Studies on some salicylaldehyde Schiff base derivatives and their complexes with Cr(III), Mn(II), Fe(III), Ni(II) and Cu(II)

The formation constants of some transition metal ions Cr(III), Mn(II), Fe(III), Ni(II) and Cu(II) binary complexes containing Schiff bases resulting from condensation of salicylaldehyde with aniline (I), 2-aminopyridine (II), 4-aminopyridine (III) and 2-aminopyrimidine (IV) were determined pH-metrically in ethanolic medium (80%, v/v). The formation constants were determined for all binary complexes. The important infrared (IR) spectral bands corresponding to the active groups in the four ligands and the solid complexes under investigation were studied. The solid complexes have been synthesized and studied by thermogravimetric analysis. The thermal dehydration and decomposition of these complexes were studied kinetically using the integral method applying the Coats-Redfern equation. It was found that the thermal decomposition of the complexes follow second order kinetics. The thermodynamic parameters of the decomposition are also reported. The electronic absorption spectra of the investigated ligands were carried out to determine the pK(a) values spectrophotometrically.     

Synthesis, characterization and antioxidant activity of naringenin Schiff base and its Cu(II), Ni(II), Zn(II) complexes

A new ligand, naringenin-2-hydroxy benzoyl hydrazone (H(5)L), was prepared by condensation of naringenin with 2-hydroxy benzoyl hydrazine. Its Cu(II), Ni(II), Zn(II) complexes have also been synthesized and characterized on the basis of (1)H-NMR, IR, UV-Vis spectra, elemental analyses, molar conductivity and thermal analyses. The general formula of these complexes was M(H(3)L) [M=Cu(II), Ni(II) and Zn(II)]. In addition, the antioxidant activities (superoxide and hydroxyl radical) of the free ligand and its complexes were determined in vitro. These compounds were found to possess potent antioxidant activity and be better than standard antioxidants like vitamin C and mannitol. In particular, the Cu(II) complex displayed excellent activity on the superoxide radical.     

Synthesis,structures, and property studies on Zn(II), Ni(II), and Cu(II) complexes with a Schiff base ligand containing thiocarbamide group

A Schiff base ligand containing thiocarbamide group of 4-phenyl-1-(4-methoxyl-1-phenylethylidene)thiosemicarbazide (HL) and its three mononuclear metal complexes of ZnL₂ (1), NiL₂ (2), and CuL₂ (3) have been synthesized. Elemental analysis, IR, and X-ray single crystal diffraction characterizations for the ligand and the three complexes have been carried out. In the three complexes, the central metallic ions of Zn²⁺, Ni²⁺, and Cu²⁺ coordinate with two deprotonated ligands of L⁻, respectively. In 1, Zn²⁺ ion adopts a distorted tetrahedral geometry, while in 2 and 3, both the Ni²⁺ and Cu²⁺ ions possess distorted square planar configurations. For the four compounds, UV–Vis spectra have been measured and DFT calculations at B3LYP/LANL2DZ level of theory prove that the electronic spectra of HL and 1 are corresponding with electronic transitions of n → π* and π → π* in the ligand itself and the electronic spectra of 2 and 3 are attributed to intraligand electronic transitions as well as d–d electronic transitions. Electrochemical investigations reveal that the different metal–ligand interactions have changed the peak shapes and peak locations, which are corresponding with the DFT-B3LYP/LANL2DZ calculational results. Fluorescence spectra measurements indicate that the ligand emits purple fluorescence and the complex 1 emits stronger blue fluorescence, while the complexes 2 and 3 quench fluorescence. The thermal analyses result show that the three complexes undergo two similar decomposition processes because of their similar geometric configurations.     

Design,synthesis, DNA binding ability,chemical nuclease activity and antimicrobial evaluation of Cu(II), Co(II), Ni(II) and Zn(II) metal complexes containing tridentate Schiff base

A novel Schiff base has been designed and synthesized using the bioactive ligand obtained from 4-aminoantipyrine, 3,4-dimethoxybenzaldehyde and 2-aminobenzoic acid. Its Cu(II), Co(II), Ni(II), Zn(II) complexes have also been synthesized in ethanol medium. The structural features have arrived from their elemental analyses, magnetic susceptibility, molar conductance, mass, IR, UV–Vis, ¹H NMR and ESR spectral studies. The data show that the complexes have composition of ML₂ type. The electronic absorption spectral data of the complexes suggest an octahedral geometry around the central metal ion. The interaction of the complexes with calf thymus (CT) DNA has been studied using absorption spectra, cyclic voltammetric, and viscosity measurement. The metal complexes have been found to promote cleavage of pUC19 DNA from the super coiled form I to the open circular form II. The complexes show enhanced antifungal and antibacterial activities compared with the free ligand.     

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 characterisation of Cu(II), Ni(II), Mn(II), Zn(II) and VO(II) Schiff base complexes derived from o -phenylenediamine and acetoacetanilide

Neutral tetradentate N₂O₂ type complexes of Cu(II), Ni(II), Mn(II), Zn(II) and VO(II) have been synthesised using a Schiff base formed by the condensation of o-phenylenediamine with acetoacetanilide in alcohol medium. All the complexes were characterised on the basis of their microanalytical data, molar conductance, magnetic susceptibility, IR, UV-Vis¹H NMR and ESR spectra. IR and UV-Vis spectral data suggest that all the complexes are square-planar except the Mn(II) and VO(II) chelates, which are of octahedral and square pyramidal geometry respectively. The monomeric and neutral nature of the complexes was confirmed by their magnetic susceptibility data and low conductance values. The ESR spectra of copper and vanadyl complexes in DMSO solution at 300 K and 77 K were recorded and their salient features are reported.     

Polarized spectroscopy and hybrid materials of chiral Schiff base Ni(II), Cu(II), Zn(II) complexes with included or separated azo-groups

Chiral Schiff base complexes containing azo-groups, bis(N-R-1-naphtylethyl-4-phenyldiazenylsalicydenaminato) nickel(II), copper(II), and zinc(II) complexes affording a distorted square planar trans-[MN₂O₂] coordination geometry were prepared newly. Organic/inorganic hybrid materials in polymethylmethacrylate (PMMA) cast films of them (a containing type) or the analogous chiral Schiff base complexes, bis(N-R-1-phenylethyl-3,5-dichlorosalicydenaminato) nickel(II), copper(II), and zinc(II), and azobenzene (AZ) (a separated type) were assembled for comparison of polarized UV light induced molecular arrangement caused by Weigert effect. Investigation of parameters for optical anisotropy of metal complexes as well as AZ suggested that the degree of increasing optical anisotropy of the containing type is higher than that of the separated type based on π-π^∗ (of which characteristic band appeared around 380 nm), n-π^∗, and d-d bands of polarized absorption electronic spectra. Rigid nickel(II) or zinc(II) complexes are easy to increase optical anisotropy than flexible copper(II) complexes for both types.     

Chiral discrimination asserted by enantiomers of Ni (II), Cu (II) and Zn (II) Schiff base complexes in DNA binding, antioxidant and antibacterial activities

Chiral Schiff base ligands (S)-H(2)L and (R)-H(2)L and their complexes (S-Ni-L, R-Ni-L, S-Cu-L, R-Cu-L, S-Zn-L and R-Zn-L) were synthesized, characterized and examined for their DNA binding, antioxidant and antibacterial activities. The complexes showed higher binding affinity to calf thymus DNA with binding constant ranging from 2.0×10(5) to 4.5×10(6) M(-1). All the complexes also exhibited remarkable superoxide (56-99%) and hydroxyl scavenging (45-89%) activities as well as antibacterial activities against gram (+) and gram (-) bacteria. However, none of the complexes showed antifungal activity. Conclusively, S enantiomers of the complexes were found to be relatively more efficient for DNA interaction, antioxidant and antibacterial activities than their R enantiomers. This study reveals the possible utilization of chiral Schiff base complexes for pharmaceutical applications.     

A new mesitylenic cyclobutane substituted Schiff base ligand and its Co(II), Cu(II), Ni(II), and Zn(II) complexes

A new ligand, 4‐(1‐methyl‐1‐mesityl‐3‐cyclobutanyl)‐2‐(2‐hydroxy‐1‐naphthylideneimino)thiazole (LH), has been synthesized starting from 1‐methyl‐1‐mesityl‐3‐(2‐chloro‐1‐oxoethyl)cyclobutane and thiourea and subsequently 2‐hydroxy‐1‐napthalaldehyde. Mononuclear complexes with a metal‐ligand ratio of 1:2 have been prepared with Co(II), Cu(II), Ni(II), and Zn(II) metals. The authenticity of the ligand and its complexes are proposed based on elemental analyses, IR, UV‐vis, ¹³C and ¹H NMR spectra, magnetic susceptibility measurements, thermogravimetric analyses, and differential scanning calorimetry. © 2001 John Wiley & Sons, Inc. Heteroatom Chem 12:42–46, 2001     

Coordination chemistry of some new Cu(II), Ni(II) and Co(II) macroacyclic (N2O4) Schiff base complexes: X-ray crystal structure of Cu(II) complex

Six new Cu(II), Ni(II) and Co(II) macroacyclic Schiff base complexes [M^II(H₂L)](ClO₄)₂ (L = L¹ and L²) (I–VI) were prepared by the reaction of two new N₂O₄ Schiff base ligands in equemolar ratios. The ligands H₂L¹ and H₂L² were synthesized by reaction of 2-[2-(2-formyl phenoxy)ethoxy]benzaldehyde (A¹) and/or 2-[2-(3-formylphenoxy)propoxy]benzaldehyde (A²) and ethanol amine and characterized with IR and ¹H, ¹³C NMR spectroscopy. All complexes were characterized by microanalysis, IR and mass spectrometry, whereas complex I was also characterized by single crystal X-ray (CIF file CCDC no. 1020055). The X-ray structure of complex I revealed that all nitrogen and oxygen atoms of ligand (N₂O₄) have coordinated to the metal ion. However, Cu²⁺ ion is in six coordination environment that can bedescribed as a distorted octahedral geometry.     

Preparation of Schiff’s base complexes of Mn(II), Co(II), Ni(II), Cu(II), Zn(II), and Cd(II) and their spectroscopic, magnetic, thermal, and antifungal studies

The potassium salt of salicylidene-DL-alanine (KHL), bis(benzylidene)ethylenediamine (A¹), thiophene-o-carboxaldene-p-toluidine (A²), and its metal complexes of the formula [(M^II(L)(A)(H₂O)] (M = Mn(II), Co(II), Ni(II), Cu(II), Zn(II), and Cd(II); A = A¹ or A²) are prepared. They are characterized by elemental analysis, magnetic susceptibility measurements, thermogravimetric analysis, and infrared and electronic spectral studies. The electronic spectral and magnetic moment data suggest an octahedral geometry for the complexes. All of these complexes, metal nitrates, fungicides (bavistin and emcarb), and ligands are screened for their antifungal activity against Aspergillus niger, Fusarium oxysporum, and Aspergillus flavus using a plate poison technique. The complexes show higher activity than those of the free ligands, metal nitrate, and the control (DMSO) and moderate activity against bavistin and emcarb. The text was submitted by the authors in English.     

The synthesis,characterization and antibacterial activities of dinuclear Ni(II), Cu(II) and Fe(III) Schiff base complexes

Schiff base; N,N′-bis-(2-hydroxy-1-naphthaldimine)-1,3-diaminopropanol (napdapOH) reacts with metal chlorides to form dinuclear complexes of the type [M₂L₂] · nCl₂ where M = Ni, Cu, Fe and n = 0, 1. Schiff base complexes were characterized by using FT-IR, LC-MS, magnetic moments and conductance measurements. Coordination was found to be through the phenolic oxygen atoms and azomethine nitrogen atoms. The electronic properties of the compounds were investigated theoretically by performing semiempirical molecular orbital theory PM3 method in Hyperchem 7 (Release). The antibacterial activities of the compounds were investigated against Escherichia coli ATCC 11230, Bacillus subtilis RSKK 244, Bacillus megaterium RSKK 5117, Salmonella enteritidis ATCC 13076, Staphylococcus aureus ATCC 25923 by using microdilution method.     

Spectral,thermal, electrochemical,biological and DFT studies on nanocrystalline Co(II), Ni(II), Cu(II) and Zn(II) complexes with a tridentate ONO donor Schiff base ligand

Co(II), Ni(II), Cu(II) and Zn(II) Schiff base complexes derived from 3-hydrazinoquionoxaline-2-one and 1,2-diphenylethane-1,2-dione were synthesized. The compounds were characterized by elemental analyses, molar conductance, magnetic susceptibility measurements, FTIR, UV–vis, ¹H NMR, ¹³C NMR, ESR, and mass spectral studies. Thermal studies of the ligand and its metal complexes were also carried out to determine their thermal stability. Octahedral geometry has been assigned for Co(II), Ni(II), and Zn(II) complexes, while Cu(II) complex has distorted octahedral geometry. Powder XRD study was carried out to determine the grain size of ligand and its metal complexes. The electrochemical behavior of the synthesized compounds was investigated by cyclic voltammetry. For all complexes, a 2 : 1 ligand-to-metal ratio is observed. The ligand and its metal complexes were screened for their activity against bacterial species such as E. coli, P. aeruginosa, and S. aureus and fungal species such as A. niger, C. albicans, and A. flavus by disk diffusion method. The DNA-binding of the ligand and its metal complexes were investigated by electronic absorption titration and viscosity measurement studies. Agarose gel electrophoresis was employed to determine the DNA-cleavage activity of the synthesized compounds. Density functional theory was used to optimize the structure of the ligand and its Zn(II) complex.     

Template synthesis and physicochemical studies of 14-membered hexaazmacrocyclic complexes with Co(II), Ni(II), Cu(II) and Zn(II): a comparative spectroscopic approach on DNA binding with Cu(II) and Ni(II) complexes

A new series of 14-membered pendant arm hexaazamacrocyclic complexes of the type [MLX₂] · [M = Co(II), Ni(II), Cu(II) or Zn(II) for X = Cl; Co(II), Ni(II), Cu(II) or Zn(II) for X = NO₃] has been synthesized by metal template condensation of 1,2-phenylenediamine and 1,4-phenylenediamine with formaldehyde in methanol. The mode of bonding and overall geometry of these complexes have been deduced by elemental analyses, molar conductance values, FT-IR, ¹H-NMR, ¹³C-NMR, EPR, ESI-mass and UV–VIS along with magnetic measurement studies. The fluorescence and UV–VIS studies revealed a significant binding ability to DNA.     

Synthesis, spectral characterization, solution equilibria, in vitro antibacterial and cytotoxic activities of Cu(II), Ni(II), Mn(II), Co(II) and Zn(II) complexes with Schiff base derived from 5-bromosalicylaldehyde and 2-aminomethylthiophene

Schiff base namely 2-aminomethylthiophenyl-4-bromosalicylaldehyde (ATS)(4-bromo-2-(thiophen-2-yl-imino)methylphenol) and its metal complexes have been synthesized and characterized by elemental analyses, IR, 1H NMR, solid reflectance, magnetic moment, molar conductance, mass spectra, ESR and thermal analysis (TGA). The analytical data of the complexes show the formation of 1:2 [M:L] ratio of the formula [ML2], where M represents Ni(II), Zn(II) and Cu(II) ions, while L represents the deprotonated Schiff base. IR spectra show that ATS is coordinated to the metal ions in a bidentate manner through azomethine-N and phenolic-oxygen groups. The ligand and their metal chelates have been screened for their antimicrobial activities using the disc diffusion method against the selected bacteria. A cytotoxicity of the compounds against colon (HCT116) and larynx (HEP2) cancer cells have been studied. Protonation constants of (ATS) ligand and stability constants of its Cu2+, Co2+, Mn2+, Zn2+ and Ni2+ complexes were determined by potentiometric titration method in 50% (v/v) DMSO-water solution at ionic strength of 0.1 M NaNO3.     

Biocatalysis,DNA–protein interactions,cytotoxicity and molecular docking of Cu(II), Ni(II), Zn(II) and V(IV) Schiff base complexes

Four mononuclear metal complexes (Cu(II) ( 1 ), Ni(II) ( 2 ), Zn(II) ( 3 ) and V(IV) ( 4 )) were synthesized using the Schiff base ligand 2,2′‐{cyclohexane‐1,2‐diylbis[nitrilo(1E )eth‐1‐yl‐1‐ylidine]}bis[5‐(prop‐2‐yn‐1‐yloxy)phenol] and structurally characterized by various spectral techniques. The catecholase‐mimicking activities of 1 – 4 were investigated and the results reveal that all the complexes have ability to oxidize 3,5‐di‐tert ‐butylcatechol (3,5‐DTBC) to 3,5‐di‐tert ‐butylquinone in aerobic conditions. Electrospray ionization mass spectrometry studies were performed for 1 – 4 in the presence of 3,5‐DTBC to determine the possible complex–substrate intermediates. X‐band electron paramagnetic resonance spectroscopy results indicate that the metal centres are involved in the catecholase activity. Ligand‐centred radical generation was further confirmed by density functional theory calculation. The phosphatase‐like activity of 1 – 4 was investigated using 4‐nitrophenylphosphate as a model substrate. All the complexes exhibit excellent phosphatase activity in acetonitrile medium. The interactions of 1 – 4 with calf thymus DNA (CT‐DNA) and bovine serum albumin (BSA) protein were investigated using absorption and fluorescence titration methods. All the complexes strongly interact with CT‐DNA and BSA protein. The complexes exhibit significant hydrolytic cleavage of supercoiled pUC19 DNA. Complexes 1 – 4 exhibit significant in vitro cytotoxicity against MCF7 (human breast cancer) and MIA‐PA‐CA‐2 (human pancreatic cancer) cell lines. Moreover, the molecular docking technique was employed to determine the binding affinity with DNA and protein molecules.     

Synthesis and characterization of Co(II), Ni(II), Cu(II) and Zn(II) complexes of tridentate Schiff base derived from vanillin and DL-alpha-aminobutyric acid

Co(II), Ni(II), Cu(II) and Zn(II) complexes of the Schiff base derived from vanillin and dl-alpha-aminobutyric acid were synthesized and characterized by elemental analysis, IR, electronic spectra, conductance measurements, magnetic measurements, powder XRD and biological activity. The analytical data show the composition of the metal complex to be [ML(H(2)O)], where L is the Schiff base ligand. The conductance data indicate that all the complexes are non-electrolytes. IR results demonstrate the tridentate binding of the Schiff base ligand involving azomethine nitrogen, phenolic oxygen and carboxylato oxygen atoms. The IR data also indicate the coordination of a water molecule with the metal ion in the complex. The electronic spectral measurements show that Co(II) and Ni(II) complexes have tetrahedral geometry, while Cu(II) complex has square planar geometry. The powder XRD studies indicate that Co(II) and Cu(II) complexes are amorphous, whereas Ni(II) and Zn(II) complexes are crystalline in nature. Magnetic measurements show that Co(II), Ni(II) and Cu(II) complexes have paramagnetic behaviour. Antibacterial results indicated that the metal complexes are more active than the ligand.     

Synthesis,characterization, crystal structure and toxicity evaluation of Co (II), Cu (II), Mn (II), Ni (II), Pd (II) and Pt (II) complexes with Schiff base derived from 2-chloro-5-(trifluoromethyl)aniline

A bidentate NO donor Schiff base, 2-(((2-chloro-5- (trifluoromethyl)phenyl)imino)methyl) phenol ( HL ¹ ) and its complexes [Co(L¹)₂(H₂O)₂] ( 1 ), [Cu(L¹)₂] ( 2 ), [Mn(L¹)₂(H₂O)₂] ( 3 ), [Ni(L¹)₂(H₂O)₂] ( 4 ), [Pd₂(L¹)₂(OAc)₂·1.16H₂O] ( 5 ), [Pt(L¹)₂] ( 6 ) were synthesized and characterized by different physico-chemical techniques including elemental and thermal analysis, magnetic susceptibility measurements, molar electric conductivity, IR, ¹H-NMR, ¹³C-NMR, UV–Vis, mass spectroscopies and X-ray powder diffraction (XRD). The molecular structures of ligand HL ¹ and two complexes ( 2 and 5 ) were confirmed by X-ray crystallography analysis on the monocrystal. In this complexes, the metal ions are in distorted square-planar environments. The copper (II) complex is mononuclear and crystallized in a monoclinic space group P21/c, whereas palladium (II) complex is dinuclear and crystallized in the trigonal crystal system R-3. The toxicity of the ligand and complexes was evaluated on both plant and animal cells, using the plant species Triticum aestivum L. and the crustacean Artemia franciscana Kellogg. At concentrations up to 100 μM the compounds presented very little toxicity on Artemia franciscana Kellogg. Moreover, the palladium (II) complex was devoid of any toxicity on the plant cells.