratio, monomer concentration, polymerization time and temperature were investigated. Activities of ca.171 kg/Nd·h were obtained under the optimum condition (CL/Nd = 1600 (molar ratio), [CL] = 2.26 mol L-1, 1 h at 50°C), giving a poly(e-caprolactone) (PCL) of number-average molecular weight Mn= 5.4 × 104 and molecular weight distribution MWD = 1.96. The conversion of CL monomer as high as 94% was observed after polymerized for one hour. The mechanism of coordination polymerization has also been illustrated.

Lanthanum heterocyclic Schiff-base complex initiated ring-opening polymerization of ɛ-caprolactone

Lanthanum complex supported by the heterocyclic Schiff-base ligand of N-(2-pyridyl)-3,5-di- tert-butyl-salicylaldimine was prepared and employed for the ring-opening polymerization (ROP) of ɛ-caprolactone (ɛ-CL). The polymers obtained with this initiator showed a unimodal molecular weight distribution implied that only one active species was present. Mechanism study revealed that the polymerization proceeds via acyl-oxygen bond cleavage.

Novel Approach for the Rapid and Efficient Synthesis of Heterocyclic Schiff Bases (III) and Azetidinones (V) under Microwave Irradiation.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.