Iron(III), cobalt(II) and copper(II) complexes bearing 8‐quinolinol encapsulated in zeolite?Y for the aerobic oxidation of styrene

A series of Fe(III), Co(II) and Cu(II) complexes of 8‐quinolinol were encapsulated into the supercages of zeolite? Y and characterized by X‐ray diffraction, SEM, N₂ adsorption/desorption, FT‐IR, UV–vis spectroscopy, elemental analysis, ICP‐AES and TG/DSC measurements. The encapsulation was achieved by a flexible ligand method in which the transition metal cations were first ion‐exchanged into zeolite Y and then complexed with 8‐quinolinol ligand. The metal‐exchanged zeolites, metal complexes encapsulated in zeolite–Y plus non‐encapsulated homogeneous counterparts were all screened as catalysts for the aerobic oxidation of styrene under mild conditions. It was found that the encapsulated complexes always showed better activity than their respective non‐encapsulated counterparts. Moreover, the encapsulated iron complex showed good recoverability without significant loss of activity and selectivity within successive runs. Heterogeneity test for this catalyst confirmed its high stability against leaching of active complex species into solution. Copyright © 2011 John Wiley & Sons, Ltd.     

Diisopropyl fluorophosphate (DFP) degradation activity using transition metal–dipicolylamine complexes

Transition metal complexes have been extensively used as catalysts for organophosphorus agent decomposition to reduce their toxicity with their performance being strongly dependent on the nature of the metal ion. To investigate this dependence, we prepared dipicolylamine (DPA)‐containing complexes of Cu(II), Zn(II), Ni(II), Co(II), and Fe(II) and analyzed their activities for the degradation of diisopropyl fluorophosphate (DFP), a nerve agent surrogate compound. Cu(II)‐DPA complex showed fastest reaction kinetics while Zn(II)‐DPA and Ni(II)‐DPA exhibited more slower reactions. This observation can be explained using frontier molecular orbital (FMO) theory, which revealed that the nucleophilicity of the oxygen atom in water molecules in these transition metal complexes was well matched with reactivity order observed in experiments. These investigations combined with theoretical study provide valuable information for designing and predicting the activity of new transition metal–organic ligand complexes as a catalyst to decompose and reduce toxicity of organophosphorus nerve agents.     

非均相Fenton催化剂的组成结构设计与性能优化

非均相Fenton催化技术解决了均相Fenton反应存在的问题,具有pH适用范围广以及催化剂易于回收利用等优点,因而成为水处理领域的研究热点。本文首先介绍了非均相Fenton反应用于降解有机污染物的发展、反应机理以及机理的研究方法。总结了非均相Fenton催化剂的种类,主要包括铁氧化物、其它金属氧化物、金属有机框架材料。重点讨论了提高非均相Fenton催化剂活性及稳定性的方法,包括通过调控催化剂的形貌、尺寸、孔结构使催化剂具有更高的比表面积,将活性组分负载在具有高比表面积的载体上,通过与其它金属复合以及引入光、超声、微波等外场。最后,对非均相Fenton催化技术的发展进行了展望。     

Catalytic Oxidative Decarboxylation of Some Benzylcarboxylic Acid Derivatives by a New Iron(III) Schiff Base Complex

A quadridentate Schiff base ligand of N,N’-bis(2-hydroxy-α-methylbenzylidene)ethylenediamine (HMBEDA) and its new iron(III) complex were synthesized and identified by analytical, spectral data (1H NMR, 13C NMR FT-IR and UV-visible) and molar conductance. A rapid and efficient homogeneous oxidative decarboxylation of some benzylcarboxylic acid derivatives was carried out by a catalytic amount of iron(III) Schiff base complex in chloroform, using tetrabutylammonium periodate as a mild oxidant in good to excellent yields at room temperature.     

Electrochemical Study on DNA Damage Based on the Direct Oxidation of 8‐Hydroxydeoxyguanosine at an Electrochemically Modified Glassy Carbon Electrode

The study of DNA damage induced by Fenton reaction (Fe²⁺/H₂O₂) in vitro was performed based on the direct electrochemical oxidation of 8‐hydroxydeoxyguanosine (8‐OH‐dG), the biomarker of DNA oxidative damage, at an electrochemically modified glassy carbon electrode (GCE). The effects of antioxidants, such as ascorbic acid, and hydroxyl‐radical scavenger (mannitol) on the DNA damage were also investigated. 8‐OH‐dG, the oxidation product of guanine residues in DNA, has shown significantly oxidative peak on the electrochemically modified GCE. The oxidative peak current of 8‐OH‐dG was linear with the damaged DNA concentration in the range of 10–200 mg/L. The experimental results demonstrate that ascorbic acid has ambivalent effect on DNA oxidative stress. It can promote DNA oxidative damage when ascorbic acid concentration is below 1.5 mM and protect DNA from damage in the range of 1.5–2.5 mM. As a hydroxyl‐radical scavenger, mannitol inhibits significantly DNA oxidative damage. The influence of Fe²⁺, as reactant, and EDTA as iron chelator in the system were also studied. The proposed electrochemical method can be used for the estimation of DNA oxidative damage from new point of view.     

Highly Active and Selective Manganese C=O Bond Hydrogenation Catalysts: The Importance of the Multidentate Ligand,the Ancillary Ligands,and the Oxidation State

The replacement of expensive noble metals by earth‐abundant transition metals is a central topic in catalysis. Herein, we introduce a highly active and selective homogeneous manganese‐based C=O bond hydrogenation catalyst. Our catalyst has a broad substrate scope, it is able to hydrogenate aryl–alkyl, diaryl, dialkyl, and cycloalkyl ketones as well as aldehydes. A very good functional group tolerance including the quantitative and selective hydrogenation of a ketone in the presence of a non‐shielded olefin is observed. In Mn hydrogenation catalysis, the combination of the multidentate ligand, the oxidation state of the metal, and the choice of the right ancillary ligand is crucial for high activity. This observation emphasizes an advantage and the importance of homogeneous catalysts in 3d‐metal catalysis. For coordination compounds, fine‐tuning of a complex coordination environment is easily accomplished in comparison to enzyme and/or heterogeneous catalysts.     

Synthesis,Characterization, Crystal Structure,and Biological Activities of Transition Metal Complexes with 1‐Phenyl‐3‐methyl‐5‐hydroxypyrazole‐4‐methylene‐8′‐quinolineimine

The Schiff base ligand, 1‐phenyl‐3‐methyl‐5‐hydroxypyrazole‐4‐methylene‐8′‐quinolineimine, and its Cu^II, Zn^II, and Ni^II complexes were synthesized and characterized. The crystal structure of the Zn^II complex was determined by single‐crystal X‐ray diffraction, indicating that the metal ions and Schiff base ligand can form mononuclear six‐coordination complexes with 1:1 metal‐to‐ligand stoichiometry at the metal ions as centers. The binding mechanism and affinity of the ligand and its metal complexes to calf thymus DNA (CT DNA) were investigated by UV/Vis spectroscopy, fluorescence titration spectroscopy, EB displacement experiments, and viscosity measurements, indicating that the free ligand and its metal complexes can bind to DNA via an intercalation mode with the binding constants at the order of magnitude of 105–106 M ^–1, and the metal complexes can bind to DNA more strongly than the free ligand alone. In addition, antioxidant activities of the ligand and its metal complexes were investigated through scavenging effects for hydroxyl radical in vitro, indicating that the compounds show stronger antioxidant activities than some standard antioxidants, such as mannitol. The ligand and its metal complexes were subjected to cytotoxic tests, and experimental results indicated that the metal complexes show significant cytotoxic activity against lung cancer A 549 cells.     

A Theoretical Investigation on the Strecker Reaction Catalyzed by a TiIV‐Complex Catalyst Generated from a Cinchona Alkaloid,Achiral Substituted 2,2′‐Biphenol,and Tetraisopropyl Titanate

The mechanism and the origin of selectivity of the asymmetric Strecker reaction catalyzed by a Ti^IV‐complex catalyst generated from a cinchona alkaloid, achiral substituted 2,2′‐biphenol, and tetraisopropyl titanate have been investigated by DFT and ONIOM methods. The calculations indicate that the reaction proceeds through a dual activation mechanism, in which Ti^IV acts as Lewis acid to activate the electrophile aldimine substrate, whereas the tertiary amine in cinchona alkaloid works as Lewis base to promote the activation and isomerization of HCN. The C? C bond formation step is predicted to be the selectivity‐controlling step in the reaction with an energy barrier of 9.3 kcal mol^?1. The “asymmetric activation” is achieved by the transfer of asymmetry from the chiral cinchonine ligand to the axially flexible achiral biphenol ligand through coordination interaction with the central metal Ti^IV. The large steric hindrance from the 3,3′‐position substitute of biphenol, combined with the quinoline fragment of cinchona alkaloid and the orientation of hydrogen bonding of iPrOH, play a key role in controlling the stereoselectivity, which is in good agreement with the experimental observations.     

Density functional theory/B3LYP study of nanometric 4‐(2,4‐dihydroxy‐5‐formylphen‐1‐ylazo)‐N‐(4‐methylpyrimidin‐2‐yl)benzenesulfonamide complexes: Quantitative structure–activity relationship,docking, spectral and biological investigations

New metal ion complexes were isolated after coupling with 4‐(2,4‐dihydroxy‐5‐formylphen‐1‐ylazo)‐N ‐(4‐methylpyrimidin‐2‐yl)benzenesulfonamide (H₂L) drug ligand. The structural and molecular formulae of drug derivative and its complexes were elucidated using spectral, analytical and theoretical tools. Vibrational spectral data proved that H₂L behaves as a monobasic bidentate ligand through one nitrogen from azo group and ionized hydroxyl oxygen towards all metal ions. UV–visible and magnetic moment measurements indicated that Fe(III), Cr(III), Mn(II) and Ni(II) complexes have octahedral configuration whereas Cd(II), Zn(II) and Co(II) complexes are in tetrahedral form. The Cu(II)complex has square planar geometry as verified through electron spin resonance essential parameters. X‐ray diffraction data indicated the amorphous nature of all compounds with no regular arrangement for the solid constituents during the precipitation process. Transmission electron microscopy images showed homogeneous metal ion distribution on the surface of the complexes with nanometric particles. Coats–Redfern equations were applied for calculating thermo‐kinetic parameters for suitable thermal decomposition stages. Gaussian09 and quantitative structure–activity relationship modelling studies were used to verify the structural and biological features. Docking study using microorganism protein receptors was implemented to throw light on the biological behaviour of the proposed drug. The investigated ligand and metal complexes were screened for their in vitro antimicrobial activities against fungal and bacterial strains. The resulting data indicated that the investigated compounds are highly promising bactericides and fungicides. The antitumour activities of all compounds were evaluated towards human liver carcinoma (HEPG2) cell line.     

Reaction pathways involved in the mechanism of AlIII chelation with caffeic acid: catechol and carboxylic functions competition.

Density functional theory calculations on the AlIII-caffeic acid system are carried out to investigate the fixing mechanism of this metal ion to the two competing complexing sites in the ligand. This theoretical study was performed to explain the complex formation of 1:1 stoichiometry observed in aqueous medium at low pH values. Both complexation with the catechol and carboxylic functions are envisaged. The reaction pathways for the formation of these two chelates are calculated at the B3LYP/6-31G** level of theory. The complexation on the more acidic group is relatively straightforward and shows the intermediate formation of a monodentate complex followed by a chelation process. The complexation reaction pathway with the catechol function is more sophisticated, and several pathways are explored. Once more, the formation of a monodentate complex is achieved and the most favorable pathway for chelation involves the successive steps: 1) coordination of AlIII on the oxygen atom of a hydroxyl group, 2) deprotonation of this hydroxyl group, 3) ring closure with the other oxygen atom, and 4) deprotonation of the second hydroxyl. From an energetic point of view, this second pathway is more favorable. Notably the energy barrier necessary to form the chelate is lower for the catechol function than that calculated for the carboxylic group. The results of this purely theoretical study are in complete agreement with spectroscopic investigations performed on this system.     

Catalytic activity of an iron(III) Schiff base complex bound in a polymer resin

An iron(III)–ferrocene complex and its heterogeneous analogue bound in a polymer resin have been prepared and employed as catalysts for the oxidation of various organic substrates. Characterization of the heterogeneous and homogeneous complexes was done by SEM, EDAX, TGA, FT-IR, DRS-UV, and spectroscopy. The catalyst’s activity, stability, and reusability were investigated through industrially relevant oxidation reactions. The solid iron(III)–ferrocene Schiff base complex gave more effective results than the solid-supported ferrocene Schiff base ligand. The antimicrobial activities of the molecular complex and free ligand were studied for Gram-positive and Gram-negative bacteria.     

Multicolor fluorescence of a styrylquinoline dye tuned by metal cations

A styrylquinoline dye with a dipicolylamine (DPA) moiety (1) has been synthesized. The dye 1 in acetonitrile demonstrates multicolor fluorescence upon addition of different metal cations. Compound 1 shows a green fluorescence without cations. Coordination of 1 with Cd(2+) shows a blue emission, while with Hg(2+) and Pb(2+) exhibits yellow and orange emissions, respectively. The different fluorescence spectra are due to the change in intramolecular charge transfer (ICT) properties of 1 upon coordination with different cations. The DPA and quinoline moieties of 1 behave as the electron donor and acceptor units, respectively, and both units act as the coordination site for metal cations. Cd(2+) coordinates with the DPA unit. This reduces the donor ability of the unit and decreases the energy level of HOMO. This results in an increase in HOMO-LUMO gap and blue shifts the emission. Hg(2+) or Pb(2+) coordinate with both DPA and quinoline units. The coordination with the quinoline unit decreases the energy level of LUMO. This results in a decrease in HOMO-LUMO gap and red shifts the emission. Addition of two different metal cations successfully creates intermediate colors; in particular, the addition of Cd(2+) and Pb(2+) at once creates a bright white fluorescence.     

Synthesis and characterization of metal complexes of azo dye based on 5‐nitro‐8‐hydroxyquinoline and their applications in dyeing polyester fabrics

New Mn(II), Ni(II), Co(II) and Cu(II) complexes of an azo dye ligand based on p ‐phenylenediamine with 5‐nitro‐8‐hydroxyquinoline were synthesized and characterized using elemental analysis, inductive coupled plasma analysis, molar conductance, powder X‐ray diffraction, thermogravimetric analysis, magnetic moment measurements, and infrared, ¹H NMR, electron ionization mass and UV–visible spectral studies. The spectral and analytical data reveal that the azo dye ligand acts as a monobasic bidentate ligand via deprotonated OH and nitrogen atom of the quinoline ring. The data support the formulation of all complexes with a 2:1 ligand‐to‐metal ratio, except the Mn(II) complex that has a mononuclear formula. All complexes have an octahedral structure. The molar conductance data reveal that all the metal complexes are non‐electrolytic in nature. From the X‐ray data, the average particle size of the ligand and its complexes is 0.32–0.64 nm. The colour fastness to light, washing, perspiration, sublimation and rubbing of the prepared ligand and its complexes on polyester fabrics and colorimetric properties were measured. The results reveal that the ligand and its complexes have a good to moderate affinity to polyester fibres.     

DFT study of the active intermediate in the Fenton reaction

Density functional theory has been used to investigate the nature of the oxidizing agent in the Fenton reaction. Starting from the primary intermediate [FeII(H2O)5H2O2]2+, we show that the oxygen-oxygen bond breaking mechanism has a small activation energy and could therefore demonstrate the catalytic effect of the metal complex. The O-O bond cleavage of the coordinated H2O2, however, does not lead to a free hydroxyl radical. Instead, the leaving hydroxyl radical abstracts a hydrogen from an adjacent coordinated water leading to the formation of a second Fe-OH bond and of a water molecule. Along this reaction path the primary intermediate transforms into the [FeIV(H2O)4(OH)2]2+ complex and in a second step into a more stable high valent ferryl-oxo complex [FeIV(H2O)5O]2+. We show that the energy profile along the reaction path is strongly affected by the presence of an extra water molecule located near the iron complex. The alternative intermediate [FeII(H2O)4(OOH-)(H3O+)]2+ suggested in the literature has been also investigated, but it is found to be unstable against the primary intermediate. Our results support a picture in which an FeIV-oxo complex is the most likely candidate as the active intermediate in the Fenton reaction, as indeed first proposed by Bray and Gorin already in 1932.     

Accelerated Hydrolysis of p-Nitrophenyl Picolinate Catalyzed by Metallomicelle Made from a Novel Macrocyclic Polyamine Copper（Ⅱ） Complex

A copper（Ⅱ） complex 1 of a novel macrocyclic polyamine ligand with hydroxylethyl pendant groups, 4,11-bis（hydroxylethyl）-5,7,7,12,14,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane （L） has been synthesized and characterized. Rate enhancement for hydrolysis of p-nitrophenyl picolinate （PNPP） catalyzed by 1 was studied kinetically under Brij35 micellar condition. For comparision, the catalytic activity of corresponding copper（Ⅱ） complex 2 of non-substituted macrocyclic polyamine ligand, 5,7,7,12,14,14-hexamethyl-1,4,8,11-tetraaza-cyclotetradecane （L＇） toward the hydrolysis of PNPP was also investigated. The results indicate that the macrocyclic polyamine copper（Ⅱ） complex 1 effectively catalyzed the hydrolysis of PNPP, and the pendant ligand hydroxyl group or deprotonated pendant ligand hydroxyl group can act as catalytically active species in the reaction. A ternary Complex kinetic model involving metal ion, ligand and substrate has been proposed, and the results confirmed the reasonability of such kinetic model.     

A simple electrochemical method for the determination of hydroxyl free radicals without separation process

Generally speaking, measurement of hydroxylated radical products of salicylic acid requires a fussy separation process. In this study, we describe a simple method to electrochemically detect hydroxyl radicals (*OH) using 4-hydroxybenzoic acid (4-HBA) as the *OH trap. The *OH is generated by the Fenton reaction from iron (II) sulfate and hydrogen peroxide in a phosphate buffer solution. Experimental results show that our method can detect the OH with high sensitivity without any separation process. The differential pulse voltammetric responses show a linear dependence on the concentration of *OH in a range of 2.0x10(-6) and 1.0x10(-3)M with a determination limit down to 5.0x10(-7)M. As a demonstration, the kinetics of the Fenton reaction was mapped by measuring the reaction product of hydroxyl radical trapped by 4-HBA. The result is in good agreement with that reported previously. All the results show that the present approach could provide a simple, inexpensive and promising method for biomedicine and iatrology.     

THE REACTIONS OF HYDROXYL RADICAL WITH SOME TRANSITION-METAL COMPOUNDS CONTAINING ORGANIC MOLECULES

Abstract— Recent reports that have appeared in the literature concerning the reactions in aqueous media of hydroxyl radical with some transition-metal compounds containing bound organic molecules are discussed and experimental results on the reactions of hydroxyl radical with some platinum complex ions are presented. Emphasis is placed on the comparison of the behavior of the free ligand relative to that of the complexed and protonated forms. The occurrence of metal-ion complexation can modify to varying degrees the reactivity of organic entities towards hydroxyl radical and the subsequent behavior of the products. The influence of the metal center is considered to involve its Lewis acidity, π-bonding capabilities as well as features such as its formal oxidation state.     

Synthesis and characterization of polyaniline nanoparticles in phosphonic acid amphiphile aqueous micellar solutions for waterborne corrosion protection coatings

Polyaniline (PANI) dispersions consisting of 270 to 380 nm sized particles were prepared by oxidation with ammonium peroxydisulfate (APS) in n‐decylphosphonic acid (DPA) micellar solutions. The green dispersions do not undergo macroscopic precipitation for more than a year. The synthesized DPA doped PANI exhibited enhanced electrical conductivity (3.6 S cm^?1 ) compared with DPA‐PANI (2.3 x 10 ^{? 4} S cm ^{? 1}) prepared by postsynthesis treatment of the PANI‐base with DPA. It was shown that through protonation with decylphosphonic acid, polyaniline showed a significantly enhanced solubility in common organic solvents like chloroform, xylene, etc. The synthesized PANI was characterized by intrinsic viscosity, solubility, FT‐IR , conductivity, SEM , and TGA measurements. The wide‐angle X ‐ray diffraction study revealed the appearance of a peak located at low angles (d = 29.4 – 35.3 Å) suggesting the formation of layered structure of PANI backbone separated by long alkyl side chains of DPA. The anticorrosive performance of the bilayer coatings composed of a bottom layer of DPA doped polyaniline covered with a polyvinyl butyral topcoat, have been demonstrated for steel exposed to neutral saline solutions. It was found that the inhibitive properties of DPA dopant provides further protection to the base metal through smart release when damage is produced on the surface of the coating. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 1606–1616     

Catching an Entatic State—A Pair of Copper Complexes

The structures of two types of guanidine–quinoline copper complexes have been investigated by single‐crystal X‐ray crystallography, K‐edge X‐ray absorption spectroscopy (XAS), resonance Raman and UV/Vis spectroscopy, cyclic voltammetry, and density functional theory (DFT). Independent of the oxidation state, the two structures, which are virtually identical for solids and complexes in solution, resemble each other strongly and are connected by a reversible electron transfer at 0.33 V. By resonant excitation of the two entatic copper complexes, the transition state of the electron transfer is accessible through vibrational modes, which are coupled to metal–ligand charge transfer (MLCT) and ligand–metal charge transfer (LMCT) states.     

Synthesis and characterization of an MRI Gd‐based probe designed to target the translocator protein

DPA‐713 is the lead compound of a recently reported pyrazolo[1,5‐a]pyrimidineacetamide series, targeting the translocator protein (TSPO 18 kDa), and as such, this structure, as well as closely related derivatives, have been already successfully used as positron emission tomography radioligands. On the basis of the pharmacological core of this ligands series, a new magnetic resonance imaging probe, coded DPA‐C₆‐(Gd)DOTAMA was designed and successfully synthesized in six steps and 13% overall yield from DPA‐713. The Gd‐DOTA monoamide cage (DOTA = 1,4,7,10‐tetraazacyclododecane‐1,4,7,10‐tetraacetic acid) represents the magnetic resonance imaging reporter, which is spaced from the phenylpyrazolo[1,5‐a]pyrimidineacetamide moiety (DPA‐713 motif) by a six carbon‐atom chain. DPA‐C₆‐(Gd)DOTAMA relaxometric characterization showed the typical behavior of a small‐sized molecule (relaxivity value: 6.02 mM^?1 s^?1 at 20 MHz). The good hydrophilicity of the metal chelate makes DPA‐C₆‐(Gd)DOTAMA soluble in water, affecting thus its biodistribution with respect to the parent lipophilic DPA‐713 molecule. For this reason, it was deemed of interest to load the probe to a large carrier in order to increase its residence lifetime in blood. Whereas DPA‐C₆‐(Gd)DOTAMA binds to serum albumin with a low affinity constant, it can be entrapped into liposomes (both in the membrane and in the inner aqueous cavity). The stability of the supramolecular adduct formed by the Gd‐complex and liposomes was assessed by a competition test with albumin. Copyright © 2013 John Wiley & Sons, Ltd.