Synthesis, crystal structure and nuclease activity of a Schiff base copper(II) complex

A new Schiff base copper(II) complex, Cu(o-VANAHE)(2) (o-VANAHE = 2-(o-vanillinamino)-1-hydroxyethane), has been synthesized and characterized. Single crystal X-ray diffraction results suggest that this complex structure belongs to triclinic crystal system, space group P1 with the following crystallographic parameters: a = 8.819(4) angstroms, b = 10.794(5) angstroms, c = 11.350(5) angstroms, alpha = 70.262(6) degrees, beta = 70.816(6) degrees, gamma = 78.360(6) degrees, V = 955.4(7) angstroms3, Z = 2, D(c) = 1.571 Mg x m(-3), and the final R1 = 0.0393, wR2 = 0.0994 for the observed reflections 2620(I > 2sigma(I)). The molecular geometry is almost coplanar. Viscosity, fluorescence spectroscopy and cyclic voltammetry have been conducted to assess their interaction between this complex and DNA. Results showed that the copper(II) complex can increase DNA's relative viscosity and quench the fluorescence intensity of EB bound to DNA. The adding of DNA to the solution of Cu(o-VANAHE)2 causes a slight decrease in the voltammetric current, as well as a slight shift in the E(1/2) to less negative potential. The interaction between the complex and DNA has also been investigated by submarine gel electrophoresis, interestingly, we found that the copper(II) complex can cleave circular plasmid pBR322 DNA to nicked and linear forms.     

Antiradical activity of different copper(II) Schiff base complexes and their effect on alloxan-induced diabetes

Considering the important role of antioxidants in biological systems, the group of copper(II) complexes derived from salicylaldehyde and alpha- or beta-alanine and its thiourea derivative and copper(II) complexes derived from pyruvic acid and beta-alanine were studied. The antiradical activity of the tested compounds was studied by both in vitro and in vivo methods. The chemical methods based on inhibition of INT-formazane or 3-nitrotyrosine formation were used for the evaluation of SOD-mimic and antiperoxynitrite activity, respectively. In the case of in vivo activity evaluation, an alloxan-induced diabetes mellitus model in mice was used, the mechanism of action of alloxan being closely connected with the formation of free radicals selectively damaging the pancreatic beta-cells. Since all the substances studied showed different positive effects, it is obvious that they have not acted only as a source of copper(II) ions but their effect is related to their specific chelate structure. The obtained results are a contribution to the knowledge of copper(II) Schiff base complexes with ligands of aldimine or ketimine type and form the basis for further preclinical tests of these bioactive agents in biological models of oxidative stress.     

Immobilized chymotrypsin by means of Schiff base copper(II) chelate

A new method for cross-linking of protein was proposed in our previous work. The method is based on the spontaneous chelate formation process involving three components, salicylaldehyde moiety, alpha-amino acid residue and copper(II). In this paper versatility of the method as a purpose of immobilization of enzyme was described. Chymotrypsin-salicylaldehyde conjugate was immobilized to the agarose gel attached alpha-amino acid residue in the presence of copper(II) ion The enzyme was not eluted from the gel by washing with a copper free buffer though it was exclusively eluted by a medium containing EDTA. Catalytic activity of the chymotrypsin salicylaldehyde conjugate was not changed upon the immobilization. The method was proposed as a new tool for reversible immobilization of enzyme.     

DNA binding affinity and antioxidative activity of copper(II) and zinc(II) complexes with a novel hesperetin Schiff base ligand

A hesperetin Schiff base ligand (H₄L) and its complexes, [H₃CuL·OAc]·H₂O and [H₃ZnL·OAc]·2H₂O, have been synthesized and characterized on the basis of elemental analysis, molar conductivity, ¹H NMR, mass spectra, UV-Vis spectra and IR spectra. The binding of these two complexes and the ligand to DNA has been investigated by ultraviolet absorption spectroscopy, fluorescence spectroscopy and viscosity measurements. The experiments indicate that all the compounds can bind to DNA through an intercalative mode and the complexes intercalate into DNA more deeply than that of the ligand. In addition, the antioxidative activity was also determined. The 50% inhibition obtained for the ligand and its complexes demonstrates that, compared to the ligand, the complexes exhibit higher antioxidative activity in the suppression of and HO.     

Synthesis and characterization of nickel(II) and copper(II) complexes with tetradentate Schiff base ligands

The 1:1 condensation of 1,2-diaminopropane and 1-phenylbutane-1,3-dione at high dilution gives a mixture of two positional isomers of terdentate mono-condensed Schiff bases 6-amino-3-methyl-1-phenyl-4-aza-2-hepten-1-one (HAMPAH) and 6-amino-3,5-dimethyl-1-phenyl-4-aza-2-hexen-1-one (HADPAH). The mixture of the terdentate ligands has been used for further condensation with pyridine-2-carboxaldehyde or 2-acetylpyridine to obtain the unsymmetrical tetradentate Schiff base ligands. The tetradentate Schiff bases are then allowed to react with the methanol solution of copper(II) and nickel(II) perchlorate separately. The X-ray diffraction confirms the structures of two of the complexes and shows that the condensation site of the diamine with 1-phenylbutane-1,3-dione is the same.     

Study on potential antitumor mechanism of a novel Schiff base copper(II) complex: synthesis, crystal structure, DNA binding, cytotoxicity and apoptosis induction activity

A new cytotoxic copper(II) complex with Schiff base ligand [Cu^II(5-Cl-pap)(OAc)(H₂O)]·2H₂O (1) (5-Cl-pap = N-2-pyridiylmethylidene-2-hydroxy-5-chloro-phenylamine), was synthesized and structurally characterized by X-ray diffraction. Single-crystal analysis revealed that the copper atom shows a 4 + 1 pyramidal coordination, a water oxygen appears in the apical position, and three of the basal positions are occupied by the NNO tridentate ligand and the fourth by an acetate oxygen. The interaction of Schiff base copper(II) complex 1 with DNA was investigated by UV-visible spectra, fluorescence spectra and agarose gel electrophoresis. The apparent binding constant (K_app) value of 6.40 × 10⁵ M^− 1 for 1 with DNA suggests moderate intercalative binding mode. This copper(II) complex displayed efficient oxidative cleavage of supercoiled DNA, which might indicate that the underlying mechanism involve hydroxyl radical, singlet oxygen-like species, and hydrogen peroxide as reactive oxygen species. In addition, our present work showed the antitumor effect of 1 on cell cycle and apoptosis. Flow cytometric analysis revealed that HeLa cells were arrested in the S phase after treatment with 1. Fluorescence microscopic observation indicated that complex 1 can induce apoptosis of HeLa cells, whose process was mediated by intrinsic mitochondrial apoptotic pathway owing to the activation of caspase-9 and caspase-3.     

Zinc(II) and copper(II) 1D coordination polymeric complexes of a reduced Schiff base ligand

The reaction of Zn(ClO₄)₂ · 6H₂O and Cu(ClO₄)₂ · 6H₂O with H₃Sas (H₃Sas = N-(2-hydroxybenzyl)-L-aspartic acid in water afforded the complexes [Zn₆(Sas)₄(H₂O)₈]·5H₂O (1) and [Cu(HSas)(H₂O)] (2), respectively, which were characterized by infrared spectroscopy, elemental analysis, thermogravimetry and single-crystal X-ray crystallography. In 1, the pentanuclear clusters formed by four H₃Sas ligands and five Zn(II) metal ions are bridged by the “[Zn(H₂O)₄]²⁺” cations to form 1D polymeric chains. While in 2, the mononuclear [Cu(HSas)(H₂O)] repeating units form a 1D zigzag chain and further extended by strong intermolecular hydrogen bonds to form a 2D sheet. The different coordination geometries of Cu(II) and Zn(II) show significant influence on the polymeric structures.     

Bimetallic copper(II) and zinc(II) complexes of acyclic Schiff base ligands derived from amino acids

The acyclic Schiff-base ligands (2-(OH)-5-(R³)C₆H₂-1,3-(HCNC(R¹)(R²)CO₂H), derived from the dialdehyde 2-hydroxy-5-R-1,3-benzenedicarboxaldehyde (R = Me or t-Bu) and two equivalents of the amino acids glycine, 2,2-diphenylglycine or phenylalanine, have been reacted with the metal acetates M(OAc)₂ (M = Cu, Zn) in the presence of triethylamine, affording the complexes [HNEt₃][M₂(CH₃CO₂)₂(2-(O)-5-(t-Bu)C₆H₂-1,3-(HCNC(R¹)(R²)CO₂)₂] (M = Cu, R¹ = R² = C₆H₅, R³ = Me (1); M = Zn, R¹ = R² = H, R³ = t-Bu (2); M = Zn, R¹ = R² = C₆H₅, R³ = t-Bu (3); M = Zn, R¹ = H, R² = CH₂C₆H₅, R³ = t-Bu (4)) in good yields. The crystal structures of 1·MeCN, 2·, 3·2MeOH, and 4·3MeOH have been determined.     

Hydrogen-bonded copper(II) and nickel(II) complexes and coordination polymeric structures containing reduced Schiff base ligands

Complexes [Cu(HSas)(H₂O)] · 2H₂O (H₃Sas = N-(2-hydroxybenzyl)-l-aspartic acid) (1), [Cu(HMeSglu)(H₂O)] · 2H₂O (H₃MeSglu = (N-(2-hydroxy-5-methylbenzyl)-l-glutamic acid) (2), [Cu₂(Smet)₂] (H₂Smet = (N-(2-hydroxybenzyl)-l-methionine) (3), [Ni(HSas)(H₂O)] (4), [Ni₂(Smet)₂(H₂O)₂] (5), and [Ni(HSapg)₂] (H₂Sapg = (N-(2-hydroxybenzyl)-l-aspargine) (6) have been synthesized and characterized by chemical and spectroscopic methods. Structural determination by single crystal X-ray diffraction studies revealed 1D coordination polymeric structures in 2 and 4, and hydrogen-bonded network structure in 5 and 6. In contrast to previously reported coordination compounds with similar ligands, the phenol remains protonated and bonded to the metal ions in 2 and 4, and also probably in 1. However, the phenolic group is non-bonded in 6.     

Double-strand DNA cleavage induced by oxindole-Schiff base copper(II) complexes with potential antitumor activity

Some oxindole-Schiff base copper(II) complexes have already shown potential antitumor activity towards different cells, inducing apoptosis in a process modulated by the ligand, and having nuclei and mitochondria as main targets. Here, three novel copper(II) complexes with analogous ligands were isolated and characterized by spectroscopic techniques, having their reactivity compared to the so far most active complex in this class. Cytotoxicity experiments carried out toward human neuroblastoma SH-SY5Y cells confirmed its pro-apoptosis property. DNA cleavage studies were then performed in the presence of these complexes, in order to verify the influence of ligand structural features in its nuclease activity. All of them were able to cause double-strand DNA scissions, giving rise to nicked circular Form II and linear Form III species, in the presence of hydrogen peroxide. Additionally, DNA Form II was also detected in the absence of peroxide when the most active complex, [Cu(isaepy)₂]²⁺ 1, was used. In an effort to better elucidate their interactions with DNA, solutions of the different complexes titrated with DNA had their absorption spectra monitored. An absorbance hyperchromism observed at 260 nm pointed to the intercalation of these complexes into the DNA structure. Further, investigations of 2-deoxy-d-ribose (DR) oxidation catalyzed by each of those complexes, using 2-thiobarbituric acid reactive species (TBARS) method, and detection of reactive oxygen species (ROS) formation by spin-trapping EPR, suggested that their mechanism of action in performing efficiently DNA cleavage occurs preferentially, but not only by oxidative pathways.     

Unusual dinuclear copper(II) and nickel(II) complexes of a novel Schiff base deriving from 2-aminoethanol

It is generally accepted that copper(II) complexes involving 2-aminoethanol or a Schiff base deriving from this aminoalcohol display a tetranuclear structure with a Cu₄O₄ ‘cubane’ core. Using a Schiff base obtained by reacting 2′-aminoacetophenone with 2-aminoethanol, we have prepared copper(II) and nickel(II) complexes whose properties are fully consistent with a dinuclear structure. The copper complex is characterized by a low antiferromagnetic interaction.     

Schiff base complexes of copper and zinc as potential anti-colitic compounds

The design, synthesis and activity of polymodal compounds for the treatment of inflammatory bowel disease are reported. The compounds, being based on a metal-Schiff base motif, are designed to degrade during intestinal transit to release the bioactive components in the gut. The compounds have been developed sequential with the biomodal compounds combining copper or zinc with a salicylaldehyde adduct. These compounds were tested in a formalin induced colonic inflammation model in BK:A mice. From these studies a trimodal compound based on a zinc Schiff base analogue of sulfasalazine was designed. This was tested against a trinitrobenzenesulfonic acid (TNB) induced colitic model in Wistar rats. The use of two models allows us to test our compounds in both an acute and a chronic model. The trimodal compound reported is observed to provide anticolitic properties in the chronic TNB induced colitis model commensurate with that of SASP. However, the design of trimodal compound still has the capacity for further development. This the platform reported may offer a route into compounds which can markedly outperform the anti-colitic properties of SASP.     

Metal-assisted light-induced DNA cleavage activity of 2-(methylthio)phenylsalicylaldimine Schiff base copper(II) complexes having planar heterocyclic bases

Ternary copper(II) complexes [CuLL'](ClO(4)), where HL is NSO-donor Schiff base (2-(methylthio)phenyl)salicylaldimine and L' is NN-donor phenanthroline bases like 1,10-phenanthroline (phen), dipyridoquinoxaline (dpq) and 2,9-dimethyl-1,10-phenanthroline (dmp), are prepared and structurally characterized by X-ray crystallography. The complexes have a distorted square-pyramidal (4+1) CuN(3)OS coordination geometry. While [CuL(phen)](ClO(4)) and [CuL(dpq)](ClO(4)) show axial sulfur ligation, [CuL(dmp)](ClO(4)) has the sulfur bonded at the equatorial site. The one-electron paramagnetic complexes exhibit axial electron paramagnetic resonance (EPR) spectra in dimethylformamide glass at 77 K. The complexes are redox active and a quasireversible electron transfer process near 0.0 V vs saturated calomel electrode (SCE) in DMF-Tris buffer (1:4 v/v at pH 7.2) involving Cu(II)/Cu(I) couple is observed for the phen and dpq complexes. The dmp complex exhibits an irreversible reduction process forming bis(dmp)copper(I) species. A profound effect of the substituents of the phenanthroline bases is observed on the binding of the complexes to the calf thymus (CT) and in the cleavage of supercoiled (SC) pUC19 DNA. The phen and dpq complexes show DNA cleavage activity in presence of mercaptopropionic acid (MPA). The dmp complex is cleavage inactive in presence of MPA. All the complexes show photocleavage activity when irradiated with a monochromatic UV light of 312 nm. The dpq complex also cleaves SC DNA on visible light irradiation at 436, 532 and 632.8 nm but with a longer exposure time and higher complex concentration. The cleavage reactions in presence of MPA are found to involve hydroxyl radical. The photocleavage reactions are found to occur under aerobic conditions showing an enhancement of cleavage in D(2)O and inhibition with azide addition suggesting formation of singlet oxygen as a reactive species. The roles of sulfur of the Schiff base as photosensitizer and the phenanthroline bases as minor groove binder, and their influence on the photocleavage activity are discussed. The quinoxaline ligand exhibits significant photosensitizing effect assisted by the copper(II) center.     

Anticandidal cytotoxicity,antitumor activities,and purified cell wall modulation by novel Schiff base ligand and its metal (II) complexes against some pathogenic yeasts

The preparation of metal (II) complexes [CoCl₂·6H₂O, Ni(CH₃COO)₂·4H₂O, Cu(CH₃COO)₂·2H₂O, and Zn (CH3COO)₂ ·2H₂O] with 2[N-(cinnamlidene) amino]-5-nitro phenol as a novel ligands and their biological evaluation against candida species was studied. The inhibitory effects of the tested metal complexes were tested against six pathogenic yeasts (Candida albicans, C. fructus, C. glabrata, C. oleophila, C. parapsilosis, and C. tropicalis). The effect of the most efficient metal complex (Zn(II) complex) was more pronounced at 1.25 μg/ml, while Ni(II) complex was exhibited the least suppressive effect. Co(II) and Zn(II) complexes act as potential antitumor agents, while Zn(II) complex has shown promising cytotoxic activity with slow candidal respiration rate. Addition of Zn(II) complex leading to suppression of cell wall components in all candidal cells accompanied with leaking out of amino acids. Purification of the cell wall mannoprotein of C. glabrata treated with Zn(II) complex was established, resulting one pure fissured protein peak. Cell wall protein modulation was showed by appearance of two new protein bands with molecular weights of 72 and 39 KDa in C. glabrata cells treated with Zn(II) complex compared with one pure protein band 55.6 KDa in the non treated yeast cell.     

Schiff base copper(II) chelate as a tool for intermolecular cross-linking and immobilization of protein

A new method for intermolecular cross-linking or bridging of protein has been proposed. The method is based on the spontaneous chelate formation process involving three components, salicylaldehyde, alpha-amino acid residue and copper(II). Reliability of the process as a tool for protein cross-linking was evaluated by chromatographic procedures. Behavior of salicylaldehyde in a column packed with Sepharose attached alpha-amino acid residue showed that salicylaldehyde was bound tightly to the gel in the presence of copper(II) ion and was eluted by the addition of EDTA. The association was shown strong enough to be applied for the purpose of cross-linking of proteins. It was also proved that BSA salicylaldehyde conjugate was immobilized specifically to the column, and the process was reversed by the addition of EDTA as well. The method is proposed to be useful not only for immobilization of enzyme but also for cross-linking of proteins since the method is free from unexpected random coupling products which are unavoidable with bifunctional cross-linking reagents.     

Mononuclear nickel(II) and copper(II) complexes with Schiff base ligands derived from 2,6-diformyl-4-methylphenol and S-methylisothiosemicarbazones

Four new square-planar Ni(II) and Cu(II) complexes with [N₂O₂] binding system were synthesized by metal-directed condensation of 2,6-diformyl-4-methylphenol with benzoyl or acetylacetone mono-S-methylisothiosemicarbazone. Only mononuclear “one-armed” complexes were obtained as a consequence of the different reactivity of the two carbonyl groups in the hydroxydialdehyde. The complexes were characterized by elemental analysis, EI MS and UV-Vis spectroscopy. The structural assignment was confirmed by X-ray diffraction analysis and NMR spectroscopy, for the Ni(II) complexes, and by ESR spectroscopy and magnetic measurements, for the Cu(II) complexes.     

Remarkable photocytotoxicity in hypoxic HeLa cells by a dipyridophenazine copper(II) Schiff base thiolate

Copper(II) complexes [Cu(satp)(L)] (1-3) of a Schiff base thiolate (salicylidene-2-aminothiophenol, H₂satp) and phenanthroline bases (L), viz. 1,10-phenanthroline (phen in 1), dipyrido[3,2-d:2′,3′-f]quinoxaline (dpq in 2) and dipyrido[3,2-a:2′,3′-c]phenazine (dppz in 3), were prepared, characterized and their anaerobic DNA photocleavage activity and hypoxic photocytotoxicity studied. The redox active complexes show the Cu(II)-Cu(I) couple near − 0.5 V for 1 and near 0.0 V vs. SCE (saturated calomel electrode) for 2 and 3. The one-electron paramagnetic complexes (~ 1.85 μ_B) are avid DNA binders giving K_b values within 1.0 × 10⁵ − 8.0 × 10⁵ M^− 1. Thermal melting and viscosity data along with molecular docking calculations suggest DNA groove and/or partial intercalative binding of the complexes. The complexes show anaerobic DNA cleavage activity in red light under argon via type-I pathway, while DNA photocleavage in air proceeds via hydroxyl radical pathway. The DFT (density functional theory) calculations reveal a thyil radical pathway for the anaerobic DNA photocleavage activity and suggest the possibility of generation of a transient copper(I) species due to bond breakage between the copper and sulfur to generate the thyil radical. An oxidation of the copper(I) species is likely by oxygen in an aerobic medium or by the buffer medium in an anaerobic condition. Complex 3 exhibits significant photocytotoxicity in HeLa cells (IC₅₀ = 8.3(± 1.0) μM) in visible light, while showing lower dark toxicity (IC₅₀ = 17.2(± 1.0) μM). A significant reduction in the dark toxicity is observed under hypoxic cellular conditions (IC₅₀ = 30.0(± 1.0) μM in dark), while retaining its photocytotoxicity (IC₅₀ = 8.0(± 1.0) μM).     

Synthesis, characterization and X-ray crystal structures of copper(II) and nickel(II) complexes with potentially hexadentate Schiff base ligands

Copper(II) and nickel(II) complexes of potentially N₂O₄ Schiff base ligands 2-({[2-(2-{2-[(1-{2-hydroxy-5-[2-phenyl-1-diazenyl]phenyl}methylidene)amino] phenoxy}ethoxy) phenyl]imino}methyl)4-[2-phenyl-1-diazenyl]phenol (H₂L¹) and 2-({[2-(4-{2-[(1-{2-hydroxy-5-[2-phenyl-1-diazenyl]phenyl}methylidene)amino] phenoxy}butoxy) phenyl]imino}methyl)4-[2-phenyl-1-diazenyl]phenol (H₂L²) prepared of 5-phenylazo salicylaldehyde (1) and two various diamines 2-[2-(2-aminophenoxy)ethoxy]aniline (2) and 2-[4-(2-aminophenoxy)butoxy]aniline (3) were synthesized and characterized by a variety of physico-chemical techniques. The single-crystal X-ray diffractions are reported for CuL¹ and NiL². The CuL¹ complex contains copper(II) in a near square-planar environment of N₂O₂ donors. The NiL² complex contains nickel(II) in a distorted octahedral geometry coordination of N₂O₄ donors. In all complexes, H₂L¹ behaves as a tetradentate and H₂L² acts as a hexadentate ligand. Cyclic voltammetry of copper(II) complexes indicate a quasi-reversible redox wave in the negative potential range.     

X-ray crystallographic analyses of complexes between bovine beta-trypsin and Schiff base copper(II) or iron(III) chelates

To establish the structural basis underlying the activity of a novel series of metal-chelate trypsin inhibitors, the structures of p-amidinosalicylidene-l-alaninato(aqua)copper(II) (1a), m-amidinosalicylidene-l-alaninato(aqua)copper(II) (1b), bis(p-amidinosalicylidene-l-alaninato)iron(III) (2a), and bis(m-amidinosalicylidene-l-alaninato)iron(III) (2b) bound to bovine beta-trypsin were studied by X-ray crystallography. The amidinium group of the inhibitor donates hydrogen bonds to Asp189, Gly219 and Ser190, as seen before in trypsin-benzamidine complexes. The copper(II) ion of 1a is situated away from trypsin's catalytic triad residues, and is octahedrally coordinated by a Schiff base and three water molecules. In contrast, the copper(II) ion of 1b is situated close to the catalytic triad and adopts a square pyramidal coordination geometry. The iron(III) ion of 2a is octahedrally coordinated by two Schiff base ligands and, like the copper(II) ion of 1a, is situated away from the catalytic triad. The p-amidinophenyl ring of a second Schiff base ligand of 2a is directed toward a hydrophobic groove formed by Trp215 and Leu99. Finally, the iron(III) ion of 2b appears to be replaced by magnesium(II), which is octahedrally coordinated by a Schiff base, Gln192 and two water molecules. One of the Schiff base ligands seen in the trypsin-2a complex or in the unbound form of 2b is replaced by water molecules and Gln192. His57 and Ser195 form water-mediated interactions with the magnesium(II) ion of 2b, and Ser195 also forms a hydrogen bond with the phenolic oxygen atom of the Schiff base ligand. These structures reveal a novel mode of interaction between metal-chelate inhibitors and serine proteases, thus providing a structural basis for the development of more potent inhibitors against a variety of trypsin-like enzymes.     

A new Schiff base copper (II) complex derived from estrone and d-glucosamine: Synthesis, characterization and its interaction with DNA

A novel copper (II) complex of Schiff base prepared through condensation between 2-formyl-17-deoxyestrone and d-glucosamine was synthesized and characterized. Fluorescence spectroscopy was conducted to assess their binding ability with CT-DNA. The results showed that the copper (II) complex could bind to DNA with a weak intercalative mode. The interaction between the copper (II) complex and DNA was also investigated by gel electrophoresis. Interestingly, we found that the complex could cleave plasmid DNA (pUC19) to nicked and linear forms through an oxidative mechanism without the use of exogenous agents.