Photooxidation of bis(ethylxanthato)nickel(II) containing aromatic nitrogen heterocyclic ligands in chloroform

The photochemistry of the complexes [Ni(Etxn)₂(N-N)] [Etxn=ethylxanthate,N-N=2,2-bipyridine(bpy), 4,4-dimethyl-2,2-bipyridine (4,4-Me-bpy), 1,10-phenanthroline (phen) or 2,2-bipyrimidine (bpym)] has been investigated. These complexes were not light sensitive in most solvents such as acetonitrile. Upon irradiation of chloroform solutions of these complexes, a photoredox reaction occurred giving the parent Ni(Etxan)₂. It is suggested that the reactive excited state is of the charge-transfer-to-solvent (CTTS) type. The energy of this state depends on the redox potentials of the solvent. When CHCl₃ as solvent was replaced by the stronger oxidant CCl₄, the photoactive wavelength region was shifted to the red. It was blue shifted when the weaker oxidant CH₂Cl₂ was used. From quantum yield measurements it is concluded that the photostability of the studied complexes decreases in the following order:bpym>phen>bpy>4,4-Me-bpy.

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Photooxidation von Bis(ethylxanthato)nickel(II) mit aromatischen Stickstoffheterocyclen enthaltenden Liganden in Chloroform

Zusammenfassung Es wurde die Photochemie der Komplexe [Ni(Etxn)₂(N-N) [Etxn=Ethylxanthat,N-N=2,2-Bipyridin (bpy), 4,4-Dimethyl-2,2-bipyridin (4,4-Me-bpy), 1,10-Phenanthrolin (phen) oder 2,2-bipyrimidin (bpym)] untersucht. Diese Komplexe waren in den meisten Lösungsmitteln wie etwa Acetonitril nicht lichtsensitiv. Bei Bestrahlung von Chloroformlösungen der Komplexe trat jedoch eine Photoreaktion auf, die zum Stammkomplex Ni(Etxn)₂ führte. Es wird vorgeschlagen, für den reaktiven angeregten Zustand einen Charge-Transfer-zu-Lösungsmittel (CTTS)-Typ anzunehmen. Die Energie dieses Zustands hängt vom Redoxpotential des Lösungsmittels ab. Bei Ersatz von CHCl₃ als Lösungsmittel durch das stärkere Oxidans CCl₄ wurde die photoaktive Wellenlänge nach Rot verschoben. Eine Blauverschiebung ergab sich hingegen, wenn das schwächere Oxidans CH₂Cl₂ verwendet wurde. Aus Messungen der Quantenausbeuten ergab sich die folgende Ordnung nach abnehmender Photostabilität der untersuchten Komplexe:bpym>phen>bpy>4,4-Me-bpy.

     

Synthesis and crystal structures of nickel(II) supramolecules containing hexaazamacrocycles and aromatic carboxylate ligands

Two new nickel(II) complexes, {[Ni(L)(4,4′-bpdc)] · 3H₂O} _n (1) and {[Ni(L)(2,6-ndc)] · 2CH₃CN} _n (2) (L = 1,8-dihydroxylethyl-1,3,6,8,10,13-hexaazacyclotetradecane, 4,4′-bpdc = 4,4′-biphenyldicarboxylate, 2,6-ndc = 2,6-naphthalenedicarboxylate), have been synthesized and structurally characterized by spectroscopic and X-ray diffraction methods. Compound 1 shows a 3-D supramolecule which is composed of two different series of 1-D coordination polymers, where each 1-D chain runs in different directions and interacts by π–π stacking at the intersection. Compound 2 contains 1-D coordination polymers in which 1-D chains run in the same direction. The 1-D chains are interconnected by hydrogen bonds in an undulated fashion to form a 3-D supramolecule.     

Precursors to water-soluble dinitrogen carriers. Synthesis of water-soluble complexes of iron(II) containing water-soluble chelating phosphine ligands of the type 1,2-bis(bis(hydroxyalkyl)phosphino)ethane

The reactions of the water-soluble chelating phosphines 1,2-bis(bis(hydroxyalkyl)phosphino)ethane (alkyl = n-propyl, DHPrPE; n-butyl, DHBuPE; n-pentyl, DHPePE) with FeCl(2).4H(2)O and FeSO(4).7H(2)O were studied as routes to water-soluble complexes that will bind small molecules, dinitrogen in particular. The products that form and their stereochemistry depend on the solvent, the counteranion, and the alkyl chain length on the phosphine. In alcoholic solvents, the reaction of FeCl(2).4H(2)O with 2 equiv of DHBuPE or DHPePE gave trans-Fe(L(2))(2)Cl(2). The analogous reactions in water with DHBuPE and DHPePE gave only cis products, and the reaction of FeSO(4).7H(2)O with any of the phosphines gave only cis-Fe(L(2))(2)SO(4). These results are interpreted as follows. The trans stereochemistry of the products from the reactions of FeCl(2).4H(2)O in alcohols is suggested to be the consequence of the trans geometry of the Fe(H(2)O)(4)Cl(2) complex, i.e., substitution of the water molecules by the phosphines retains the geometry of the starting material. The formation of cis-Fe(DHPrPE)(2)Cl(2) is an exception to this result because the coordination of two -OH groups forms two six-membered rings, as shown in the X-ray structure of the molecule. DHBuPE and DHPePE reacted with FeSO(4).7H(2)O in water to initially yield cis-Fe(P(2))(2)SO(4) compounds, but subsequent substitution reactions occurred over several hours to give sequentially trans-Fe(DHBuPE)(2)(H(2)O)(SO(4)) and then trans-[Fe(DHBuPE)(2)(H(2)O)(2)]SO(4). The rate constants and activation reactions for these aquation reactions were determined and are consistent with dissociatively activated mechanisms. The cis- and trans-Fe(L(2))(2)X (X = (Cl)(2) or SO(4)) complexes react with N(2), CO, and CH(3)CN to yield trans complexes with bound N(2), CO, or CH(3)CN. The crystal structures of the cis-Fe(DHPrPE)(2)SO(4), trans-Fe(DHPrPE)(2)(CO)SO(4), trans-Fe(DHBuPE)(2)Cl(2), trans-[Fe(DHBuPE)(2)(CO)(Cl)][B(C(6)H(5))(4)], trans-Fe(DMeOPrPE)(2)Cl(2), trans-Fe(DMeOPrPE)(2)Br(2), and trans-[Fe(DHBuPE)(2)Cl(2)]Cl complexes are reported. As expected from using water-soluble phosphines, the complexes reported herein are water soluble (generally greater than 0.5 M at 23 degrees C).     

Synthesis,characterization and DNA interaction studies of a new platinum(II) complex containing caffeine and histidine ligands using instrumental and computational methods

A new Pt(II) complex, [Pt(Caff)(His)(Cl)] (Caff is Caffeine (3,7-dihydro-1,3,7-trimethyl-1H-purine-2,6-dione) and His is l-Histidine), was synthesized and characterized using different physicochemical methods. The interaction of this complex with calf thymus DNA (ct-DNA) was investigated by absorption, emission, circular dichroism (CD), and viscosity measurements and molecular docking techniques. The calculated binding constant, K_b, was 5.3 × 10³ M^?1. In fluorimetric studies, the enthalpy and entropy of the reaction between the complex and ct-DNA showed that the reaction is exothermic (?H = ?184.07 kJ mol^?1, ?S = ?551.97 J mol^?1 K^?1). CD spectra of DNA in the presence of different amounts of the complex showed little changes in both the negative and positive band intensities, which imply a non-intercalative mode between the DNA and the platinum complex. Furthermore, the study of molecular docking also indicated that the complex binds to DNA via a groove binding mode.     

Synthesis and spectroscopic studies of copper(II) and nickel(II) complexes containing hydrazonic ligands and heterocyclic coligand

Two types of copper(II) and nickel(II) complexes derived from benzophenone anthranoylhydrazone (L1), 2-acetonaftanone anthranoylhydrazone (L2), 4-phenylacetonaftonone anthranoylhydrazone (L3), benzophenone salicyoylhydrazone (L4), 2-acetonaftanon salicyoylhydrazone (L5), 4-phenylacetonaftanon salicyoylhydrazone (L6) and bidentate heterocyclic base [1,10-phenanthroline (phen)] with general stoichiometry [ML2] and [ML(phen)]Cl have been synthesized and characterized by elemental analysis, infrared spectra, UV-vis electronic absorption spectra and magnetic susceptibility measurements. The effect of varying pH and solvent on the absorption behavior of both ligands and complexes have been investigated. According to the IR spectra, the ligands act as monobasic bidentate and coordination takes place in the enol tautomeric form.     

Heterocyclic nickel(II) dithiocarbamates with aromatic thiols as bridging ligands

Binuclear NiII dithiocarbamates, with aromatic monothiols as bridging ligands, of composition [Ni(-L) (Rdtc)]2 [dtc = S2CN, R = C4H8O (morph), C5H10 (pip), C4H8 (pld); HL = thiophenol, 4-methylthiophenol or 2-thionaphthol] and [Ni(-L)(HR1dtc)]2 {R1 = C11H11N2O (aap)} have been prepared and characterized by elemental analyses, i.r. and electron spectroscopy, magnetochemical and conductivity measurements, and thermal analysis. The methods used indicate that the complexes are diamagnetic, complex non-electrolytes with two square-planar NiS4 chromophores.     

Synthesis and reactivity of water-soluble platinum(II) complexes containing nitrogen ligands

A series of water-soluble platinum(II) complexes containing bidentate imino pyridine ligands L of the general formula LPtX₂ (X=Cl or Me) have been prepared. The dichloro complexes are very stable in water or dimethyl sulfoxide (DMSO), even at elevated temperatures, whereas the dimethyl complexes are less stable in these strongly polar solvents. In DMSO, an equilibrium between the complex LPtMe₂ and (DMSO)₂PtMe₂ is observed, whereas in water decomposition is observed within 1 day at room temperature.     

多种光谱方法研究除草剂利谷隆与DNA的相互作用

在生理条件下(pH 7.4),采用紫外-可见光谱法、荧光光谱法、圆二色谱法(CD)和傅里叶红外光谱法(FT-IR)并结合粘度实验和熔点测量技术,研究了利谷隆与小牛胸腺DNA(DNA)的相互作用。实验发现,利谷隆可以置换出嵌入DNA中的亚甲基蓝,并使DNA的熔点和粘度升高,表明二者发生了嵌插作用。利谷隆的存在引起DNA的CD光谱收缩,表明DNA发生了B构象向C构象的转变;红外光谱分析表明嵌入DNA双链的利谷隆芳环主要作用于G、A碱基。     

Ferromagnetism in a dinuclear nickel(II) complex containing triethylenetetramine and tricyanomethanide

Triethylenetetramine (L(4)) was used as a tetradentate blocking ligand that, after complexation with Ni(II), leaves two sites ready for ligation with tricyanomethanide. The formed binuclear complex [L(4)Ni(NCC(CN)CN)(2)NiL(4)](ClO(4))(2) exhibits a ferromagnetic coupling with J/hc = +0.15 cm(-1) and g(Ni) = 2.126; below 16 K, a ferromagnetic ordering is evidenced by ac magnetic susceptibility (both in-phase and out-of-phase), magnetization, field-cooled magnetization, and zero-field-cooled magnetization measurements.     

Reversible DNA condensation induced by a tetranuclear nickel(II) complex

DNA condensing agents play a critical role in gene therapy. A tetranuclear nickel(II) complex, [Ni^II₄(L?2H)(H₂O)₆(CH₃CH₂OH)₂] ? 6NO₃ (L=3,3',5,5'‐tetrakis{[(2‐hydroxyethyl)(pyridin‐2‐ylmethyl)amino]methyl}biphenyl‐4,4'‐diol), has been synthesized as a nonviral vector to induce DNA condensation. X‐ray crystallographic data indicate that the complex crystallizes in the monoclinic system with space group P2₁/n, a=10.291(9), b=24.15(2), c=13.896(11) Å, and β=98.175(13)°. The DNA condensation induced by the complex has been investigated by means of UV/Vis spectroscopy, fluorescence spectroscopy, circular dichroism spectroscopy, dynamic light scattering, atomic force microscopy, gel electrophoresis assay, and zeta potential analysis. The complex interacts strongly with DNA through electrostatic attraction and induces its condensation into globular nanoparticles at low concentration. The release of DNA from its compact state has been achieved using the chelator ethylenediaminetetraacetic acid (EDTA) for the first time. Other essential properties, such as DNA cleavage inactivity and biocompatibility, have also been examined in vitro. In general, the complex satisfies the requirements of a gene vector in all of these respects.     

Halide copper(II) complexes of aromatic N-donor containing ligands: Structural,magnetic and reactivity studies

The preparation of four new copper(II) complexes with different N-donor ligands [CuBr₂(2-benzylpyridine)₂] (1), [CuBr₂(2-benzylpyridine)(2,2′-bipyridine)]·H₂O (2), [CuBr₂(3-methyl-2-phenylpiridine)₂] (3), [Cu(picolinate)₂]·KI (4) from copper(I) halides as starting material is described. During the preparation of compound 4 a ligand oxidation reaction took place to give the picolinate ligand starting from 2-(2-methylaminoethyl)pyridine. The complexes were characterized by elemental analyses, IR spectroscopy and crystallographic studies. Single crystal X-ray diffraction analysis of the complexes reveals their monomeric penta- and tetracoordinated nature. For all compounds, the copper(II) present a common square planar coordination except for compound 2 which is five coordinated in a quasi-square pyramidal configuration with τ of 0.29. The Cu–N distances for these compounds are in the range of 1.959(4)-2.041(3) Å, Cu–O distance was 1.961(3) Å and Cu–Br distances were in the range of 2.4052(4)-2.4381(6) Å for the square base configuration while for apical distance it was 2.6745(7) Å. Magnetic properties have been investigated for all compounds in the temperature range 2-300 K. Compound 1 shows weak antiferromagnetic intermolecular interaction.     

Supramolecular assembly and DNA cleavage activity of a nickel(II) complex

A new mononuclear nickel(II) complex, [NiL₂] (HL = ((2-(5-fluoro-2-hydroxybenzyl)(2-(imidazole-2-yl)ethyl))imine), has been synthesized and characterized by IR, UV–vis and X-ray diffraction technique. The X-ray crystal structure of the complex shows that the coordination environment around Ni(II) ion is an approximate octahedron. Each molecule connects with four adjacent neighbors through strong hydrogen bonding interactions (N–H···O, d(N–O) = 2.687 Å and ∠N–H···O = 158.3(1)°), forming a supramolecular network. The interaction of the complex with DNA was monitored using agarose gel electrophoresis. The results show that the complex has DNA cleavage activity. The cyclic voltammogram shows one pair of anodic and cathodic peaks with E_1/2 = ?1.06 V, assigned to the Ni(II)/Ni(I) couple.     

Kinetic studies of complexation reactions of water-soluble hydrazones with nickel(II) and palladium(II) ions

The kinetics of complexation reactions of five water-soluble heterocyclic hydrazones with nickel(II) and palladium(II) ions have been investigated by stopped-flow spectrophotometry. Rates of complexations with nickel(II) and palladium(II) in the absence of chloride ion were found to be proportional to the first order of the ligand and metal ion concentrations and to the inverse first order of the hydrogen ion concentration except for the complexation of alpha-(2-benzimidazolyl)-alpha-(5-nitro-2-pyridyl)hydrazono-3-toluenesulfonic acid with palladium(II). Rates of complexation with palladium(II) in the presence of chloride ion were best described by a two-term expression, both terms being first order in the palladium ion and ligand concentrations and inverse first order in the hydrogen ion concentration. The first term has zero dependence of the chloride ion concentration, whereas the second is first order with respect to the chloride ion concentration. The rate constant for each complexation reaction was determined. The complexation of the hydrazones with nickel(II) was estimated to go according to an Eigen mechanism and that with palladium (II) according to the associative mechanism.     

Nickel(II) complexes with different chromospheres containing macrocyclic ligands: spectroscopic and electrochemical studies

The mixed donor tetradentate (L(1)=N(2)O(2)) and pentadentate (L(2)=N(2)O(2)S) ligands have been prepared by the interaction of 1,3-diaminopropane and thiodiglycolic acid with diamine. These ligands possess two dissimilar coordination sites. Different types of complexes were obtained which have different stoichiometry depending upon the type of ligands. Their structural investigation have been based on elemental analysis, magnetic moment and spectral (ultraviolet, infrared, (1)H NMR, (13)C NMR and mass spectroscopy methods). The Ni(II) complexes show magnetic moments corresponding to two unpaired electrons except [Ni(L(1))](NO(3))(2) which is diamagnetic. Ligand field parameters of these complexes were compared. N(2)O(2)S donor ligand complexes show higher values of ligand field parameters, which are used to detect their geometries. The redox properties and stability of the complexes toward oxidation waves explored by cyclic voltammetry are related to the electron-withdrawing or releasing ability of the substituents of macrocyclic ligands moiety. The Ni(II) complexes displayed Ni(II)/Ni(I) couples irreversible waves associated with Ni(III)/Ni(II) process.     

Synthesis and characterization of nickel(II) maltolate complexes containing ancillary bisphosphine ligands

Cationic nickel(II) complexes containing chelating O,O′-donor maltolate or ethyl maltolate ligands in conjunction with bidentate bisphosphine ligands Ph₂P(CH₂) _n PPh₂ were prepared by a one-pot reaction starting from nickel(II) acetate, bisphosphine, maltol (or ethyl maltol), and trimethylamine, and isolated as their tetraphenylborate salts. An X-ray structure determination of [Ni(maltolate)(Ph₂PCH₂CH₂PPh₂)]BPh₄ shows that the maltolate ligand binds asymmetrically to the (slightly distorted) square-planar nickel(II) center. The simplicity of the synthetic method was extended to the synthesis of the known platinum(II) maltolate complex [Pt(maltolate)(PPh₃)₂]BPh₄ which was obtained in high purity.     

Synthesis,characterization and comparative DNA interaction studies of new copper(II) and nickel(II) complexes containing mesalamine drug using molecular modeling and multispectroscopic methods

Complexes of copper(II) and nickel(II) containing the drug mesalamine (5-ASA) have been synthesized and characterized by FT-IR, mass and UV–vis spectra, elemental analysis, and theoretical methods. The binding interactions between mesalamine and its Cu(II) and Ni(II) complexes with calf thymus DNA (ct-DNA) were investigated using absorption, fluorescence emission and circular dichroism (CD) spectroscopies, and viscosity measurements. Absorption spectra of 5-ASA, Cu(II) and Ni(II) complexes showed hypochromism. The calculated binding constants (K_b) obtained from UV–vis absorption studies were 1.27 × 10³, 1.6 × 10³, and 1.2 × 10⁴ M^?1 for 5-ASA, Cu(II) and Ni(II) complexes, respectively. The compounds induced detectable changes in the CD spectra of ct-DNA (B → A structural transition, B → C structural transition and stabilization of the right-handed B form, for mesalamine, Cu(II) and Ni(II) complexes, respectively). The competitive binding experiments with Hoechst 33258 indicated that 5-ASA and copper complex could interact as groove binders. Furthermore, Ni complex had no effect on the fluorescence intensity and peak position of MB-DNA system. Finally, the results obtained from experimental and molecular modeling showed that complexes bind to DNA via minor-groove binding.     

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.     

μ-Peroxodicobalt(III) complexes containing aromatic ligands

A series of new μ-peroxodicobalt(III) complexes have been prepared and characterized. Studies of the chemical and physical properties of these complexes were carried out using IR, electronic and NMR spectroscopy along with conductivity, magnetic susceptibility and thermogravimetric measurements. The complexes [Co₂(dpk·dien)₂ (dpk·H₂O)O₂] (ClO₄)₄·H₂O, [Co₂(dpk)₄(py)₂O₂](ClO₄)₄·4H₂O, [Co₂(dpk·H₂O₄(py)₂O₂] (ClO₄)₄, and [Co₂(dpk)₂(terpy)₂O₂](ClO₄)₄ were prepared by bubbling oxygen through a solution containing Co(NO₃)₂, NaClO₄, and the appropriate ligand mixture. Electronic spectral studies are consistent with the formulation as binuclear peroxo complexes. Thermogravimetric studies reveal the stoichiometric loss of O₂ and H₂O below 100°C. The auxiliary ligands, pyridine (py), diethylenetriamine (dien) and terpyridine (terpy) are lost at higher temperatures. Molar conductance of these complexes is indicative of a 4:1 electrolyte while magnetic susceptibility measurements indicate the diamagnetic character of the above four complexes. Three additional complexes of Co(II) containing di-2-pyridyl ketone (dpk) and terpy were prepared to compare spectral changes upon oxygenation.     

Synthesis and 1H NMR studies of paramagnetic nickel(II) complexes containing bis(pyrazolyl)methane ligands with dendritic substituents

The substituted bis(pyrazolyl)methane ligands RCH(3,5-Me2pz)2(R=SiMe3, CH2Ph, G1, G2, and G3; Gn=Fréchet-type dendritic wedges of generation n) have been prepared starting from H2C(3,5-Me2pz)2. Reaction of these didentate ligands with [NiBr2(DME)] is a straightforward procedure that allows the synthesis of the nickel(II) complexes [NiBr2{RCH(3,5-Me2pz)2}]. The molecular structure of compound (R=CH2Ph) has been determined by X-ray diffraction studies. The nickel centre coordinates two bromine and two nitrogen atoms in a tetrahedral environment, and the metallacycle Ni(NN)2C adopts a boat conformation with the benzyl group in an axial position. 1H NMR studies have been carried out to characterize these paramagnetic nickel compounds in solution. Valuable information about the disposition of the ligands and dendritic wedges in solution has been obtained thanks to the influence of the paramagnetic centre on the proton resonances.