Synthesis and characterization of a thioether Schiff base ligand and its metal complexes and crystal structure determination of the nickel(II) complex

Reactions of 1,2-di(o-aminophenylthio)ethane with 3-ethoxy-2-hydroxybenzaldehyde yield the new hexadentate N₂S₂O₂ donor thioether Schiff base 1,2-bis(2-((2-(thio)phenylimino)methyl)-6-ethoxyphenol)ethane (H₂L). Ni(II), Zn(II), Cd(II), and Hg(II) complexes of this ligand were prepared. Of these complexes, [NiL]·2H₂O has been structurally characterized by X-ray crystallography. The coordination geometry around Ni(II) was described as octahedral. Zn(II), Cd(II), and Hg(II) complexes and the Schiff base ligand have been characterized by CHN analyses, molar conductivity, UV–vis, FT-IR, ¹H, and ¹³C NMR spectroscopy.     

A new stepped tetranuclear copper(II) complex: synthesis,crystal structure and photoluminescence properties

Binuclear and tetranuclear copper(II) complexes are of interest because of their structural, magnetic and photoluminescence properties. Of the several important configurations of tetranuclear copper(II) complexes, there are limited reports on the crystal structures and solid‐state photoluminescence properties of `stepped' tetranuclear copper(II) complexes. A new Cu^II complex, namely bis{μ₃‐3‐[(4‐methoxy‐2‐oxidobenzylidene)amino]propanolato}bis{μ₂‐3‐[(4‐methoxy‐2‐oxidobenzylidene)amino]propanolato}tetracopper(II), [Cu₄(C₁₁H₁₃NO₃)₄], has been synthesized and characterized using elemental analysis, FT–IR, solid‐state UV–Vis spectroscopy and single‐crystal X‐ray diffraction. The crystal structure determination shows that the complex is a stepped tetranuclear structure consisting of two dinuclear [Cu₂(L )₂] units {L is 3‐[(4‐methoxy‐2‐oxidobenzylidene)amino]propanolate}. The two terminal Cu^II atoms are four‐coordinated in square‐planar environments, while the two central Cu^II atoms are five‐coordinated in square‐pyramidal environments. The solid‐state photoluminescence properties of both the complex and 3‐[(2‐hydroxy‐4‐methoxybenzylidene)amino]propanol (H₂L ) have been investigated at room temperature in the visible region. When the complex and H₂L are excited under UV light at 349 nm, the complex displays a strong blue emission at 469 nm and H₂L displays a green emission at 515 nm.     

Synthesis,X-ray crystal structure,and electrochemistry of polynuclear azido-bridged manganese(III) and copper(II) Schiff base complexes

New azido-bridged [Mn^III(salabza)(μ-1,3-N₃)]_n (1), and [Cu^II₄(salabza)₂(μ-1,1-N₃)₂(N₃)₂(HOCH₃)₂],(2) complexes with an unsymmetrical Schiff base ligand, {H₂salabza = N,N’-bis(salicylidene)-2-aminobenzylamine}, have been synthesized, characterized by spectroscopic and electrochemical methods, and their crystal structures have been determined by X-ray diffraction. In complex 1, each manganese(III) atom is coordinated with N₂O₂ donor atoms from salabza and two adjacent Mn(III) centers are linked by an end-to-end (EE) azide bridge to form a helical polymeric chain with octahedral geometry around the Mn(III) centers. Complex 2 is a centrosymmetric tetranuclear compound containing two types of Cu(II) centers with square pyramidal geometry. Each terminal copper atom is surrounded by N₂O₂ atoms of a salabza ligand, and the oxygen atom of the methanol molecule. Each central copper(II) ion is coordinated with two phenoxo oxygen atoms from one salabza, one terminal azido, and two end-on (EO) bridging azido ligands. The central copper(II) ions are linked to each other by the two end-on (EO) azido groups.     

Self-activated DNA cleavage of a water-soluble mononuclear Cu(II) complex with polyquinolinyl ligand

The synthesis and characterization of a water-soluble mononuclear Cu(II) complex, [CuLCl₂]·2CH₃CH₂OH, where L = bis(2-quinolinyl methyl)benzyl-amine has been reported. L is a tridentate polyquinolinyl ligand, coordinated to Cu(II) via NNN donors. The central copper ion of 1 has N₃Cl₂ donor set in a distorted trigonal-bipyramidal geometry. The dimer existing in the solid state resulted from hydrogen bonds and π–π accumulation between two mononuclear units. The interaction of 1 with CT-DNA has been explored by absorption and emission titration methods, revealing partial intercalation between 1 and CT-DNA. Moreover, 1 could make pBR322 plasmid DNA cleaved by a self-activated oxidative process; hydroxyl radical and singlet oxygen may be the main reactive oxygen species species in the process. Complex 1 may quench the intrinsic fluorescence of bovine serum albumin in a static quenching process, which has been investigated by UV–visible and fluorescence spectroscopic methods. 1 also demonstrates potent cytotoxity against Hela cells with IC₅₀ value of 2.84 μM, which shows it to be a potential candidate as an anticancer metal-based drug.     

Cu(II), Ni(II), Zn(II) and Fe(III) complexes containing a N2O2 donor ligand: Synthesis, characterization, DNA cleavage studies and crystal structure of [Cu(HL)Cl]

A polydentate ligand, H₂L “[1-(5-isopropyl-2-methyl phenoxy)-3-(N-2-hydroxy benzyl-N-((pyridine-2-yl)amino) propan-2-ol]”, containing a N₂O₂ donor moiety was synthesized by refluxing 2-((5-isopropyl-2-methylphenoxy)methyl)oxirane and HBPA (N-(2-hydroxybenzyl)-N-(2-pyridylmethyl)amine). This synthesized ligand was used for the preparation of complexes with different metal ions, viz. [Cu(HL)Cl] (1), [Ni(HL)Cl] (2), [Zn(HL)Cl] (3) and [Fe(HL)Cl₂] (4). The ligand and metal complexes were characterized by ¹H NMR, mass, ESI-MS, elemental analysis, IR, UV-Vis and electron paramagnetic resonance (EPR) spectroscopy. The crystal structure for one of the complexes, [Cu(HL)Cl], was solved from the X-ray crystallography data. The structure of the complex, based on the trigonality index tau, suggests an intermediate geometry between square pyramidal (sp) and trigonal bipyramidal (tb). Both the ligand and the metal complexes show oxidative cleavage of plasmid DNA (pBR322) without addition of any exogenous agent, even at a concentration of 5 μM. The binding constants for these compounds were found to be in the range 5.33-0.065 × 10⁵ M⁻¹.     

Synthesis,structure, DNA binding and cleavage ability of a new copper ciprofloxacin complex

The structure of 1 consists of [Cu(HCp)(phen)(H₂O)]²⁺ (HCp is ciprofloxacin and phen is 1,10-phenanthroline), two acetates, and four free water molecules. In each cation, copper displays a distorted square pyramid, coordinated to ring 3-carboxylate and 4-oxo oxygen from HCp, two nitrogens from phen, and one water molecule. There are five water molecules in each discrete complex with one coordinated to Cu center, and the other four linked to each other by intermolecular hydrogen bonds. Two uncoordinated acetates make the compound neutral. The complex exhibits higher DNA binding compared to HCp at the same conditions by fluorescence and viscosity measurements. Combining its structure with the DNA-binding result, the binding mechanism may be explained by intercalation. Moreover, 1 shows significant cleavage of DNA in the presence of a reducing agent, such as ascorbate by gel electrophoresis using supercoiled pBR322 DNA in Tris-HCl buffer (pH 7.4). The complex also has a higher activity against Gram-positive bacteria Staphylococcus aureus and Gram-negative bacteria Klebsiella pneumoniae than HCp.     

Synthesis,magnetic properties,DNA binding and cleavage activity of a new oxalato bridged copper(II) complex

A novel oxalato‐bridged copper(II) complex has been prepared and structurally characterized: [Cu(bpa)(μ‐C₂O₄)].H₂O (bpa = bis(2‐pyridylmethyl) amine). In the complex, the copper ion is linked in an unusual μ_1,2,3‐C₂O₄^2? bridging mode, generating one‐dimensional zigzag chain disposition. Variable‐temperature magnetic susceptibility studies (2–300 K) reveal a weak ferromagnetic coupling, J = 0.63 cm^?1, between the copper ions. The interaction of the complex with CT‐DNA has been studied using UV–visible absorption and emission spectral methods, and the binding constant of the complex with CT‐DNA is K_app = 9 × 10⁴ m ^?1, which indicates that the interaction of the complex with DNA is a moderate intercalative mode. Furthermore, the complex cleaves supercoiled plasmid DNA efficiently in the presence of hydrogen peroxide. The mechanistic investigations suggest that the hydroxyl radical and singlet oxygen are involved in the DNA degradation. Copyright © 2012 John Wiley & Sons, Ltd.     

Cu(II) complexes with 4-amino-3,5-dimethyl isoxazole and substituted aromatic aldehyde Schiff bases: synthesis,crystal structure,antimicrobial activity,DNA binding and cleavage studies

Three isoxazole Schiff bases 2-((E)-(3,5-dimethylisoxazol-4-ylimino)methyl)-6-methoxyphenol (L¹), 2-((E)-(3,5-dimethylisoxazol-4-ylimino)methyl)-4,6-diiodophenol (L²), 2-((E)-(3,5-dimethylisoxazol-4-ylimino)methyl)-6-bromo-4-chlorophenol (L³), and their Cu(II) complexes [Cu(L¹)₂] (1), [Cu(L²)₂] (2) and [Cu(L³)₂] (3) were synthesized. All the complexes have been characterized by elemental analysis, FT-IR, ESI mass, UV-Visible, ESR, TGA, magnetic moments, and single-crystal X-ray diffraction analysis. Based on analytical data, a square planar geometry is assigned to the Cu(II) complexes with N₂O₂ donors from the Schiff base ligands. The single-crystal X-ray diffraction measurements of 1 and 2 confirmed the square planar geometry. DNA binding studies from electronic absorption titrations, viscosity measurements, and fluorescence quenching studies indicated an intercalation mode of binding of Cu(II) complexes with CT-DNA. DNA cleavage experiments of Cu(II) complexes with supercoiled plasmid pBR322 DNA have also been investigated by agarose gel electrophoresis in the presence of H₂O₂ (oxidative cleavage) and UV light (photolytic cleavage). The synthesized compounds were screened for antibacterial (Escherichia coli, Pseudomonas putida, Klebsiella pneumoniae, Bacillus subtillis and Staphylococcus aureus) and antifungal (Candida albicans and Aspergillus niger) activities by the paper disk method. The Cu(II) complexes showed better activity than corresponding Schiff bases.     

DNA cleavage activities of tetraazamacrocyclic oxamido nickel(II) complexes

The DNA cleavage activities of nickel(II) ion and four closely related macrocyclic nickel(II) complexes NiL¹ ∼ NiL⁴ in the absence of any added redox cofactors are compared and the structure of NiL³ methanol solvate has been characterized by single crystal X-ray analysis, where L¹ ∼ L⁴ are the dianions of tetraazamacrocyclic oxamido Schiff bases. In NiL³·MeOH, the macrocyclic [N₄] ligand coordinates to the central Ni(II) ion forming a distorted square–planar geometry. The adjacent mononuclear molecules are linked by O–H?O hydrogen bonds and Ni?O and Ni?L van der Waals forces into 2D supramolecular structure. Agarose gel electrophoresis studies indicate that the ability of these nickel(II) complexes to cleave DNA is highly dependent upon the ligand employed. In the absence of any added oxidizing agents, only NiL³ is a relatively good DNA cleavage agent, and the process of plasmid DNA cleavage is much sensitive to ionic strength and pH value. The NiL³-mediated DNA cleavage reaction is a typical pseudo-first-order consecutive reaction, and the rate constants of 0.148 ± 0.007 h⁻¹ (k₁) and 0.0118 ± 0.0018 h⁻¹ (k₂) for the conversion of supercoiled to nicked DNA and nicked to linear DNA are obtained in presence of 0.5 mmol L⁻¹ NiL³. The results of DNA cleavage experiments, combining with those of circular dichroism (CD) and fluorescence spectroscopy indicate that the main binding modes between DNA and the complexes should be groove binding and electrostatic interaction.     

新型双肟四核苦味酸铜(Ⅱ)化合物的制备、结构及抗菌性能

室温下,H2L(H2L=6,6'-二甲氧基-2,2'-[(1,4-亚丁基)二氧双(氮次甲基)]二酚)和苦味酸铜在丙酮溶剂中反应,制备了一种新型的四核苦味酸铜(II)化合物[Cu4L2(pic)4(H2O)2]·2H2O(1)。采用红外光谱、元素分析及X射线单晶衍射等手段对化合物的结构进行了确认。结构解析表明,1属单斜晶系,空间群C2/c,晶胞参数为a=3.4376(4)nm,b=1.3750(3)nm,c=2.2418(2)nm,β=106.689(3)0,V=10.150(2)nm3,Z=4,Mr=2011.44,Dc=1.316 g/cm3,μ=0.916 mm-1,F(000)=4096,R1=0.0979,wR2=0.2010。1的对称单元中含有4个Cu(II)原子,2个配位H2L分子,4个配位苦味酸根阴离子,2个配位水分子和2个游离水分子组成。中心4个Cu(II)的配位数均为6,以每个Cu(II)原子为中心均形成了扭曲八面体结构的配位几何构型,分子间氢键和π-π堆积作用形成了三维超分子结构。抗菌性能测试结果表明,化合物1的抑菌活性高于H2L,二者对金黄色葡萄球菌、大肠杆菌和枯草杆菌均有显著的抑菌活性。     

Synthesis, crystal structure and imine bond activation of a copper(II) Schiff base complex

A new copper(II) complex [Cu(HL)(ClO₄)](ClO₄) (1), where HL is a multidentate Schiff base N,N′-(2-hydroxypropane-1,3-diyl)bis(pyridine-2-aldimine), is prepared, structurally characterized by X-ray crystallography and its spectral and electrochemical properties studied. The complex forms a one-dimensional chain in the solid state structure in which the monomeric Cu(HL) units are linked by the perchlorate ligand. The complex has an axially elongated six coordinate geometry (4+2) with a CuN₄O₂ core in which the Schiff base ligand displays a tetradentate mode of bonding in the basal plane. The axial ligand is perchlorate with a significantly long Cu–O bond of ca. 2.6 Å. The one-electron paramagnetic complex displays a cyclic voltammetric response for the Cu(II)/Cu(I) couple at 0.01 V versus SCE in MeCN–0.1 M TBAP. The azomethine bond of the Schiff base in 1 on treatment with H₂O₂ undergoes oxidative conversion to form a bis(picolinato)copper(II) · dihydrate species through the formation of an amido intermediate as evidenced from the solution infrared spectral studies.     

Mononuclear copper(II) complex with terpyridine and an extended phenanthroline base, [Cu(tpy)(dppz)]: Synthesis, crystal structure, DNA binding and cytotoxicity activity

The new dipyrido[3,2-a:2′,3′-c]phenazine (dppz) copper(II) complex, [Cu(tpy)(dppz)]²⁺, where tpy is 2,2′:6′,2″-terpyridine, has been prepared and fully characterized by spectroscopic methods and single-crystal X-ray diffraction. Its DNA binding and in vitro cytotoxicity have been also studied. The molecular structure shows a distorted trigonal bipyramidal CuN₅ coordination geometry around the copper atom. The bidentate dppz ligand binds in the equatorial plane, while tpy exhibits axial-equatorial bonding. The interaction of the complex with DNA has been investigated by electronic absorption, competitive fluorescence titration, linear dichroism, voltammetric techniques and a gel electrophoresis mobility shift assay. It is proposed that the binding mode of the complex to DNA is of an intercalation nature with the planar dppz ligands located between the base pairs of double-stranded DNA.An in vitro cytotoxicity study of the complex on human breast adenocarcinoma (MCF7) cell line by an MTT assay indicates that the title complex may have the potency to act as an effective anticancer drug, with an IC₅₀ value of 4.57 μM (3.62-5.77).     

Cytotoxic copper(II) complex of tripyridoquinoxaline with DNA hydrolase activity

A monomeric copper(II) complex, [Cu(tpq)₂(H₂O)₂](ClO₄)₂, (tpq = tripyridoquinoxaline), has been synthesized and characterized spectroscopically. This complex has been found to bind DNA intercalatively and the DNA binding constant, K_b, for this complex has been determined from absorption measurements and was found to be (5.7 ± 0.3) × 10³ M⁻¹. This complex successfully promotes hydrolytic cleavage of plasmid DNA, producing single and double DNA strand breaks in the absence of any added cofactor. The amount of conversion of the supercoiled form of plasmid to the nicked circular form depends on the concentration of the copper complex as well as the duration of the incubation of the complex with DNA. The rate of conversion of SC to NC has been determined to be 2.65 × 10⁻⁴ s⁻¹ at pH 7.2 in the presence of 80 μM of the complex. This complex has also been shown to be cytotoxic towards A549 lung adenocarcinoma cells. This complex has been shown to bring about apoptosis of the cancerous A549 cell line.     

New anthracene based Schiff base ligands appended Cu(II) complexes: Theoretical study,DNA binding and cleavage activities

New anthracene based Schiff base ligands L ¹ and H( L ² ), their Cu(II) complexes [Cu( L ¹ )Cl₂] ( 1 ) and [Cu( L ² )Cl] ( 2 ) , (where L ¹  = N¹,N²‐bis(anthracene‐9‐methylene)benzene‐1,2‐diamine, L ²  = (2Z,4E)‐4‐(2‐(anthracen‐9‐ylmethyleneamino)phenylimino)pent‐2‐en‐2‐ol) have been prepared and characterized by elemental analysis, NMR, FAB‐mass, EPR, FT‐IR, UV–Vis and cyclic voltammetry. The electronic structures and geometrical parameters of complexes 1 and 2 were analyzed by the theoretical B3LYP/DFT method. The interaction of these complexes 1 and 2 with CT‐DNA has been explored by using absorption, cyclic voltammetric and CD spectral studies. From the electronic absorption spectral studies, it was found that the DNA binding constants of complexes 1 and 2 are 8.7 × 10³ and 7.0 × 10⁴ M^?1, respectively. From electrochemical studies, the ratio of DNA binding constants K₊/K₂₊ for 2 has been estimated to be >1. The high binding constant values, K₊/K₂₊ ratios more than unity and positive shift of voltammetric E_1/2 value on titration with DNA for complex 2 suggest that they bind more avidly with DNA than complex 1 . The inability to affect the conformational changes of DNA in the CD spectrum is the definite evidences of electrostatic binding by the complex 1 . It can be assumed that it is the bulky anthracene unit which sterically inhibits these complexes 1 and 2 from intercalation and thereby remains in the groove or electrostatic. The complex 2 hardly cleaves supercoiled pUC18 plasmid DNA in the presence of hydrogen peroxide. The results suggest that complex 2 bind to DNA through minor groove binding.     

Synthesis and characterization of Co(II), Ni(II), Zn(II) and Cu(II) complexes with a new tetraazamacrocyclic Schiff base ligand containing a piperazine moiety: X-ray crystal structure determination of the Co(II) complex

Two macrocyclic Schiff base ligands, L¹ [1+1] and L² [2+2], have been obtained in a one-pot cyclocondensation of 1,4-bis(2-formylphenyl)piperazine and 1,3-diaminopropane. Unfortunately, because of the low solubility of both ligands, their separation was unsuccessful. In the direct reaction of these mixed ligands (L¹ and L²) and the appropriate metal ions only [CoL¹(NO₃)]ClO₄, [NiL¹](ClO₄)₂, [CuL¹](ClO₄)₂ and [ZnL¹(NO₃)]ClO₄ complexes have been isolated. All the complexes were characterized by elemental analyses, IR, FAB-MS, conductivity measurements and in the case of the [ZnL¹(NO₃)]ClO₄ complex with NMR spectroscopy.     

Synthesis,crystal structure,magnetic property,and nuclease activity of a binuclear iron(III) complex

A μ-oxo-di-μ-carboxylato-bridged iron(III) complex containing two tridentate nitrogen ligands, {[Fe₂(bpma)(bpea)(μ-CH₃COO)₂ μ-O)] · (ClO₄)₂ · 0.5CH₃OH} (1) (bpma = N, N-bis(2-pyridylmethyl)methyl-amine, bpea = N,N-bis(2-pyridylmethyl)ethylamine), has been synthesized and determined by X-ray diffraction. Complex 1 crystallizes in the monoclinic space group P2₁/c with a = 10.9434(12) Å, b = 23.118(3) Å, c = 15.8721(18) Å, β = 92.736(2)° and Z = 4. In 1, each Fe(III) has a distorted octahedral geometry with a N₃O₃ donor set. The Fe(III) atoms are bridged by two carboxyl groups and one μ-oxo oxygen with Fe1–Fe2 separation of 3.064 Å. Susceptibility data of 1 indicate strong intramolecular antiferromagnetic coupling of the high-spin Fe(III) atoms with J = ?121.0 cm^?1 and g = 2.04. The interaction with calf thymus DNA was investigated by UV absorption and fluorescent spectroscopy. Results show that the complex binds to ct-DNA with a moderate intercalative mode. The interaction between 1 and pBR322 DNA has also been investigated by submarine gel electrophoresis; the complex exhibits effective DNA cleavage activity in the absence of activating agents under similar physiological conditions.     

Synthesis, crystal structure and DFT analysis of a new trinuclear complex of copper

The new trinuclear complex [Cu₂(μ-L)₂CuCl₂] has been synthesized and characterized by elemental analysis, IR, UV-Vis and X-ray spectroscopy, where L is a dianionic tetradentate Schiff base ligand with N₂O₂ donor atoms. The molecular structure of [Cu₂(μ-L)₂CuCl₂] was determined by X-ray crystallography. In the complex, the most remarkable aspect of the trinuclear complex is that it adopts a bent structure for the three copper atoms, with a Cu1Cu3Cu2 intramolecular angle of approximately 90.62(2)°. All three copper atoms are five coordinate, with a slightly distorted square pyramidal geometry. In the two terminals moieties, the basal plane of the square pyramidal is formed by two oxygen atoms and two nitrogen atoms of the Schiff base ligand, and the apical position at the Cu atom is occupied by the bridging Cl1 anion. The Cu1Cl1Cu2 angle is 110.51(5)°. The central copper atom also has a five-coordinate, slightly distorted square pyramidal geometry, with four phenolato oxygens belonging to the Schiff base ligands from Cu(salpn) units describing the square planar base and the Cl anions being apical. The optimized structure of the complex has been studied using the B3LYP/6-31G(d)/LanL2TZf level of theory. The calculation shows that all the copper atoms are five coordinate with distorted square pyramidal structures, which is consistent with experimental data.