Synthesis, crystal structure and photo-induced DNA cleavage activity of ternary copper(II) complexes of NSO-donor Schiff bases and NN-donor heterocyclic ligands

New ternary copper(II) complexes [CuLⁿB](ClO₄) (1-3), where HLⁿ is the NSO donor Schiff base derived from the condensation of 2-mercaptoethylamine hydrochloride with salicylaldehyde (HL¹) or 2-hydroxy-3-methoxybenzaldehyde (HL²) and B is NN-donor heterocyclic base like 2,2′-bipyridine (bpy, 1), 1,10-phenanthroline (phen, 2) or 2,9-dimethyl-1,10-phenanthroline (dmp, 3), are prepared, structurally characterized by X-ray crystallography and their DNA cleavage activity studied. The complexes show distorted square-pyramidal (4 + 1) CuN₃OS coordination geometry in which the NSO-donor Schiff base is bonded at the basal plane and the NN-donor heterocyclic base displays axial-equatorial mode of bonding [Cu-S distance: ∼2.4 Å]. The one-electron paramagnetic (μ_eff = ∼1.9 μ_B) complexes display axial EPR spectra in DMF glass at 77 K giving g_∥ = ∼2.2 (A_∥ = 162 G) and g_⊥ = ∼2.0, indicating {d_x²-y²}¹ ground state. The complexes exhibit visible spectral d-d band in MeCN near 650 nm and two charge transfer bands near 400 nm. Complexes 1 and 2 display quasireversible cyclic voltammetric response in DMF-Tris buffer (1:4 v/v, pH 7.2) for the Cu(II)/Cu(I) couple at ca. −0.1 V vs. SCE. Complex 3 exhibits an irreversible reduction process forming [Cu^I(dmp)₂]⁺. Binding of 1-3 to calf thymus DNA shows the relative order: 2 (phen) ? 3 (dmp) > 1 (bpy). Complex 2 efficiently cleaves supercoiled pUC19 DNA in the presence of mercaptopropionic acid (MPA) forming hydroxyl radical or on irradiation with light of 312, 532 and 632.8 nm wavelength in a type-II process. Complexes 1 and 3 are cleavage inactive.     

Synthesis, crystal structure, DNA binding and photo-induced DNA cleavage activity of (S-methyl-L-cysteine)copper(II) complexes of heterocyclic bases

Ternary S-methyl-L-cysteine (SMe-l-cys) copper(II) complexes [Cu(SMe-L-cys)(B)(H(2)O)](X) (1-4), where the heterocyclic base B is 2,2'-bipyridine (bpy, 1), 1,10-phenanthroline (phen, 2), dipyridoquinoxaline (dpq, 3) and dipyridophenazine (dppz, 4), and X is ClO(4)(-) (1-3) or NO(3)(-) (4), are prepared and their DNA binding and cleavage properties studied. Complexes 2 and 4 are structurally characterized by X-ray crystallography. Both the crystal structures show distorted square-pyramidal (4+1) CuN(3)O(2) coordination geometry of the complexes in which the N,O-donor S-methyl-L-cysteine and N,N-donor heterocyclic base bind at the basal plane with a water molecule as the axial ligand. In addition, the dppz structure shows the presence of a 1D-chain formed due to covalent linkage of the carboxylate oxygen atom belonging to another molecule at the elongated axial site. The crystal structures show chemically significant non-covalent interactions like hydrogen bonding involving the axial aqua ligand and pi-pi interactions between dppz ligands. The complexes display a d-d band in the range of 605-654 nm in aqueous dimethylformamide (DMF) solution (9:1 v/v). The redox active complexes show quasireversible cyclic voltammetric response near 0.1 V in DMF assignable to the Cu(II)/Cu(I) couple. The complexes show good binding affinity to calf thymus (CT) DNA giving the order: 4 (dppz)>3 (dpq)>2 (phen)>1 (bpy). The intrinsic binding constants, obtained from UV-visible spectroscopic studies, are 1.3x10(4) and 2.15 x 10(4) M(-1) for 3 and 4, respectively. Control DNA cleavage experiments using pUC19 supercoiled (SC) DNA and minor groove binder distamycin suggest major groove binding propensity for the dppz complex, while the phen and dpq complexes bind at the minor groove of DNA. Complexes 2-4 show DNA cleavage activity in dark in the presence of a reducing agent 3-mercaptopropionic acid (MPA) via a mechanistic pathway involving formation of hydroxyl radical as the reactive species. The complexes also show efficient photo-induced DNA cleavage activity on irradiation with a monochromatic UV light of 365 nm in absence of any external reagent. The cleavage efficiency follows the order: 3>4>2. The complexes exhibit significant DNA cleavage activity on irradiation with visible light of 633 nm. Control experiments show inhibition of cleavage in presence of singlet oxygen quenchers like sodium azide, histidine and enhancement of cleavage in D(2)O, suggesting formation of singlet oxygen as a reactive species in a type-II process. The photosensitizing effect of the thiomethyl group of the amino acid is evidenced from the observation of significant DNA photocleavage activity of the phen complex 2 as the phen ligand itself is not a photosensitizer.     

Synthesis, crystal structures, DNA binding and cleavage activity of l-glutamine copper(II) complexes of heterocyclic bases

Ternary l-glutamine (l-gln) copper(II) complexes [Cu(l-gln)(B)(H₂O)](X) (B = 2,2′-bipyridine (bpy), , 1; B = 1,10-phenanthroline (phen), , 2) and [Cu(l-gln)(dpq)(ClO₄)] (3) (dpq, dipyridoquinoxaline) are prepared and characterized by physicochemical methods. The DNA binding and cleavage activity of the complexes have been studied. Complexes 1-3 are structurally characterized by X-ray crystallography. The complexes show distorted square pyramidal (4+1) CuN₃O₂ coordination geometry in which the N,O-donor amino acid and the N,N-donor heterocyclic base bind at the basal plane with a H₂O or perchlorate as the axial ligand. The crystal structures of the complexes exhibit chemically significant hydrogen bonding interactions besides showing coordination polymer formation. The complexes display a d-d electronic band in the range of 610-630 nm in aqueous-dimethylformamide (DMF) solution (9:1 v/v). The quasireversible cyclic voltammetric response observed near −0.1 V versus SCE in DMF-TBAP is assignable to the Cu(II)/Cu(I) couple. The binding affinity of the complexes to calf thymus (CT) DNA follows the order: 3 (dpq) > 2 (phen) ? 1 (bpy). Complexes 2 and 3 show DNA cleavage activity in dark in the presence of 3-mercaptopropionic acid (MPA) as a reducing agent via a mechanistic pathway forming hydroxyl radical as the reactive species. The dpq complex 3 shows efficient photo-induced DNA cleavage activity on irradiation with a monochromatic UV light of 365 nm in absence of any external reagent. The cleavage efficiency of the DNA minor groove binding complexes follows the order: 3 > 2 ? 1. The dpq complex exhibits photocleavage of DNA on irradiation with visible light of 647.1 nm. Mechanistic data on the photo-induced DNA cleavage reactions reveal the involvement of singlet oxygen (¹O₂) as the reactive species in a type-II pathway.     

Photocytotoxicity and near-IR light DNA cleavage activity of oxovanadium(IV) Schiff base complexes having phenanthroline bases

Oxovanadium(IV) complexes [VO(L)(B)] (1-3), where H₂L is a Schiff base ligand 2-(2-hydroxybenzylideneamino)phenol and B is 1,10-phenanthroline (phen for 1), dipyrido[3,2-d:2′,3′-f]quinoxaline (dpq for 2) or dipyrido[3,2-a:2′,3′-c]phenazine (dppz for 3), have been prepared, characterized and their DNA binding property and photo-induced DNA cleavage activity studied. Complex 3 which is structurally characterized by X-ray crystallography shows the presence of an oxovanadium(IV) moiety in a six coordinate VO₃N₃ coordination geometry. The complexes show a d-d band within 800-850 nm in DMF. The complexes display an oxidative response near 0.7 V versus SCE for V(V)-V(IV) and a reductive response within −1.1 to −1.3 V due to V(IV)-V(III) couple in DMF-0.1 M TBAP. The complexes are avid binders to calf thymus DNA giving binding constant values of 4.2 × 10⁴ to 1.2 × 10⁵ M⁻¹. The complexes do not show any “chemical nuclease” activity in dark. The dpq and dppz complexes are photocleavers of plasmid DNA in UV-A light of 365 nm via ¹O₂ pathway and in near-IR light (752.5 to 799.3 nm IR optics) by HO^• pathway. Complex 3 exhibits significant photocytotoxicity in visible light in HeLa cells giving IC₅₀ value of 13 μM, while it is less toxic in dark (IC₅₀ = 97 μM).     

Synthesis, crystal structure and DNA cleavage activity of a novel Ni(II)-Cd(II) coordination polymer

A novel one-dimensional heterometallic complex, {Cd₂[NiL]₂(SCN)₄(H₂O)}_n (1), has been synthesized and characterized by single-crystal X-ray analysis, where L is dianion of 2,3-dioxo-5,6,13,14-dibenzo-9,10-cyclohexyl-7,12-bis(ethoxycarbonyl)-1,4,8,11-tetraazacyclotetradeca-7,11-diene. The most striking feature of 1 is that in the structure there is one type of S-S bond (1.823(13) Å) formed by two thiocyanate groups which has not been reported to our knowledge. The DNA cleavage activity of 1 in the presence of H₂O₂ was compared with those of nickel(II) ion, cadmium(II) ion and corresponding mononuclear precursor NiL (2). The DNA cleavage kinetics was studied and the corresponding activation parameters of 1 were obtained.     

Synthesis, structure, DNA binding and DNA cleavage activity of oxovanadium(IV) N-salicylidene-S-methyldithiocarbazate complexes of phenanthroline bases

Ternary oxovanadium(IV) complexes [VO(salmdtc)(B)] (1-3), where salmdtc is dianionic N-salicylidene-S-methyldithiocarbazate and B is N,N-donor phenanthroline bases like 1,10-phenanthroline (phen, 1), dipyrido[3,2-d:2′,3′-f]quinoxaline (dpq, 2) and dipyrido[3,2-a:2′,3′-c]phenazine (dppz, 3), are prepared, characterized and their DNA binding and DNA cleavage activity studied. Complex 3 is structurally characterized by single-crystal X-ray crystallography. The molecular structure shows the presence of a vanadyl group in six-coordinate VN₃O₂S coordination geometry. The S-methyldithiocarbazate Schiff base acts as a tridentate NSO-donor ligand in a meridional binding mode. The N,N-donor heterocyclic base displays a chelating mode of binding with an N-donor site trans to the vanadyl oxo-group. The complexes show a d-d band in the range of 675-707 nm in DMF. They exhibit an irreversible oxidative cyclic voltammetric response near 0.9 V due to the V(V)/V(IV) couple and a quasi-reversible reductive V(IV)/V(III) redox couple near −1.0 V vs. SCE in DMF-0.1 M TBAP. The complexes show good binding propensity to calf thymus DNA giving binding constant values in the range of 7.4 × 10⁴-2.3 × 10⁵ M⁻¹. The thermal denaturation and viscosity binding data suggest DNA surface and/or groove binding nature of the complexes. The complexes show poor chemical nuclease activity in dark in the presence of 3-mercaptopropionic acid (MPA) or hydrogen peroxide. The dpq and dppz complexes show efficient DNA cleavage activity in UV-A light of 365 nm via a type-II mechanistic pathway involving formation of singlet oxygen (¹O₂) as the reactive species.     

Synthesis, DNA binding, photo-induced DNA cleavage, cytotoxicity and apoptosis studies of copper(II) complexes

Two new Cu(II) complexes, [Cu(acac)(dpq)Cl] () and [Cu(acac)(dppz)Cl] () (acac = acetylacetonate, dpq = dipyrido[3,2-d:20,30-f]quinoxaline, dppz = dipyrido[3,2-a:20,30-c] phenazine), have been synthesized and their DNA binding, photo-induced DNA cleavage activity and cell cytotoxicity are studied. The complexes show good binding propensity to calf thymus DNA in the order: 2(dppz) > 1(dpq). Furthermore, two complexes exhibit efficient DNA cleavage activity on natural light or UV-A (365 nm) irradiation via a mechanistic pathway involving formation of singlet oxygen as the reactive species. The photo-induced DNA cleavage activity of the dppz complex 2 is found to be more efficient than its dpq analogue. In vitro study of the photocytotoxicity of two complexes on HeLa cells indicate that both of them have the potential to act as effective anticancer drugs, with IC₅₀ values of 5.25 ± 0.83 μM (1) and 4.40 ± 0.52 μM (2) in the natural light, and 2.57 ± 0.92 μM (1) and 2.18 ± 0.52 μM (2) in UV-A light. In addition, to detect an apoptotic HeLa body, cells were stained with Hoechst 33342 dye.     

An oxamato bridged trinuclear copper(II) complex: Synthesis, crystal structure, reactivity, DNA binding study and magnetic properties

A linear tri-nuclear oxamato bridged copper(II) complex [Cu₃(pba)(dpa)₂(H₂O)(ClO₄)](ClO₄)·H₂O (1) (pbaH₄ = 1,3-propanediylbis(oxamic acid), dpa = 2,2′-dipyridylamine) was isolated from the reaction mixture of Na₂[Cu(pba)]·3H₂O, copper perchlorate hexahydrate and dipyridylamine in methanol. On reaction with dpa or DMF in basic medium (KOH) at ambient temperature complex 1 changed to dinuclear oxalate bridged copper(II) derivatives, [Cu₂(μ-C₂O₄)(dpa)₄](ClO₄)₂ (2) and [Cu₂(μ-C₂O₄)(dpa)₂(DMF)₂](ClO₄)₂ (3), respectively. The complexes 1, 2 and 3 have been characterized by physicochemical and spectroscopic tools, and also by the X-ray single crystal analysis. The hydrolysis of 1 in basic medium and thermo-gravimetric analysis has been studied. Absorption and emission spectral studies showed that complex 1 interacts with calf thymus-DNA (CT-DNA) with a binding constant (K_b) of 4.01 × 10⁴ M⁻¹ and linear Stern-Volmer quenching constant (K_sv) of 6.9 × 10⁴. A strong anti-ferromagnetic interaction with a coupling constant J_CuCu of 320.0 ± 0.3 cm⁻¹ was observed from the study of magnetic behavior of complex 1 in the temperature range of 2-300 K. Electrochemical equivalency of three copper(II) ions in 1 was identified by getting only one quasi reversible cyclic voltammogram.     

Synthesis, crystal structure, antibacterial assay and DNA binding activity of new binuclear Cu(II) complexes with bridging oxamidate

Two new binuclear copper complexes, [Cu₂(oxpn)(bpy)(pic)(H₂O)](pic) (1) and [Cu₂(oxpn)(Me₂bpy)(pic)](pic) (2) [H₂oxpn = N,N′-bis(3-aminopropyl)oxamide; Hpic = 2,4,6-trinitrophenol; bpy = 2,2′-bipyridine; Me₂bpy = 4,4′-dimethyl-2,2′-bipyridine], have been synthesized and characterized by elemental analyses, conductivity measurements, IR, UV-visible spectroscopy and single crystal X-ray analyses. Both complexes have similar molecular structures. In complex 1, the central two Cu(II) atoms are bridged by cis-oxpn²⁻ with the Cu1-Cu2 separation of 5.221 Å and the polyhedron of each copper atom is a square-pyramid. Similarly, complex 2 is a cis-oxpn²⁻-bridged binuclear complex with the Cu1-Cu2 separation of 5.196 Å. Cu1(II) central atom situated in a tetrahedral geometry is four-coordinated and Cu(II) atom situated in a square-pyramidal geometry is five-coordinated. Hydrogen bonding interactions and π-π stacking interactions link the binuclear copper complex 1 or 2 into a 2D infinite network. The antibacterial assays indicate that the two complexes showed better activities than their ligands. The interactions of the two binuclear complexes with herring sperm DNA (HS-DNA) have been studied by UV absorption titration, fluorescence titration and viscosity measurements. The results suggest that the two binuclear complexes bind to HS-DNA via an intercalative mode.     

Synthesis, crystal structure, magnetic property and nuclease activity of a new binuclear cobalt(II) complex

One new binuclear Co(II) complex of N,N,N',N'-tetrakis(2-benzimidazolylmethyl)-2-hydroxyl-1,3-diaminopropane (HL), [Co(2)L(mu(2)-Cl)](ClO(4))(2) x 3CH(3)CN x C(2)H(5)OC(2)H(5) (1), has been synthesized and its crystal structure and magnetic properties are shown. In 1, each Co(II) atom has a distorted trigonal bipyramidal geometry with a N(3)OCl donor set. The central two Co(II) atoms are bridged by one alkoxo-O atom and one Cl atom with the Co1-Co2 separation of 3.239 A. Susceptibility data of 1 indicate strong intramolecular antiferromagnetic coupling of the high-spin Co(II) atoms. In this paper, the interaction with calf thymus DNA was investigated by UV absorption and fluorescent spectroscopy. Results show the complex binds to ct-DNA with a intercalative mode. The interaction between complex 1 and pBR322 DNA has also been investigated by submarine gel electrophoresis, noticeably, the complex exhibits effective DNA cleavage activity in the absence of any external agents.     

Synthesis, structure and DNA cleavage activity of two 4,4′-dimethyl-2,2′-bipyridyl manganese(II) complexes

Two new mononuclear Mn(II) complexes, Mn(dmbpy)₂(OCN)₂ (1) and Mn(dmbpy)₂(dca)₂ (2) (dmbpy = 4,4′-dimethyl-2,2′-bipyridine, dca = dicyanamide), have been synthesized and characterized by IR, elemental analysis, and single crystal X-ray analysis. Both complexes have similar molecular structures. The coordination sphere of the Mn(II) ion in 1 or 2 is a seriously distorted octahedron formed by two dmbpy ligands and two OCN⁻ or dca anions in cis positions. For both complexes, the most striking feature is that the mononuclear molecules are linked together by plentiful weak C-H?N hydrogen bonds into a compact 3D supramolecular structure. DNA cleavage studies show that the complexes can promote plasmid DNA cleavage in the presence of H₂O₂ under physiological conditions, and their cleavage activities are obviously both pH value and complex concentration-dependent. The cleavage mechanism between the complexes and plasmid DNA is likely to involve hydroxyl radicals as reactive oxygen species.     

Synthesis, crystal structure, spectroscopic and magnetic properties of copper(II) complexes with 2-(2-pyridyl)imino-N-(2-thiazolin-2-yl)thiazolidine (PyTT)

The copper(II) complexes [Cu(PyTT)₂(H₂O)](NO₃)₂ (A) and [CuCl₂(μ-PyTT)₂CuCl(H₂O)]Cl · 3H₂O (B) were synthesized and characterized by single crystal X-ray diffraction, IR spectroscopy, UV-Vis-NIR diffuse reflectance and magnetic susceptibility measurements. In the mononuclear compound A the copper ion is in a distorted square pyramidal geometry, with the equatorial plane formed by two thiazoline nitrogen atoms, one imino nitrogen atom and one water molecule, whereas the axial site is occupied by one imino nitrogen atom. The compound B is dinuclear and both Cu(II) centres present environments that can be described as slightly distorted square pyramidal geometries. The observed molar magnetic susceptibility for A (μ=2.13 BM) allows to exclude metal-metal interactions, supporting a monomeric structural formulation for this compound. In compound B, magnetic susceptibility measurements in the temperature range 6.2-288 K show an intradimer antiferromagnetic interaction (J=−11.8 cm⁻¹).     

Ternary copper(II) complexes of levofloxacin and phenanthroline derivatives: In-vitro antibacterial,DNA interactions,and SOD-like activity

A series of ternary copper(II) complexes have been derived using levofloxacin and five phenanthroline derivatives. Complexes were characterized using infrared spectroscopy, Thermogravimetric (TG)-analysis, fast atom bombardment mass spectroscopy and reflectance spectra. Synthesized complexes exhibit the only d-d band at ～ 666?nm points toward a distorted square pyramidal geometry at metal centre with one unpaired electron responsible for paramagnetic behaviour of whole moiety. Binding behaviour of the complexes toward Herring Sperm DNA were determined using ultraviolet-Vis (UV-Vis) absorption titration and viscometric titration experiment, where as the cleavage efficacy of the complexes toward pUC19 DNA was determined by electrophoresis in presence of ethidium bromide. Complexes exhibit superoxide dismutase–like activity with their IC₅₀ values ranging from 0.7917 to 1.7432 µM.     

Synthesis, crystal structures and magnetic properties of the copper(II) complexes containing isophthalate anion as coligand

Two new dinuclear isophthalato-bridged copper(II) complexes [Cu₂(ntb)₂(μ-ipt)](ClO₄)₂·4CH₃OH·0.33H₂O (1), [Cu₂(bbma)₂(μ-ipt)(NO₃)(CH₃OH)]NO₃·CH₃OH (2) and one mononuclear complex [Cu(bbma)(ipt)(CH₃OH)_0.67(H₂O)_0.33]·2CH₃OH (3) containing tetradentate and tridentate poly-benzimidazole ligands were synthesized, where ntb is tris(2-benzimidazolylmethyl)amine, bbma is bis(benzimidazol-2-yl-methyl)amine and ipt is isophthalate dianion. All of the complexes were characterized by elemental analysis, IR spectra and X-ray crystallography. The structures of complexes 1 and 2 consist of μ-ipt bridging two Cu(II) centers in a bis(monodentate) bonding fashion. The coordination geometry around the Cu(II) ions of both compounds has a distorted square pyramidal geometry. The Cu···Cu distances are 9.142 and 10.435 Å for 1 and 2, respectively. Complex 3 has a distorted square pyramidal geometry achieved by the three N-atoms of the bbma ligand, one isophthalate-oxygen atom and one oxygen atom from a coordinated methanol molecule. The magnetic susceptibility measurements at variable temperature over the 2-300 K range for complexes 1 and 2 are reported, with J values to be −0.013 and −0.32 cm⁻¹, respectively. The results show that the two complexes exhibit very weak antiferromagnetic interactions between the dinuclear copper(II) centers.     

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.     

Synthesis and crystal structures of di- and tetra-nuclear dicarboxylate-bridged copper(II) complexes

Three new Cu(II) complexes, [Cu₂(C₃H₂O₄)(phen)₂(H₂O)₃](NO₃)₂(H₂O)₂ (1) (C₃H₂O₄ = malonate, phen = 1,10-phenanthroline), [Cu₂(C₄H₄O₄)(phen)₂(H₂O)₂](NO₃)₂ (2) (C₄H₄O₄ = succinate), and {[Cu₂(phen)₂(H₂O)(NO₃)]₂(C₅H₆O₄)₂}(NO₃)₂ (3) (C₅H₆O₄ = glutarate) have been synthesized and characterized by elemental analysis, infrared spectroscopy, thermogravimetric analysis, and single crystal X-ray diffraction. The X-ray analysis reveals that the structures of 1 and 2 are of dinuclear copper(II) complexes bridged by malonate and succinate dianions, respectively, and 3 is a tetranuclear species formed by two {[Cu₂(phen)₂(H₂O)(NO₃)](C₅H₆O₄)} fragments. The copper ions in 1 and 3 show square-pyramidal coordination geometry, while the copper ions in 2 exhibit a square planar geometry. In each complex, the dicarboxylate ligand is coordinated to copper ions as a chelate and monodentate (1), bis-monodentate (2), and bis-bridging ligand toward the copper ions with syn-syn coordination mode (3).     

Electrochemical synthesis and crystal structure of iron(II), cobalt(II), nickel(II) and copper(II) complexes of dianionic tetradentate N4 Schiff base ligand

The electrochemical oxidation of anodic metal (iron, cobalt, nickel and copper) in an acetonitrile solution of the potentially chelating Schiff base N,N(dithiodiethylenebis-(aminylydenemethylydene)-bis(1,2-phenylene)ditosylamide (H₂L) afforded stable complexes of empirical formula [ML]. The compounds obtained have been characterized by microanalysis, IR spectroscopy and ES-MS mass spectrometry. The crystal and molecular structures of [FeL]·CH₃CN (1) [CoL]·CH₃CN (2), [NiL]·CH₃CN (3) and [CuL]·CH₃CN (4) have been determined by X-ray diffraction in all complexes, the metal atom is in a distorted tetrahedral environment with the Schiff base acting as a tetradentate N4 donor.     

Synthesis, structure, DNA binding and cleavage properties of ternary amino acid Schiff base-phen/bipy Cu(II) complexes

Ternary Cu(II) complexes [Cu(II)(saltrp)(B)] (1,2), (saltrp = salicylidene tryptophan, B = 1,10 phenathroline (1) or 2,2′ bipyridine (2)) were synthesized and characterized. Complex 2 was structurally characterized by single crystal X-ray crystallography. The molecular structure shows a distorted square pyramidal coordination geometry (CuN₃O₂) in which the ONO donor Schiff base is bonded to the Cu(II) in the basal plane. The N,N donor heterocyclic base displays an axial-equatorial binding mode. CT-DNA binding studies revealed that the complexes show good binding propensity (Intrinsic binding constant, K_b = 3.32 × 10⁵ M⁻¹ for 1 and K_b = 3.10 × 10⁵ M⁻¹ for 2). The catalytic role of these complexes in the oxidative and hydrolytic cleavage of DNA was studied in detail. Complex 1 binds and cleaves DNA more efficiently as compared to 2. From the kinetic experiments, rate constants for the hydrolysis of phosphodiester bond of DNA backbone were determined as 1.94 h⁻¹ and 1.05 h⁻¹ for 1 and 2 respectively. It amounts to (2.93-5.41) × 10⁷ fold rate enhancement compared to uncatalyzed double stranded DNA, which is impressive as compared to related Cu(II) Schiff base complexes.     

Synthesis, characterization, and crystal structures of hydrotris(2-mercapto-1-imidazolyl)borate-based zinc(II) and copper(I) complexes

The reaction of the tripod ligand hydrotris(2-mercapto-1-imidazolyl)borate Tm^xylyl with zinc(II) perchlorate in methanol afforded the mononuclear complex of the type [Tm^xylyl-Zn(mim^xylyl)]ClO₄ (1). Whereas under the same conditions, the reaction with copper(II) perchlorate gives rise to the simultaneous formation of the dinuclear copper(I) complex [Tm^xylylCu]₂ (2). The chemical formulae of the complexes have been characterized by elemental chemical analysis, IR-NMR spectroscopies, and single crystal X-ray methods. In complex 1, the zinc(II) atom displays a distorted tetrahedral environment. While in complex 2, the Tm^xylyl ligand bridges the two copper(I) atoms in an asymmetric manner with trigonal geometry. The inverted conformation of the ligand Tm^xylyl at the boron center, allows the B-H units to be directed towards the copper centers. The greater reactivity of the borohydride groups towards metal centers enhances the reduction of Cu(II) to Cu(I). The obtained kinetic results for the methylation reactions of 1 and 2 indicate that these bound thione complexes are less suitable to electrophilic attack than the thiolate ligand.     

Two new copper(II) polyamine compounds: Synthesis, characterization and crystal structure

Two new compounds of Cu(II) of stoichiometry CuCl₄(polyamineH₂) containing the polyamines (PA): spermidine or spermine were prepared. Their synthesis, spectroscopic and structural characterization are herein described. The obtained complex with spermidine was characterized by elemental and thermogravimetric analysis, electronic and infrared spectroscopy. In the case of the compound with spermine, crystals were obtained. So, beside all other techniques the compound was also characterized by single crystal X-ray diffractometry. In both cases the species [CuCl₄]²⁻ is present and displays a similar polymeric structure. The X-ray, infrared and electronic spectra are herein discussed based on structural peculiarities of the compounds.